Wednesday, March 20, 2013

It's Spring! So let's talk snow...

Naturally, since today is the first day of spring, we should be watching highways getting brined and meteorologists pouring over model data looking at precipitation timing and critical temperature thresholds right??  In the crazy world of weather, saying "it's not going to happen" is a taunt to Mother Nature, who may decide to hit you with a snowball of humility.

Alas, a Winter Storm Watch has been issued by the National Weather Service for the entire metro, except Tunica and Tate counties, valid from 1pm Thursday until 7am Friday (see map below).  No this is not a joke and April Fool's is not here (but it's not that far off!).

Winter Storm Watch in blue, valid Thursday afternoon and night
Computer models have been having a tough time with this system, which is an upper level disturbance (albeit a potent one) in a pattern called "northwest flow" (which means jet stream-level winds are blowing from the northwest over our area). However, today the models, while still disagreeing somewhat on amounts and exact placement, are more in agreement on the occurrence of winter weather.  The main placement issue is in the eastern and southern extent of accumulating snow - which happens to be over the metro!

Below are the morning instances of the GFS and NAM computer models showing expected snowfall accumulations.  We use other models as well, but these are the most referred to in the short-term (3 days or less) and show the general pattern fairly well.  I have purposefully hidden the legends on these maps to not show the exact amounts they are forecasting, as neither is probably right just yet on how much we'll see.  They are used for reference on where the potential for more snow is, which happens to be across the northern sections of the metro (northern Crittenden, northern Shelby, Tipton, and possibly Fayette).

What to we think?  The bottom line...

What time? light precipitation will start in the metro after lunch Thursday, more likely closer to 3pm and intensify by rush hour into the early evening, with light precipitation continuing overnight and into Friday.

What type? Precip should start off as light rain, maybe with some sleet mixed in as the air saturates and cools. As temps fall from near 40 at lunchtime into the mid 30s during the afternoon, we'll change to rain/snow, then likely to all snow by rush hour into the evening. After 9-10pm, any wintry precip should change back to rain.

How much? The million dollar question and hardest to answer. We are forecasting less than an inch in the southern metro (north MS), an inch or two along the I-40/Hwy 64 corridor, including Memphis and Shelby County and Fayette Co, and 2-3" for  northern Crittenden Co into Tipton Co. This is less than what the NWS is calling for but their Winter Storm Watch is for a much larger area that could see more snow and a longer impact. Our forecast is specifically for the 8-county Memphis metro.

After snow changes to rain during the evening hours, rain (mostly light) will continue overnight and it appears we could have a wet Friday and Saturday, at least lengthy periods of both days/nights. Temperatures tonight in the 20s and dewpoints in the teens with clouds arriving tomorrow morning could keep temperatures cooler than forecast on Thursday, which could affect snow amounts. This is still a big question mark.  We'll continue to monitor.

Forecasting snow in Memphis in MARCH is about as tricky a forecast as they come. We do our best to take a shot at it, leave the hype to others, and will gladly eat crow if we miss!  Follow us on Facebook and Twitter (links below) for the latest information as we head into what HOPEFULLY is our last gasp of winter for 2012-2013!  However, don't be surprised when we stay cool well into next week and also expect that we will see some thunderstorms early Sunday as this whole system finally kicks out. The complete forecast can be found here or on our mobile apps.

Follow MWN on Facebook, Twitter, and Google+
Visit on the web or on your mobile phone.
Download our iPhone or Android apps, featuring a fresh new interface and StormWatch+ severe weather alerts!

No comments: