12 November, 2022 09:15

.Forecast Update…
Issued at 910 AM EST Sat Nov 12 2022

Wintry precipitation in the form of snow, sleet and even freezing drizzle continues to work across southern IN and central KY. Observations from the public along with KYTC and INDOT traffic cameras show slushy road conditions along and north of I-64. This area was located under the left exit region of a strong upper jet streak increasing the intensity of the snow. This swath has produced a quick inch of snow with isolated location getting near 2 inches. Temperatures, thanks to strong CAA and dynamic cooling, have dropped to or below the freezing mark.

Updated the grids to account for the faster movement of the
precipitation and expect most if not all of the wintry weather to be out of our area by midday to 1pm EST. The rest of the forecast remains on track but will be updated as needed through the rest of the morning.


.Short Term…(Today and tonight)
Issued at 310 AM EST Sat Nov 12 2022

…Minor Snow Accumulations on Elevated Surfaces This Morning…

Main concern this morning will be the chances for a dusting of snow, with a small chance for up to an inch of accumulation.

As of 3 AM EST, RAP 500 mb analysis and WV imagery showed height falls from west to east working across the Ohio River Valley with an associated high amplitude trough of low pressure moving across the central portions of the CONUS. Temperatures across the region ranged from 32 degrees at Huntingburg, IN to 45 in Frankfort, KY with mostly cloudy to overcast skies. Good amounts of moisture ahead of an incoming area of subsidence in front of the trough is progged to move into the forecast area later this morning, which will bring the chances for additional rainfall and a wintry mix with some snow accumulations.

Latest model soundings show a plethora of scenarios between rain, sleet, and some snow potential based on a warm nose of air off the surface in the lower levels of the air profiles. The data suggests mostly rain as the precip type on a line from
Tompkinsville/Burkesville to Campbellsville to Frankfort and eastward today (including Lexington) with little to no snow accumulation as moisture exits later this morning into the early afternoon. West of this line is where a mixed precip type is more likely, especially between 8 AM and 1 PM EST.

The greatest chances for a dusting of snow (60-70% chance) is on a line from Hartford to Elizabethtown to Shelbyville, and even up to an inch is possible (10-30% chance) for elevated surfaces. The main tricky part of this forecast is the very warm ground temperatures, since the warm weather has just left the region. Four inch soil temperature observations from around the region are still in the upper 50s to lower 60s, and KY mesonet observations show 2 inch soil temps in the mid 50s. Although snow could fall in a showery burst, the warm temps are unlikely to allow for snow to accumulate for very long, except perhaps on elevated road surfaces.

Latest snow forecast is tending to be closer to the 75th percentile for snow amount probabilities, with 50th percentile amounts closer to 0.5 of an inch or less. 90th to 95th percentiles have between 1 inch and 1.5 inches, which is the maximum amount we could see with this system. Confidence is high for a dusting vs. seeing
accumulating snow of an inch, but it is not out of the realm of possibilities.

Precipitation will end and move eastward this afternoon, and much colder air will filter into the region tonight. Low temperatures are still on track for the low to mid 20s for most locations, which is on the order of 10 degrees below normal for mid November.

.Long Term…(Sunday through Friday)
Issued at 330 AM EST Sat Nov 12 2022

Synopsis: Below normal temperatures are expected throughout the entirety of the extended forecast period as broad mid- and upper- level trough persists across the eastern two-thirds of the CONUS. Surface high pressure will extend across the Ohio and Tennessee Valleys Sunday into Monday, bringing dry weather for the end of the weekend and the start of the upcoming week. A mid-level shortwave and attendant surface low will move across the southern Plains and into the Ohio Valley Monday night into Tuesday, bringing light-to- moderate precipitation amounts. Temperature profiles look very marginal, but could be just cold enough for some snow or rain/snow mix Tuesday morning before changing to all rain. Only minor snowfall accumulations are expected with this system. Dry conditions are favored again for the mid-to-end of week time frame, although ensemble guidance does hint at a modest possibility for other waves of precipitation toward the end of next week.

