bluewave

Late last November into early December the EPS and GEFS were forecasting the +PNA -EPO to extend through the holidays. But they greatly underestimated the Pacific Jet and we got the big jet extension which lead to the record +EPO and warmer pattern later in the month. I was highlighting the warmer risks back in the threads going into early December last year. Then we got the big January suppression pattern with the record snowstorm on the Gulf Coast. There was a kicker coming into Western Canada at the time that contributed to that suppression. The MJO 8 was really brief in phase 8 on the RMMS last January but we had lingering forcing on the VP charts near the Maritime Continent which may have prevented the Pacific Jet from fully relaxing like our last successful MJO 8 in January 2022. Then in early February the extended EPS was trying to forecast a snowy gradient pattern near NYC. I mentioned that the gradient would probably shift to the north. Then we got the record Great Lakes cutter with the -5SD Greenland block which linked with the Southeast ridge and Toronto hot the record snows. Since the models underestimated the Southeast ridge again. This is why I don’t have any confidence when models show big patterns in the week 2 and week 3 time ranges. If a big pattern shows up under 120 hrs, then I will get on board.

Looks like a little warmer than average as we head into the last week of November. Storm track remains through the Great Lakes. So the warm ups will be a bit more impressive than the cool downs which follow. But nothing too extreme in terms of temperatures and storms.

Models really struggle with the December forecast progression of the pattern in late November. That’s why I would like to see everything play out over the next few weeks before getting too excited this early. Let’s see what the Euro monthly comes up with on the December 5th release. There is a bit of a late November forecast barrier for getting the mid into late December patterns correct. Since we can go back to most years at this time in the long range forecasts and watch numerous changes as the calendar actually gets into the first 5 days or so of December. Plus we have the backdrop of only 3 Decembers in the last 14 years that lead to major I-95 snowstorms since 2011. So December has faced some challenges for the snowfall after having 7 out of 11 snowy years between 2000 and 2010.

It’s a main feature of the pattern which has been stuck in place for the last 7 years with a brief relaxation during 20-21 and Jan 22. Very hostile Pacific pattern for snow in the I-95 corridor. Good patterns for snow produce classic KU benchmark storms which were in abundance from 2010 to 2018 with the much weaker Pacific Jet. Happened too many times for me to count from 2010 to 2018. Plus I started getting excited about the 20-21 winter during that October with my first successful use for the October MJO indicator for La Ninas. The most recent time was later in December 2021 after the highly amplified December MJO 6-7 stall that month which really pumped the Southeast ridge. But around the holidays the models started showing a legit MJO 8 for January 2022 which verified. So that was the last successful MJO 8 passage. We have had many model forecasts for phase 8 since then. But none have worked out due to interference from the WPAC warm pool. So I would like to see all the VP anomaly charts showing weakening forcing within week 1 near the Maritime Continent for the forecast to be believable.

The pattern never developed which could have produced a KU. That’s why it didn’t happen. Need the Pacific Jet to relax for storm tracks like that.

This is the actual 500mb pattern last winter on the 11 days which .20 or more of precipitation fell from Philly to Boston. Very fast extended Pacific Jet along with a Southeast ridge linking up with the Greenland block with a warm storm track through the Great Lakes. So the NYC average temperature last winter during the days with the heavier precipitation was 41° which was too warm to reach anywhere near average seasonal snowfall. Long range models consistently missed this pattern beyond 1 week out. Has nothing to due with luck or Monday morning quarterbacking. The storm track is a function of the pattern. I still think it’s possible to change things up a bit. But I am not going to make that forecast based on a week 2 or 3 model forecast. It has to show up in the short term in order to be believable. 11 day 500 mb composite DJF 24-25 when .20 of precipitation fell from Philly to Boston

