336 FXUS64 KHUN 071152 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 552 AM CST Thu Feb 7 2019 .UPDATE... For 12Z TAFS. && .NEAR TERM...(Today) Issued at 330 AM CST Thu Feb 7 2019 Although no rainfall can be seen on area radars in northern Alabama and south of Tullahoma (TN), widespread low clouds are still occurring across the Tennessee Valley. A tight pressure gradient continues across northern Alabama and southern middle Tennessee, as the surface front remains stalled over northeastern Texas into northwestern Arkansas and into the Mid-Atlantic states. Sustained south to southwesterly winds between 10 and 15 mph with higher gusts up to 25 mph are occurring and should continue into the early morning hours today. The combination and these winds and abundant cloud cover should make for a very warm start to the day, with temperatures this morning in the mid 60s in many locations. In more sheltered valley locations some lower 60s should be more common. Overall, models continue to show stronger upper level ridging build northward into the area this morning into the early afternoon hours. This occurs ahead of an approaching strong longwave trough axis and accompanying cold front over the Midwestern states as it catches up with the stalled front to our northwest and pushes the front eastward into the area. This should strengthen low level winds even more to between 35 and 40 knots most of the day around 925 mb, where it appears most models show the atmospheric column mixing up to. This should provide very breezy conditions today, with sustained southwesterly winds increasing to between 20 and 25 mph with gusts between 30 and 35 mph this afternoon. Will have to monitor winds during the day for Wind Advisory potential, but at this time believe conditions will be just below this criteria. Temperatures this morning look to be a tad warmer than temperatures around daybreak on Wednesday, when high temperatures reached record values (Huntsville - 73 and Muscle Shoals- 75). With even warmer 925 mb temperatures (17-18 degrees Celcius) expected to advect northeast today ahead of the front through much of the afternoon hours, highs should again climb above record levels (Muscle Shoals - 74R in 1921/Huntsville -73R 1999). For now, forecasting highs in the mid to upper 70s across much of northern Alabama and southern middle Tennessee. Given the thinning nature of cloud cover and moisture aloft in numerous soundings, not sure some peaks of sunshine won't occur towards noon. If this occurs highs may top out in the lower 80s in some locations near and east of I-65. The building upper level ridging and overall drying of the atmospheric column should keep any precipitation chances out of the area until very late in the afternoon and mainly in northwestern Alabama and southern middle Tennessee. .SHORT TERM...(Tonight through Saturday) Issued at 330 AM CST Thu Feb 7 2019 At this point, it looks like the actual front and shower and thunderstorm activity along and just ahead of it won't push into northwestern Alabama until sometime between 4 and 7 PM. As it pushes eastward into northwestern Alabama and our southern middle Tennessee counties later this evening, the strongest upper level forcing and wind energy above 700 mb quickly moves more northeastward into northern Tennessee and the Ohio Valley. This should keep most of the better elevated instability, forcing, and thunderstorm activity northeast of the area by 8 PM or so. However, there still appears to be a short window for isolated thunderstorm activity between about 4 and 8 PM, mainly west of I-65 and in southern middle Tennessee. There is enough bulk shear still in place during this period for organized strong to marginally severe thunderstorm activity. However, the better severe weather parameters remain farther northward over Tennessee and Kentucky in model output. Also, with a fairly strong low level inversion (cap) to overcome, confidence in strong to severe thunderstorm development is very low over locations near and west of Interstate 65 between 4 and 8 PM. Expect rainfall to likely be on the light to moderate side with between one quarter and one half of an inch accumulating before precipitation exits into Georgia and eastern Tennessee around 3 or 4 am on Friday. This could be locally higher in a few spots if stronger thunderstorm activity is realized. Much colder air will push into the area behind the front. This will not be a push of arctic air into the area, still cold. Despite sunshine much of the day, highs will likely struggle to climb into the upper 30s to