Now, from the same site, look at what you see when only looking at mid level shear.
Thursday, September 3, 2009
T.S. Erika
Now, from the same site, look at what you see when only looking at mid level shear.
Monday, August 31, 2009
With Danny Gone, Eyes Turn to Next System
Thursday, August 27, 2009
Danny Update... Next Feature Flares Up in Eastern Atlantic
But fear not all you tropical enthusiasts, as the next system may be forming in the eastern Atlantic, as we do have a wave that has flared up nicely, and is in an evnvironment that right now isn't too bad, so in the next few days, we could have Erika on the map. My guess right now is that this will have a hard time ever being a threat to the U.S, given that we will likely have at least one weak upper low dancing underneath the Atlantic ridge, which will probbaly act to guid this storm north of the Lesser Antilles, and then it would probably get steered back out to sea given the strong upper trough headed into the eastern U.S. next week, which probably will split and send a piece tailing into the Southeast. But obviously we're talking a long way out here, and plenty of time to watch this one.
Wednesday, August 26, 2009
We Have Danny!
While not a "major" system, it could make things interesting right along the coast, though into the big cities of the East, I still think heavy rain is really the only notable threat here. I guess the track I have laid out would put New York and Boston at a higher risk for more periods of tropical storm force wind gusts, but still there I tend to think rain is a bigger issue than wind (keep in mind I mean the metro areas, not right along the shores of Long Island or over to Cape Cod).
This also puts us actually a little ahead of schedule for the 4th named storm, which typically occurs around September 1st... interesting given the slow start to the season!
Tuesday, August 25, 2009
The Hiatus Is Over - Tropical Threat to East Coast?
But for now, it is still summer (which FINALLY came to the eastern U.S. this month), and we are still in tropical mode as well, even now with a threat to the East Coast perhaps! All eyes are on "Invest 92", an area of disturbed weather north - northeast of the Lesser Antilles, which is heading to the west-northwest currently. As of now, conditions are not all that favorable for development, at least not very quickly, but should improve over the next day or two, and I do think we'll have Tropical Storm Danny out of this. Now, where does it go? Well if you believe the U.S. models, it will turn harmlessly back out to sea. But other models say not so fast, and with good reason in my opinion. The GFS model seems pretty quick to develop this, and perhaps a bit north of where the true low level center will eventually wind up. Because a more developed system can be tugged north by any weak upper features, the GFS, by virtue of being faster with development, sends Danny-to-be off into the westerlies much faster, and stays well offshore. But given that the shear is not that favorable right now, I'd lean toward a slower development curve, and a path farther west. A pretty potent trough will dive into the Midwest this weekend, and that should mean we have enough ridging downstream in the western Atlantic, which also leads me to believe a farther west path, closer to the other modeling. This says to me that "Danny" has a much greater shot to impact the East Coast than Bill ever did, though I don't think this system gets as strong. It could organize enough to reach hurricane status, but the incoming trough should start adding enough shear to make it a tropical storm up the coast, so not the best of weekends at the coast, but where most people live in the I-95 corridor, it is probably more a rainmaker. What else will need to be looked at is the potential for the storm to interact with the incoming front and enhance rainfall even more, perhaps leading to some flooding concerns.
So the bottom line is that we should see Danny out of this, and my best guess right now would be a storm moving close to or into eastern North Carolina this weekend, then northward up the coast, probably as a tropical storm, presenting heavy rain concerns up the eastern seaboard, with most of the significant wind issues right along the coast.
Friday, June 26, 2009
First Tropical Storm of Season?
In any case, it looked better earlier, but is not in an ideal environment right now to develop. It should continue to drift northwest, perhaps passing just east of the Yucatan Peninsula of Mexico this weekend. Wind shear will be gradually subsiding some as well, so it is possible that by Monday it is able to organize into Tropical Storm Ana.
