2330 EST 18 JAN …. STARDATE 201201.18
I love forecasting snowstorms in the Pacific Northwest. It doesn’t happen very often but when it does happen… is really quite interesting and very different from what we get in the northeast US. Back in the winter of 2006-7 or 2007-8 a really great pattern set up for the Pacific Northwest around Christmas time and that region got hammered with significant snow and ice storms –even Christmas Day in Seattle and Portland and much of the northwest. My experience over the past few decades has been that if you are not getting the Pacific Northwest right –the West Coast and general but especially the Pacific Northwest– than the rest of your forecast is going to suck Moose balls.
I am not going to spend a lot of time talking about the moderate snow event which is likely to move through portions of the upper Midwest the Great Lakes and the interior of the Northeast US on JAN 20-21. In fact if this was a regular winter this should be a pretty ordinary event and not get any intention are all. Essentially what happens is that a wave of Low pressure develops on the front as the large cold high over the north these slides off the Maine coast. The Low tracks into WVA then through PA. It’s a pretty weak system and a dozen have a lot of moisture with it and it’s moving pretty fast. Still for the snow lovers in the NE… some snow for folks in the Northeast is better than NO snow.
Now I know many of you in the eastern U.S. and especially in the northeast are probably shrieking or thinking “Hey DT you ignorant geek … who Gives a rat ass about the the Pacific Northwest?…” If you are asking that question or thinking those thoughts… then you’ve got a problem because you are missing something really important about this particular snowstorm. Not so much about the Pacific NW snowstorm per se… but what is causing it …the implications for the entire pattern as we move into February. So pay attention there sparky and let me tell you how Big Bertha and her huge Butt plays into this whole thing .
By now I am sure some of you have heard or read about the potential for significantly different pattern setting up over the next two weeks so that February and perhaps March 2012 end up being colder than normal or… at least the threat or the possibility of it being colder than normal over the eastern CONUS . There are strong indications are this MIGHT happen but we have to be careful here. We have been down this road a couple times before… and every time we have gotten close or looks like the pattern is starting to change… it turns to Moose Crap. So if you have your snow boggles on and you all excited because somebody in Pennsylvania or in New England is telling you that this time it’s really really really gonna happen… be careful.
A word to the wise. Saying the same thing over and over and over again… or in this case forecasting the pattern change the pattern change the pattern change… only to see the pattern finally change… is not REALLY forecasting weather. What you are doing is saying the same bullshit over and over and over. In other words if your forecasting skills in the extended and long range have been really good in the last two winters… But now you seem to have trouble figure out was going to happen and when / IF the pattern change is going to occur… that is probably a clue you are doing something wrong.
This first image shows us the long terms trends of the NAO and the AO since September.
As you can see from the image it is readily apparent that the NAO and AO have only drop into the negative territory twice since the up SEPT 15 !!! But more importantly since December there had been a several tries or surges where both the NAO and the AO have reached the Neutral Line — which I have Number as you can see. And every case the model data showing the AO or the NAO would drop to negative territory but in every instance - EVERY INSTANCE– both the AO and the NAO bounced back up strongly into positive territory and all of the model data turned out to be disastrously wrong. So again if you’re absolutely certain that the pattern to turn around and that it is going to turn out to be a great February and March 2012… BE CAREFUL. The trend here is not your friend. Of course that’s not to say the trend can not be broken but it does need to be respected .
This next image shows the overall pattern back on January 15. As you can see from the image itself I’ve highlighted the massive explosion in the WPO as a turn negative and built a huge rage into the Bering sea…. and Alaska… that expanded all the way into the western and Asian side of the Arctic circle. This explosiove Ridge developemnt was caused primarily by the stratospheric warming event. Also keep in mind that when the models of first detected this development – back in late DEC and early JAN– most of them showed this would lead to a much colder middle and the latter January… Which as we all now know… did NOT happen. Instead… the huge Ridge in the Bering sea and the western side of the Arctic circle moved into eastern Siberia. This in turn allow the polar vortex to move into western Canada and eventually into the Gulf Alaska were it is currently situated. It was this very movement of the PV which is WHY the arctic air came pouring over the Rockies in the continental divide into the Pacific Northwest and the Seattle Portland metro areas!!!
But more importantly is how the pattern slowly evolves. This next image shows the 72 hr — 12z JAN 18 run- valid JAN 21. I have highlighted the individual disturbances or impulses and Pacific jet stream and you can clearly see the amazingly cold bitter arctic air mass over Northern Canada that is associated with this super positive AO. This is one of the reasons why having such a strongly positive arctic oscillation is so bad for those wanting winter storms over the central or eastern CONUS. As you look at this image you can clearly see that in this sort of flow there is very little way to get that cold air to come southward .
96 HRS ECMWF… We can see a new development which is a core or center of the PV reemerging or developing over anchorage or in the Gulf of Alaska. Meanwhile more strong impulse is a batter the West Coast move across the Rockies into the planes bringing in much milder air
120 HR ECMWF VALID JAN 23… In this image I have highlighted the upper air map at 500 MB and the SURFACE map. The piece of energy in the central Plains develops into a significant winter storm for the Great Lakes which pulls up a lot of warm air into the northeast U.S. Chicago COULD have another significant snowstorm however. More importantly however it is this buildup of warm air along the East Coast which is driven northward into the high latitudes and forces the Heights to rapidly warm or increase over Eastern Canada. Sometimes is buildup of warm air and increasing Heights can cause the NAO to flip especially when it’s followed by several surges of warm air from the eastern U.S. into eastern and southeastern Canada.
