Blocking is King

The term "atmospheric blocking" is something often used exclusively in the winter season, as it is typically a more influential feature to look out for during the cold months. I, however, personally think it doesn't get enough play in the summer. Sure it isn't as strong of a signal, but can still have quite an influence. Don't believe me? Well, the Arctic Oscillation has been quite negative the entire month of June so far, indicating more high latitude blocking. So below, I have posted first the map of June's anomalies to date (image courtesy of the fine folks at MDA), and second, the map showing the typically pattern when blocking in prominent in June. I'll let you be the judge here, but it looks clear cut to me that it can play quite a role. Also, the astute one may notice a lot of years in the second composite come from years where we either were heading hard into el nino or already had one in progress. Coincidence? I tend to think not!

Some Bootleg June Stats

Interesting how so far, this summer (yes I know I'm calling it summer, as it is in the meteorological sense beginning June 1) has started off on the cooler side in most areas, other than for me down here in Texas... Yuck! I stole an idea from the easteruswx.com weather board, and went back and looked at some stats on 90 degree days in June for a few of the big cities in the East to see when the last time there was a June without a 90 degree day. There was a thread on this board about the last time New York has had a June without hitting 90, and I went back and looked at Philly and Boston as well. The reason I chose these sites is that they have not had a 90 so far this month, and do not seem likely to for the next week or perhaps two, taking us into late June. So if this idea is right, the window of opportunity would be getting pretty small. In any case, the last time Boston failed to get 90 in June was back in 1998. For New York, it was 1996, and for Philly you have to go back to 1982! It has been awhile indeed. This, it is possible we could get all the way into July, having had the hottest weather of the last few months in the East occur in late April rather than May or June!

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.

Racing Toward El Niño

The last couple of months has certainly brought about a rapid warming of the tropical Pacific waters, terminating the two year la nina event (yes the nina was interrupted for a bit last summer, but quickly returned). Now the focus is on what looks to be an oncoming el nino as we haed through this warm season and into next fall / winter. Of course nothing is a lock in weather, but given how rapidly the warming has occurred, and the time of year, it seems the move toward el nino will be tough to fight off, and a high end weak to moderate event is possible. Looking just statistically, if we reach the critical +0.5 above normal threshold in nino region 3.4 by June or even July, a moderate nino is the most likely, and even strong nino becomes more likely than weak. So from a probability standpoint, moderate has highest odds, then strong, folowed by weak, and lastly neutral. Again, this is only looking at the stats, not subsurface, PDO, or anything else. The state of the PDO, while it will rise in the next few months, in my view should help fight off attempts for any "strong" event, though something like 1972 cannot be ruled out. Looking at the subsurface, we appear to at least as warm or warmer than any of the devloping moderate ninos at this stage of the year, at least the ones in which we have data for. Thus, a moderate nino would appear to be the most likely call right now.

This of course would mean a less active hurricane season in terms of numbers than we have seen in most of the last 10-15 years if correct, but where the storms go is still the important factor anyway. There is always too much made of the number of storms, though to be fair, it is tough to predict who will see the most impacts from landfalls in a seasonal forecast, regardless of what anyone will tell you.

Anyway, in looking at the Spring pattern, we see a lot of things are very typical of a year in which we are seeing a developing nino. I know some have felt the nina ruled the roost for much of Spring, or that we haven't seen a lot of true nino effects yet, but the following two maps to me say otherwise. The first map shows the upper air anomalies for this Spring (Mar-May, as far as I plotted last week), and the second one is a composite of all Springs when we were heading toward a nino from a nina or neutral state. I think a lot of the major anomaly centers match up well, but you can be the judge.

Late Spring Doldrums

Haven't posted in awhile, partially due to some mostly uneventful weather recently, and also focusing more on research. There was actually some noteworthy items this week though. An "unexpected" surge of heat came into parts of the Plains and Upper Midwest this week, sending Minneapolis to 97 degrees on Tuesday, May 19th, marking the earliest on record that they have hit a temperature that high. There was a solid front to the north though. In fact, at 5pm that day, temperatures just in Minnesota ranged from 34 up in the northeast to 100 in the southwesern part of the state! Unreal contrast for any time of year but especially in mid to late May! Wednesday was impressive as well. Ashland, WI saw a morning low of 33, yet hit 90 that afternoon. Try dressing for that weather! Or you could have been in Sky Harbor, where the temperature moved from 46 to 86 in 20 minutes, topping out at 88, and then falling back to 45 just 40 minutes after that peak! I would have loved to be outside there during that event. The Lakes are still cool, so when the wind was off the lake, they were stuck in the 40s, but for 90 minutes or so, the wind turned SW and brought in the much, much warmer air that sat just inland... wild stuff, but can happen when you get shallow cold layers like this that quickly mix out.

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.

Incoming!

Haven't posted for awhile, as I figured I'd leave the hurricane talk near the top for a bit, but had to throw this in here today, as we're witnessing one of the more impressive thunderstorm complexes I have seen in quite some time rolling across Missouri and headed into northern Arkansas and western half of Tennessee and Kentucky. These "MCS"s (mesoscale convective systems) are common in the spring when you get impulses in the upper levels interacting with a very warm, moist (and thus unstable) air mass, but this one has been exceptionally strong, with gusts estimated as high as 100 mph when it passed through eastern Kansas this morning. Baseball size hail and a couple of tornadoes have occurred as well in Missouri. Just glancing at radar / satellite imagery, you'd think a hurricane was moving through the region! What is also fascinating is that some of the strongest winds have actually occurred behind the strongest line of thunderstorms, as high as 85 mph as much as 30 minutes after the worst of the thunderstorms has passed! Very wild and impressive stuff! I've seen plenty of damage reports coming in from the affected areas, so hopefully everyone stays safe who is in the path of this over the next few hours.


Here is an image from around 8:00 central time this morning. Wow!

Hurricane Season Just Over a Month Away!

Hard for me to believe, but we're steamrolling toward the start of another hurricane season. June will be here before you know it, and speculation about what type of season we will see is of course in full swing. The consensus seems to be for a near to slightly above normal year in terms of the number of named storms, though expected by most to be one of the quieter seasons we have seen in recent years, which of course have tended to produce more storms, or at least have more swirls named. The two big reasons citied for this are 1) cooler water in the Atlantic, and 2) a possible shift toward an el niño pattern.


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.

Vacation Done... Back to Weather

The worst part about vacations is that they have to end. I think I found my new favorite city in Zurich, Switzerland. What a fabulous place, from the scenery, to the easy access to public transportation, and just an all around good place to relax. Rome was nice as well, and even though I'm not Catholic, being in the Vatican as the Pope delivered his Easter Sunday message was quite an awesome experience.

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!