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FXUS64 KOHX 090429 AFDOHX

Area Forecast Discussion National Weather Service Nashville TN 1029 PM CST Fri Dec 8 2023

New AVIATION

UPDATE
Issued at 752 PM CST Fri Dec 8 2023

Forecast is pretty much on track for this evening. Some light rain has blossomed across our western counties, as expected, but other than that, not much going on.

I wanted to talk a little about tomorrow, based on what I'm seeing in some of the latest CAMs and other models. When I'm looking at severe potential, I always ask myself, what is going to keep this from happening? What severe parameter is weak and is going to stifle tornado development or us getting damaging straight line winds?

Granted, I've been away. I don't have days of models to go off of mentally, but looking at the last 3 extended runs of the HRRR and the 18Z GFS, honestly, I'm not seeing much stifling going on.
If I had to pick one or two: 1) Soundings are saturated. That can discourage tornado development and downward momentum for wind and B) Wind profiles are *almost* unidirectional. Neither of these will negate tornado or damaging wind potential, but they're worth pointing out. If anything can keep us from seeing severe weather, it'll be morning rain/extra cloud cover to minimize destabilization.

In a nutshell, I have to continue to agree with the afternoon forecasters in the potential for all modes of severe weather tomorrow afternoon and into the early evening hours on the Cumberland Plateau, to include hail! I don't think we see monster hail. That's not typically a December thing, but forecast sounding lapse rates suggest we'll get some hail reports, too. Storm intensities should drop off pretty rapidly after sunset, so storm threats should be over by 9-10 pm.

Some may also be wondering about rainfall totals. 24 hours ago, I know we were talking about 2-3 inches of rain, but latest guidance has backed off of this considerably. I think 1-2 inches is a good possibility in several spots, but the flooding threat is relatively low.

The midnight crew will delve further into the evening suite of models and have more analysis, but wanted to get some thoughts going for tomorrow.

SHORT TERM
(This afternoon through Sunday night)
Issued at 115 PM CST Fri Dec 8 2023

Latest surface observations shows its a very pleasant December day thanks to the ongoing strong WAA with temperatures in the mid to upper 50s on the Plateau and low to mid 60s elsewhere. South winds have also been quite gusty and reaching the 20-30 mph range at times, while dewpoints have risen as high as 50 in our southwest. Moisture will continue to increase the rest of today, and by 00Z or so scattered showers should break out over our western counties and gradually spread eastward through the cwa tonight. Continued WAA will keep temperatures very mild overnight with lows only dropping into the upper 40s on the Plateau and 50s elsewhere, which are closer to our normal highs for this time of year.

Main weather story continues to be potential for severe thunderstorms tomorrow afternoon/evening as a 100kt H5 jet streak rounds the base of a positive-tilt upper trough over the Plains and moves into the Midwest, putting our area in the right entrance region of the jet streak. As this occurs, a strong cold front will approach from the west and reach the Tennessee River by Saturday evening. 12Z models and CAMs have unanimously trended higher with CAPE and shear tomorrow over the western two-thirds of the midstate, with peak MLCAPE reaching the 500-1000 J/Kg range during the afternoon and effective low level shear peaking in the 200-300 m2/s2 range. These values would be favorable for scattered severe thunderstorms with hail, damaging winds, and even a couple of tornadoes, with the highest potential for severe storms along and west of the I-65 corridor between roughly 20Z-01Z. Uncertainty still exists on the degree of severe threat tomorrow. Some CAMs such as the HRRR are more robust with the threat and indicate a few supercells are possible during the afternoon hours across our western half before activity congeals into a QLCS and moves through our eastern half during the evening.
Other guidance shows less potential for supercells or a more messy storm mode, leading to a lower severe threat. Regardless, forecast soundings and ensembles indicate the severe threat will decrease rapidly after 01-02Z as instability diminishes and a low level temperature inversion develops, so the severe threat on the Plateau looks minimal at this time.

After the QLCS moves through, rain is expected to continue across the area Saturday night into Sunday morning before exiting the midstate Sunday afternoon. WPC has lowered their forecast QPF, but overall guidance and WPC still indicate 1 to 2 inches of rain areawide. Models have trended quicker with moving precip out of the area, giving less time for cold enough air to arrive and potentially change the light rain to a light rain/snow mix or light snow on the Plateau. Could still be a brief window of opportunity for a little snow on the northern Plateau late Sunday afternoon or early Sunday evening, and can't rule out a dusting.

LONG TERM
(Monday through next Friday)
Issued at 115 PM CST Fri Dec 8 2023

In the wake of the weekend system, dry weather and colder temperatures are expected much of next week, with lows in the 20s/30s and highs in the 40s/50s. However, these temperatures are near or above normal for mid-December. No significant weather is expected Monday through Thursday, with our next chance of rain arriving by Friday or Saturday of next week.

AVIATION
(06Z TAFS)
Issued at 1027 PM CST Fri Dec 8 2023

Over the next several hours, cigs should start to drop with the arrival of scattered showers. MVFR will start the drop, followed by IFR by mid-morning and these should stick around for the rest of the period. TS are expected at CKV by 21-22Z, then spread to remaining mid-state terminals through 03Z.

Winds are expected to get gusty again over the next couple of hours. Southerly gusts of 20-25 kts can be expected for the remainder of the cycle. Of course, with any direct impact of TS, winds may be gust higher.

PRELIMINARY POINT TEMPS/POPS
Nashville 55 68 40 47 / 50 90 100 50 Clarksville 56 65 37 43 / 50 90 90 20 Crossville 46 60 38 49 / 70 60 100 80 Columbia 55 66 40 46 / 50 80 100 40 Cookeville 51 65 39 47 / 60 80 100 70 Jamestown 47 62 39 47 / 60 70 100 80 Lawrenceburg 54 66 41 47 / 50 80 100 50 Murfreesboro 53 68 39 48 / 60 80 100 60 Waverly 54 65 37 44 / 50 90 90 20

OHX WATCHES/WARNINGS/ADVISORIES
None.

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