943 FXUS64 KHUN 222352 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 552 PM CST Mon Feb 22 2021 .UPDATE... For 00Z TAFS. && .NEAR TERM...(Tonight) Issued at 239 PM CST Mon Feb 22 2021 Surface high pressure centered over the Gulf Coast will dominate our weather throughout the next several days. For tonight, this means light southwest winds and clear skies. As the drier air mass filters in, dew point depressions should remain too deep for fog to develop, but patchy fog will be possible in sheltered valley locations or near large bodies of water. Otherwise, low temperatures drop to the low to mid 30s overnight. .SHORT TERM...(Tuesday through Wednesday night) Issued at 239 PM CST Mon Feb 22 2021 As mid level ridging builds in across the Gulf of Mexico early this week, surface high pressure will slide eastward into the Atlantic. Height rises coupled with warm, moist flow from the Gulf will result in a warming trend through Wednesday, with highs in the mid 60s Tuesday and upper 60s on Wednesday. Due to the recent cold bias, these high temperatures are a few degrees above suggested guidance and closer to MOS values than DMO. While we are enjoying the warmer weather Tuesday and Wednesday, a shortwave trough will descend through the Northern Plains into the Ohio Valley, pushing a surface low into the Great Lakes region. This surface low will push into New England Wednesday night, and drag a weak cold front through the Southeast. With such a warm air mass in place, despite a lack of broad synoptic lift due to displacement from both the parent low and mid level shortwave trough, isolated to scattered showers are possible Wednesday night. Fortunately, no major change in air mass is expected behind this cold front. .LONG TERM...(Thursday through Sunday) Issued at 239 PM CST Mon Feb 22 2021 One more dry day is expected on Thursday as high pressure over the Ohio Valley will still the biggest influence in our weather. With a mostly sunny sky developing by the afternoon, would expect high temperatures peaking in the upper 50s to lower 60s will be common. This will all change heading into Thursday evening and night as an area of low pressure develops along the northern Gulf Coast that will gradually move ENE across the Deep South into the Carolinas. Weak isentropic lift will result in isolated to widely scattered light shower activity Thursday evening that will gradually increase in coverage through the night as a warm front lifts north into central and potentially northern Alabama by early Friday morning. Models have trended wetter in recent runs due to better confidence in this boundary making it a little further to the north. As such, have increased PoPs to "likely" during the day on Friday. With a boundary in place and deep southwesterly flow parallel to this front, moderate to locally heavy downpours will be possible during this window. As the initial low pressure system shifts off to the east, expect more of a lull in the action of sorts Friday night into Saturday -- though with deep southerly flow and a warm, moist air mass in place, think some scattered light shower activity seems plausible. A secondary area of low pressure will develop Saturday night and shift NE along a stronger frontal boundary draped from the Ohio Valley into the Mid-South and into eastern Texas. As this boundary shifts SE into the Tennessee Valley on Sunday, another round of moderate to heavy rainfall seems more likely. Deep southwesterly flow will advect an anomalously moist air mass into the region along/ahead of this boundary, with PWATs increasing to around 1.6" by 00z Monday at KMSL and KHSV. This would put them at record values for February 28th per the KBMX sounding climatology. The combination of the deep, tropical moisture, strong lift, and mean flow parallel to this boundary would encourage the development showers/storms capable of training and producing moderate to heavy downpours. The presence of some weak, but appreciable elevated CAPE would suggest some deeper convection and isolated storms will be possible during this period as well. Combined with the earlier rainfall from Friday, feel reasonably confident we'd see flooding issues and most definitely rises on rivers if this plays out. What we'll be watching for over the next few days will be where exactly the boundary stalls -- which will give us confidence where the axis of heaviest rain will setup Sunday and Sunday night. Stay tuned! && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 552 PM CST Mon Feb 22 2021 VFR conditions will prevail through the TAF period at KHSV and KMSL. Winds will slack after sunset leaving light winds and clear skies overnight. Patchy fog overnight should remain limited to rivers and valleys, otherwise wind shear is possible at both terminals around 09-13Z with winds reaching 35kts at 2kft. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...30 SHORT TERM...30 LONG TERM...AMP.24 AVIATION...JMS For more information please visit our website at weather.gov/huntsville.