Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 050447 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1147 PM EST Thu Mar 4 2021 .UPDATE... Issued at 1147 PM EST THU MAR 4 2021 A few lower clouds are working into far eastern Kentucky, but this has mostly been few to scattered in nature. This likely brought on by a weaker wave. Outside of this cold air continues to work southward tonight under the northerly flow around a surface high pushing into the Great Lakes. Updated the forecast to align mainly hourly temperatures closer to the latest obs and trends. Also added a little more cloud coverage in far eastern Kentucky. UPDATE Issued at 933 PM EST THU MAR 4 2021 Surface high pressure is pushing southward into the Ohio Valley this evening. This is providing cold air advection under northerly flow. Adjusted the temperatures to handle the latest obs and trends, but otherwise there are no other changes planned at this time. && .SHORT TERM...(This evening through Friday night) Issued at 640 PM EST THU MAR 4 2021 An amplified upper level pattern is currently in place, with a deeper upper level low across eastern Quebec, allowing for troughing along the Eastern Seaboard. Sharper ridging is aligned from western Canada down through the northern Rockies, with an upper level low undercutting the ridge axis rotating towards the southern Plains. At the surface, high pressure is sprawled from north central Canada down through the Tennessee Valley. Delayed cool air advection, combined with sunny skies and plenty of low level dry air, allowed for another overachieving high temperature forecast. Readings topped out in the upper 50s and lower 60s across the southern half of the forecast area, with mainly mid to upper 50s seen north. The upper level pattern will continue to amplify through the short term, with broad troughing expanding further west from the Eastern Seaboard with time. By early Saturday, the trough will reside over most locations east of the Mississippi River. This will result in cooler temperatures across the Ohio and Tennessee valleys, but also continued tranquil weather, thanks to dry air being maintained in the low and mid levels. Cooler nights and days are ahead for eastern Kentucky, as low level flow becomes more north to northwest through the period, as high pressure gradually builds in across the Ohio Valley. Lows will average in the low to mid 20s in the valleys, with mid to upper 20s on the ridges. Highs on Friday will range from the mid to upper 40s for most locations, with a few lower 50s across the far southwest. Skies will be mostly clear, besides some passing high clouds Friday afternoon and evening. .LONG TERM...(Saturday through Thursday) Issued at 450 PM EST THU MAR 4 2021 Quiet weather, courtesy high pressure, will persist through most of the long-term period as the models remain in excellent to good agreement into the middle of next week. A storm system could bring rain chances by next Thursday or Friday but significant model spread remains. Beginning Saturday morning, the latest models show ~1035 mb surface high pressure dropping southward from western Ontario/eastern Manitoba while a ridge of high pressure extends southeastward to over the Carolinas. This will keep a dry northwesterly flow over eastern Kentucky for Saturday and Sunday. The high pressure center will gradually move southeastward and crest over the Ohio Valley and Great Lakes late Sunday and over the Carolinas on Monday. Southwesterly flow will develop along the back side of the high, ushering in moderating temperatures and slowly rising humidity levels. Dry weather will continue into mid-week before a cold front and its supporting upper level trough approach from the northwest on Wednesday with increasing mid-to-upper level moisture and a tightening pressure gradient. Some rain chances are possible by Thursday or Friday. In sensible terms, look for clear to partly cloudy skies through Tuesday. Initially, a chilly northwesterly breeze on Saturday will keep high temperatures in the 40s to possibly 50s near the Tennessee border. That breeze should slacken on Sunday allowing the bright sunshine to boost highs to within a few degrees of 50. The moderating trend will continue on Monday with temperatures nearing 60 and reaching well into the 60s for Tuesday. The combination of light winds, clear skies, and very dry air will result in sharp ridge-valley temperature splits each night. The coldest nights will be Saturday and Sunday nights when some of the more sheltered valleys could drop well into the mid-to-upper teens; but the thermal belt ridges should bottom out in the mid to upper 20s. Relative humidity levels will drop sharply each morning, bottoming out between 20 and 35 percent on each afternoon through Tuesday. Fortunately, winds should remain fairly light. Southwesterly flow will strengthen and become gustier on Wednesday and Thursday. While much of the guidance suggests that humidity levels will recover to above critical fire levels by Wednesday, warmer than than currently forecast temperatures could result in lower humidity levels. Given this potential, those with fire weather concerns may want to monitor forecast trends as we approach the middle of next week. By Thursday or Friday, increased cloud cover and rising rain chances return. The NBM guidance has generally been too diurnally limited and moist in recent days relative to observed values. This might be due, at least in part, to the various models struggling to resolve strong sensible daytime heating and also the NBM time-lagged bias corrections. Therefore, high temperatures were adjusted 2 degrees higher than NBM guidance for each afternoon through Tuesday. Low temperatures were also lowered sharply towards COOP MOS in valley locations to account for rapid radiational cooling each night. Dew points were lowered toward the raw model guidance and the GFS MOS through the entire period. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) ISSUED AT 708 PM EST THU MAR 4 2021 There is the potential for some high clouds by late in the period, but outside of this no issues with CIGs or Vis. The front has passed bringing mostly lighter northerly flow to the region at around 5 to 10 knots. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...GEOGERIAN LONG TERM...GEERTSON AVIATION...DJ

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