Saturday, November 10, 2018

It's #Novembrrr and precip is coming! Time to talk about "S***"

** An update to this blog as of Sunday night is available here **

As recapped in our October Climate Summary blog, generally cooler than average weather has been with us since the extreme warmth of the first 10 days of October (remember when we were reaching near 90 degrees every day in early October??). With the exception of a day here or there and that short stretch of warmth around Halloween, we've only experienced six days in which the daily temperatures have been above average since October 11, and two of those were a single degree above normal.

First Arctic blast of fall 2018

But this weekend we are feeling the early signs of winter as the first Arctic blast of the year envelopes the eastern U.S. This morning's official low of 30° at Memphis International Airport (just 3° above the record low) brings the 2018 growing season to an end. That means that, although we will experience freezing temperatures again in the coming week (multiple times in fact...), no additional Freeze Warnings will be issued for the metro until spring. Regarding the freeze, although it seems winter is starting early (after a late end to summer), the average first freeze in Memphis is November 12, so we're actually right on time! The difference is a daytime high in the 40s that makes it feel more like winter, despite the sunshine.

Saturday high temperatures are well below normal for most of the U.S. as shown by a temperature anomaly map. ( via Ryan Maue)

The cold weather continues into Sunday with lows in the 20s, thanks mostly to much less wind, which allows low-level temperatures to cool more efficiently. Some clouds arrive Sunday, but we should get highs up closer to 50 in the afternoon. It'll feel warmer with less wind as well. While the cold continues, the dry weather is interrupted Monday by low pressure moving across the southeast U.S. This will drag precipitation north into the Mid-South by morning with a wet day in general on tap. Combined with a brisk north wind, it'll be an ugly day - wet and cold as temperatures top out in the lower to mid 40s.

Forecast precipitation totals (liquid) for Monday and Monday night. (NWS via PivotalWx)

So are we really expecting snow?

Monday night is where things get interesting, especially for mid-November. As the moisture draws northeast out of the region overnight, even cooler air drops in behind the departing precipitation with temperatures falling into the 30s after dark. Temperatures aloft (which are critical for potential winter precipitation shenanigans) also rapidly cool. In sum, we could have a short window overnight in which light snow mixes with the departing rain. There, I said it!

The Saturday morning GFS model depicts expected precipitation Monday evening with precipitation type as of midnight (green = rain, blue = snow). Also shown, the 35° temperature line (blue) and freezing line (blue). (WxBell)

Before you go crazy filling your gas tanks, buying sleds, asking about snow days, or the like, I do NOT expect much in the way of significance to this event, other than it's just not that common this early in the year. Mixed with rain and temperatures just above freezing, there should be no accumulation when the steadiest of precipitation occurs. Late in the night, after midnight, we could see what lingering moisture remains become all snow with temperatures near freezing.  However, there is likely to be little, if any, moisture left that could amount to any accumulation.

Bottom line it for me

In sum, for the Memphis metro, I do not expect accumulation, or even really any impacts. A strong north wind should help dry streets fairly quickly once precipitation departs. The only uncertainty in my mind is whether there could be some freezing spots around Tuesday morning for rush hour, as lows look to be near 30. It's too early to know that. This early in the year, despite the cold weekend, ground temperatures are still pretty warm, so that is a plus.

The same GFS model as above, showing accumulated snow through Tuesday evening. Areas along and north of I-40 may have a dusting, but with warm ground and some rain mix, there should be little if any impact. Areas to our north could see a swath of accumulation. (WxBell)

We'll continue to monitor incoming model data for any changes, but the "flip-flopping" of medium-range models the past few days is subsiding and they are getting a bit more in line. (Which is why I have, on purpose, not started talking about the "S" word until now.) We'll have additional short-range and high-resolution model data available this weekend as well that should bring the situation additional clarity. Or as clear as forecasting November snow in the Mid-South could possibly be!

Here are a few early season Memphis snow facts:

Earliest trace of snow - Oct. 19, 1989
Earliest measurable snow - Nov. 2, 1951 (0.2")
Earliest 1" snow - Nov. 14, 1976 (1.2")
Last time with 1" snow in November - Nov. 28-29, 2011

The rest of the week - moderating cold

Behind the departing system, Tuesday will see increasing clouds, but not temperatures. It could be a raw day with 30s most of the day and a biting wind. From there, we slowly start to warm back up as we head towards the weekend with no precipitation in sight for several days. However, there will be a few more mornings with below freezing temperatures. You can always get the latest details in the MWN Forecast in our app or on the web. Links are below.

Erik Proseus
MWN Meteorologist

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