Forecast Discussion 21:17:35.8044

.Forecast Update…
Issued at 915 PM EST Sat Nov 12 2022

It’s a cold, cloudy evening with temperatures right around the freezing mark. An upper level trough is translating eastward over the Great Lakes and Ohio Valley. A fairly potent mid-level vorticity maximum will rotate through the base of the trough over the Ohio River tonight. Moisture depth is shallow, but forecast soundings show steep low-level lapse rates with good saturation below an inversion near 800 mb. And with the top of the saturated layer at about -12 C, scattered flurries will be possible tonight.

The low stratus looks to hang on for much of the night, with a clearing trend beginning west of I-65 tomorrow morning. Temperatures will slowly dip into the mid/upper 20s by early Sunday.


.Short Term…(This evening through Sunday)
Issued at 225 PM EST Sat Nov 12 2022

Model soundings along with relative humidity time-height cross section show saturation below 800mb at the start of the period. Low stratus will remain over the area through the first half of the overnight before breaking up and clearing from the northwest to the southeast during the early pre-dawn hours. Vort max at the base of the upper level trough axis will be swinging through the Ohio Valley at the start of the period. When you factor this along with the aforementioned low-level moisture and stratus deck decided to carry flurries through the first half of the tonight forecast. It will be cold overnight with lows in the mid/upper 20s which is 10 degrees below normal for mid November.

High pressure currently over the Dakotas will build in over the Ohio Valley by tomorrow. Good subsidence along with increasing heights as upper ridging develops will provide mostly sunny skies. Temperatures will be warmer than today but still 10-15 degrees below normal as highs will only top out in the low 40s.

.Long Term…(Sunday night through Saturday)
Issued at 300 PM EST Sat Nov 12 2022

Sunday Night – Monday…

Cold surface high pressure will be in control to end the weekend and start the new work week. Given nearly calm winds and mostly clear skies, we should have pretty decent radiational cooling for Sunday night/Monday morning. As a result, expect low temps well into the 20, with even some upper teens possible in some of the cooler spots. Highs Monday are expected to be in the 45 to 50 degree range for most under mostly sunny skies. Outside of temperatures, expect a dry period as SW flow aloft holds over the area, but lacks deep moisture or any notable forcing features.

Monday Night – Tuesday Evening…

On Monday night, a shortwave will be quickly ejecting out of the southern Plains and then travailing up through the Ohio River Valley by Tuesday. This feature is expected to tap into a bit of Gulf of Mexico moisture ahead of arrival, which is creating some varying model solutions on just how much QPF falls, and where. Looking like a marginal thermal profile for the time period Monday night into Tuesday, however do expect to see some mixed precipitation during the overnight hours into Tuesday morning, before temps warm back more solidly above freezing. Forecast soundings do show pretty good saturation up through 600mb, with some saturation into layers colder than -10c, so also some periods of all snow are possible in areas where temps are at or near freezing.

Saturation becomes more shallow through the day on Tuesday as the deepest moisture departs with the exiting shortwave. However, low level lapse rates do look to steepen a bit, so could see a few lingering and non-impactful rain or snow showers with temps above freezing on Tuesday. Overall, the trend will be drying the later into the day and evening we get.

Tuesday Night – Saturday…

The shortwave will have exited by Tuesday evening with dry and cold conditions expected to mostly prevail. Can’t rule out a few
instances of light rain or snow showers with any individual vort lobe rotating through the mean flow during the week, however most of the activity looks to remain to the north with the parent trough. There could also be a subtropical jet impulse to keep an eye on late week, but this feature is farther south in current deterministic runs. Any phasing potential that far out can be pretty low
confidence. Will keep the forecast dry in line with previous shift for now until some of the finer details of any one disturbance become higher confidence.

Highs each day will continue to run mostly in the 40s. Meanwhile, lows each night will be in the 20s and 30. A few upper teens are possible again Friday and Saturday morning in the coolest spots.


.Aviation…(00Z TAF Issuance)
Issued at 705 PM EST Sat Nov 12 2022

High confidence in MVFR stratus through the first six hours of this TAF period, followed by slow improvement/scattering of the low ceiling from west to east after 06z Sunday. BKN MVFR stratus should linger over LEX and surrounding areas in the Bluegrass throughout the morning hours.

An upper level trough over the Upper Midwest this evening will translate eastward across the Great Lakes and Ohio Valley tonight. There may be just enough low-level moisture to produce occasional flurries or freezing drizzle. Think it would most likely be flurries as the lower levels continue to gradually cool tonight, but there have also been reports of freezing drizzle this evening in central Indiana. Northwesterly winds will be strongest late this evening and diminish slightly 06-12z Sunday.




Short Term…BTN
Long Term…BJS