Where would it go from there? Well, a fairly strong trough will dig into the eastern half of the nation, which probably has enough influence to turn whatever is in the Gulf toward Florida. This path would not be one that would allow any storm to strengthen much though, as wind shear is forecast to increase in the northern Gulf by Tuesday in response to the incoming eastern trough. See the second image below for the forecast shear, valid Tuesday evening (courtesy of the fine folks at MDA!). Values greater then 20 knots are certainly unfavorable. This means that, while possibly holding on to "named storm" status, this would be pretty much just a rainmaker for Florida, as it could not possibly intensify much with this pattern in place.
The other option is that the trough does not pick up whatever is there early next week, which would probably mean a path more toward south Texas or Mexico given the ridge that would be to its northwest. But the environment could be a little more favorable for development on this course. I'd rate this as less likely than option one discussed above though. At least we have something to watch!
Carribean Satellite:
http://www.ssd.noaa.gov/goes/east/carb/avn-l.jpg
Thursday, June 25, 2009
Record Heat in Houston!
What was odd about the 104 here yesterday is that we were able to achieve that without a 500 mb ridge of at least 5940m in intensity. That is hard to pull off, but the fact that much of this area has seen no measurable rain for 31 days is helping that, as with no moisture in the ground, all of the sun's energy goes into heating the air rather than some of it getting used up in evaporating moisture.
Looks like, barring something strange, this will be a top 3 hottest and top 3 driest June on record here. Hopefully we won't follow the trend of the other 2 hottest Junes on record, being 1980 and 1998, and July of those years also went on to be hot (especially in 1980). Unfortunately for those of us down here though, it is hard to forecast anything other than "above normal" for Texas in July given the pattern we have in place.
Tuesday, June 16, 2009
Blocking is King
Friday, June 12, 2009
Some Bootleg June Stats
In some ways, the lack of heat isn't a big shock considering the developing el nino and the impacts that such an occurrence tends to have on the global pattern, but even in similar years, you usually get a brief spike or two somewhere, so we'll see if we get on before the month is done.
Monday, June 1, 2009
Racing Toward El NiƱo
Friday, May 22, 2009
Late Spring Doldrums
The craziness in the Upper Midwest is gone, leaving things kinda blah again since the system in the Gulf is just a rainmaker (and was / still is a hefty one in parts of Florida!). Hard to believe the month of may is about over, and we're about to begin meteorological summer as well as the hurricane season! But will the developing el nino (or so it appears to be developing) squash any chance for noteworty extremes in both cases? It could. Most of the best-fit analogs are not hefty in the total number of named storms department, suggesting mostly numbers in the 9-12 storm range. That would not mean a dud of a season though, since it just takes one to make a season memorable. As for the summer, the consensus seems to be for a relatively benign (or near normal) summer for much of eastern U.S, perhaps even below normal in some places, with warmth favored in interior West. We do have to be cautious of the 2002 analog though, which is arguably the best match to what has actually been happening this Spring globally and overall in North America, and that turned out to be a fairly hot summer nationally, so this is not a slam dunk. It does appear the el nino is for real though, perhaps going moderate by fall / next winter.
Friday, May 8, 2009
Incoming!
Here is an image from around 8:00 central time this morning. Wow!
Friday, April 24, 2009
Hurricane Season Just Over a Month Away!
The cooler water in the Atlantic should not surprise anyone, as we have had two years of la nina (though it rested last summer) hammer away at it. For those not aware of this, la nina tends to, over time, spill over into the Atlantic and result in stronger trade winds which can cool the waters of the tropical Atlantic. I have posted an image below of years at this time which followed two years of la nina (using the MEI, which is always my measure of ENSO) to show the tendency toward this cooler tropical Atlantic.
Compare to actual SST anoms shown here:
http://weather.unisys.com/surface/sst_anom.html
Now, given that we do not appear to have entered the long term negative AMO state yet, and the fact that la nina is fading away (or arguably has faded away), the waters could easily recover some, so this is not the end-all factor to look at here. In fact I'd be surprised if they don't recover some in the next few months, but probably not nearly enough to compete with the warmth of the waters in many of our super-active years.
