Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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899 FXUS64 KHUN 261738 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1238 PM CDT Sun May 26 2024 ...New AVIATION... .NEAR TERM... (Rest of Today and Tonight) Issued at 948 AM CDT Sun May 26 2024 Lots to talk about in the update this morning. While a majority of our attention today will be on severe weather potential tonight, another dangerous threat has consistently been presented in the models for this afternoon that we must discuss: excessive heat. HIRES models show greater than 90% chances of NW AL meeting or exceeding 90 degrees today. While chances are slightly lower for the remainder of the area (40-70%) those that don`t meet 90 will still have highs in the upper 80s with real feel temperatures in the low to mid 90s area wide. Today will likely be one of the hottest days of the year so far thus, it is important to resume practicing proper heat safety for anyone participating in outdoor activities. This includes staying hydrated, wearing sun protection, and taking frequent breaks in shaded or air conditioned area. As for our main severe threat, models have remained consistent in a line of storms moving through the area from around midnight to 7 AM. All hazards remain the same with potential for damaging winds, hail, and tornadoes. A full discussion of overnight environmental parameters and threats can be found in the short term forecast discussion. The remainder of this discussion will go over what remains uncertain at this time. Ongoing convection well to both our north and west will play a pivotal role in any pre frontal convection today. If any outflow boundaries from ongoing convection move into our area this afternoon, the environment will be very favorable for supercells with all hazards possible. There is very low confidence in this currently. The other parameters we will be closely monitoring through the duration of the afternoon will be the evolution of any CAP and presence of any directional shear. These two parameters will pay a pivotal role in determining our tornado threat overnight. Current models indicate the presence of a CAP at the start of the line yet are inconsistent in maintaining it or eventually degrading it. Likewise, models are still inconsistent in favoring speed vs direction shear. If directional shear begins to be favored and the CAP is able to erode, this would increase our threat for embedded tornadoes. If the CAP remains and speed shear prevails, straight line winds will be our primary concern. Regardless, with this being an overnight event, we want to make sure everyone has multiple ways to receive warnings including ones that will wake you up while you sleep. && .SHORT TERM... (Tonight through Wednesday) Issued at 351 AM CDT Sun May 26 2024 Tonight, a line of strong to severe storms is forecast to impact the Tennessee Valley from the northwest ahead of a cold front. Models have begun becoming slightly more consistent with timing for this, bringing the line into NW AL and portions of southern middle TN around 6Z and pushing it southeastward until it exits the area by around 12Z. With this primary line, the following threats will be possible: large hail (medium confidence), damaging winds (medium confidence), heavy rainfall/flooding (low- medium confidence), and tornadoes (low confidence). MUCAPE of 2000+ J/kg in addition to steep mid level lapse rates (7.5-8.0 C/km) will allow large hail to be a medium threat, however, with high PWATs (1.5-1.9" per the HREF, which is above the 90th percentile for BMX climatology), there is a potential for melting of large hail. Damaging winds will be supported by DCAPE values reaching 900+ J/kg as well as increased shear (30-50 kts). While heavy rainfall is likely, flooding may be mitigated by fast storm motion. Our tornado threat remains a low confidence one due to a cap that is consistently in model soundings. However, if the cap erodes, tornadoes will be more of a threat due to backed sfc winds and a low level jet (40-50 kts). However, the HRRR is indicating a potential for an outflow boundary to move in from the northwest around 1Z. If this occurs, this would force our severe timing window to be earlier than previously discussed. This would also change our initial storm mode to be supercell clustering that would eventually upscale into a linear form. This would increase rain totals and cause concern for flooding due to runoff. Regardless of the arrival time, we have medium confidence storms will exit the area by 12Z with low-medium chances (20-40%) of lingering showers behind the cold front. Dry weather should return to the TN Valley Monday night with clear skies as sfc high pressure filters in from the Mississippi Valley. Highs on Monday and Tuesday are forecast to reach the 80s with overnight lows in the upper 50s/60s. Wednesday will be slightly cooler, but still warm, with highs in the upper 70s to low 80s. && .LONG TERM... (Wednesday night through Saturday) Issued at 351 AM CDT Sun May 26 2024 As upper level ridging moves in from the Mississippi Valley through end of the work week, dry weather and mostly clear skies will continue to dominate the long term period. Friday afternoon through Saturday, low chances (30% or less) of showers/storms are possible as an upper level shortwave forms in the lower Mississippi Valley. Otherwise, high temperatures during this time are forecast to be in the upper 70s to 80s with overnight lows in the 50s/60s. && .AVIATION... (18Z TAFS) Issued at 1238 PM CDT Sun May 26 2024 Mostly VFR conditions will prevail for the first half of the TAF period. After 0Z is when we will see lower ceilings move in ahead of a line of strong convection. The line will move through from NW to SE from around 4-12Z. The leading edge of the line will be associated with the strongest storms prevailing MVFR conditions expected. Brief periods of IFR and even LIFR are possible as the line moves through however confidence is low. After the line moves through rain and storms will likely linger behind it for several hours. While this will be significantly less intense than the initial line, it will likely still lower ceilings and visibilities. Conditions should begin to clear after 12Z with a gradual return to VFR expected by 18Z. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...RAD SHORT TERM....HC LONG TERM....HC AVIATION...RAD