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March 11th-13th Winter Weather Event. Winter's last gasp?


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Early Congratulations @Knoxtron! Baby previous page. I agree roads will be fine or at least easily passable by Monday. 

Free for All Friday: MRX refers to kissing jets. I want to make love to the upper level set-up.

I was going to say the obligatory last-minute bump-up of snowfall totals. Appears justified this time.

Normally I'm skeptical just-in-time cold. However we have key factors. We get classic jet induced / PVA upward vertical motion with thick DGZ. Also the isentropic lift. All juxtaposed with cold and moisture for once around here.

NO transfer to the Coast; instead, the back wave (our wave) is the stronger one behind what went through the Carolinas today. Kissing jets is the Carolinas jet-let interacting favorably with what's coming out of the Plains. Areas of lift associated with each jetlet/jet stream interact. 

Kissing jets is the opposite of what often happens here, where they are out of phase and/or sinking motion of the Coastal nixes the lift. Again that's not a concern. It's fairly easy to model both ways, so the kissing jets carries solid confidence. MRX highlights below.

National Weather Service Morristown TN
345 PM EST Fri Mar 11 2022

There is a very high degree of confidence that accumulating snowfall
will be seen across the entire forecast area. There is also high
confidence that a short period (roughly 2-4 hours) of heavy snowfall
rates will be seen. Model plan views show the CWA between two
distinct jet structures which will favor strong upward motion.
Additionally, cross sections show this deep upward omega along with
saturated air extending through the dendritic growth zone and also
into regions of negative saturated EPV. All of this supports the
idea of high synoptically driven precip rates with the potential for
some enhancement via convective processes and resulting 2"/hr
snowfall rates. All of this has lead to a broad increase in expected
snow accumulations, especially over the central and parts of the
southern TN valley, which are locations that should be favorably
positioned beneath upper jet structures. That being said, there
remains a fair amount of uncertainty in a few areas. Geographically
speaking, the southern and far northeastern TN valley are areas of
concern. For areas east of I-75 in the southern valley, the question
is whether the heavier precip rates will have a long enough
residence time over the cold air to result in the higher amounts
we`ve put in. Trends have been to support higher amounts so that`s
the direction the forecast has gone. In the northeast TN valley,
models want to hang on to some warmer temperatures near the surface
for a bit longer than other areas, resulting in lower snow amounts
relative to areas in the immediate vicinity. This is present in both
hires model output as well as courser models like the GFS. Still,
the trends have been upward there too. Lastly, going back to the
convective element, this could easily lead to some overachieving of
storm total snow amounts in places while other locations may be very
close or possibly lower than forecast. This is something we simply
will not know until we`re in the middle of the event.
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Updated point forecast. 

 

Detailed Forecast
Tonight
Rain likely before midnight, then snow. Low around 21. Blustery, with a southwest wind 5 to 10 mph becoming north 15 to 20 mph in the evening. Winds could gust as high as 35 mph. Chance of precipitation is 100%. Total nighttime snow accumulation of 3 to 7 inches possible.
Saturday
Snow likely, mainly before 9am. Cloudy, then gradually becoming mostly sunny, with a high near 22. Wind chill values between 4 and 9. Blustery, with a northwest wind 15 to 20 mph, with gusts as high as 35 mph. Chance of precipitation is 60%. New snow accumulation of 1 to 2 inches possible.

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Yeah the GFS is trying to do something mesoscale in southeast Tenn. It could happen somewhere. Thunder would of course promote such totals, but wherever it sets up. Thank your brother's family for us down in Chatty!

Though that mesoscale feature is a question, intensity and location, the synoptic setup looks good. Cold, lift and moisture are timed together. We don't have to pray for a trowal on the back side. Instead it'll get cold enough quick enough with the main lift.

Last post for the afternoon. Chattanooga members of the board are cautiously optimistic.  

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There has been a trend this evening in showing a convective feature running along I-75 from Hamilton county up through Knox county. Wherever that sets up is in for quite a show from Mother Nature tonight. It reminds me of the MCV that formed in the February 2014 storm over Birmingham and travelled up the I-59 and I-75 corridors. I got around 4” additional snow (and some thunder) just from that feature during that event.

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1 minute ago, McMinnWx said:

I’m hoping it dumps snow here. 

All the ingredients are checked off...enough cant be said how the timing couldn't have been much more perfect (overnight) to max out potential (takes solar aspect out of it). Someone in the southern valley is in for a helluva show.

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At this point I’m looking for the fly in the ointment. I can’t help but notice robust convection originating in the gulf around 200 miles due south of the FL/AL border. It is persistent and appears unmoving. I’m wondering what affect it will have on moisture transport later if it doesn’t clear.

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1 minute ago, dwagner88 said:

At this point I’m looking for the fly in the ointment. I can’t help but notice robust convection originating in the gulf around 200 miles due south of the FL/AL border. It is persistent and appears unmoving. I’m wondering what affect it will have on moisture transport later if it doesn’t clear.

Depends on the orientation between Mobile and Tallahassee...more perpendicular it is, the more it can disrupt transport. Seen the opposite as well if it is  orientated NNW.

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