Some active thunderstorms across central Florida this evening — a reminder of what “warm convection” looks like as we move into mid-December

HRRR 18z | Next 48-Hours into Tuesday Early Afternoon

• Another storm system for Virginia — not intense but decent snowfall accumulations

• Atmospheric river crashes into Washington

• Moisture then heads into the Midwest to be captured by “Clipper systems”

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

Headlines Sunday Evening

1. Powerful Alberta Clipper system Tues-Wed across the Midwest and Great Lakes

2. 72-hours of “atmospheric river” event “boatloads” of moisture into the Pacific Northwest

3. Strong Western U.S. ridge remains anchored — and firmly in charge for the next 10-14 days (at least)

4. Blocking ridge out west —> Arctic air continues to spill out of Canada and Alaska as lobes of the polar vortex are extended southward by passing shortwaves — vorticity / energy packets from the North Pacific riding down the polar front boundary.

5. COLD — even for mid-December — peaking Sat/Sun across the Midwest/Great Lakes.

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

Atmospheric river systems into the Pacific Northwest — narrow at first, and then quite a wide swath by Tues/Wed — 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 surges southeast out of Western Canada into the Midwest into next weekend.

West coast atmospheric river (AR — Category 5) = pineapple express out of Hawaii

Temperature Anomaly | Next 15-days

Flagship European model ensemble solution for temperature anomaly next 15-days shows intense cold pool formation over Alaska and Western Canada while a very warm/persistent blocking ridge remains stuck across the Western U.S.

Main uncertainty is ability of this ridge to extend east across the Rockies — and perhaps transition to a much warmer pattern into the 3rd week of December, but it’s not guaranteed (yet)

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 — 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.

Temperature Anomaly Days 3-6 | Into Saturday morning

Exceptionally cold air spills into the Midwest and Great Lakes

RTMA | Current Temperature Analysis | 8:00 PM ET

Temperature Anomaly | 8:00 PM ET

Lower 48 Temperature Anomaly was -2.4°F below normal

NWS Precipitation Next 72-hours

NWS Snowfall Next 72-hours

More snowfall for Midwest — Great Lakes but looks to mainly miss Minneapolis, Chicago, and Detroit — big bummer for large population if you like travel disruptions!

Blend of Models | 7 Days Precipitation Total

Upwards of 10-20 inches of precipitation — including liquid equivalent of snowfall in the Cascades from AR event

Blend of Models | Total Snowfall Next 10-Days

Completely snow free — zip/zero/zilch across California and the Great Basin

Plenty of opportunity for Lake Effect snow showers to crank up as Arctic air flows over the still much, much warmer Great Lakes.

Monday Morning Low Temperatures

175 million below freezing (Lower 48 average low is 26.1°F) … 6 million below 0°F

Single digits across Michigan —- across the lake into Toronto, and interior New England.

Subzero in the Midwest — but could worse — it will get colder into next weekend.

Monday High Temperatures

Around 10 million at/above 80°F in Florida! 118 million don’t get above freezing!

20s across the Great Lakes and Northeast — chilly!

… still in the mid-80s in South Florida — escaping the Arctic air mass completely.

Tuesday Morning Low Temperatures

200 million below freezing (Lower 48 average low is 27.9°F)

Coldest compared to “normal” in the Northeast more than 15°F to 20°F below average lows — in the single digits to below 0°F

Tuesday High Temperatures

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

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

Integrated Vapor Transport Next 10-days | North America

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

Integrated Vapor Transport Next 4-days | South America

Powerful storm system forms over Southern Brazil — a cut-off low with huge moisture flow coming in off Atlantic = major rainfall/flooding risk

ECMWF 18z | Snowfall | Next 6-days

ECMWF EPS 12z | Ensemble Median Snowfall Next 15-days

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

We’ll be monitoring the 1” chance of snowfall for a “White Christmas” in the coming weeks. This map is through late December 20th.

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

6-inches is sufficient for a “big storm” and Lake Effect machine diagnostic

Next 15-days Temperature Anomaly | Ensemble Mean to December 21

The western ridge is STRONG … and should provide enough Pacific moisture and moderating mild air to temper the longevity and intensity of any Arctic blasts that sink from the massive cold pool over Western Canada.

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

5-Day Chunk #1 | Temperature Anomaly | Dec 7 - Dec 11

5-Day Chunk #2 | Temperature Anomaly | Dec 12 - Dec 16

5-Day Chunk #3 | Temperature Anomaly | Dec 17 - Dec 21

Maps sourced from weathermodels.com designed and innovated by yours truly! Please subscribe there for real-time access to the newest maps, charts from all of the weather models including ECMWF and AIFS, NOAA AI-GFS/AI-GEFS

Active coupon codes:

Group subscription discount > 2 memberships (25% off)

Upgrade to yearly membership (25% off)