Thursday, January 17, 2019

Arctic airmass intrusions and snow chances

While the cool, damp conditions and overcast skies of late are fairly normal for winter in Memphis, it appears Mother Nature may be poised to send "real" winter our way starting this weekend. While that means the collective antennae of Mid-South meteorologists are "up" for winter precipitation chances, the most likely result of this pattern change will be shots of Arctic air that intrude well into the mid-latitudes, including the Mid-South. Let's dive in!

Today and Friday - mild and mainly dry

Preceding the Arctic air, we'll get a taste of well above normal temperatures the next 48 hours or so, just to re-acclimate you to something semi-pleasant before lowering the Arctic hammer. Today's rain has shifted east for the most part with a weak Pacific cold front moving through late this afternoon. While that will briefly shift our wind around to the north, it won't get too cold behind that front. Look for lows to remain in the 40s overnight - no ice scraping in the morning! Friday will see continued mostly cloudy conditions, but most of the daylight hours will be dry with highs well back into the 50s as wind turns back around towards the south ahead of the next major weather player.

The NWS forecast chart for Friday shows low pressure to our west poised to move east with Arctic air on it's north side. A series of fronts are across the Mid-South. Most of the day will be dry but rain arrives by evening. (NWS)

Friday night through Saturday mid-day - warm and wet

Rain moves in Friday night with wind becoming gusty out of the south, which should hold temperatures up in the 50s during the overnight hours. A rumble of thunder is possible late Friday night into Saturday due to the strength of the incoming low pressure system and accompanying front. Rain continues into Saturday as we see temperatures rise to about 60 Saturday morning.

The NWS/Weather Prediction Center precipitation forecast for Friday at 6pm through Saturday at 6pm calls for more than an inch of rain for Memphis. (NWS/WPC)


Saturday afternoon/evening - the Arctic hammer

By Saturday afternoon though, it'll be as if Memphis was picked up and dropped 1000 miles north in Minnesota! That rude front will bring a doozy of an Arctic blast with temperatures dropping some 25 degrees by evening - into the 30s - and a north wind blows at 30+ mph! That's when things could get interesting for a minute as the Arctic hammer gets dropped...



While some precipitation will linger into the evening, the cold airmass could advance quickly enough to change the lingering precip over to the white variety. As of now (Thursday afternoon), I think we've got better than a 50% chance of seeing snowflakes after dark Saturday evening. However, I don't think it will amount to much. The dry Arctic air will wring out the atmosphere pretty quickly, and precipitation will be quick to exit. Accumulation chances appear to range from none to an inch with most of the metro likely to see 1/2" or less.

The NWS/WPC forecast as of Thursday morning for the "most likely" snowfall expected Saturday morning through Sunday morning. Note the 1" area sits just northwest of Memphis. (NWS/WPC)

The NWS/WPC forecast for a "reasonable worst case" (or best case?) for snowfall totals Saturday morning through Sunday morning. These values have only a 10% chance of being exceeded. So 1-2" is likely the most we could expect to receive and even that is not considered likely. (NWS/WPC)

Nearly all models are on board with the "less-than-an-inch" solution at this point. The holdout of late, our typically-esteemed European colleague, has lowered the potential as of this morning. The situation can still change of course, but that move brings it more in line with the American-bred models, raising confidence in the solution. More impact-ful snow totals and some ice is expected north of the Memphis region.

Sunday chill

By Sunday morning, all precipitation will be gone and clouds will be departing as well, but not the cold air! A brisk north wind will keep temperatures from rising much above freezing despite sunshine. That means wind chills in the teens in the morning and 20s in the afternoon. Brrr! One thing to be on the lookout for. especially Sunday morning, will be patchy ice. Temperatures drop quickly, after dark, immediately behind departing rainfall. It's conceivable that a "flash freeze" could result in spotty black ice. With lows in the mid-upper 20s and a stiff breeze blowing, I think our chances of that occurring are fairly low, but it's worth keeping an eye on.



Sunday night will be the coldest night of the forecast period as high pressure quickly builds in and shuts off the wind machine, allowing the mercury to dive, possibly into the teens outside the city.

Longer term - more of the same?

As quick as it turned cold, the Arctic high shifts east, "return flow" (southerly wind) re-engages, and we warm back up on Tuesday in time for an aftershock - more rain, warmer temperatures, and another Arctic front Tuesday night that could have us watching precip types again Tuesday night!

