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Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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223 FXUS64 KHUN 160856 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 356 AM CDT Fri Aug 16 2024 ...New NEAR TERM, SHORT TERM, LONG TERM... .NEAR TERM... (Today) Issued at 357 AM CDT Fri Aug 16 2024 A storm system continues to affect central and eastern portions of the U.S. CONUS this morning. The parent low of this system is centered over north central portions of Minnesota with frontal boundaries extending into the Ohio Valley and Oklahoma/Texas. Several disturbances have been producing areas of convection along or ahead of these boundaries this evening. The most intense area of convection currently is developing over southern Missouri. The evolution of this disturbance and convection/cloud cover associated with it will be the primary driver of conditions today. Mainly westerly 0-6 km flow suggests that most of the energy associated with this disturbance will move through northern Tennessee and southern Kentucky than further south. However, by the mid afternoon hours, plenty of instability will be in place over northern Alabama and southern middle Tennessee. Also, 25 to 30 knots of shear (30 knots mainly in our southern middle TN counties) does develop along/ahead of the convergence boundary that extends SSW from this disturbance aloft. With DCAPE values forecast to be between 1000 and 1400 J/KG and low level lapse rates between 6.5 and 7.0 degrees, strong along with a few severe storms look possible. Convection may be a bit more organized in our southern middle Tennessee counties. The main threats with this activity will be heavy rainfall, frequent lightning, and damaging winds. Timing though is tricky, but based on current radar and observations given the expected mean flow, expect any stronger convection to develop between 2 and 4 pm in southern middle Tennessee. Further south, likely closer to between 4 PM and 6 PM. Despite increasing cloud cover later this afternoon and the convection expected, temperatures will likely climb into the mid to upper 90s (925 mb temperatures 27 to 30 degrees depending on the model) this afternoon, mainly in northern Alabama. Though mixing of drier air aloft will occur this afternoon in northern Alabama, dewpoints may remain between 71 and 76 degrees in southern middle Tennessee and portions of NE Alabama. This will likely keep apparent temperatures up just enough to warrant continuing the current Heat Advisory that is in effect from 11 AM through 5 PM CDT today. && .SHORT TERM... (Tonight through Saturday night) Issued at 357 AM CDT Fri Aug 16 2024 This activity will likely push east of the area after 9 or 10 PM and dissipate. The highest and better chance of showers and strongest thunderstorms looks to be near and east of the I-65 corridor into southern middle Tennessee. Temperatures will still be rather warm when you wake up on Saturday morning (68-73 degrees) given expected cloud cover. Highs look like they will be hard pressed to climb above the 90 to 94 degree range. This should keep heat index values at bay. They could briefly hit 105 degrees for an hour, but not long enough to entertain another Heat Advisory yet. The actual cold front associated with this storm system doesn`t really move much on Saturday. Additional disturbances move either ESE or SE along the front Saturday into Saturday night. Just how they move will have a big impact on the forecast on Saturday. For now, going with the clustering of most guidance, which moves another disturbance east from southwestern Missouri into the area on Saturday. This appears like it could be more widespread coverage of showers and thunderstorms on Saturday afternoon into Saturday night in northwestern Alabama. Shear will be strong with more widespread shear of 35 to 40 knots shown in most models over the area. However, due to more prevalent cloud cover with showers/convection likely starting a bit sooner by the late morning/early afternoon, instability and lapse rates don`t look as good as on Friday. Despite this, there will still be enough instability (1000-2000 J/KG) for at least marginally severe storms to occur. Main threat again will be damaging winds, frequent lighting, and heavy rainfall. && .LONG TERM... (Sunday through Thursday) Issued at 357 AM CDT Fri Aug 16 2024 Consensus guidance from the 16/00Z suite of global models suggests that a mid-level longwave trough will become established across eastern North America early in the period, with moderately strong NNW flow aloft predicted to remain in place across the TN Valley through the middle of next week. At the surface, an area of low pressure will shift east-northeastward across southern Quebec and into western New England on Sunday/Sunday night, with the trailing cold front expected to cross the CWFA at some point Sunday afternoon. Thus, a low-medium (20-40%) chance for showers and a few thunderstorms has been maintained in the grids through late Sunday morning. Although some wrap-around stratus clouds may impact the northeastern portion of the region on Sunday night/Monday (in the wake of the departing cyclone), probabilities for any light rain showers or sprinkles remain very low (5-10%). Light-moderate N-NE flow will advect a cooler/drier continental airmass southward early next week, with highs falling into the m-u 80s for most of the region beginning Monday, and lows dropping into the u50s-l60s Tuesday morning (and perhaps m-u 50s Wednesday morning). Present indications are that low- level ESE flow will return Wednesday night as a subtle surface trough retrogrades westward across the region, and this will allow for a minor increase in both low-level moisture and chances for showers on Thursday. && .AVIATION... (06Z TAFS) Issued at 1226 AM CDT Fri Aug 16 2024 VFR conditions are expected at both terminals through much of the TAF period. A low chance of -TSRA is possible after 16Z at both terminals, however due to uncertainty at KMSL only included VCTS. Winds will turn to the WSW around 10 knots with some gusts to around 16 knots possible after 16Z at both terminals. At KHSV though, expect enough coverage to warrant a tempo group for -TSRA between 20Z and 24Z. During this period, MVFR VSBYS or CIGS could occur. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Heat Advisory from 11 AM this morning to 5 PM CDT this afternoon for ALZ001>007-016. TN...Heat Advisory from 11 AM this morning to 5 PM CDT this afternoon for TNZ096. && $$ NEAR TERM...KTW SHORT TERM....KTW LONG TERM....70/DD AVIATION...KTW