Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
554 FXUS64 KHUN 211137 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 537 AM CST Tue Nov 21 2017 .UPDATE... For 12Z TAFS. && .NEAR TERM...(This morning) Issued at 330 AM CST Tue Nov 21 2017 Surface analysis this morning shows the high pressure ridge axis nearly bisecting AL as it remains centered over Carolina coast line. Gradient flow itself is fairly weak, with winds currently under 5 knots across the CWA. GOES R IR bands continue to show a thin layer of cirrus clouds over parts of S. Middle TN and NE AL (DeKalb/Jackson). This has kept temps a bit higher compared to obs site further west. Temps have only dipped into the upper 30s/low 40s across the TN counties and parts of DeKalb thanks to the cloud cover. West of I 65 has observed temps already in the low 30s. .SHORT TERM...(Today through Thursday) Issued at 330 AM CST Tue Nov 21 2017 Our gradual warming trend will continue today as deeper southerly flow develops ahead of an approaching cold front, progged to pass through the region early Wednesday. Regardless of the warmer temps and slight moisture return from the south, ridging through around H7 along with a decent subsidence inversion in place will keep rain chances minimal. It is worth noting that a few global and regional models were hinting at a possibility of some showers today for parts of DeKalb and eastern Jackson associated with a surge of moisture from the Gulf. However, expect that feature to remain east of the CWA as the mid/upper level trough will swing through the area during the afternoon hours. Late Tuesday/early Wednesday timeframe will feature a dry cold front quickly shifting through the area, helping to reinforce some cooler than average temps. Thanks to the cold air advection, temps on Wednesday will likely only push into the upper 40, maybe mid 50s for our southern zones. Expect temps to fall into the upper 20s by early Thursday. This cold air mass will gradually moderate by Thursday. Low level flow will start to lose its northern component as the ridge shifts east, however mid/upper level winds will keep N/NW flow in place. So while temps will be warmer Thursday and Friday morning compared to the previous day, we will still trend below average for mid/late Nov. temps. .LONG TERM...(Friday through Monday) Issued at 330 AM CST Tue Nov 21 2017 On Day 4 (Fri) an upper shortwave axis will be dropping southeast through the TN valley into the existing trough position over the central Gulf Coast and Gulf of Mexico. This will produce little more than a few high clouds with the baroclinic zone/surface low will be developing/moving northeast across the FL peninsula and east of the Carolinas. A sprawling high pressure ridge will follow behind from the central Appalachians through the western Gulf Coast on Friday. Then, another shortwave and fast moving cold front will drop southeast Friday night into Saturday morning (GFS) and Saturday during the day (ECMWF). The suggested blends yield high temps in the upper 50s/lower 60s Saturday, followed by about a 10 degree drop for highs on Sunday. With the surface high on the GFS dropping right over the TN valley (and the ECMWF ridge over the area as well) ideal conditions for radiational cooling are expected. This means another widespread hard freeze is likely again on Monday morning with raw model dew points suggesting lows could drop into the 20s areawide. The models depict a rather quick airmass modification on Days 7-8 as a mid to upper level ridge shift east into the southeast U.S. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday morning) Issued at 537 AM CST Tue Nov 21 2017 VFR conditions will prevail through today. South winds will gradually veer toward the west through the day today ahead of an approaching dry cold front. The front is expected to sweep through the area late tonight/early Wed. morning. While no significant convection is expected, winds will shift to the north between 3-6Z. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...Barron SHORT TERM...Barron LONG TERM...17 AVIATION...Barron For more information please visit our website at weather.gov/huntsville.