Looking ahead to Monday night snow and trailing Arctic cold

All eyes are on Monday night. I know because I have heard from you, especially the teachers out there! 🙂 But let’s take a quick trip through the weekend before we delve into the arrival of yet another, more prolonged perhaps, cold snap.

Saturday and Sunday

A few flurries flew across the Mid-South last night as an upper level disturbance encountered some mid-level moisture. Most of us in the immediate metro wouldn’t have guessed this morning though as the clouds cleared out and there were no signs of any wintry precip. With southwesterly wind today, highs are close to average for late January, or near 50. Some clouds are expected tonight, but overall a seasonal night is expected with lows remaining just above freezing. Sunday features more sunshine and highs near 50 once again, probably a couple degrees warmer than today with light wind.

Photo from Olive Branch Saturday morning, taken by former mayor Sam Rikard.

Monday

The next round of Arctic air will be diving towards the area Monday, but most of the daylight hours will be spent ahead of the front with temperatures well into the 50s after a morning low near 40 and gusty southwest wind contributing. Clouds will be on the increase though with a few rain showers possible in the afternoon. The cold front arrives around rush hour.

Monday night

This is where all the focus is, as the post-frontal airmass will be bitter and make its presence known fairly quickly. Temperatures plummet from the 50s to the 30s during the evening, escorted by strong northwest wind. Precipitation appears likely, but also not necessarily heavy. The better moisture ahead of and just behind the front lies to our southeast. Cold air will make a strong statement though. The question is how much moisture lingers as the “cold enough” air arrives to change precipitation from rain to snow.

The Saturday morning run of the European model, valid from mid-day Monday through Tuesday morning, indicates that areas south and east of Memphis could be more favored for light snow than we are, thanks to more abundant moisture. (WeatherModels.com)

The nitty-gritty details

Friday, the models provided some hope for snow-lovers with forecasts of a couple of inches (perhaps more!) of the white stuff. But the synoptics (the overall atmospheric setup and progression of the pressure centers and fronts) are not of the type that typically favor much snow. [Aside: we like to see cold air already in place and a low pressure center move across the Deep South for healthy snowfall amounts. While lingering moisture behind a fast moving front from the northwest doesn’t preclude snow, amounts are typically light as the dry continental airmass behind the front pushes moisture out quickly.]

Alas, the overnight and Saturday morning models seem to be recalling that situation, as well as lowering the expected atmospheric moisture overall. The snow-lover’s dreams of yesterday are perhaps becoming their nightmares of “reality” today.

We’re starting to move from the forecast time period where model ensembles rule the day to having a little more precise actual forecast guidance, now that we are within 72 hours, though ensemble data is still very much a useful tool.

Ensembles are basically a particular model executed multiple times (how may varies) with slightly different parameters that allows us to derive the probability of an event and therefore confidence in the forecast.

Here’s what those ensembles say:

12Z (Sat AM) GEFS Ensemble /based on the American GFS model/: Less than 1/2″ of snow. Of the 21 “members” in the GEFS country club, only 8 vote for any accumulation at all and 4 have 1″ or more. No teachers belong to this club apparently.
09Z (Sat early AM) SREF Ensemble /based loosely on the American NAM model/: 1.5″ of snow. Though if you throw out the 3 students that snuck in with votes of 4-6″, that 1.5″ drops to 1″. Of those, only 7 of the remaining 23 members expect more than an inch.
15Z (Sat mid-morning recount) SREF Ensemble: 1.8″ of snow. Once again, throwing out 4 students or teachers with greater than 4″, that 1.8″ drops to 1.15″ of snow, with a range from nothing to 3.5″.
00Z (Fri night) EPS Ensemble /based on the high-brow Euro model/: 1″ of snow. Of the 51 EPS members, about half voted for 1″ or a bit more. 6 will likely be expelled from the club for expecting more than 2″.
12Z (Sat AM) EPS Ensemble: About 1/2″ of snow. The number of members voting in favor of 1″ or more dropped from 23 to 7 in this run and the number with more than 2″ fell from 6 to 4.
Finally, the NWS Weather Prediction Center also has a probabilistic winter weather forecast. It currently indicates a 50% chance of 1″ of snow and a 30% chance of 2″ of snow (both down from early today). It also indicates that the most likely amount of snow right now is about an inch roughly along and south of I-40 with a “boom” amount (10% chance) of 2″ and 1 bust amount of nothing.

Finally, the regular (“deterministic,” or single run) model data says this:

12Z (morning) American GFS: No accumulation. (And has been fairly consistent of late on that forecast.)
12Z American NAM: Less than 1/2″ with about an inch a couple counties south of Memphis.
12Z European: No accumulation. (It had about 3/4″ on last night’s run.)
The high-resolution models are not yet within range of this event, but will start to be late tonight.

The NWS snow probability forecast indicates a 50% (or “most likely”) scenario of about an inch of snow in the metro with higher amounts to our east. (NWS/WPC)

The verdict

Given the recent trends in the data, the ensemble guidance that is also lowering with each recent run, and the typically unfavorable synoptic pattern, I expect that light rain likely will change to snow Monday late evening, but I’m taking the “under” on a forecast of an inch of snow in the greater metro. There is obviously still time for this to change so stay tuned, especially to our social media channels, for future updates.

Tuesday

The potential saving grace for those who want their Tuesday interrupted by winter weather is the fact that there will be very little recovery Tuesday morning to improve conditions for whatever falls. Temperatures fall to the lower to mid 20s by sunrise Tuesday, and despite sunshine, highs may not get above freezing during the day. While wind and sun will take care of any *possible* accumulation in exposed areas, shady areas could see any snow linger. We could be dealing with some slippery conditions on Tuesday early morning. It’s still too early to know for sure.

European model high temperature forecast for Tuesday. 31° in Memphis. (WeatherModels.com)

Wednesday-Thursday

An Arctic airmass will continue to envelope the northern and eastern U.S., with the Mid-South on its southern fringes. You will likely hear about this “polar vortex” over and over in the days ahead. While the bitter cold air is not the vortex itself, just a result of it, we won’t argue semantics for now. Just know that temperatures will continue to be well below normal (some 15-20° below) for the mid-week period. But hey, at least it’ll be above zero! Prepare for wind chills in the teens to perhaps single digits though, and highs in the 30s with lows in the teens to low 20s. The prolonged period of cold air should prompt you to consider protecting pipes, plants, people, and pets!

The GEFS ensemble (mentioned above) temperature anomaly (departure from average) at 5000′ for the period from next Tuesday through Saturday. The 5000′ value is used as a proxy for surface temperature and shows a massive area of well below normal temperatures next week in the central/eastern U.S. Values are in °C. (WeatherModels.com)

Stay tuned for later details on Monday night’s snow potential, as well the the Arctic blast arriving behind it!

Erik Proseus
MWN Meteorologist

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