This leads us to the ENSO state. A lot of models are on board with a move toward el nino as we move through the next few months, and the SSTA link above shows some warmer waters starting to show up in the tropical Pacific already. But it isn't always the actual ENSO state that is important, but rather, which way the trend is going. For example, the shift out of a nina pattern can be led by the atmosphere itself, meaning some nino-like characteristics can be present before an actual nino is seen or declared. Thus, in some cases, a weakening nina can have similar effects as an actual nino. So, regardless of whether or not we go into an official nino by later in the hurricane season, these factors would seem to support less activity than what we have averaged this decade (even removing the massive 2005 season total). The farther we get on the nino side of the spectrum, the less activity I'd expect. I'm not sure we move far enough into a nino to get a year quite as quiet as 2006 though, as somewhere between warm-neutral and weak nino seems a better guess to me right now (MEI somewhere in the 0.2 to 0.6 range?). In addition, it is worth pointing out that all these guesses as far as number of namded storms is kinda pointless in a sense, as it only takes one big one to make the season memorable, and really, it is very tough to pinpoint where storms will go, as they depend on the pattern present at the time of formation, so no matter what, everyone needs to always stay prepared if you live near the coast. The consensus of 11-13 named storms from most outlets I have seen is pretty tough to argue with though.
What could allow for more activity? Well should the waters warm more solidly and the atmosphere jolt back toward la nina, then we could see more than the consensus calls for, so that is where to look in the next couple of months. Typically it is late spring / early summer when ENSO "decides" its course.
Thursday, April 23, 2009
Vacation Done... Back to Weather
It helped that the weather was absolutely beautiful... very warm with sunshine every day we were there. In fact, temperatures were running a good 12-15 degrees above normals on most days. We expected to need a sweater and light jacket on some days based on normal temperatures for time of year, but that wasn't the case at all (and no I had not spent a ton of time trying to forecast what it would be like haha).
But now things are back to the normal routine. It looks anything but "normal" though in the eastern U.S. this weekend into early next week, with a very impressive (for late April) surge of warmth that will bring a chance for at least a couple of days of 85-90 from the Carolinas all the way up to perhaps Boston. The good news is that this time of year does not bring much in the way of humidity, so it won't be as bad as the same temperatures in say, June through August. Still, highs 15-20 above normal for the time of year is pretty warm, so for those of you living in these areas, enjoy your early taste of summer!
Thursday, April 9, 2009
Vacation Time!
Last week's severe weather event (talked about last time I actually posted) went about as planned. It just was not the setup for a major outbreak. Maybe I'll do some case studies or something at some point in the future as far as some key things to look for, for those who aren't already aware.
We had some wild stats from the Plains the other day. Gage, OK had a morning low of 14 Tuesday, but rose to 82 in the afternoon! Try dressing appopriately for that kind of day!
Anyway, I don't see a major outbreak of severe weather on the horizon the next few days, but some smaller scale events are possible per SPC's discussions. We may have to wait for the end of the month or early May for a more favorable overall synoptic setup, assuming continued progression of current Madden-Julian wave. These waves will also help play a role in the state of ENSO in the coming months, which of course has big implications on summer and even next winter (yes I know many are already wondering about that!).
I'll be back to posting after my trip.
Thursday, April 2, 2009
Severe Weather Update
Wednesday, April 1, 2009
Severe Threat for Tomorrow, 4/2/09
Monday, March 30, 2009
Basketball > Weather... Maybe More Interest Thursday?
Wednesday, March 25, 2009
Severe Weather Threat Today... In My Backyard!
A more significant outbreak of severe weather is still possible Friday and Friday night in far eastern TX into AR, LA, and MS. I still find it hard to imagine such a strong upper level storm like the one that is coming out of the Rockies (which will be a hefty late season snow producer from eastern Colorado into KS, OK, and parts of MO) can clash with such a warm, moist air mass without some fireworks. My guess right now is that SPC will go moderate risk in tonight's day 2 outlook for this event. As mentioned yesterday, this threat carries into the Southeast Saturday, still with some tornado potential.
