02/22/16 Mo Mo: Figuring Out What's Left Of Winter

Good Morning,

So far this winter has thrown the entire kitchen sink at us. Record temperatures in December, a Roidzilla for most in January, and sub-zero temperatures earlier this month. These have been the highlights. I think most would agree this has been a divided winter. Areas N&W of NYC are well below their seasonal snowfall while those in and S&E of NYC reached or surpassed their seasonal snowfall. Only 1 more week of February is left. This means we're down to our last week of Meteorological Winter. 

Light to moderate snow may be coming down Tuesday afternoon as a weak wave tracks up the coast. Snow should change to a mix then rain by late Tuesday. A minor 1 to 2 inches of snow is possible for those N&W and N&E of NYC. Some models are showing much more in the way of accumulation but I do not think the wave is strong enough to support high precipitation amounts. Wave 2 will be stronger but since it will be tracking well west of the area that means temps will go soaring into the 50's so rain will be the main concern. Rain may continue through Thursday morning. Overall, a soggy and overcast week. 

Once the storm tracks into Canada, it will shift winds from the south to the north and help bring colder air back into the area. 

To finish out the month the GEFS and EPS are in agreement the NW flow will return and below normal temps are likely the 27th-29th. The trough axis does not support the development of any major snowstorms. The PV is over the Hudson and the flow across the country is more zonal than meridonial. We'll see as we get closer to this time frame if models begin showing any southern stream energy eject out of the STJ and possibly interact with upper energy out of the polar jet. That would support at least a moderate snowfall. At this time, models do not show that but instead think it'll be mainly cold with possibly an arctic front bringing light snow to the area. 

The March 1st-5th time frame looks more favorable for winter storm chances. The PV is east of the Hudson and the trough axis is sharper. Additionally, the NAO looks to be negative at this time. This is shown by the higher than normal heights across Greenland into Baffin Bay / Davis Strait. The PNA will remain positive thanks to the anomalous trough over the Aleutian Islands and the AO will also remain negative. The key will be to see how much staying power this pattern has. If it's transient, it will be difficult for a storm to get organized in time before it breaks down. The timing will be critical for whatever upper energy we have to work with. So, keep in mind the March 1st-5th time frame for a possible winter storm. At the very least, it should remain cold (dating back to the February 27th period). 

According to the CFS OLR forecast, the last week of February will feature impressive negatives over the Dateline which supports a trough over the Aleutian Islands and a ridge up the west coast. As we just saw, the Ensembles do a nice job of depicting just that. Notice by the time we get into March, especially after the 6th, the negative OLR anomalies begin to shift east closer to 120W than 180. With forcing shifting east, this will also push the trough over the NPAC east and break down the +PNA. If you think back to December and early January, this was basically the same situation where tropical forcing was east of the International Dateline. 

The CFS Weekly does a nice job showing the NPAC trough gradually shifting east week 1 to week 2 of March. Notice the negative anomalies beginning to show up over the western U.S. with the higher heights focused across Canada. 

The CFS is not the only piece of guidance showing this pattern change. The GEFS and EPS agree negative heights will spread into the west coast by the 6th of March. The ridge will shift into Canada and the flow across the U.S. will be mainly progressive with little amplification. We will see how deep the trough gets over the western U.S. The deeper the trough, the more amplified the southeast ridge gets over the east and the warmer our temperatures get. 

While the mean trough will try to stay confined to the Aleutian Islands, it looks like lobes of upper energy will break off it and come crashing into the west coast to prevent the PNA from going positive. Again, this is reminiscent of the pattern we saw in early January. In December, the PNA was very negative and the east was seeing temps way above normal. I do not see that type of pattern returning just yet, but even early January was a frustrating time for winter weather lovers located in the east. 

In sum, I think February 27th-March 5th will be a cold period with 1-2 winter storm chances. Once the 2nd week of March rolls around, I think the unseasonable colder air will retreat north and our temps will hover around normal to slightly above depending on how deep the negatives get in the western U.S. Normal temps for CPK NY in early March are in the lower 50's. If the aforementioned pattern comes to fruition winter will be coming to a vast ending sooner than later. 

