January 2023 Medium/Long Range Pattern Discussion Thread

[Carvers Gap]

@Math/Met, what are your thoughts about the upcoming wind event?

[snowmaker]

Them 2 storms in the long range are in a good spot for the long range I think. As it sits it isn’t real good for west tenn and I am on far northwest flank. It doesn’t look like it would take much of a northwest jog in the scenario to put much more of Tennessee in play. Just 50-70 miles. Of course I realize that is just one control run at a very long range so I am just talking hypothetically. I do like how the last few runs all models are trending colder.

[Math/Met]

1 hour ago, Carvers Gap said:

@Math/Met, what are your thoughts about the upcoming wind event?

There is potential for a significant wind event. Fountainguy's post above illustrates that. It's really a matter of how far north the strongest core of the LLJ gets. Initially, the LLJ builds in from the south and the 850mb flow is more SE across the mountains. In my experience, mountain waves can be slow to establish is this scenario. There's often too much low level lift in this scenario, so parcels don't really oscillate in a wave manner.  Once the LLJ gets far enough north, the flow at 850mb veers slightly, to a more traditional direction, and the overall atmospheric profile improves for mountain waves.

The 00z NAM would probably be the most significant outcome. It produces a few hour window of a VERY strong wind event, because it lifts the strongest LLJ winds pretty far north and gets the 70+ kt 850mb winds to the north of the mountains. The 18z Euro is less aggressive with bringing the 70+ kt portion of the LLJ this far north. It would still produce some strong winds but probably not a high end MW event.

So the potential is there for a relatively brief high end event, but my confidence for the severity is lower than normal due to the reasons above.  I'll be watching future model runs for how the LLJ evolves.

[Carvers Gap]

@fountainguy97I thought this was a great write-up by MRX and ties into your comments about winter wx this week...  As for everyone else, lots of great information in here.

National Weather Service Morristown TN
326 PM EST Tue Jan 24 2023

...New SHORT TERM, LONG TERM...

.SHORT TERM...
(This evening through Wednesday)
Issued at 256 PM EST Tue Jan 24 2023

Key Messages:

1. A significant mountain wave wind event will develop on Tuesday
night and continue through Wednesday; strong winds will mix down
into the Valley on Wednesday.

2. Rain spreads into the area after midnight tonight, peaking
Wednesday morning with a period of locally heavy rainfall possible.

Discussion:

A significant mountain wave event owing to a very dynamic low
pressure system will impact our area beginning overnight lasting
into tomorrow. The low currently brewing today in Texas will slide
into the Ohio River valley by tomorrow morning bringing with it
moderate to heavy rain showers, high winds in the mountains, and
strong, gusty winds in the valley.

High clouds associated with the incoming storm system will stream
into the area through the remainder of the day. Rain will arrive in
the overnight hours, and the bulk of the showers will push through
during Wednesday morning per CAM guidance. NAM shows some marginal
amounts of CAPE above the inversion at Chattanooga, and NBM had
thunder, so could hear a roll of thunder in the convective line of
showers as they rumble through overnight.

Ahead of the system the 850 mb winds associated with the low level
jet will strengthen to a 75 knot peak at 12z Wednesday morning.
These potent winds and the strengthening pressure gradient along the
mountains will promote a strong mountain wave wind event along our
Appalachian Mountains. After the showers push out of the area, the
low level inversion in the valley will lift and stronger winds will
be able to mix down to the surface. NBM shows 25-30 mph winds in the
valley along with HREF showing gusts to 40 mph. Overall going to be
quite gusty behind the rain. The current wind advisories and high
wind warnings for the zones are unchanged for this forecast package,
everything looks to be on track for significant winds.

The remainder of Wednesday will be mainly dry outside of an isolated
shower or two, and the gusty winds will gradually begin to diminish
from the southern valley north as the afternoon wears on.

&&

.LONG TERM...
(Wednesday night through next Tuesday)
Issued at 256 PM EST Tue Jan 24 2023

Key Messages:

1. Wednesday`s high winds will continue to drop off in the
evening.

2. Lingering wrap around moisture and steepening lapse rates with
colder air aloft will produce scattered showers for late Wednesday
night through Thursday evening. Greatest coverage will be late
morning and afternoon Wednesday. Snow showers for the Plateau and
higher terrain. A mixture of rain and snow for the Tennessee valley.
Light snow accumulations anticipated for the higher terrain.

3. Another fast moving system Sunday and Tuesday.

Discussion:

For Wednesday night through Thursday night, overall broad upper
trough across the Ohio and Tennessee valleys. Initial short-wave
will have moved northeast with a good deal of wrap-around low-
level moisture across the region. Another wave into the broad
trough keeping cold air aloft with relatively steep low-level
lapse rates. Model soundings show low-level CAPES of 40-60 which
will produce scattered showers.

