Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, 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
935 FXUS63 KLMK 220033 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 733 PM EST Thu Nov 21 2024 ...Forecast Update... .KEY MESSAGES... * The best chance for any local minor impact will be from southeast Indiana to the Bluegrass region of Kentucky. * Gusty winds tonight and Friday, with some gusts around 35 to 40 mph. The strongest gusts likely today. * Gusty winds during snow showers will likely result in brief periods of reduced visibility. * Much colder weather tonight and Friday with wind chill values in the 20s and 30s. && .UPDATE... Issued at 733 PM EST Thu Nov 21 2024 Light snow has been ongoing for a couple/few hours across the region, and to this point, haven`t picked up a whole lot of accumulation. Most areas have seen a trace to a few tenths of an inch of accumulation on grassy/elevated surfaces. We are seeing some stronger returns moving into our NE CWA ahead of the main vort lobe beginning to rotate into the region. These periods of moderate snow are likely to produce some slightly better accumulations, especially with surface temps hovering around the freezing mark over much of the Winter Weather Advisory area. Still think we could see some values in the 1 to 2" range on grassy and elevated surface. Advisory seems to be placed pretty well given the expected trajectory of the heaviest snow showers mainly east of I- 65. Will be monitoring this system over the next 3-6 hours before it winds down from NW to SE across the area. No advisory expansions or cancellations expected at this time. The forecast overall looks to be on track. && .SHORT TERM /THROUGH TONIGHT/... Issued at 346 PM EST Thu Nov 21 2024 This evening, an upper low will be centered near southwest Pennsylvania. The circulation has two surface lows rotating around it, one over northwest Indiana and the other just off the New Jersey coast. Throughout the night, the surface low over Indiana will continue to weaken as it gets pushed southeast towards Lexington, opening into a positively tilted surface trough. The other surface low, in the Atlantic, will become stacked under the upper low near New York Friday morning. The surface low dropping across Indiana and heading towards the CWA is part of a larger shortwave rotating around the aforementioned upper low. It`s this shortwave that is driving the forcing of the snow showers, currently over central Indiana and areas to the north and northwest, that are headed towards southern Indiana and central Kentucky. Besides pushing the precipitation, the deep layer low pressure circulation is driving northwest flow into the region at all levels, resulting in deep cold air advection. Model soundings continue to show the warmest air in the column is at the surface with the rest of the column well below freezing with no hint of a warm nose. P-type isn`t really an issue. If the near surface temperature gets too warm to support snow, a few areas could see rain, but in most places snow will remain until reaching the surface. As the snow moves into the region, model sounds shower deep saturation, including saturation of the DGZ, but on the back side of the precipitation around 2-3z in southern Indiana, soundings show the DGZ drying with saturation remaining below the DGZ. When this occurs, snow will end and a short window of drizzle could be possible. Surface temperatures are expected to remain above freezing for most of the night, but areas east of Interstate 65 near Madison, Indiana and in the Bluegrass region of Kentucky are expected to see temperatures at least touch freezing before temperatures start to warm again on Friday. Warm surface temperatures and borderline air temperatures will limit impacts on road surfaces. Accumulation will be driven more by rates than freezing temperatures. Most roadways are expected to remain wet with snow melting on contact. Grassy and elevated surfaces will see better accumulations. The forecast has the northeast half of the CWA seeing between 0.1" to 2.8" with most seeing 1" to 1.5" of snow. The highest amounts will be in the cooler areas between Madison, IN and Lexington, KY. These totals are what is expected to fall from the sky and doesn`t take into account melting which is again expect to be substantial. The Winter Weather Advisory will remain in place to cover conditions tonight. During the day on Friday, the shortwave bringing the heavier snowfall will be well out of the area. Skies are expected to remain mostly cloudy, and with cold air advection remaining in place, kept high temperatures on the cooler side of guidance in the low to mid 40s. Remaining deep layer moisture streaming south over Indiana is expected to cause rain over southeast Indiana and the Bluegrass region during the afternoon. && .LONG TERM /FRIDAY THROUGH THURSDAY/... Issued at 346 PM EST Thu Nov 21 2024 The upper low bringing the cold and blustery conditions over the next few days will begin to lift into the Canadian Maritimes over the first half of the weekend. As is common in a pattern with an exiting upper low, low-level moisture is expected to remain trapped below a mid-level subsidence inversion, keeping grey skies and cool temperatures in the region Friday night into Saturday morning. With surface pressure ridging moving into the area by Saturday evening, cold advection should ease on Saturday, with temperatures warming into the upper 40s and low-to-mid 50s Saturday afternoon, and temperatures may warm more if clouds are faster to clear. For the second half of the weekend, the overall pattern will become more zonal, with subtle upper ridging moving over the area on Sunday. As the sfc/low-level high moves into the southeast U.S., return flow should set up over the Ohio Valley, continuing the upward trend in temperatures into Sunday. The next chance for precipitation across the region is expected on Monday as a low-amplitude upper wave moves across the Great Lakes. Sfc low pressure will develop over the upper Midwest Sunday night, with a cold front extending south into the mid-Mississippi Valley. While the ECMWF and GEFS ensemble mean depict an 850 mb jet strength exceeding the 90th percentile Monday morning, this jet will be fairly zonally oriented, and will thus be unable to fully tap into Gulf moisture. As a result, moisture should be limited and total precipitation amounts should be modest. Current 25th-75th percentile QPF range is between 0.10 and 0.30" for the Monday-Monday night system. Ahead of the cold front on Monday, temperatures will remain above normal, with highs expected in the low-to-mid 60s. High pressure moving across the area on Tuesday should bring a reprieve in rain chances, though this should be fairly brief as the overall pattern remains progressive. As we approach Thanksgiving, run-to-run model consistency and forecast confidence decreases, though there is a fairly consistent signal for a return to active weather across the region. A large-scale wave ejecting out of the western CONUS with baroclinity/zonal flow downstream will create a setup where multiple disturbances ride along a boundary, bringing multiple chances for precipitation during the mid-late week period. At this time, the precipitation is expected to be predominantly liquid, though a cooling trend is likely as we head through the last week of November. && .AVIATION /00Z TAFS THROUGH 06Z SATURDAY/... Issued at 659 PM EST Thu Nov 21 2024 Light to briefly moderate snow is ongoing across the region as a strong mid level disturbance rotates through. Seeing a mix of MVFR and IFR conditions where the snow is the heaviest. These conditions will be most likely at SDF, LEX, RGA, although HNB will likely get in on low MVFR ceilings as well into the overnight. Most of the gusts have subsided with low level lapse rates becoming less steep with the loss of heating, however few gusts up around 20-25 mph may still be possible overnight. Expecting snow to end around midnight at SDF, and in the early morning hours at LEX/RGA. Surface winds will quickly veer around from a W component this evening to a NW component later tonight as the surface low quickly moves through. Then, a steady WNW to NW continues through tomorrow with continued mostly MVFR ceilings. The best chance for a brief break in lower ceilings will be from around sunrise through mid to late morning. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...Winter Weather Advisory until 7 AM EST Friday for KYZ031>037- 039>043-047>049-055>057-066-067. IN...Winter Weather Advisory until 7 AM EST Friday for INZ079. && $$ UPDATE...BJS SHORT TERM...KDW LONG TERM...CSG AVIATION...BJS