Tuesday, November 13, 2018

#Novembrrr continues - decent snow chance on Wednesday

UPDATE: 8:00pm 

Based on the latest model data, there is a low risk of a bit of mixed wintry precipitation (freezing rain, sleet, or snow) in the morning between about 7-10am. We'll be watching this closely, but be aware of this during the morning rush. Most of this mix should occur southwest in the metro in AR, but it 's worth mentioning.

Also, the light precipitation overnight Wednesday night, mainly after midnight, could also mix with light freezing drizzle. If this were to occur, even the veyr small amount that would occur could quickly slick up bridges and overpasses Thursday morning. Stay tuned!

If you are wondering if we skipped fall and went straight to winter this year, I can't blame you. 

We don't typically deal with multiple snow threats in the same week in the fall. But here we are. After a brief round this morning (most of you were sleeping and missed it, but the airport officially reported light snow for one hour between 1-2am), we're looking at a more favorable setup on Wednesday into early Thursday.

Typically cold air invading behind a front as precipitation moves out is not the optimal way to get much snow. The timing is rarely right for more than flurries.

However, a strong upper level low moving overhead with cold air in place? Now we're talking. That is the scenario for the next 48 hours or so. See the loop below as a strengthening low pressure system (the bowling ball sporting the flaming hot Cheetos livery) as it moves basically directly overhead.

An developing upper level low will move directly overhead the Mid-South on Wednesday night per all model solutions. This loop is taken from the Tuesday morning run of the GFS model. (WeatherModels.com)

So what can we expect in the Memphis metro? 

1) The cold air will stick around. Temperatures remain in the 30s (mostly the lower half) through today, tonight (lows will be near 30), and tomorrow (when temperatures should get back to just above freezing for the afternoon hours).

2) A Winter Weather Advisory has been issued for the metro. This means that expected winter weather could cause significant inconvenience, but won't rise to the level required for a warning (i.e., heavy snow, sleet, or freezing rain with widespread impacts).

2) Light snow could begin as early as mid- to late-morning Wednesday. The initial stages of the precipitation should be very light as moisture is drawn north ahead of the low. There's a possibility of some light sleet or rain mixing in initially, but I'm expecting most precipitation to be snow.

3) The steadiest snow will be mid-afternoon through evening (i.e., 3-9pm or so). As the upper low moves into the area, enhanced lift will combine with the arrival of the coldest air aloft to produce steady precipitation. This is also the best chance for any accumulation.

4) Accumulation could be around an inch, perhaps more north of the city. During that window mentioned above, we could see an inch of wet snow on grassy or bare ground and exposed surfaces in the immediate metro. Areas just north and west, in northwest TN and northeast AR, could see a few inches of snow. The best data we have available (it's sparse in the metro) suggests that pavement and sub-surface temperatures are fairly warm still: 40s to low 50s. That should keep paved surfaces from accumulating much, if at all. I would still be cautious on the elevated roadways, especially after dark.

Graphic created by NWS-Memphis early Tuesday morning. This information is subject to change.

5) Light snow or flurries will continue into the overnight hours. As the low pulls by to our north, the precipitation will move north with it, leaving behind the possibility of additional very light snow or maybe just flurries overnight. No additional overnight accumulation is anticipated at this time.

6) Subfreezing temperatures early Thursday could result in some travel headaches. Depending on how much precipitation we actually receive and the wetness of the pavement, temperatures that drop to near 30 Thursday morning could result in some slick spots. We won't know that for sure this early, but keep it in the back of your mind. By mid-morning, temperatures should be back above freezing.

7) Warmer days are ahead! Highs Saturday could reach 60°.

We'll have the latest information on our social media channels throughout the event and of course the MWN Forecast will also have the latest official forecast from us. Links are below. Plan ahead, stay safe, and I'll get back to working on patching the #SnowDome.

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Sunday, November 11, 2018

Update on #Novembrrr cold & wintry precip chances Tuesday.... and Thursday

This is the promised follow-up to Saturday morning's blog on precipitation early Tuesday morning, as well as broaching yet another possibility from a system the models have just started picking up on in the past 24 hours or less. Let's take them one at a time... (And yes, seriously, why are we talking about multiple "potential" events in mid-November! There should be a law.)

Monday/Monday night

First, Monday remains on track to be cold and wet. Get the waterproof winter coats out because low 40s on the thermometer, rain, and a north wind gusting to 20-25 mph is NOT going to feel great. The trend with this system the past 24 hours though, as far as the wintry precipitation is concerned, is positive (unless you want a snow day).

As discussed in yesterday's blog, models tend to move the precipitation out faster and the cold air in slower as we draw nearer to an event. Not always, but many times. That is happening this time. A general drying trend should take place, especially after midnight (early Tuesday). In addition, the "sufficiently-cold" temperatures for snow production are dragging their heels just a bit.

The morning run of the GFS model mirrors other model solutions in depicting almost no precipitation after midnight Monday night when temperatures finally fall far enough to produce snow.  Notice that the precipitation shifts to the east as the freezing line arrives from the west. Not atypical for our area, especially in November. (WxBell)

The result is that I have pulled all snow from the forecast on Monday night. There could be a few flurries in the wee hours Tuesday morning with temperatures just above freezing. You likely wouldn't even see them unless you work on the FedEx or UPS ramp overnight. Tuesday looks to be dry and very cold with highs in the 30s and wind chills in the 20s. I've also become more "negative Nelly" on sunshine Tuesday. Yuck.


The negativity on Tuesday sunshine is directly influenced by another system that now looks like it might have an impact on mid-week weather. If it does, 3 T's - timing, track, and temperatures - will play major roles in its impact on our area.

As the main system Tuesday departs to our northeast, a piece of upper level energy now looks to be orphaned behind over the southern plains. Multiple models are now forecasting that energy to strengthen into a potent upper level low and move near the Mid-South. Because this feature is just now being picked up by models, the track and speed (timing) are different between the respective models. The only certainty is that the solutions will change over the coming days, so I'm not ready to get too excited by it. But apparently some of your weather crap apps are!

A loop of the atmospheric energy at about 18,000' (500 mb) from Wednesday morning through Friday morning, as depicted by the Sunday morning GFS model. That "bowling ball" of reds and purples is a strong upper level low pressure system that will bring a round of precipitation and very cold air aloft. Models still differ on track and timing, but it is worth watching. (PivotalWx)

The same model as above (Sunday morning GFS) only showing the surface precipitation amounts associated with the forecast track of the upper low. Note the colors are NOT precipitation type, but amount. The blue lines that encircle the Mid-South as it moves north are sub-freezing air at 5000' and indicate a potential for snow if surface temperatures are also cold enough. (WxBell)

We'll take the cautious approach for now, as the track, timing, and most importantly, temperatures in the mid and low levels of the atmosphere, will determine A) if we get any precipitation and B) what form it is in. These deep lows are carriers of very cold air aloft, so if temperatures near the ground are near freezing (and that depends on timing), there is another chance we could see some flakes. For now, the only flakes are those that randomly spit snow totals for Thursday. :-)

We'll keep you posted. In the meantime, here's a look at the temperatures for the week ahead, subject to change based on the ultimate fate of the mid-week system. The latest forecast can always be found in our mobile app or on the website. Links below. Stay warm!

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder