{ "number": 819, "headline": "December 17, 2025 Wednesday Evening Maps", "standfirst": "Colder air will lower snow levels across West as atmospheric rivers take aim on California", "desk": "winter", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2025-12-18", "published": "2025-12-18T02:51:30.331000Z", "updated": null, "access": "free", "body_html": "
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This is post number 819: Good Evening \u2014 new weather maps and headlines to keep the ball rolling \u2026 sorry about the late update \u2014 I was swimming upstream all day with AI-GEFS upgrade and other fun data wrangling. Author: Dr. Ryan Maue (X @RyanMaue X @weathertrader)

North Pacific Atmospheric River next 6-days \u2014> Pineapple Express from Hawaii

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New: NOAA launched their AI-GFS, AI-GEFS, Hybrid GEFS into operations today at 12z. Press Release from NOAA

NOAA 18z AI-GFS | 500 mb Temperature to monitor the polar vortex in the troposphere

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HRRR 00z | Next 48-Hours through Friday 7 PM ET

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Wind Gusts \u2014> hurricane force \u2014 upwards of 80-100 mph maximum gusts as powerful low pressure systems move eastward through Southern Canada

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Storm System Parade Across Canada | Next 6-days | MSLP

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Sequence of 3 powerful storm systems measured by central pressure over land in southern Canada. These mobile cycles quickly track east over the next 6-days \u2026 each time providing a \u201cclash of air masses\u201d between warmer Pacific origin air to the south and the Alaska/Canadian cold pool to the north.

Maximum Wind Gusts from NWS Next 72-hours

Red is > 50 mph and the brown is hurricane force > 73 mph

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Precipitation Type | Weather Next 6-days | ECMWF 18z

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Headlines Wednesday Evening

  1. Storm track across Southern Canada north of the jet stream = blustery/gusty winds for the Lower 48 but not a lot of precipitation east of the Rockies

  2. Couple more brief Arctic blasts of cold air from that replenished Western Canada \u201ccold pool\u201d for the Midwest and Great Lakes Friday and again this weekend.

  3. Christmas looks quite warm for almost the entire Lower 48 relative to normal for December 25th. This is great for travelers and the economy.

  4. Holiday Coupon code 50% off Annual Upgrade \ud83c\udf85

Next 6-days Temperature Anomaly

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Chunks of the Western Canada cold pool break off with passing storm systems \u2014 and sweep eastward to be replaced by the warm front \u2026 roller coaster for the week across the Midwest and Great Lakes.

Weather Trader is an entirely subscriber-supported publication [sweat equity] from Dr. Ryan Maue. To receive all new posts, consider becoming a free or paid subscriber, and please LIKE and SHARE posts. Coupon code [50% off Annual Upgrade \ud83c\udf85]

Christmas Day Temperatures | Morning Lows

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Only 91 million below freezing for low temperatures

Christmas Day Temperatures | Daily Highs

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Over 80 million at/above 70\u00b0F on Christmas Day! Only 9% of the Lower 48 by area will be freezing on Christmas Day \u2014 according to Blend of Models (v4.3)

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

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

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The Lower 48 settles into a MUCH ABOVE NORMAL temperature pattern \u2014 eventually \u2014 once we can finally block off the \u201cpolar vortex\u201d by the weekend.

Temperatures surge to well above normal for much/all of the Lower 48 by Christmas

The Alaska / Western Canada cold pool replenishes strongly into the New Year, but the Lower 48 blocking ridge remains firmly in charge.

RTMA | Current Temperature Analysis | 9:00 PM ET

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Average Lower 48 temperature was 44.5\u00b0F with only 17 million below freezing.

Temperature Anomaly | 9:00 PM ET

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Lower 48 Temperature Anomaly was a whopping 9.0\u00b0F ABOVE normal

Thursday Low Temperatures

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127 million below freezing and a handful (290k) below 0\u00b0F along Montana/North Dakota border with Canada.

Thursday High Temperatures

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76 million at least 70\u00b0F as the Great Lakes warm up into the 40s \u2026 wow, that will feel wonderful

NWS Precipitation Next 72-hours

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NWS Snowfall Next 72-hours

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Blend of Models | 10 Days Precipitation Total

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Enormous rainfall totals across the Pacific Northwest continue into California

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Blend of Models | Total Snowfall Next 10-Days

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Huge snowfall for Manitoba \u2026 colder air from Gulf of Alaska will lower snow levels across the entire Western U.S.

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

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The blocking ridge centers over the Lower 48 \u2014 but it\u2019s not big enough / honking to keep the troughs on its edges from dipping southward.

Western U.S. \u2014> trough = pattern shift \u2014> much colder and even more rain/snow

Northeast U.S. \u2014> trough = repeated mini-blasts of colder air to stay wintry

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

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Polar Vortex (tropospheric) monitor \u2014> the pink = coldest at 500 mb and we see the arrival of some cold air from Siberia over the pole into the New Year to reinforce the PV over Alaska and Canadian Arctic.

ECMWF 12z | Integrated Vapor Transport Next 10-days

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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 15-days

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Probability of 1-inch or more Snowfall in the next 15-days

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Probability of 6-inches or more Snowfall in the next 15-days

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

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5-Day Chunk #1 | Temperature Anomaly | Dec 18 - Dec 22

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5-Day Chunk #2 | Temperature Anomaly | Dec 23 - Dec 27

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5-Day Chunk #3 | Temperature Anomaly | Dec 28 - Jan 1

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Snowfall Analysis Season to Date

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While the next 2-weeks won\u2019t see much snow, as we head into 2026, hard to complain about what snow has fallen so far \u2026 need to keep it going into January and February!

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

North Pacific Atmospheric River next 6-days \u2014> Pineapple Express from Hawaii

New: NOAA launched their AI-GFS, AI-GEFS, Hybrid GEFS into operations today at 12z. Press Release from NOAA

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