Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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027 FXUS64 KHUN 240451 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1151 PM CDT Thu May 23 2024 ...New AVIATION... .NEAR TERM... (Rest of tonight) Issued at 953 PM CDT Thu May 23 2024 Regional doppler radar data this evening indicates a broad region of showers and thunderstorms moving slowly northeastward into the southern/central Appalachians, with this activity related to the MCV that brought convection to our region earlier this afternoon. Although there is currently a dearth of precipitation across northern AL/southern TN, a mesoscale boundary trailing southwestward from this feature into our CWFA could result in occasional development of light-moderate showers (generally north of the TN River) from the present time through 8-9Z, and we will leave a low (15%) POP in the grids to account for this possibility. Beyond 9Z, the general expectation is for gradual redevelopment of thunderstorms (particularly across the western half of the forecast area), as another convectively-induced vort max lifts east-northeastward into western portions of the TN Valley, enhancing deep-layer vertical motions to the north of a marine warm front extending from southern AR/northern LA eastward into central AL. Guidance from the 12Z HREF suggests that elevated CAPE will begin to increase (perhaps to 1000-1250 J/kg) in the 9-12Z timeframe, which could support a few stronger cells in conjunction with WSW flow aloft of 25-35 knots. Although we have increased POPs during this period (especially west of I-65), the majority of this activity will likely occur after 12Z. Aside from changes to POP/weather grids mentioned above, other elements of the forecast are on track, with abundant mid/high-level clouds and light SSE winds promoting lows in the m-u 60s. && .SHORT TERM... (Friday through Sunday) Issued at 336 PM CDT Thu May 23 2024 An unsettled weather pattern will continue as we go into the Memorial Day weekend. A southerly lower level flow and passing upper level systems from the west will keep chances of more showers and thunderstorms continuing. With minimal large scale forcing, coverage of this activity is expected to occur on a diurnal basis (with better chances in the afternoon and evening). Going more with blended output, an upper system approaching the area should bring scattered to numerous showers/thunderstorms forming late tonight, and continuing into Fri afternoon. With more clouds than sun, high temperatures to close out the workweek should warm into the lower 80s. More of a diurnal trend is expected over the weekend, with mainly afternoon convection. Highs on Saturday should warm into the mid/upper 80s, and in the upper 80s/near 90 on Sunday. Because of the warmth and resultant instability (CAPES rising into the 1000 to +2000 J/kg and mainly weak shear), some of the storms could become strong to severe in intensity, with strong to damaging wind gusts the main threat. && .LONG TERM... (Sunday night through Wednesday) Issued at 441 AM CDT Thu May 23 2024 A stronger synoptic storm system moving from the eastern Plains to the Great Lakes will bring another round of more organized convection Sunday and into Sunday night. Model trends seemed to take a more northern track with the parent low. But it will be close enough, to bring a risk of severe storms to the Tennessee Valley. Most of the area is within a Slight Risk for severe weather on the Storm Prediction Center Day-4 forecast. A strong cold front is forecast to move across the area Sunday night. Very steep lapse rates, strong shear, high DCAPE values, and strong instability (3000 to 4000 J/KG) will provide the impetus for a MCS that develops along this front as it pushes into and through the area overnight into Monday morning. Saturated soils by then could produce a more enhanced threat for flash flooding or river flooding from this rainfall. Models differ on how quickly this system pushes through the area though, so activity cloud linger into the afternoon on Monday. However, the atmosphere will likely be worked over from earlier convection earlier in the day, so severe weather should not be much of an issue if that occurs. Finally northwest flow aloft and dry weather builds back into the area Tuesday into Wednesday. Highs will drop back into the upper 70s to lower 80s again thankfully with lows dropping back into the mid 50s to lower 60s. && .AVIATION... (06Z TAFS) Issued at 1151 PM CDT Thu May 23 2024 A few SHRA or perhaps a TSRA will be possible thru 9Z in the vicinity of a subtle outflow boundary positioned north of the TN River, but confidence in coverage is too low to include precipitation in the TAFs initially. However, an approaching upper air disturbance will likely begin to initiate additional convection to our west around or shortly after 9Z, which should spread eastward, warranting TEMPO groups for MVFR cig/vsby reductions from 11-15Z/MSL and 12-16Z/HSV. AWWs for lightning and brief strong wind gusts may be issued during this period, as well. In the wake of morning precipitation, additional SHRA/TSRA will be possible along a trailing outflow boundary late tomorrow aftn, with a broader cluster of storms potentially spreading southeastward thru at least the western portion of northern AL tomorrow evening. Due to this, we have included PROB30 groups btwn 22-04Z, although timing will likely need to be adjusted as we move forward in time. Prevailing conditions outside of convection will remain VFR, with sfc winds from SSE-SSW at speeds of 5-10 kts. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...70/DD SHORT TERM...RSB LONG TERM...KTW AVIATION...70/DD