And now we have a few models that show another storm around the middle of next week which could be a severe weather producer in the same areas, along with another snow threat from eastern Colorado into Kansas and perhaps parts of Oklahoma. Lots to keep track of here the next few days, so stay tuned!
BTW, here is today's tornado risk map courtesy of SPC, which I have no major disagreements with.
Tuesday, March 24, 2009
More Severe Weather On the Way
Looking ahead, there is no rest for the weary, as severe weather season seems ready to take off as we move through the next couple of weeks. Each of the next few days we have chances for severe weather, all the way to Saturday. I don't want to downplay the next couple of days (which could include strong to severe storms in my own backyard tomorrow into tomorrow night), but clearly the most glaring feature on the maps the next few days is Friday into Saturday. The current system moving into the Midwest is not able to push far enough south to really "clean out" the warm, moist air mass in place, which will allow the late week storm to have a lot of "juice" to work with. Here is the GFS valid Friday afternoon, which is one of the more ominous model depictions:
That's a pretty potent upper level system coming out of the central / southern Rockies, which by the way will be an impressive snowstorm from Denver out into parts of Kansas and perhaps up into Nebraska then the Upper Midwest for this time of year. The GFS also has a sufficient low level jet in place across the lower Mississippi Valley. Take note also of the vort max shown over the TN / KY region. That is a key also, as subsidence in the wake of this feature may allow sunshine to maximize destabilization from eastern Texas into AR / LA / MS ahead of the main upper low, though again, this model solution is probably the most ominous, but all models show what could be a dangerous storm in these areas (again maybe down toward me, though capping usually squashes the threat here for the most part... we'll see), though some other models do not depict much of a low level jet in place. While the GFS may be overdone, it's hard to see how such a system at 500 mb wouldn't generate enough of a LLJ for some severe weather (you don't need a 40+ knot LLJ anyway), especially with the warmth and moisture in place. Anyway, can't really get too specific yet other than this, but everyone from eastern Texas across the South will need to keep an eye on this, and the threat may extend into the Southeast Saturday.
Longer term, numerous models show a trough more or less anchored in the means near the Rockies, so we probably are not done with severe threats after this week, provided enough warm, moist air stays in place. We also may see a trough hanging around off the Northeast as well, but if you recall the image I posted a long time ago (I'll have to dig it up again) that showed the "optimal" tornado pattern, you often see this. The reason is that such a setup leads to higher pressure in the East, with a south to southeasterly return flow in the middle of the nation, and this keeps low level flow backed enough to maximize directional wind shear. Bottom line... We probably will have a lot to watch in the next week or two at least.
Monday, March 23, 2009
Update on Severe Threat Today... More on the Way?
Friday, March 20, 2009
Severe Weather Threat Early Next Week?
The second map is also a 500 mb plot, but has the winds at that level rather than vorticity. Notice peak winds in the jet core coming into the Plains are over 90 knots, which is solid and easily can support a severe threat.
The third map below is the low level jet at 850 mb, which exceeds 50 knots in its core, again, well over what you need to see to generate strong to severe storms. Given the low level jet's intersection with the 500 mb jet over central Kansas, this would be a favored area for severe weather, provided enough moisture and instability is in place, which may be the limiting factor. The final map shows that dewpoints are expected to be mostly in the 50s, as opposed to 60s, which would be a more favorable environment for storms. Also, this return flow looks rather dirty to me, meaning clouds and light precipitation may cover much of the warm sector, limiting how unstable the atmosphere gets, and indeed models show the highest instability will be limited to a narrow strip ahead of the front.
