bluewave

In great winter storm patterns over the years for our area, it wasn’t unusual for at least one of the long range model runs to correctly see the storm potential. During late January and early February 2021, it was an OP GEM run that had a correct KU forecast from a week out. With the poor storm track patterns for big snows since February 2022, none of those OP runs showing numerous KUs long range have verified.

I suspect that the issues the models have been having long range are related to the much faster Northern Stream of the Pacifc Jet which continues. It’s not typical to get a strong -WPO +EPO couplet at the the same time in December. So the shortwaves in the fast Pacific flow are lowering heights over Eastern Alaska while the -WPO ridge stands firm. At least into mid December the +EPO and stronger Pacific are trying to have the ridge roll out into the Plains while the -WPO would have the ridge axis more in the West. So a tug of war between two competing influences that we normally don’t see at the same time. My guess is that the ridge eventually comes east at some point during the 2nd half of December as the Pacific Jet eventually wins out in these situations. Notice how the 10 year December strong -WPO composite features a more -EPO and a relaxed Pacific Jet. Much stronger Pacific Jet and unusual +EPO in mid-December for a very strong -WPO block Past 10 strongest December 500 mb -WPO blocks didn’t have to compete with such a strong Pacific Jet and +EPO

Models usually don’t get exact timing for the relaxation of a pattern which has persisted for several weeks. This is why I have been using the general recent climatology in December. Every year since 2011 from Philly to NYC there was at least 1 day reaching 55 or greater from the 17th to the 25th. That period is still 9-17 days out which is beyond the reliable model skill. It doesn’t mean every day or even most days were this warm since 2011. Some years it was only a 1 day warm up with other years more than a day reaching these temperatures. But the general December patterns over the years which have had a cold December 1-16th had moderated in the departures from the 17th through the 31st. The degree of this moderation has also been variable.

Miss the 2010-2018 KU benchmark era when we could lock in a 168 hr euro control run showing a near 950 mb low close to the benchmark and have it be correct. https://www.weather.gov/okx/Blizzard_Jan42018

Better to rely on the the various ensemble means at this point which show a less amplified solution than the OP GFS due the fast flow and kicker lows coming into the West Coast at that time.

Occasionally, we do get a colder month across the CONUS. This is the first several weeks of colder conditions since January. But these colder periods have been few and far between. So they tend to stand out when they occur and get more attention than the persistent warmth which has become the new normal. I will update the chart below when December data gets posted.

30 years since the mid 90s and over 100 years prior to that period isn’t a small sample size. What you describe as rigid is actually a very comprehensive approach which I have used with great success for long range outlooks. Since my approach is data driven, I haven’t come to any firm ideas yet on whether we can eventually shift back to at least some occasional benchmark tracks in the future. But the long term decline in snowfall has been unmistakable. So I leave open the idea of a bounce off these lows in coming years if we can weaken the Pacific Jet a bit. But this is very uncertain since the recent shifts have been so extreme.

We haven’t had a single average or above average snowfall season since the mid 90s without having at least one NESIS 1 or higher BM KU snowstorm. So KU benchmark storms have been mandatory for reaching average to above average snow since 93-94. Prior to the mid 90s this wasn’t the case in the much colder climate. We could string together a series of smaller snow events and reach into the 20s for snowfall.

Fits the Great Lakes cutter, I-78 to I-84 hugger and Rain-snow gradient, and suppressed Southern stream which has dominated since 2018-2019. Very difficult to achieve a true benchmark KU track with such a fast Pacific Jet. Way too many issues with kicker lows, amplified ridges pushing the gradient just north of NYC, and generally very poor wavelength spacing with so many shortwaves racing through the fast flow.

Ski resorts continue to be the big winner the overpowering Northern Stream of the Pacific Jet.

My early guess for January is that it will be warmer on average across the entire CONUS than last January was which finished as the 33rd coldest. All our multi year La Nina’s last 30 years have had one January which was on the colder side like last January while the others have been milder. But don’t have feel yet what the general 500mb pattern will be and where the warm and cold anomalies will set up or how much warmer specifically this January will be.

After midnight highs today. This happens quite a bit with Arctic fronts. Some of the great Arctic outbreaks from 77 to 94 would have had lower daily maxes if the front was just a little faster. SXUS51 KOKX 080557 OSOOKX New York City Metropolitan Area Weather Roundup National Weather Service New York NY 100 AM EST MON DEC 08 2025 CITY SKY/WX TMP DP RH WIND PRES REMARKS Central Park PTCLDY 38 24 57 VRB7 30.05R WCI 33 LaGuardia Arpt PTCLDY 40 21 46 W16G23 30.03R WCI 31 Kennedy Intl PTCLDY 37 27 67 W9 30.05R WCI 30 Newark Liberty PTCLDY 37 25 61 W8 30.04S WCI 31 Teterboro Arpt PTCLDY 36 25 64 W7 30.03S WCI 30 Bronx Lehman C N/A 37 27 65 W6 N/A WCI 33 Queens College N/A 39 27 60 W9 N/A WCI 33 Breezy Point N/A 37 N/A N/A W12 N/A WCI 30 Brooklyn Coll N/A 39 28 65 W10 N/A WCI 32 Staten Island N/A 36 28 75 W6 N/A WCI 31

This has been due to the inability of the models to resolve the split forcing pattern which has been in place this month so far. So the first 16 days of the month will verify significantly colder than the long range forecasts were indicating back in late November. La Nina’s often had colder patterns in December so this isn’t that much of a surprise. The interference pattern has created a cold MJO 6 type and not the canonical MJO 8 pattern and storm track. This is due to the forcing near the MJO 4-6 regions with the standing wave. So now that the models have a consolidation of forcing there as the forcing weakens over the Western Hemisphere, they are showing the seasonal moderation in temperatures we often see beginning in mid-December. The last few days have been the first time in a while that they are actually raising heights more than in earlier runs. So the ridge coming east faster is a function of the big Jet extension and MJO 4-6 forcing. Remember last early December how the models underestimated the mid to late December Jet extension and lower Pacific heights. New run faster Pacific Jet lowering heights more over Western North America and raising heights in the East

These charts below do a good job showing the current burst of stronger forcing in the MJO 4-6 areas. I suspect it’s one of the reasons we aren’t getting the canonical MJO 8 even with the RMMS in that space. This is why I like to look at the total forcing when they are out of alignment with the RMMS. Notice that the Pacific Jet hasn’t relaxed and we have a dominant northern stream. So even though we are experiencing a colder pattern since late November, the warmer storm track of the last 7 years hasn’t varied. This was the case during some of the colder intervals last winter also. Models are beginning to come into better agreement for the relaxation of the cold as the falling AAM and MJO 4-6 forcing supports a broad ridge across the U.S. mid to late month. This is a seasonal shift that we have seen frequently approaching mid to late December over the last decade. We had a big jet extension last December at this time also when the temperatures moderated.

The current standing wave in MJO 4-6 will consolidate the forcing there leading to a jet extension in around 10 days and the ridge getting pushed east with the falling AAM.