The storm track pattern most of the time since 2018-2019 has been Great Lakes cutter, I-78 to I-84 hugger, and suppressed Southern Stream. This has been a result of the record WPAC warmth both in the subtropics and midlatitudes with a much faster Northern Stream of the Pacific Jet along the thermal gradient between the Siberian cold and WPAC to south of Aleutians warmth. Storm track #1 features a trough in the West and a Southeast ridge. So the low deepens crossing the Great Lakes with a warm storm track and mostly rain along the I-95 corridor from DC to Boston. Track# 2 features poor wavelength spacing in the fast Pacific flow so the storm hugs the I-78 to I-84 corridor favoring the interior regions away from the coast for the heaviest snows. Both these tracks feature too strong of a Southeast Ridge. Track #3 has a kicker low coming into Western North America in the fast Pacific flow keeping the Southern Stream suppressed and preventing a true 40/70 benchmark snowstorm track. Southeast ridge relaxes too much and the low slips to the Southeast. Even with a winter average temperature closer to the long term average last year, there was no deviation in this storm track pattern. Many times since February 2022 the long range forecast models have show big pattern changes during weeks 2 and 3. But we are yet to see a big change in this model bias. So this is why I like to temper long range expectations and wait until an actual pattern change shows up in the short term for it to be believable. RMM chart forecasts showing solid MJO 8 passages beyond 10 days out have either weakened before phase 8 due to the warm pool near the Maritime Continent or made it into 8 with lingering forcing hanging back near the Maritime Continent. So we didn’t get the true MJO 8 like we last had in January 2022. There have also been several events involving the stratosphere which haven’t panned out for snow or cold here. So this is why I don’t trust long range models to actually show pattern changes during weeks 2 and 3 since we have been through this numerous times before. But if we can actually get a shift in this pattern into the under 120 hr model forecast, then it will be something to be happy about.

We have had numerous model forecast attempts beyond 10 days to try and shift the storm tracks pattern since February 2022. But none have made to under 120 hrs on the models It’s still possible that something could eventually shift. But it won’t be believable until it shows up under 120 hrs.

Looking more like a reflective event at this point in time.

It’s better to be realistic about the model errors beyond 10 to 15 days and the frequent repeating patterns. I get it that many on here like cold and snowy weather. But you want to see the cutter, hugger, and suppressed Southern Stream storm tracks shift in order to be more optimistic about our snowfall prospects.

The one constant every December since 2011 from Philly to NYC Metro has been at least one 55°+ warm up between December 17th to 25th even when the long range models forecasts were cold like last year.

SSWs or wave reflection events don’t automatically mean cold and wintry conditions around our area. Plus the sample size of December SSW events since the late 80s is very small at only three years during La Nina’s .Those three didn’t really do much for us. Hopefully, we can see some improvement over those limited past early cases. Even if the RMMs eventually make it into phase 8, the VP charts still have convection lingering near the Maritime Continent. Doesn’t take much convection there in concert with the gradient between Siberia and the mid latitude WPAC warm poll to enhance the Pacific Jet. The faster Pacific Jet has resulted in the dominant Great Lakes cutter, l-78 to I-84 hugger, and suppressed Southern Stream storm tracks since 2018-2019 when the mid-latitude WPAC Pacific became warm. So when we have had troughs in the East during recent years, they usually got pulled in behind a departing Great Lakes cutters or hugger tracks. Then we went cold and dry for a while the Southern Stream got suppressed. Then the Southeast ridge has usually rebounded with more cutters and huggers.

Getting a clean phase 8 pattern during December is going to be a challenge with any convection lingering near the Maritime Continent.

The 5 day forecast mean has a deeper trough in the West and stronger Southeast Ridge than the typical phase 7. That’s why I used the term elements or similarities. Still no change in the dominant storm track through the Great Lakes into early December.

The EPS tends to dampen the convection near the Maritime Continent beyond day 10 too much. For some reason the GEFS tends to do better. That region near 150E will probably have more forcing showing up in future EPS runs as we get closer to early December.