Vertical temperature profile is cold enough for all snow for the
Plateau and Mountains with a mixture of rain/snow showers for the
valley. Best coverage of showers will be along and north of
interstate 40. Model ensemble/probabilities show chances of 1 inch
or more snow limited to the highest terrain.

Overall for Thursday, a cold and raw day with low-stratu hanging
around with temperature struggling to climb to 40 degrees in the
valley.

For Friday and Saturday, upper flow becomes more zonal with return
of sunshine and moderating temperatures.

For Sunday, a fast moving jet across the mid-section of the nation
within the west to southwest flow aloft will move to the Ohio
valley. Associated low-level southerly jet will increase the
isentropic lift into the Tennessee valley producing widespread rain.
GEFS and ECMWF ensemble shows light QPF amounts generally 0.25 inch
or less.

For Monday, drier conditions but cloud cover will be slow to erode.

For Tuesday, a strong storm system will move toward the southern
Appalachians. A lot of uncertainties on how much phasing occurs
between the northern and southern jets.

[Math/Met]

Regarding the mountain wave event, the 18z 3km NAM is about as impressive as you will see in regards to the strength and location of the LLJ by tomorrow morning. Greene Co schools are closed tomorrow due to the wind forecast. That's probably a good decision. You don't want buses on the road in southern Greene County with such a high ceiling to this wind event.  I still think there are a few potential limiting factors (as I mentioned previously), but there's likely to be a few hours of possibly damaging winds in the favored locations.

[Daniel Boone]

Good discussion by them other than the lumping the entire Valley with the same High Temp Thursday.  Nothing major, just a pet peeve of mine, lol. 

     The next week to 10 days has potential. 

[Jed33]

Since NW TN is in our forum area and Paducah could, I guess be part of it (might be stretching it though) I’ll post this image, courtesy of RadarScope. It’s got to be hammering, if only for a brief time. I bet it’s fun to see right now! 

[Math/Met]

It looks like Camp Creek has gusted to 78mph so far. 

[dwagner88]

Winds have been underwhelming thus far in the valley. We had far worse with the storm last week.

[8283 El Nino Baby]

19 minutes ago, dwagner88 said:

Winds have been underwhelming thus far in the valley. We had far worse with the storm last week.

Same here on the plateau. Max gust of 21. Did get an inch of rain.

[Matthew70]

Same here outside Nashville.  The winds have been less than 20-25mph. 

[Carvers Gap]

Gusts here have been 30+mph which is the forecast by MRX for MBY.

[Math/Met]

3 hours ago, Math/Met said:

It looks like Camp Creek has gusted to 78mph so far. 

Just to follow up on this. I haven't looked to see how bad it was in other areas, but I don't really consider 78mph to be a particularly strong mountain wave event for Camp Creek. This type of system (the evolution and orientation of the LLJ)has underperformed several times at CC in my years of studying them. That's why I was kind of reluctant to go all in on a high end event.  Still a decent mountain wave event though.

[fountainguy97]

hrrr looking good for some streaky snow totals over the next two days.  Bullseye over Unicoi with 5" IMBY. I'll take it haha

[Daniel Boone]

50 minutes ago, fountainguy97 said:

hrrr looking good for some streaky snow totals over the next two days.  Bullseye over Unicoi with 5" IMBY. I'll take it haha

Alas, it's the hrrr...Actually, it's probably right with the scattered and banding snshrs. It usually does a rather abysmal job for far SWVA irt snowfall.  Of course, that's typically with synoptic setup's so who knows maybe it does better with this type. 

[Carvers Gap]

Strongest winds of the day here @Math/Met, it is howling.   

[Jed33]

Same here! The wind is rough right now!

[Carvers Gap]

Looks like some light snow showers or flurries will be moving along the TN/KY border this morning.  One line is coming off the Plateau and one line is moving onto the eastern rim.

[Carvers Gap]

Light snow, sleet, and rain falling in west Sullivan Co.

[matt9697]

1 hour ago, Carvers Gap said:

Looks like some light snow showers or flurries will be moving along the TN/KY border this morning.  One line is coming off the Plateau and one line is moving onto the eastern rim.

Yea went through a grapple shower on I-65 south just coming into Nashvegas this morning

[Carvers Gap]

Definitely our heaviest sleet shower so far.  Very wintry day.

[fountainguy97]

Man that squall east of Nashville looks awesome.

 

[Daniel Boone]

Recorded a dusting overnight. Light snshwrs and periods of steady light snow has been falling through the Morning but, melts as temp Is above freezing now(33.9). There's measurable Snow above 2000ft. 

[Carvers Gap]

So, January(after crazy warmth) would close with an ice storm in middle and west TN.  West TN, Arkansas, northern MS....those regions appear to have had it the worst.  The ice storm would roll into February as it has one foot in one month and one in another.   There is a thread dedicated to this event.