So my guess is that we will have a few severe storms from central Nebraska into Kansas, Oklahoma, and north Texas, with a few supercells possible despite limited moisture content. The area at greatest risk to me would appear to be central Kansas if I har to pick a spot, with perhaps a secondary area in southern Oklahoma / north Texas as core of 500 mb jet punches eastward in the evening Monday. An isolated tornado or two cannot be ruled out in my opinion as initial storms form Monday afternoon or early evening, but the flow has a strong southerly component at all levels, and the instability axis is pretty narrow, so my guess is storms will "line out", or aggregate together in a linear fashion quickly, making hail and gusty strightline winds a bigger threat as the event unfolds Monday afternoon / evening. There may be a threat for isolated severe storms Tuesday farther east toward the Mississippi Valley, but should be less of a threat than on Monday.
Tuesday, March 17, 2009
Biggest Piece of Evidence Yet of Global Warming
I received this in my email this morning. Nothing like a little light-heartedness on what is a rather dull weather day! Ooh but the GFS is ready to put the eastern U.S. back into the ice box toward next weekend (not this coming one) and beyond! Stay tuned!
Monday, March 16, 2009
Weather Doldrums
We did get some exceptional cooling into Texas last Friday through yesterday. In fact, if you go back and look at historical records, a co-worker of mine found that for the 3 day period of March 13-15, each day from Friday to Sunday ranks in the top 5 coolest days in terms of how low the daytime high was (the highs these 3 days were 46, 48, and 54 respectively). So it was definitely an impressive event for down here.
Elsewhere, we're still locked into a la nina base state overall, and in fact, forecasts for this week are now warmer in much of the middle of the nation than what was in the forecasts back on Friday, which is no surprise since it is here where a la nina spring tends to focus its warmth. You often will get cooling opportunites closer to both coasts. The global angular momentum isn't as low as it has been though, but it remains to be seen if this is a sign of the end for this la nina state. Most long term modeling is actually favoring more of an el nino look down the road (later this year), so figuring this out will be key in figuring out what goes on this summer, and for you winter lovers, what type of winter we may see next year. But let's not get too far ahead of ourselves here.
I do still plan on typing up a quick review of this winter sometime soon, and will talk about how things turned out versus the consensus forecasts. We'll point out the good, the bad, and the ugly. Perhaps during this weather "downtime" I can also go into some of the global teleconnections and what they mean, if there is an interest there.
Wednesday, March 11, 2009
Texas Chill... Still Not Done With Winter?
Next topic... Still unable to say the books are closed on winter. It remains a possibility that some wet snowflakes fly with that southern stream energy in the Lower Apps / Mid Atlantic (down into VA) Friday morning, though shouldn't amount to much with marginal temperatures. Only the mountains are fair game really for a small accumulation I would think, but something to watch. And then there is next week, as the European model wants to bring one final dumping into the East around the middle of next week, with a very amplified pattern, which I have shown below. Is this possible? Well, sure it has a chance, but the Euro model seems to be an outlier right now with this kind of amplification, so I wouldn't hold my breath on this, not that most people would do this anyway given it is the middle of March, but stranger things have happened! Really the same key would apply as has been the rule all winter... getting a slower / more amplified northern stream, and frankly, with AAM not jerking strongly in one direction or the other as of this writing, it is a tough call a week away. We got it to work out once... We'll see if luck can strike twice. Stay tuned!
Monday, March 9, 2009
Welcome to DST!
Although there isn't much in the way of extreme weather to talk about in the near term, with the exception of the possible blizzard in the northern Plains in the next couple of days, we do still have some things to watch for. First is the chance for isolated severe weather in the Midwest the next couple of days, but it doesn't look like a big event, so I won't talk much about that. I will turn more toward severe weather though as larger threats come down the road, so stay tuned for that. I showed in my last post the big temperature contrast from the warm side of this week's front to the cold side, and it does still look like quite a reversal later this week, starting in the Plains / Midwest and spreading east. I also said I was watching a southern stream feature in case it can produce any wintry mischief (or fun, depending on your perspective) this weekend, and this is still on the table. Sure, it is a long shot, but somewhere from the Apps of the Virginias into the Northeast could see something out of it given the cold in place, if the feature can come far enough north. Most recent GFS run says to at least keep an eye out.
