2000 EST 26 NOV 2011…. STARDATE 201111.26
While thanksgiving is over and MOST the turkey has been eaten so it’s time to get back to the weather biz. (although I am a anticipating one more delicious Turkey left over lunch on Sunday afternoon) First I’m extremely happy with the way this weekend forecast turned out. Up and down the entire East Coast and in to the Ohio and Tennessee Valley this has been an extremely nice long thanksgiving weekend. I do believe one could make the case that this has been nicest thanksgiving weekend in the last 50 years or more! Given a that I made this forecast here on the WEB page and over on FACEBOOK for the 1st time back on NOV 15-16… I am darn happy.
However when I made that forecasts and in the subsequent updates to that I talked about how of as we came out of the holiday weekend — NOV 27 – it could be a difficult travel day for many areas over the eastern U.S. The ixssue is a slow moving but important cold front which can be seen crossing the Midwest and the Delta regions on the Saturday early evening radar. Over the past several days the weather models have slowed the system down a bit so that by the time and reaches this maximum intensity it will actually be Monday the 28th.
That being said … the overall scenario really has not changed …its just a timing issue. All the model data shows that energy coming into the base of the trough over the Delta region will cause an upper Low to form and separate itself from the main trough over the Midwest. When this happens is called a CUTOFF LOW. But in this case… the cutoff Low develops a negative tilt. …which is a sign of a very strong and rapidly developing system over the TN and Ohio valleys.
To show you what this looks like here is the 12z SATURDAY GFS Model at 60 72 and 84 hrs at the 500 MB level. I have drawn in the trough axis or the tilt of the upper low and you can see it’s running from the northwest towards the southeast…. which is by definition a negative tilt.
At the surface a second area of Low pressure is going to form over the Gulf coast states and be pulled northward then northwest under this deep closed cutoff Low . In addition the strong area of High pressure off the East Coast — the feature giving the eastern US this great weekend.. will still be a factor. The High off the coast will be feeding a significant inflow of very moist air from the southwest Atlantic into the the entire East Coast region. Over the Appalachian mountains and into the elevated terrain of TN and KY rainfall amounts will be quite impressive over the next three days. Possibly as much as 6 inches a rain and some locations.
BUT then things get tricky. Note in those GFS 500 MB maps how many of those Black Lines develop around the upper Low. At 72 hrs the GFS shows 4 closed contours around this very impressive “monster” upper Low. That represents a great deal of very cold air in the middle and upper levels of the atmosphere and as result the GFS Model shows that the low levels COULD become cold enough over the high terrain for the rain to go over snow Monday night into Tuesday over Northern Alabama portions of Tennessee into Indiana and much of Michigan.
For this reason I have issued a FIRST GUESS map with regard to this potential for snow. This is a very risky forecast and it is quite possible that the cold air never gets down to the surface in time to cause force the rain to change over snow.
Further to the east it is pretty clear that there is going to be a large band of heavy showers and thunderstorms developing over the coastal areas of GA and SC then move into all of North Carolina southern and western Virginia… central Virginia and all of WV and into MD and western PA. However as this band pushes to the north and northeast it will weaken and fall apart once it reaches central and northeastern Pennsylvania and New Jersey.
Longer term we can see some major changes occurring in the overall pattern. Of course it may not mean much for your particular location BUT…. if you want to take a look of the big picture there are some things to point out which are significant.
In this image we can see the Upper air pattern (500 mb) from November 21 and compare it to the forecast to the day 10 European model valid for December 8. We can see some major differences. Note that the huge vortex and deep troug in the gulf Alaska and the Eastern Pacific Ocean on November 21 has been replaced by a very strong Ridge that pushes up to the coast of Alaska! Also the ridge over the central CONUS is now being replaced by a fairly deep trough. The strong Ridge over Europe gets replaced by a deep trough. So things are changing.
If we look at some other Teleconnection indices however we see some discrepancies. If we look of the two week forecast in Trends from the GFS ensemble from the ESRL web site… the regular GFS and the PSD version of the GFS both showed the NAO staying strongly positive for most of the time frame ( perahps beginning to move towards a Neutral by day 13-14). However they do NOT agree on the PNA. The regular GFS model shows moderately strong positive PNA through day 10-11…. whereas the PSD version of the GFS shows an extremely strong negative PNA.
Clearly these two things are not the same. The reason is that the PSD definition of what constitutes a -PNA vs a +PNA is not the same as CPC/ NCEP definition.
We see the same sort of problem looking at the Western Pacific and EPO Teleconnection trends. Both versions of the GFS are in pretty good agreement over the next 11 to 12 days with regard to the Western Pacific Teleconnection. But they do not agree over the EPO trends. As you can see the PSD version of the GFS shows wild swings back and forth fromn positive to negative then negative back the positive with regard to the EPO.
One of the ways and getting around this sort of discrepancy is to look of the European model and the European ensembles. I have placed the operational European run at day 10 next to the day 10 European ensemble. The European ensemble has a weaker ridge over the southeastern CONUS so temperatures are somewhat colder east of the Mississippi River. But the important thing here is that both the Operational Europeran and the European ensemble show a very strong Ridge over the eastern Pacific pushing up towards the coast of Alaska . To be sure this is NOT massive or highly amplified Ridge… but it clearly shows that the PNA is going to be in the positive phase at day 10.
Clearly the PSD run of the GFS is wrong.
If we look at the GFS ENSEMBLE temperatures at Day 7 we can see a lot of dark blue and some purple actually showing up over portions of the eastern U.S.– mainly over the southern portions of the U.S. while over the Northeast and the Great Lakes sees seasonal early DEC temperatures. At Day 13… we see more of the same…
Finally I suppose it’s fair to say that there are TWO ways to look at the first 10 or 12 days of December 2011. It is clearly not going to be as cold as what some of the private energy forecasters have been calling for. On the other hand given the fact that +PNA is only of average intensity… the AO this still clearly positive as is the NAO… it is almost a miracle that Deep South looks cold while the Great Lakes and the Northeast looks seasonal for early December.
1900 EST NOV 23 2011… STARDATE 20111.23
I am hearing report some various meteorologists both within the private commercial sector and in the energy sector which are either killing off the winter of 2011-12 over the eastern half of the CONUS …. Or they are significantly downplaying it.
I suppose to a lot of folks this sort of decision doesn’t make a lot of sense especially given that we’re just now entering the thanksgiving holiday. From my point of view of I agree. I think part of the problem… may be that the last two winters were so significant over so much of the country east of the Rockies and especially east the Mississippi River… that many have become spoiled. And because there have been 2 significant winters in a row ..the anticipation and build up… the excitement about the potential for this winter… especially given some of the early forecast calls… have all contributed significantly to ” expectations” . As a result …IF it turns out that this winter is not going to be as impressive as the last two winters… and you have been telling folks and your clients that thid winter WILL be… well then you may have a problem.
We now KNOW that November 2011 will end up been pretty mild and there has been a real lack of cold air over any portion of North America. Of course as I pointed out in a previous posting November 2010 was pretty mild as well… So this current Mild NOV does necessarily mean anything. But you have to understand if you are weather hobbyists WHY some of these other forecast services and private forecasters are already downplaying and/or backpedaling on the winter of 2011-12.
Essentially they have been following the overall pattern and they see the number of things wrong with it and they figure that by the time things change so that we are seeing even “seasonal cold” temperatures it may be DEC 10 or 15. Of course past the past December we still have January February and for most of the CONUS a good portion of March as well. There is just too much data and indication out there — the above and much above normal snowfall over the northern hemisphere and especially over Eurasia… the super warm North Atlantic ( the +AMO) … the weak negative QBO and the fact that the La Nina has NOT strengthened steadily or dramatically over the past few weeks (recall last Sept and OCT the La Nina dropped like a Rock) to bail out on the Winter.
So at this point I have not given up in the winter and I certainly have not given up on December still being at least seasonally cold or fairly close to being seasonally cold for a good portion of the central and eastern CONUS. That being said some of us are just going to have to get used to the fact the last couple winters have been really good with respect to EARLY season cold and snow for large portions of the central and eastern U.S. The last 2 winters really got cranking in December… but there have been a lot of winters in the weather history of the country in which December was either Mild or just OK ( DEC 93 of the winter of 1993-94 comes to mind) that did not get cracking until January and February.
If we take a look of the latest MJO plots
you will see that most of the Plots show the current MJO swings around into Phase 3 and 4 and 5 over the next 2 weeks. As you can see here in DEC Phase 4 and 5 are very Mild temps patterns for the central and eastern US. This would lead one to believe that the mild pattern over the central and eastern US is going to continue into the first 10 days of December.
However that most of the medium range models do not agree with that scenario. Keep in mind tha the current MJO impulse is pretty weak and it is very possible that it might collapse into the ” circle of Death”.
For example here is the first image which shows the DAY 10 European model hemispheric projection from 0z FRIDAY NOV 23. As you can see it does not show a very promising looking pattern at all. All the cold air is bottled up across the arctic region and the overall pattern across the CONUS looks pretty darn benign.
However the 12z NOV 23 European model both at the operational and the ensemble level looks much more significant and promising. At the operational level we can see ( the Hemispheric projection) a major Ridge developing in the eastern Pacific pushing North into the Yukon and Eastern Alaska… and a rapidly in deepening major trough over Western Canada pushing into the Pacific Northwest and northern Rockies. That certainly is a major change from the 0z Operational European run! The day 10 operational European model at day 10 shows a 3 WAVE pattern – 3 distinct troughs over the hemisphere.
Focusing more on the CONUS at day 10 you can see the very impressive amount of cold air pouring south at a Western Canada driving across the continental divide trying to reach location such as Seattle and Boise.
At the Ensemble Level Day 10 day the 12z European shows a more improved pattern both at the hemispheric level and at the regional level. At the hemispheric perspective we can see two distinct polar vortexes : One is over northeastern Canada and the other is over eastern Siberia. This is a significant change from earlier in the month when we have the PV in Alaska and the Yukon. In addition we no longer have a deep trough in the gulf Alaska slamming into Western Canada but now we have a “flat” or Broad Ridge. Again NOT good for serious serious cold air getting into the CONUS but its not nearly as awful when you compare it to what the pattern is look like over the past 10-14 days.
It is quite possible that the deep trough over Western Canada will swing through an across the Rockies the Plains the Midwest and into the East Coast during early in the middle portions of December. It is also quite possible that the trough may stay over the western U.S. and perhaps just reach portions of the Plains. Certainly that is what the MJO amd its forecast of Phase 4-5 is indicating.