Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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169 FXUS64 KHUN 251140 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 640 AM CDT Sat May 25 2024 ...New AVIATION... .NEAR TERM... (Today) Issued at 359 AM CDT Sat May 25 2024 As an outflow boundary moves in from the west this morning, an unorganized line of storms has formed in the Mississippi Valley. Guidance from CAMs shows the line weakening as it moved into our area and dissipating. However, development behind it is likely due to lingering stratiform rainfall creating a temperature- driven boundary. Threats through this afternoon will include the following: Heavy rainfall/localized flooding (medium confidence) Damaging winds(medium confidence) hail (low confidence) and a tornado or two (very low). Tornadoes remain a very low confidence threat throughout the day. In the morning to early afternoon hours, we remain capped with sufficient shear in place. However, there is a low chance this cap can be overcome and allow an increased low level streamwise vorticity to support a potential tornado threat. As we move into the afternoon hours, wind shear decreases significantly and the possible tornado threat decreases as well. Therefore, it is a conditional threat depending on if the cap is able to erode while there is enough environmental wind shear to support the formation of one or two tornadoes. Heavy rainfall and damaging winds will be our primary concerns through tonight. Any storms that form are forecast to move slowly and have a potential for backbuilding. PWATs in these storms are forecast to be around 1.7-1.75", which is exceeding the 90th percentile sounding climatology per BMX. Model soundings support DCAPE values around 800-1,000 J/kg this morning into the late afternoon/evening hours, supporting a damaging wind threat. As we move into the afternoon hours, low level lapse rates increase to around 8.0 C/km as atmospheric mixing occurs, supporting the potential for strong downdrafts. Due to the high PWATs and possible waterloading, hail has been kept as a low confidence threat. While this morning`s storms are more unorganized linear clusters and we are able to time them, this afternoon`s storms will likely be a different story for timing. Their timing depends on where the secondary boundary sets up, however, we are currently thinking this will be somewhere around 12-14Z (7-9 AM CDT). After this secondary cluster, we will be looking at more of a pop up microburst situation through the evening hours. On the other hand, there is also a low chance that redevelopment does not occur and we are able to get through the day without any strong to severe storms throughout the TN Valley. We will be closely monitoring this mesoscale-driven situation. Storm total rainfall through tonight is forecast to be less than an inch, however, higher amounts are likely in areas that receive rainfall during these sporadic, additional rounds. && .SHORT TERM... (Tonight through Tuesday) Issued at 359 AM CDT Sat May 25 2024 The potential for microbursts will continue into the evening hours before subsiding with the loss of diurnally driven instability around sunset. Overnight, a break in rainfall will take place for most of the TN Valley. However, low chances (around 30% or less) have been kept in due to lingering showers. Sunday into Monday, high sfc pressure off the southern coast of Florida will cause southerly winds to advect moisture from the Gulf to the Tennessee Valley. This will support increased dew points and subsequently an increased heat risk (to be discussed at the end of this short term section) ahead of a cold front. A slight risk (level 2/5) is in place for most of the area (primarily north of the TN River). Timing continues to shift later, however, it is looking like storms will move in from the NW around 1 AM CDT and continue southeastward through noon. These storms will bring risks of damaging winds (medium confidence), heavy rainfall/localized flash flooding (medium confidence), hail (medium confidence), and one or two tornadoes (low confidence). Forecast soundings currently have us capped overnight, however, there is sufficient shear in place as well as low level streamwise vorticity to support a relatively higher tornado risk if that cap is broken. Steep mid level lapse rates (7-8 C/km) and MUCAPE around 1700-1900 J/kg will also support a hail risk. DCAPE around 900-1100 J/kg also exists in these model soundings, accompanied by sufficient shear to warrant a damaging wind risk. We will continue to monitor this system closely. As mentioned previously, high dew points will contribute to an increased, moderate heat risk with high temperatures forecast to reach the low 90s Sunday. During this time, heat will affect individuals most sensitive to heat, especially those without effective cooling and/or adequate hydration. Max heat indices during this period will be around 95-99 degrees F. Overnight Monday into Tuesday, dry weather returns (PoPs 10% or less) as high pressure filters in from the northwest and lows drop into the 60s before rising back into the low to mid 80s during Tuesday afternoon. && .LONG TERM... (Tuesday night through Friday) Issued at 359 AM CDT Sat May 25 2024 Sfc high pressure allows for dry weather to settle over the region through the mid week. Upper level shortwaves will allow a very low chance of showers (10% or less) during this time, however, confidence is low in this occurring. High temperatures during this period are forecast to be in the 80s with overnight lows in the 50s/60s. && .AVIATION... (12Z TAFS) Issued at 640 AM CDT Sat May 25 2024 A line of storms will continue to push eastward out of the area this morning. Additional development is possible later this afternoon and evening but confidence in timing and placement remains too low to warrant more than a PROB30 at this time. Otherwise, VFR conditions prevail. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...HC SHORT TERM....HC LONG TERM....HC AVIATION...30