Models Completely Lost - February 8th-10th Storm Threats

Temperatures neared 60 degrees today with heavy rainfall and localized flooding. The snow pack left from the Roidzilla almost two weeks ago is quickly melting away. It has been your typical El Nino winter to this point. As shown in the video I put together the pattern beginning this weekend is going to lead to a long stretch of below normal temperatures and an active period for tracking snowstorms. I want to focus my attention in this blog looking at the potential storm threats next week. If you're interested about how the upcoming pattern is coming together (tropical forcing / minor Sudden Stratospheric Warming Event) please watch the video.

Weather models are advertising 2 possible storms for early next week. During this write up I will refer to them as Wave #2 and Wave #3. Wave #1 is a minor event that may bring light snow accumulations to the Jersey Shore, NYC, and Long Island. At this time I think this is a C-2 inch ordeal that may not stick very well to roadways. Timing would be after Midnight late Thursday through 7am Friday morning. 

Here is this afternoon's run of the 12z EURO 500mb height anomaly valid 1pm Super Bowl Sunday. I labeled both waves and the northern s/w (short wave) over eastern Canada. Earlier in the week models were keying in on Wave #2. The 500mb trough was closing off further west allowing heights to rise along the EC (east coast) to track a strong surface low up or just off the coast. Recently, models disagree with that notion and are now keying in on Wave #3. Where Wave #2 tracks, how strong the storm gets, and its speed of departing the region DIRECTLY influences how Wave #3 comes together. According to the latest EURO run, the 500mb trough associated with Wave #2 closes off too far S&E which tracks the storm east of the BM (benchmark). It's fair to say Wave #3 de-amplified the trough from Wave #2 which is one reason why H5 closed off too late. 

Moving along to 7am Monday, Wave #3 is struggling to come together. You can see Wave #2 is east of the BM but the spacing between it and Wave #3 is too close to allow amplification in the 500mb trough. Further, notice the green "X" over the Great Lakes. This is where this afternoon's run of the EURO closed off H5. The 500mb upper low ends up staying stationed over the Great Lakes instead of digging into the CONUS. The purple "X" is where the 00z EURO run from last night had the 500mb upper low. It dug nicely into the CONUS then tracked east to bring a powerful Miller-B type storm to the area Tuesday of next week. 

To get an idea of why the EURO did not dig the H5 upper low nearly as much as its 00z run, let's take a look at the 500mb vorticity map valid 7pm Super Bowl Sunday.  We'll stay with the green and purple theme. Green is today's 12z EURO run and purple was the 00z EURO run from last night. In the 00z run, the EURO consolidated the upper energy better and dug it into the central U.S. On the 12z run, the EURO is a bit more scattered with the upper energy and tracks it more east than south. This is the main reason why the 12z run closes H5 off over the Great Lakes while the 00z run closed off in the east-central U.S. Meanwhile, Wave #2 is still hanging around the Southeast U.S. dampening heights. You can see it also is struggling with consolidating upper energy at the base of the trough. The trough remains open and positively tilted. 

Taking this information into consideration, here are my thought's:

1. I do not like Wave #2 very much. I think the short wave trough in eastern Canada acts as too much confluence to allow heights to rise along the EC. Sounds familiar, right? Except the Roidzilla two weeks ago did not have another storm right on its heals. Wave #2 and Wave #3 are basically de-amplifying each others flow. 

2. One of two things need to happen to get either Wave #2 or Wave #3 to pan out for the area. Either Wave #3 slows down and separates itself from Wave #2 more, or Wave #2 moves out faster than currently modeled to give Wave #3 more space to amplify into the east coast. With an anomalous western ridge I do not see how the upper energy associated with Wave #3 does not dig into the eastern CONUS. I think if Wave #2 was out of the picture this afternoon's run of the EURO would have looked like its 00z run. 

3. Unfortunately we run the risk neither wave comes to fruition. If the spacing between both waves remains this close, I fear the upper energy will not come together to promote cyclogenesis. Over the next few days it will be very interesting to see if models focus less on one wave and more on another. Maybe Wave #2 and Wave #3 come together as one wave. I think that's unlikely right now but you never know based off model performance this year. 

The upper energy associated with both waves is still located over the eastern and central Pacific Ocean. We have seen drastic changes in modeling once the sampling of these upper energies became clearer. It is important to keep in mind we're working with a ++PNA (again, watch the video) and an EPO / AO going from positive to negative. I personally think these type of signals under an El Nino regime means one of these two storms will come to fruition. It's just a matter of which one. We'll know more by the weekend! 

Thanks for reading. 

Best,

Francesco Paparatto