Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
931 FXUS63 KJKL 110905 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 505 AM EDT Sat May 11 2024 .KEY MESSAGES... - Some showers and perhaps a storm or two are possible, at times, this afternoon. - Precipitation free weather is anticipated from Saturday night into Monday morning, before more unsettled weather returns. - Expect rather cool temperatures through the weekend, with milder weather then returning. && .SHORT TERM...(Today through Sunday) Issued at 505 AM EDT SAT MAY 11 2024 08Z sfc analysis shows low pressure and a cold front approaching the area from the northwest. Ahead of this, a bubble of high pressure has been enough to keep the skies mostly clear and winds light through the bulk of the night. As a result, fog formed rather quickly in the valleys and has become thick. Now, a smattering of low clouds is moving through the area during these early morning hours and that should limit the expanse of the fog. An SPS is in effect for most of the area for areas of dense valley fog through 9 am. Otherwise, the conditions with this high has allowed for a small ridge to valley difference to set up. Specifically, readings vary from around 50 on the hilltops to near 40 in the more sheltered spots of the east. Meanwhile, dewpoints are within a degree or two of temperatures at most observation sites. The models, and their individual ensemble suites, are in excellent agreement aloft through the short term portion of the forecast. They all depict a clipper trough dropping into the Ohio Valley this morning and passing by to the northeast of Kentucky through the afternoon in northwest mid level flow. Slight 5h height falls and a brush by of the shortwave`s energy will affect eastern Kentucky into the evening. Heights will then slowly rebound tonight with ridging starting to push into the region from the west and practically overhead during the day, Sunday. The model spread remains quite small with these key features so the NBM was used as the starting point for the short term grids along with the incorporation of the CAMs details for PoPs and timing through this afternoon. Sensible weather features another day on the cool side with a passing threat for some showers as a result of an arriving cold front. While showers will be the predominate form of precipitation today - a few cells may find enough instability to break a cap just above 700 mb and grow deep enough for some fleeting thunder. Just a small amount of QPF are expected from the rainfall today - around a tenth of an inch or less for most places. Post frontal, the convection pulls out to east the tonight with clearing conditions and another bout of ridge to valley temperature differences developing along with some more limited valley fog as the winds stay up better than this night. High pressure builds back into the area on Sunday coincident with the rising heights of the upper level ridge. This will mean a mostly sunny day with temperatures a notch warmer than those of today - closer to normal in the mid 70s. The main adjustments to the NBM starting point consisted of adding in some terrain details to the hourly temperatures and lows both this morning and again tonight. As for PoPs - the NBM values were adjusted to include some CAMs details for the shower and scant thunder chances through the afternoon hours with the passing cold front. .LONG TERM...(Sunday night through Friday) Issued at 433 AM EDT SAT MAY 11 2024 Operational models are in good agreement through the first half of the extended with synoptic features, and diverge from there. In general, eastern Kentucky resides in a split flow pattern through the period, with stronger wind fields (westerlies) across the Deep South and to our north along the Northern Tier and Great Lakes. Because of the weaker wind fields aloft, one main trough only manages to crawl through the OH/TN valley regions from late Monday through Wednesday. A second southern stream trough tracks through the region late in the period, Dy7...or Friday. At the surface, low pressure lifts out of the Great Plains and through eastern Kentucky Tuesday into Wednesday, then a second low pressure system moves into the TN valley by the end of the forecast window. Sensible weather features generally unsettled weather through the extended with two main rounds of weather to deal with, the first from late Monday through Wednesday, then a second round from Thursday night through Friday. There are two periods of dry weather, or at least a lull in shower activity, at the start of the extended...Sunday night into Monday and then again Wednesday night into Thursday. Due to a general lack of instability and shear across the area through the period...and relatively weak flow aloft, thunderstorm activity will likely be limited and occur primarily during peak heating, or during the afternoon and early evening time frame. Not seeing signals that would suggest much hazardous weather through the period, though WPC does have eastern Kentucky within a marginal risk for excessive rainfall Tuesday and Tuesday night. Thinking is that this risk is primarily due to the slow speed of the first system`s progression through the Ohio and Tenn valleys. With limited instability and shear, and by extension a lower risk of strong and/or severe thunderstorms over our forecast area, it is difficult to see convection being a primary ingredient to an overall hydro risk. Freezing levels are not particularly high, generally below 11 kft through that portion of the forecast. Wind fields are on the lighter side, but storm motion is still greater than 10 kts until Tuesday night. By late Tuesday night steering winds do drop to between 5-10 kts. PWATS are up close to 1.4 inches, or 75th percentile of climatology. Thus, while the threat of hydro issues is low at this time, it would appear that if there were any problems, a Tuesday through Tuesday night window of time would be most likely time frame of concern. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) ISSUED AT 220 AM EDT SAT MAY 11 2024 VFR conditions are still holding at all sites at the start of the forecast period. With mostly clear skies and light winds, though, valley fog formation is kicking into overdrive, some of which may impact the TAF sites with IFR or lower conditions for a time. To account for this, a TEMPO group for fog down as low as 1SM visibility was kept in the forecast along with low CIGs. Expect west to west-southwest winds to increase through the morning ahead of a cold front and upper disturbance that brings showers to the area from late morning through much of the afternoon. Sustained winds up to 12 kts will transition to a more northwesterly direction with passage of that boundary in late morning and afternoon - then diminishing after dark. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...GREIF LONG TERM...RAY AVIATION...CMC/GREIF