Area Forecast Discussion
Issued by NWS Paducah, KY
Issued by NWS Paducah, KY
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211 FXUS63 KPAH 241947 AFDPAH Area Forecast Discussion National Weather Service Paducah KY 247 PM CDT Tue Sep 24 2024 .KEY MESSAGES... - A brief period of relatively dry weather is expected this evening through Wednesday following the passage of a cold front. - Chances for widespread heavy rain will ramp up Thursday night through Sunday as the remnants of Hurricane Helen interact with an upper-level disturbance. - The heaviest rain looks to fall Thursday night through Saturday night, though lighter rain showers may linger through early next week. - Event total rainfall amounts of two to three inches are likely across the region, with areas of higher totals possible. && .DISCUSSION... Issued at 247 PM CDT Tue Sep 24 2024 Tonight through Wednesday night...Isolated to widely scattered showers and thunderstorm are occurring across western KY this afternoon ahead of a surface cold front that is pushing eastward through the region. These storms have been rather benign, with the better environment for organized convection located east of the region. Tonight, an upper-level low centered over the Upper Midwest will shift southward towards the region. This will bring continued cloud cover, and perhaps some light rain showers or drizzle overnight along the I-64 corridor. However, confidence was too low to include in the forecast at this time. Where we do have breaks in the clouds, fog development is likely, especially over areas that saw heavy rain yesterday. Overnight lows will fall into the lower to middle 60s. The upper-level low will become centered over the region during the day Wednesday. Most of the area will be dry, but isolated showers/sprinkles are possible during the afternoon hours. Plentiful cloud cover will keep high temperatures confined to the middle to upper 70s. Thursday through Monday night...The forecast for this period is about as complex as you will see in this region. There are two players, and how they interact will determine how the weather shakes out. The first player is the aforementioned upper-low. This feature will become cut off from the main synoptic-level flow and remain stalled over the region. The other player is the remnants of Tropical Storm Helen, which is forecast to make landfall on the FL Panhandle late Thursday as a major hurricane. Most model guidance takes Helen`s surface circulation through the southern Appalachian Mountains and eastern TN River Valley through Friday and into central TN/KY by Saturday. The wrinkle in this setup is that the upper- level low over our region will begin to siphon Helen`s tropical moisture, developing a deformation-band like swath of heavy rain around the upper-level low. Assuming all the pieces line up, the heaviest rains should fall during the Thursday night through Saturday night period, with a gradual diminishment in rainfall coverage and intensity Sunday and Monday. The latest WPC QPF forecast for the Thursday-Sunday period is very aggressive, perhaps a bit too aggressive, with a broad brush of 3 to 6 inches of rain falling during this time. This is higher than what most global model ensembles are showing, which is more like 2 to 4 inches. Furthermore, NAEFS ensemble guidance is not bullish on extreme precipitable water or specific humidly levels during this time, a signal that rainfall processes may not be very efficient as usually observed in tropical rainfall events. A third wrinkle to consider will be the presence of dry pockets of air that will be absorbed into the upper-level low from the north. These dry slots could cut off the rainfall activity for several hours at a time, limiting rainfall totals significantly. Either scenario will include at least a minor flooding risk, but given the 72 hour time frame for this rainfall and below normal soil moisture, much of this rain may percolate into the soil rather than running off and causing flooding issues. Will need to watch closely how things trend over the next 24 hours for the need for an ESF or Flood Watch. Gradient winds will pick as the remnant tropical low approaches, but gusts should remain well below advisory levels, peaking around 20-25 kts on Friday. Clouds and rain chances will keep temperatures rather uniform as well, with highs in the middle to upper 70s and overnight lows in the lower to middle 60s. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1121 AM CDT Tue Sep 24 2024 As a cold front moves through the region, widespread shower activity is exiting the region to the east. However, widespread MVFR to low VFR cigs will persist through this afternoon at the terminals. Some clearing and lifting of cigs is possible tonight, but this will allow for fog development during the 06-13z window, especially at fog-favored sites like CGI. Additionally, MVFR cigs will push southward into the MVN/EVV/OWB areas in the 09-12z window Wednesday and persist through the rest of the forecast period. Winds will be mainly from the W at 8-12 kts, relaxing under 5 kts tonight from the NW, then becoming N to NE AOA 5 kts after 12z. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ DISCUSSION...DWS AVIATION...DWS