{ "number": 807, "headline": "December 4, 2025 Thursday Evening Weather", "standfirst": "Huge cold pool forms in western Canada and Alaska into mid-December", "desk": "winter", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2025-12-05", "published": "2025-12-05T01:45:39.245000Z", "updated": null, "access": "free", "body_html": "
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This is post number 805 \u2026 evening update to keep the ball rolling into the wild winter ahead | Author: Dr. Ryan Maue (X @RyanMaue X @weathertrader)

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Temperature Anomaly | Next 15-days

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Flagship European model ensemble solution for temperature anomaly next 15-days shows the cold pool formation and intensification over Alaska and Western Canada \u2014 a more typical Polar Vortex dump with strong surface high pressure blasting southward along and east of the Rockies into the central U.S. in the 2-week time frame \u2014> remnants of our recent/ongoing stratospheric warming event \u2014> and then another one in the coming 10-12 days!

Note, there are fast moving disturbances or short-waves riding along the polar front from the Gulf of Alaska through the Pacific Northwest and then in the Midwest and Great Lakes. These features are spaced out in time \u2014 so the ensemble mean blends or smooths out 51 solutions that ALL have cold blasts but intermixed with warm periods. The end result is a rather smoothed continuous blob of cold connecting Alaska with the Northeast U.S.

This has potential for VERY cold Arctic blast outbreaks!

Weather into Friday morning | Fronts this evening

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Southeast Storm System \u2014> Heavy Rain for Gulf Coast + Mix/Snow into TN/VA this evening \u2014 as the moisture rides northward into much colder Arctic air \u2014 thankfully not a big ice or freezing rain ordeal

HRRR 23z | Next 18-Hours into Friday Noon

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NWS has ticked up snowfall amounts in western VA into the more impactful range > 3\u201d but still minor dusting or light snow in Washington D.C. for the 5th of December.

Precipitation Type | Weather Next 6-days | ECMWF 186z

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Boatloads of moisture coming into the Pacific Northwest with 2 major atmospheric river events in next 6-days \u2026 and Alberta Clippers pick up whatever makes it through the Rockies to take into the Midwest and Great Lakes with weak storm system snow events \u2014 eventually these start adding up!

Headlines Thursday Evening

  1. Very cold evening across the Midwest and Great Lakes \u2014> bottom dropping out with temperatures from clear skies, calm winds, and snow cover

  2. Still not seeing any strong systems across the Eastern U.S. but quick moving \u201ccutter\u201d or Clipper Systems could provide wintry precipitation especially with the cold air in place \u2014> typical with negative AO/negative NAO

  3. Major atmospheric rivers into the Pacific Northwest will be impactful \u2014 on the front end of a surge of Pacific / West Coast warmth that will try very hard to nose across the Rockies \u2014 and bust into the Arctic air mass. Ridging into Week 2 across the central U.S. would be a welcome reprieve from the Arctic air mass, but I\u2019m less certain about the cold breaking in a sustained manner. There\u2019s a HUGE load of cold air that will form over Alaska/Western Canada and be ready to dump southward into mid-December.

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ECMWF 18z Precipitable Water Next 6-days | My favorite parameter

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Atmospheric river systems into the Pacific Northwest \u2014 narrow at first, and then quite a wide swath by next Tues/Wed \u2014 see how shortwave disturbances along the polar front (polar vortex edge) pick up the moisture = Alberta clipper systems

White colored precipitable water = absence of moisture = cold/polar air mass

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Temperature Analysis | 7:45 PM ET

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Temperatures crashing across eastern Iowa, northern Illinois, and southern Wisconsin

Temperature Anomaly | 7:45 PM ET

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Lower 48 Temperature Anomaly was -6.7\u00b0F below normal

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NWS Precipitation Next 72-hours

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NWS Snowfall Next 72-hours

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Just light dusting for Washington D.C. maybe 0.5\u201d at most of light snow \u2014 but more across Virginia, painting within the lines of the state border!

Blend of Models | 10 Days Precipitation Total (includes liq from snow)

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Enormous precipitation totals in the Cascades \u2026 upwards of 20\u201d of QPF or more would translate into outrageous snowfall totals

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Blend of Models | Total Snowfall Next 10-Days

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Friday Morning Low Temperatures

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180 million below freezing (Lower 48 average low is 25.0\u00b0F)

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Friday High Temperatures

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Still 16 million at/above 80\u00b0F in Florida! 87 million don\u2019t get above freezing!