Sunday and Monday…

Lingering cloud cover across the Bluegrass thanks to low-level moisture and cyclonic mid-level flow should clear on Sunday as the mid-level trough axis shifts east of the Appalachians. High pressure ridge will extend N-S across the Ohio Valley Sunday afternoon, gradually shifting eastward during the day on Monday. This will keep things dry and generally sunny both days, which will help things feel somewhat warmer, although temperatures will still be well below normal. Expect highs in the 40s both days (warmer on Monday), with lows falling into the 20s (a few colder valleys may hit the teens) Sunday night.

Monday Night through Tuesday Night…

A compact mid-level shortwave will bottom out near the Texas Panhandle Monday afternoon before lifting NE across the southern Plains and into the Ohio Valley Monday night into Tuesday. An associated sfc low will develop in the lee of the Rockies Monday morning, following a similar trajectory to the mid-level shortwave. Ahead of this disturbance, low-level warm advection is expected Monday afternoon and evening across our region, which should help keep temperatures warmer Monday night, with lows only expected to bottom out in the low-to-mid 30s. Ensemble guidance generally agrees on the existence of this disturbance; however, there is some disagreement in its overall strength and the richness of the moisture associated with it. ECMWF ensembles generally lean toward a weaker, drier disturbance, while GFS ensembles show strong moist isentropic upglide in the mid-levels across the region Tuesday morning, leading to greater precipitation. Current blended solution seems to account for a good balance of both families of solutions.

In addition to uncertainties about the system as a whole, there is also the question of precipitation type as thermal profiles could be just cold enough for wintry precipitation in the morning hours on Tuesday. Freezing rain and sleet would not be favored with this system as forecast soundings are almost entirely void of a warm layer aloft. The uncertainty in precipitation type will lie in the near-surface layer, which will likely be above freezing, especially outside of the Bluegrass and southern IN. Depending on how deep this above-freezing layer is, precipitation could either fall as rain or snow. At this point, ensemble guidance favors more snow across southern IN and north central KY, with areas along and south of the Western KY/Bluegrass Parkways favored to see predominantly rain. Regardless, snowfall accumulations would be light and ephemeral as diurnal warming should cause everything to change over to rain by late morning Tuesday (given the current most likely forecast scenario). Precipitation will clear the region from west to east Tuesday afternoon, ending for all by late Tuesday evening.

Wednesday and beyond…

Forecast confidence will be suppressed for the remainder of the extended period as ensembles diverge after the mid-week time period. While large-scale troughing is expected to continue across most of the CONUS, mid-range models continue to show smaller disturbances pivoting around the base of the trough. Depending on phasing of northern and southern stream disturbances, additional systems may approach the region later in the week. However, given a lack of model convergence on any one precipitation chance in the ensembles, will keep PoPs silent through the end of the extended forecast period. Higher confidence exists in temperatures remaining below normal, as the thermal trough should remain fixed across the central and eastern CONUS.


.Aviation…(12Z TAF Issuance)
Issued at 629 AM EST Sat Nov 12 2022

MAIN IMPACT: MVFR to IFR ceilings and visibilities with mixed wintry precipitation for the next 6 hours, MVFR ceilings to linger for the next 12 hours.

DISCUSSION: Latest radar trends and area observations show rain, sleet, and snow moving into the region and already affecting area terminals. Model forecasts continue to have the quick-hitting disturbance bring a round of light mixed precipitation to the region this morning with a mix of light snow, rain, sleet, and lingering drizzle and exiting by early afternoon. MVFR visibilities and ceilings with brief periods of lower in any snow shower bands, will be possible. Low clouds will hang around through the afternoon, and eventually returning to VFR by this evening. Steady northwest winds around 10kts will prevail overnight with clearing skies.





Short Term…MK
Long Term…CSG