The week 2 (Jan 25-31) temperature probability outlook for the U.S. indicates well below average temperatures are likely for the eastern half of the nation. For Memphis, the Climate Prediction Center puts those odds at 77% for Memphis specifically. (NWS/CPC via PivotalWx)

The European model seasonal forecast indicates enhanced odds of below normal temperatures for the eastern half of the country during February. (WeatherModels.com)

It appears that this pattern of rising and diving temperatures may continue a while, as we head into a period of generally (on average) below normal temperatures that continues well into February according to most semi-reliable data. Like I stated in a previous blog, the long-range trends continue to show below normal temperatures for the eastern half of the country from next week through the end of the winter season. We'll see what the groundhog has to say about that in a couple weeks!



Erik Proseus
MWN Meteorologist

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Sunday, January 13, 2019

A weather smorgasbord this week, with an eye towards an Arctic air intrusion

We had a few nice days this past week with mild temperatures and some sunshine that allowed the ground to dry out a bit. Of course, that was followed quickly by more rain and, today, cold weather and dreary cloud cover. Looking ahead, we'll get a mix of clouds, some sun, cold weather, warming temperatures, and rain - all in the next 5 days. By next weekend, a significant pattern change is on the horizon.

Sunday night - Monday clouds

Despite high pressure building in, as we sometimes experience in winter with low sun angles and lots of low-level moisture, clouds will stick around tonight into Monday. We stayed near 40 today with a cold wind, but decreasing dewpoints on that north wind means temperatures will drop to near or just above freezing tonight. The clouds will keep the mercury from rising much Monday with highs very near what they were today, but just a bit less wind.

Sunday afternoon visible satellite imagery shows the Mid-South locked under widespread cloud cover. The clouds will persist through Monday at least. (College of DuPage)

The cloud party should break up Monday night as high pressure moves overhead with calm conditions and lows near 30.



Tuesday - Wednesday sun

For now, we believe abundant sunshine is ahead on Tuesday with highs back into the upper 40s. The NAM model, which is typically-more-aggressive with low clouds, thinks otherwise, but I feel optimistic.



Despite some high clouds moving over on Wednesday, south wind should finally being our temperatures back above normal. Morning lows in the upper 30s will rise to the mid 50s Wednesday afternoon and conditions remain dry.

Thursday rain - Friday dry

Thursday appears to be our next wet day as a weak system moves by in fast westerly flow at the jetstream level. It will be above normal temperature-wise though with lows in the 40s and highs in the upper 50s. Rain should not be heavy on Thursday. Thursday night into Friday looks dry and mild as we sit between systems, keeping a wary eye to the west. A few showers may arrive Friday evening, but not before highs climb above 60 degrees on south wind.



Weekend pattern shift

The "wary eye" mentioned above is because we'll be seeing an Arctic airmass drop into the Plains late this week that pushes into the Mid-South on Saturday. Timing of that cold air arrival is still TBD, but for now, we project a fairly wet day Saturday with a chance of thunderstorms due to the strength of the front moving in and a fair amount of wind. Temperatures will drop precipitously behind the front, potentially during the day Saturday, but very likely by Saturday night.

The Sunday morning GFS model forecast of surface features and precipitation from this Thursday night through next Sunday shows next Saturday's storm system moving through with rain and a potential for some light snow. At this point, various models disagree on the timing of cold air and moisture departure, and thus snow chances. The nature of the system though doesn't lend itself to more than light snow, if anything. (WeatherModels)

Will all the precipitation be gone before the cold air arrives? Model solutions vary on that as well. We'll be monitoring. Needless to say, behind that front, a bitterly cold airmass arrives, sending temperatures well below freezing by Sunday morning. Even with sunshine on Sunday, we may not reach the freezing mark for highs! That will be some 20-30 degrees colder than Saturday.

The European Model ensemble system predicts about a 25% chance that Memphis will get above freezing next Sunday, based on 50 runs of the European model this morning. (WeatherBell)

Winter arrives!

The long-range outlook indicates that next Sunday is the beginning of an overall pattern shift that brings in a run of below normal temperatures, perhaps continuing into early February. It's a pattern that will make precipitation forecasting somewhat tricky with each front/low pressure system that affects the area after that. Winter is NOT over snow-lovers! Do not give up hope just yet!


The NOAA temperature outlook for the end of January and first week of February indicates more cold air is likely on the way for the eastern half of the U.S. Stay tuned!

As always, look to the web or our MWN mobile app for the latest forecast information and to our social media platforms for the most up-to-date current trends. All links are below.

Erik Proseus
MWN Meteorologist

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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