That is exactly what happens over the JAN 24-25-26 time frame.
This image is a hemispheric shot of the European model at DAY 6 .. JAN 24 . I have highlighted some important features which are occurring at this time over the hemisphere. The most important is feature #1 which shows a another Ridge exploding northward into the arctic regions from the northern Pacific however this is significantly different than what we saw back on January 14-15. That ridge exploded northward over the Bering sea and we did not have a PV (Polar Vortex) in the gulf Alaska which will likely have JAN 24-25. This Ridge develops over eastern Siberia… because of the new vortex which forms over the Sea of Japan. The development of a deep vortex / 500 Low in the Sea of Japan is text book teleconnection for a much colder pattern over the eastern U.S.
ASSUMING this is correct the Ridge in Eastern Siberia will begin to drive the PV in the gulf Alaska… to the east into Western Canada which begins to alter the entire pattern.
At Day 7 JAN 25… The Great Lakes Low is now over southeastern Canada but it’s still feeding up warm air into southeastern Canada. However right behind that we see a major trough amplification over the entire Plains and the Midwest ( see THICK BLACK Line). This forces another surge of very warm air into the East Coast. Meanwhile over the West Coast and the eastern north Pacific the Gulf of Alaska PV is being driven east while a ridge is beginning to form off the California Coast.
DAY 8 … Again I have matched up the upper air map at 500 Mb with the surface map so YOU can follow how things develop. The new trough over the Mississippi Valley has caused a surface Low to form over Alabama… while warm air surges from the Deep south all the way into the Northeast U.S. Again I cannot stress how important this warm areas with respect to feeding the developing or Building 500 Mb heights over eastern Canada … Which in turn brings about the face change in the NAO. So even though I know winter weather lovers in the eastern U.S. will hate these warm temperatures the two serve a purpose!
In this next image DAY 9 … We can compare the European vs. the GFS from a hemispheric perspective. Both models or a remarkably good agreement as they BOTH show the PV in the gulf Alaska… They both show some sort of Ridge trying to form off the Southern California Coast in the eastern Pacific… And they both show some sort of building or increasing Heights over Eastern Canada.
By DAY 10 –lets use the EURO ENSEMBLE 500 mb maps – the changes are underway big time. Big Bertha has now left the gulf Alaska… or rather is leaving the gulf Alaska and sliding into Canada. It’s doing so because of the developing ridge over the Bering sea and eastern Siberia. In addition the Heights are rising rapidly over Eastern Canada and southern Greenland which indicates the possible development of a -NAO.
The 12z GFS ensemble – JAN 18 run — strongly agrees with this overall development of the pattern. In this image we can see the 6-10 day 500 MB height CHANGES. This is useful in showing us where things are trending.. We can see a very strong negative anomaly over the gulf Alaska which is the strong Polar Vortex. But we can also see the Heights beginning to increase over Eastern Canada.
Looking at the same product but now for the 11 to 15 day… We see major changes. The GFS ensemble shows the vortex that was in the gulf Alaska has now shifted east into western or Central Canada. The Heights are rapidly building in the Gulf of Alaska and we see increasing Heights over Greenland as part of a -NAO.
If we look at the 12z GFS ensemble itself — the 500 mb mean – at DAY10… We can see a very close match to what the European ensemble model is showing. Note the strong vortex over the Sea of Japan! Note the ridge over far eastern Siberia and the Aleutian islands… And notice the dark purple the long date and shading extending from North Central Canada down to NW Ontario Canada. This tells me that the model is showing the PV is splitting apart or redeveloping.
312 HR the 12z GFS Ensemble has evolve into a completely different and full blown winter pattern over the north American continent. As I have highlighted here… There is a new deep PV over the Sea of Japan… A very strong Ridge e over the Bering sea and new PV with 2 centers: one over far N central Canada and the otther over James bay . If we accept this model as verbatim or being fairly close to the truth… We now have a raging +PNA pattern a – AO a – NAO and the eastern U.S. is now in business for February winter storms.
WHAT CAN GO WRONG?
This is probably the most important part of the whole discussion given what’s happened this winter. There are so many things that could go wrong with this sequence of events as shown by the weather models. But it’s important to do this because you don’t want get caught up in the mental loop or trap of believing that the pattern change HAS to occur because the weather models say it has to occur.
1) the development of the deep 500 Low that becomes a new polar vortex feature in the Sea of Japan. If this feature does not develop THEN the entire pattern change will fall into a pile of Moose crap. It is this feature which causes the Ridge to develop over eastern Siberia and the Bering sea. If there is no big 500 mb Low in the sea Japan in the last few days of January then the ridge will act TOTALLY different… And it will not cause the changes to occur across North America.
2) this is related to #1 above. Suppose the PV in the Gulf of Alaska it does not move. Say goodbye to the pattern change.
3) THE WARMTH over the eastern US does NOT reach into eastern Canada … Which in turn would mean a much weaker -NAO. Or it might only force the NAO to go to briefly neutral… which as I stated at the beginning of this essay has been the trend all winter long.