A wet Sunday leads to a December chill as cold Canadian air plunges south

With Thanksgiving in the rearview mirror, the 2020 calendar is about to flip one more page to December… and it can’t come soon enough! However, if the weather for the month ahead is anything like the first week of December promises to be, I might have to reconsider.

Weekend weather (enjoy today!)

Today might be the last “decent” day in the 7-day forecast period, depending on how you define decent. While we’ll have a handful of pretty-to-look-out-the-window-at days, the the cold air shifting our way is no joke for early December. Expect plenty of sunshine for your Saturday with highs in the mid to perhaps upper 50s with a northeast breeze. It’ll be a good day to make sure your plants and pets are ready for the arrival of Canadian air on the horizon, as Sunday will be cold and wet. Dry weather continues overnight, but by lunchtime Sunday, rain will be arriving and continue into the evening hours as surface low pressure moves by to our south. The rain and cloud cover will result in temperatures in the 40s throughout the day. A cold north wind will mean heavier raincoats or layers will be the best option if you plan to get out.
The high-resolution NAM3 model forecast precipitation from 6am Sunday to 6am Monday shows the likely progression of rainfall across the Mid-South.

Sunday night flakes?

Sunday evening into Monday morning has been an interesting forecast this week. While surface temperatures stay above freezing (but in the 30s), temperatures in the lowest few thousand feet of the atmosphere are likely to fall below freezing by evening as a cold pocket under an upper level low moves overhead. If it gets cold enough, and precipitation lingers, light rain could mix with a few wet snowflakes with surface temperatures in the mid to upper 30s. These would be “no-worry flurries” that would splat and melt on the ground, and are more likely across parts of west TN northeast of the metro. 
The profile of the atmosphere for Sunday night at midnight shows warm surface temperatures (comparably) but cold (at or below freezing) temperatures between about 3,000-8,000 feet. The big question is whether any frozen precipitation aloft melts before it gets to the ground. (Pivotal Weather)

For now, the chances appear very low in the metro proper, but don’t be shocked if you see some. Finally, as the low departs a couple models-in-the-minority want to squeeze out a few snowflakes Monday morning. Doubtful, but not impossible. With temperatures at or above freezing all night, no issues are expected for Monday morning’s commute either way. (I see you, teachers heading back to class Monday morning…and I understand.)

The blob of cold air aloft moves over the area Monday and likely keeps some cloud cover around for a good part of the day with clearing sometime in the afternoon or maybe evening. With cold air advection (or, movement of air) continuing, we’ll spend most of Monday in the 30s (you read that right) and a northwest wind gusting to 25 mph. Just brutal. Stay in if you can. 
Wind chill forecast for noon Monday according to the NAM3 model. That says “21” for Memphis! (Pivotal Weather)

Early December chill

As the clouds clear and wind dies down Monday night, we’re in for the coldest night since before the pandemic (late February to be precise) with temperatures falling into the mid to upper 20s by early Tuesday morning. (See below for a little “Weather 201” on that cold airmass.) That will make it hard to warm a lot on Tuesday, with sunshine only pushing the high temps into the mid 40s. Another hard freeze Wednesday morning (upper 20s) before temperatures get closer to normal again on Wednesday with highs in the lower 50s and dry weather.
This plot is called a “backwards trajectory” and shows where air originated and where it ends up at a certain place/time. In this case, the low-level air over central Canada this (Saturday) morning will move south and be over Memphis Tuesday morning when our temperatures are in the 20s! Where the airmass originates can tell us a lot about the character of that air, even though it will be modified somewhat by the time it gets here. (NOAA/ARL)

Unsettled late week

The next series of atmospheric disturbances move through Thursday into the first weekend of December. The first of these appears weak and models are having issues latching on to how the end of the week and weekend play out. However, rain chances are back in the forecast Thursday, maybe Friday and maybe Saturday. Temperatures will continue to be cold with lows in the mid 30s and highs in the upper 40s. It’s way too early to determine if any more s**w chances will be needed, but we’ll keep an eye on things and report more when able. 

In a nutshell, December starts out very cold, which means you need to move any sensitive outdoor plants inside, probably winterize the outdoor faucets in the next 24 hours, and make sure that outdoor pets have a place to stay warm and plenty of food and water (not ice). The cool-ish trend looks like it might continue into the second week of December as well!
The week two temperature outlook from the Climate Prediction Center indicates a chance that cooler than average weather continues from December 5-11. (NWS)

Stay warm and well, friends!

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

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