White Christmas Around the World

We should still have snow on the ground in the Midwest, Great Lakes, and Northeast including some freshly fallen … as it won’t be warm enough (30s and 40s) to do much damage to the snowpack. Where it’s going to be much warmer in the 60s or even 70s+ we don’t expect a White Christmas in a typical year. Canada is almost entire snow covered as well as vast majority of Russia —> Siberia. However, Europe will only have snow at higher elevations, and in the northern reaches of Scandinavia.

Headlines Monday Evening

A lot going on — and this post got way too big, and I need to hit publish

• Main story will be heavy precipitation in California from a complex of storms rotating within a “Polar Vortex” lobe — directing atmospheric rivers (conveyor belts within frontal zones) into the coast —> Christmas Eve + Day

• Extreme cold continues to build and build in Western Canada and Alaska — brutal temperatures in the minus 50s … and that won’t be changing much

• Major question is how long does the Lower 48 blocking ridge maintain its firm grip — before breaking down and allowing the Arctic air to dip/blast into the Midwest and Great Lakes

• Ridge isn’t strong enough to prevent “polar vortex” origin troughs from whipping through the Northeast keeping temperatures below normal for the next 2-weeks on average —> Not participating in the Christmas Week warmth!

• Weekend storm system for the Northeast? Snowfall in NYC (?)

• Blow torch Christmas —> 70s across the central and southern U.S. —> Santa Claus in shorts.

ECMWF 18z | Next 6-days Temperature Anomaly

The western Canada cool pool is looking to escape in any direction and sends a blast of cold air out in the Pacific with a “Polar Vortex” lobe and upper-level trough — all linked with a complex of powerful surface storm systems (low pressure) off the California coast.

New England sees a puff of much colder air toward Friday and it lingers into the weekend.

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

• White/gray/black colored precipitable water = absence of moisture = cold/polar air masses

• West Coast atmospheric rivers coming from multiple attack vectors — but all onshore with landfalling ARs, powerful storm systems, and enormous rainfall + snowfall on the way. Major impacts —> then High Pressure + offshore flow takes hold —> Santa Ana winds?

ECMWF 18z Precipitation Type and Intensity | Next 6-days

Northeast Winter Storm Chances = Saturday highest probability of significant winter precipitation (Snow/Mix/Slop)

Powerful West Coast Storm Systems — Wednesday and Thursday

High Pressure builds across the Pacific off the West Coast into the weekend — so the atmospheric rivers will be directed into Alaska and British Columbia

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This evening’s winter weather —> into Tuesday Noon —> continues into tomorrow evening (See the 48-hour GIF)

HRRR 18z | Next 48-Hours Sim Radar through Wednesday 1 PM ET

RRFS-A Total Snowfall Through 84-hours —> Friday 1 AM

RRFS-A Total Precipitation Through 84-hours —> Friday 1 AM

Enormous precipitation across Southern California | Wed-Thurs

Southern California Zoom | RRFS-A

NWS Precipitation Next 72-hours Doesn’t Capture Entire California Event

NWS Snowfall Next 72-hours

RTMA | Current Temperature Analysis | 7:00 PM ET

Average Lower 48 temperature was 49.0°F with 30 million below freezing.

Brutally cold in Alaska and Yukon, Canada into the minus 50s (actual temperatures)

Temperature Anomaly | 7:00 PM ET

Lower 48 Temperature Anomaly was scorching (!) 12.4°F ABOVE normal

Tuesday Morning Low Temperatures

66 million below freezing with the edge of brutal subzero air along the Canadian border in Montana and North Dakota

Tuesday High Temperatures

More than 81 million at/above 70°F

Christmas Eve Low Temperatures

Only 77 million below freezing … but not too bad. Seasonable.

Christmas Eve High Temperatures

Almost 124 million at least 70°F — comfortable in the Midwest, Great Lake and Northeast in the 30s and 40s

Christmas Day Temperatures | Morning Lows

78 million below freezing for low temperatures Christmas morning

Christmas Day Temperatures | Daily Highs

109 million at/above 70°F on Christmas Day … very warm across the southern half of the eastern U.S.

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

Ridge breaks down by Monday/Tuesday of next week allowing an Arctic Blast to dump out east of the Rockies — then the ridge returns (!)

Alaska / Western Canada go into the DEEP freeze while Greenland warms up + Lower 48 is much above normal.

Blend of Models | 7 Days Precipitation Total

Enormous rainfall totals across California | Deluge

Blend of Models | Total Snowfall Next 7-Days

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

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

Polar Vortex (tropospheric) monitor —> 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

Look at the IVT source from the Tropical Pacific heading westward out of the Caribbean and then pulled northward into Southern California and the U.S. Southwest.

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)

ECMWF 18z | Snowfall | Next 6-days

Snowfall for New England —> could be significant in a narrow band as winter is not taking a break. 5” in NYC — mainly on Saturday and up to 8”-10” to the WNW

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

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

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

The Northeast will be below normal for the 15-day period in the -6°F range with some blue (-2°F) south into Florida. Of course, this is a 15-day average of ensemble mean temperature anomaly — so a LOT of smoothing going on here.

5-Day Chunk #1 | Temperature Anomaly | Dec 22 - Dec 26

5-Day Chunk #2 | Temperature Anomaly | Dec 27 - Dec 31

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

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