lower 40s. However, with such warm temperatures the day before on Thursday, it will be a shock to the system (drop in high temperatures from Thursday to Friday look to be on the order of around 30 degrees). Most guidance shows strong easterly flow advecting into the area late Friday night into Saturday. This should quickly modify the cold and dry air mass that settled into the area on Friday. Lows will likely drop into the mid to upper 20s before warming even more towards daybreak on Saturday. Highs should rebound significantly on Saturday into the mid to upper 40s with some afternoon sunshine. Cloud cover returns Saturday evening, keeping lows a bit warmer, in the mid to upper 30s. .LONG TERM...(Saturday night through Wednesday) Issued at 400 AM CST Thu Feb 7 2019 On Sunday morning, A broad sub-tropical ridge will be centered off the FL coast in the Bahamas, while a trough will begin taking shape over the West CONUS. A general West-East oriented polar front will be located to our north, stretching from the Central Plains into the OH Valley/Grt Lakes regions and into the NE. As a sfc ridge moves into the mid-Atlantic region, low-level winds will gradually veer from the S then SW, while mid/upr winds maintain a WSW orientation. A mid/upr wave traversing quickly across the CONUS, and mainly to our NW, will cause backing of flow aloft and enhanced moisture advection from the south. At the same time, favorable upr jet dynamics aligned generally across the TN Valley region will aid in broad scale lift and precipitation production sometime on Sunday. At this point, it looks as if precipitation could begin as early as Sunday morning, but chances look better later in the day. Nevertheless, if precipitation does form sufficiently early, residual cold air on Sunday morning could result in a light mix of rain/snow mainly in a few spots in NE AL. However, the chances for precipitation on Sunday morning during this period are just about 20%. The main axis of precipitation on Sunday and Sunday night is expected to be just to our north, where the best dynamic forcing will likely exist. A S-N gradient in precipitation will set up somewhere across the region and this will still need to be refined in subsequent forecasts. Currently, it looks as though precipitation in our area from Sunday through Sunday night would just be about one quarter of an inch, but the main precip axis could still shift a little south (or north) from current thinking. The pattern will continue to favor generally WSW flow aloft and increasing warm air and moisture advection from the S-SW at low levels into Tuesday. This will continue to fuel precipitation production as a series of short wave troughs move rapidly along the upper jet across the TN/OH Valleys. Where exactly the main axis of precipitation will set up remains to be resolved with a high degree of specificity, but will likely be in the TN Valley region. What is still looking likely is that the parent trough in the West CONUS will advance eastward from Tuesday into Wednesday, leading to cyclogenesis in the lee of the Rockies and frontogenesis in the Central/Southern Plains. The sfc low will likely move NEWRD into the Midwest with the trailing cold front pushing into our area perhaps late Tuesday or into Wednesday morning. Overall kinematics may be fairly strong with this next system (increasing low-level jet and developing deep-layer shear), but instability appears to be limited at this time. The forecast does not include a mention for thunderstorms yet with probabilities generally near or below ~10%. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 550 AM CST Thu Feb 7 2019 MVFR CIGS remain in place at both terminals at this time. Southwesterly winds between 10-15 kts will continue and become stronger after 15Z producing some gusts to around 20 kts. Expect MVFR CIGS to climb to around 5000 feet and become VFR around 18Z. Expect southwest winds to strengthen to between 15-20 kts with gusts nearing 30 kts after 18Z. Showers could impact KMSL around 07/22Z and KHSV around 08/00Z. Confidence is low though for specific timing, so only included VCSH and no VSBY impacts (but CIGS will likely drop back into MVFR realm at both terminals). By 00Z at KMSL expect showers or possibly a TSRA to directly impact the terminal. This should occur a bit later at KHSV around 08/02Z. This may produce lower VSBYS or CIGS at both TAF sites. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...KTW SHORT TERM...KTW LONG TERM...KDW AVIATION...KTW For more information please visit our website at weather.gov/huntsville.