027 FXUS63 KJKL 180313 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1013 PM EST Mon Feb 17 2020 .UPDATE... Issued at 1013 PM EST MON FEB 17 2020 Decided to go ahead and stick with earlier trend of slowing down precipitation onset and not having rain entering forecast area until around 12Z, which is about 3 hours earlier then day shift forecast. Of note, the departing dayshift forecast did mention that it may be necessary to slow down precip onset tonight due to large amount of dry air that is currently in place. Ingested the latest obs into the forecast grids to establish new trends. Updated zone forecast text product has been issued. UPDATE Issued at 636 PM EST MON FEB 17 2020 The 18Z run of model data has suggested that precipitation onset will be a few hours slower than previously forecast. With the latest CONSHORT, NAM12, GFS, and HRRR models all suggesting a slower onset, decided to go ahead and update the forecast to reflect this new timing. This supports the idea that dry air that is currently in place could hinder the eastward progression precip in our area and the ability of said precip to reach the ground before evaporating. Also ingested the latest obs into the forecast grids to establish new trends in the very near term. && .SHORT TERM...(This evening through Tuesday night) Issued at 353 PM EST MON FEB 17 2020 The current surface analysis as of 20Z features high pressure over the Northeast retreating east. To the west, crossing the central Plains is the next low pressure system developing and shifting east. This feature will begin to move into the OH Valley tonight into tomorrow morning. The one forecast challenge setting up for this system is the dry surface layer. Dew point depressions across the area are on the order of 15 to 20 degrees. This will make it difficult for the boundary layer to saturate. Thus, have lowered the pops at onset and brought the bulk of the measurable rainfall after 08Z. Due to this tonight, there will likely be some ridge to valley temperature differences as cloud cover will likely not be thick enough for significant insulation. Have adjusted the ridge and valley temps for lows tonight according to this. By 12Z tomorrow morning, ceilings will finally lower with the column finally saturating. 850MB winds will be at 40 to 50 knots with the low level jet impacting the area from the southwest. By Tuesday morning, a low level inversion setting up will keep the stronger winds from mixing to the surface but, still some 20 to 30 mph gusts are not out of the question. As well, give weak instability, have gone with showers across the area but not expecting thunder at this time. Through the day, southwest flow will continue with highs reaching into the mid 50s with the cold front passing through in the afternoon. The air mass moving in behind this front will bring clearing skies with temps dropping into the upper 20s for lows. The bulk of the moisture will exit the area before the colder air changes the precip to snow with the exception of the higher elevations. Overall, this will lead to more normal values for lows Tuesday night. .LONG TERM...(Wednesday through Monday) Issued at 320 PM EST MON FEB 17 2020 Models are in good agreement with features aloft through the period. Interestingly, noticed that the 12Z solution of the ECMWF trended towards the GFS for the last 36 hours of the extended, where some significant differences had previously existed. The pattern is best described as a mean zonal flow regime with two main features of interest, the first a northern stream positively tilted trough that will drop southeast across the eastern CONUS Thu/Fri. The second feature will be a southern stream trough or low that will lift out of the far southwest, push through the Great Plains and into the Tennessee/Ohio valley regions by the end of the forecast. At the surface, strong Canadian high pressure will build into the eastern half of the nation, tracking from the Northern Plains to the Appalachians during the first 72 hours of the period. A disturbance will develop over the far southeast Thu/Fri, a weak reflection of the aforementioned positively tilted trough. This disturbance will produce generally light, but widespread precipitation from the Tennesseee Valley southward. It appears our area remains dry, though some solutions do suggest a slight chance of precipitation along the KY/TN state line. Otherwise mid, and especially high level clouds, will blanket the much of the region. Ridging aloft and surface high pressure will then transit the Ohio and Tennessee valleys. Thereafter, a storm system approaches from the west by the end of the weekend or start of the following week. Sensible weather features generally dry weather through the period. With Canadian high pressure ushering in dry/colder air into the region and high pressure centered over the central Ohio Valley Friday and Saturday morning, expect temps to run below normal for that time frame. Temps look quite cold (into the teens) by Friday morning and while closer to normal, still drop to around 20, or mid 20s Saturday morning. A few locations in our typically colder eastern valley areas could slide into the mid teens again Saturday morning. Thereafter, temps moderate through to the end of the forecast with an increase in clouds and the threat of precipitation as our next weather maker approaches from the west. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) ISSUED AT 639 PM EST MON FEB 17 2020 Expect VFR conditions to begin the TAF period with generally light and variable winds. Winds will slowly begin to increase out of the south through tonight and into tomorrow morning before shifting to the southwest. Ceilings will begin to drop tonight as the cold front approaches from the west. Expect some below IFR cigs by 12 to 13Z with rain dropping vis to IFR conditions as well. These conditions will then persist through the rest of the TAF period. The one thing in question at this point, is how fast will this drop in conditions occur. Dry air in place, may hinder the drop in cigs and vis pushing the occurrence back a few more hours, which is now reflected in the TAF forecast. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...AR SHORT TERM...SHALLENBERGER LONG TERM...RAY AVIATION...AR