Yes, the GFS 6.5 days from now is not the most reliable, but hey, I said it's a long shot, and it is (though not impossible), but at this point is all we have to really watch in the eastern U.S.
Turning to my own backyard, I'm torn on this weekend. I have outdoor plans for the first time in awhile, and wouldn't you know it, it looks rainy, which hardly ever happens down here anymore. To make matters worse, it looks quite chilly for this time of year too. Some of the cold air coming out of Canada gets down here later this week, and at the same time, the southern stream feature in the Southwest (same one to watch in the east toward the weekend) comes out, and moisture "overruns" the cooler air at the surface. Typically, a southwesterly flow bring in warmer air, but in this case clouds and rain effectively trap cooler air in the low levels. Below is the GFS model's idea for Saturday afternoon. Yes that is 40s shown for most of Texas even in the afternoon, with the chilly rain to go with it. Yuck. This model may be overdoing the cool air, but right now I tend to think much of Saturday is spent no warmer than low / mid 50s down here. Good news is we need the rain badly, though I'd like it to wait a couple of days longer.
Sunday, March 8, 2009
Back in the Saddle
This week is pretty interesting though in and of itself. There is a minor snow event for parts of New England tonight into tomorrow. We also have a lot of warm air from the Midwest (some severe weather today, which I haven't really had time to analyze) into the South that will battle (and lose out in many areas) to some very strong cold sitting to the north, which pushed south and east this week. Parts of Canada are looking at temperatures over 30 degrees below normal early this week! Below I have posted one model's prediction of temperatures by Tuesday evening, and you can see the battle underway.
That is 70s showing up in parts of the lower Midwest, and below zero up in parts of North Dakota! The Dakotas in fact will get quite a blizzard out of this. To most people, this isn't interesting since not that many people live there. Fine. But I will say that as this cold pushes east, a lot of folks especially from the Midwest to Northeast may be surprised by its intensity, especially given the warm start to the week in a lot of areas. This, by the way, is in response to the AAM spike I talked about a couple of posts back, which is temporarily taking us out of the la nina base state (yes I stole this whole "base state" talk from NOAA's Ed Berry, as I think it is a good way to describe things). Can we get a storm to arrive as the colder air is here for any late snow threats? Nothing definite is showing up on the horizon, but watch a southern stream wave next weekend that could pull some funny stuff from, say, Kansas to the Mid-Atlantic.
The nina base state I think should come back later in the month though, and models are starting to fall into line with this idea (maybe that should worry me given how bad they've been at times?). This nina state in Spring typically means warmer than normal from Central Rockies to western Midwest and down to Texas, though leaves a risk for coolings along both coasts. Going a little IMBY here (you weather board folks know what this means!), la nina base states in spring with a very dry Texas already in place do not please me when thinking about summer, but that is for another time.
Thursday, March 5, 2009
Global Warming on Hold?
Please read the above link. Back when I started this blog, I posted about how global temperatures have stopped rising, and opined that this halt in warming (perhaps even with some global cooling) could persist for the next 10-20 years given some of the climate shifts and odd solar behavior we are seeing. Well, it seems that this has dumbfounded some climate "scientists". I put scientists in quotes because I cannot figure out how some of the junk they say is even worthy of being called science. Consider a portion of what is shown in the article concerning the halt in the warming in recent years.
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"This is nothing like anything we've seen since 1950," Kyle Swanson of the University of Wisconsin-Milwaukee said. "Cooling events since then had firm causes, like eruptions or large-magnitude La Ninas. This current cooling doesn't have one."
Instead, Swanson and colleague Anastasios Tsonis think a series of climate processes have aligned, conspiring to chill the climate. In 1997 and 1998, the tropical Pacific Ocean warmed rapidly in what Swanson called a "super El Nino event." It sent a shock wave through the oceans and atmosphere, jarring their circulation patterns into unison.