AI-GFS 18z | 500 mb Temperatures | Polar Vortex Watch Next 10-days

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Fancy new tool from NOAA (AI-GFS) shows the reorientation of the tropospheric polar vortex to ditch the cold pool over Hudson Bay \u2014 and instead dip/focus across Western Canada

NOAA GFS 18z | Dynamic Tropopause | Next 10-days

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I haven\u2019t shown the GFS in a while \u2014 just want to highlight the location of tropospheric polar vortex (big white fuzzball) swirling over Hudson and James Bay \u2014 not moving from its anchor position very much in 10-days.

ECMWF AIFS-Single 18z | Height Anomaly (500 hPa) Next 10-days

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Strong trough = coldest air across the Midwest and Great Lakes at Day 7 \u2014> but we have relief in sight with a building central U.S. ridge

Let\u2019s hope this sticks around for as long as possible \u2014 and the Western Canada PV doesn\u2019t arrive ahead of schedule (2-weeks)

Integrated Vapor Transport Next 10-days | North America

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Parameter used for monitoring \u201catmospheric rivers\u201d usually along the U.S. west coast, but the idea works well for many other areas \u2014 highlighting midlatitude storm systems with warm conveyor belts (moisture plumes)

ECMWF 18z | Snowfall | Next 6-days

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ECMWF EPS 12z | Ensemble Median Snowfall Next 10-days

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Instead of just the median \u2014 let\u2019s look at the 90th Percentile \u2014 if the model ensemble was operating in the 1 in 10 worst snowfall category \u2026 most places it\u2019s not a major difference BUT it can be \u2014> ECMWF EPS 12z | Ensemble 90th Percentile Snowfall Next 15-days

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The difference between the 75th and 25th Percentiles is the interquartile range (IQ) and shows the ensemble spread to a good approximation! Even when we show the median snowfall amounts, there is a +/- range of sometimes a similar magnitude of the median/mean \u2026 and that\u2019s why ensemble means of precipitation into the medium range can be misleading during storm events where 100 miles makes the difference between yes/no snowfall/rain \u2014 the average is not really a solution

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Interquartile Range (75% minus 25%) EPS 12z Snowfall | Next 10-days

ECMWF EPS 12z | Ensemble Snowfall Probability > 1\u201d | Next 15-days

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We\u2019ll be monitoring the 1\u201d chance of snowfall for a \u201cWhite Christmas\u201d in the coming weeks. This map is through late December 18th.

ECMWF EPS 12z | Ensemble Snowfall Probability > 6\u201d | Next 15-days

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6-inches is sufficient for a \u201cbig storm\u201d and Lake Effect machine diagnostic but 12\u201d is even better \u2014>

ECMWF EPS 12z | Ensemble Snowfall Probability > 12\u201d | Next 15-days

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Next 15-days Temperature Anomaly | Ensemble Mean to December 18

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Main story for the week is cold air entrenched in the Midwest, Great Lakes, and Northeast with the main tropospheric polar vortex perilously close to the Lower 48 locked onto a fulcrum over Hudson and James Bay. However, ridging across the Western U.S. will push eastward and displace the Arctic air \u2014 hopefully, as a new cold pool forms over Western Canada

Temperature Anomaly | Next 15-days | ECMWF EPS 12z

5-Day Chunk #1 | Temperature Anomaly | Dec 4 - Dec 8

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5-Day Chunk #2 | Temperature Anomaly | Dec 9 - Dec 13

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5-Day Chunk #3 | Temperature Anomaly | Dec 14 - Dec 18

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", "body_key": null, "teaser_html": "

Flagship European model ensemble solution for temperature anomaly next 15-days shows the cold pool formation and intensification over Alaska and Western Canada \u2014 a more typical Polar Vortex dump with strong surface high pressure blasting southward along and east of the Rockies into the central U.S. in the 2-week time frame \u2014> remnants of our recent/ongoing stratospheric warming event \u2014> and then another one in the coming 10-12 days!

Note, there are fast moving disturbances or short-waves riding along the polar front from the Gulf of Alaska through the Pacific Northwest and then in the Midwest and Great Lakes. These features are spaced out in time \u2014 so the ensemble mean blends or smooths out 51 solutions that ALL have cold blasts but intermixed with warm periods. The end result is a rather smoothed continuous blob of cold connecting Alaska with the Northeast U.S.

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