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This Swanson guy is a climate scientist? So he mentions that large la ninas can lead to cooling, yet cannot find any explanation at all as far as what is going on. Hello! You might want to actually check out some actual data! Or we could just choose to ignore the fact that we are in the second year of a LA NINA, which was actually a pretty strong one last year. And the second paragraph above... the strong el nina jarred circulations into unison? That doesn't even make any sense, but since a supposed climate scientist cannot even tell we've been in a solid la nina, I guess nothing more should be expected.
At the end of the article, Swanson then states that this "halt" may go on for 30 years, but says "explosive" warming WILL resume thereafter! Gee, thanks. I'm supposed to believe that someone who apparantly cannot recognize a la nina, and admits to not having a clue what is going on right now somehow has what will happen 30 years and beyond all figured out. Forgive me for having no faith in this.
As I have said previously, the point is not that I doubt the role of human influence in global warming (some will read this and make that blind assumption). I think it probably is there. We just don't know if we account for 5%, 50%, 75%, or whatever. Until we have a better understanding of natural cycles (which this shows we obviously don't), there is no way to quantify our role in it.
Wednesday, March 4, 2009
Can We Close the Books on Winter?
Anyway, to the present... We are about to get an impressive warm surge into the East this weekend to erase much of the snowpack built up the other day. We could see temperatures reach at least 75 in Washington D.C, and perhaps flirt with around 70 in New York City. Even back to Chicago and Detroit should see temperatures reach the 60s. Certainly this will turn most people's thoughts to Spring, but we do have another interesting situation atmospherically going on currently. Note the first map below. It is the tendency of the global angular momentum (AAM), and is currently off-the-charts positive. We have been in the tank negatively for awhile, and recall negative AAM is a nina-like state, while +AAM is more typical of a nino state. And yes even in a la nina or el nino you can get temporary AAM cycles that support an opposite pattern. This spike upward in tendency indicates we may do just that. This should lead to addition of westerly flow coming off eastern Asia, and push the upper ridge currently in the north-central Pacific closer to the West Coast. This would lead to chances for colder air intrusion again farther east. Indeed, the second map, showing the model prog for 10 days away shows this ridge west / trough east alignment, and for those of you who know your climo, you can see this is a more nino-is look than nina. Also there is a hint of blocking in the Atlantic too, which can sometimes occur at times as a result of AAM spikes reverberating through the global atmosphere also.
So we have a favorable setup to get some colder air back into the pattern after the weekend into early next week warmth. Will it be enough? Well, as mentioned, it gets tougher this late in the season, so all you can say is that it gives you something to watch for. Then we have to consider how long this pattern would last. Given the tendency of the atmosphere to want to jolt back toward the nina side of the AAM charts recently, the window of opportunity may not last long until we can say we are waltzing into Spring (keeping in mind up north can stay in the game into April).
AAM Tendency
Day 10 Model Forecast
Monday, March 2, 2009
March Comes in like a Lion
The second map below map is at the 500 mb level (approximately 18,000 feet above sea level). The colors here show vorticity, which is a measure of spin in the atmosphere. Ahead of strong areas of vorticity, called "positive vorticity advection", you have stronger rising motion. Behind them you have sinking motion, or "negative vorticity advection". With sufficient moisture in place, the lift from an incoming vorticity maximum (vort max for short) causes clouds and precipitation. I have circled the main vort max with this storm. The track of this feature was similar to that of the 700 mb low shown in the first map. So if you look at this map, you see the areas of greatest moisture content, which coupled with the strong vort max, led to bands of very heavy snowfall just to the west of the track of these features today. These bands typically can produce several inches of snow in one area, and very little not too far away, which is what I tried to show with the sharp cutoff in snowfall on the forecast map.
So hopefully you had a chance to not only enjoy the storm, but learn from it as well. The idea here is that even if a storm like this is a slow starter, don't ever give up on it if you are just west of the forecast track of the 700 mb low with a strong upper level vort max in play. You can often get a pleasant surprise in such a setup. Once the storm is totally done, I'll look at verifications versus the forecast issued yesterday.