Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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753 FXUS64 KHUN 071458 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 958 AM CDT Tue May 7 2024 ...New NEAR TERM... .NEAR TERM... (Rest of Today) Issued at 958 AM CDT Tue May 7 2024 Low clouds across the area will become more cellular over the next couple hours, allowing more significant heating to take place. A shortwave impulse over AR/LA along with moisture transport axis along the MS valley shifting east will result in shower and thunderstorm development during peak heating this afternoon. The thunderstorms will enter northwest AL after 12-1 pm, and shift east with time this afternoon. The 12Z BMX RAOB indicated a moderate capping inversion around 780mb, but temperatures warming into the lower to middle 80s along with the shortwave should erode that fairly easily, especially with dew points around 70. SBCAPE values of 2000-2500 j/KG and 6km bulk shear values of 30-40kt will be sufficient for supercells capable of large hail and isolated damaging wind. We may need to increase PoPs later, but for now stayed somewhat conservative at this point based on CAMs from 00Z. The forecast for tonight looks good, and will have to watch closely for an east-west orientation of thunderstorms late tonight that could create some excessive rain issues. && .SHORT TERM... (Tonight through Thursday night) Issued at 427 AM CDT Tue May 7 2024 Afternoon storms may continue for a couple of hours after 00Z across the southeastern portion of the forecast area, before gradually diminishing in coverage/intensity with the onset of the diurnal cooling cycle. However, to our northwest, additional convection may develop late this afternoon or early this evening in the vicinity of another surface trough extending from the Central OH Valley southwestward into eastern AR/western TN. This activity may tend to expand in coverage as it spreads southeastward into Middle TN early Wednesday morning, perhaps reaching the northern portion of our forecast area between 9-12Z. During this same timeframe, additional storms may develop along and north of a surface trough extending southeastward into central MS/AL from an area of low pressure tracking eastward across northern OK, and POPs have been increased for the entire region between 6-12Z. Although instability will weaken to some extent overnight, the environment will continue to feature steep lapse rates and strong vertical shear, thus warranting concern for a few severe storms through early Wednesday morning. It still appears as if any convection in our forecast area around 12Z Wednesday will spread northeastward and out of the region by 15Z, as the surface trough across central AL/MS begins to lift northward before eventually eventually transitioning into an effective warm front attached to the synoptic cyclone advancing northeastward into the Mid-MS Valley. Widespread severe thunderstorms are anticipated along and immediately north of this warm front Wednesday afternoon, which should extend from the Ozarks east-southeastward into the southern Appalachians. However, our region will likely remain warm, dry and capped for much of the day. That said, a few models suggest that isolated warm sector thunderstorms (likely supercellular in structure) may develop to our southwest very late Wednesday afternoon and shift northeastward early Wednesday evening, posing a risk for severe wind/hail. Of more concern for our region is development of thunderstorms along the cyclones trailing cold front, which should extend from the low southwestward into northeastern TX late Wednesday afternoon. This activity will likely grow upscale in an intense MCS over the course of the evening, that would spread southeastward through our region early Thursday morning (6-12Z timeframe). Although a similar background kinematic and thermodynamic environment will exist ahead of the MCS, there are indications that a subtle increase in the low-level jet can be expected ahead of this rather large convective complex, and for this reason, a minor increase in the risk for tornadoes is expected overnight (in addition to large hail and damaging winds). Current expectations are that the MCS should be spreading southeastward and away from the region around 12Z Thursday, with trailing stratiform rain expected to end from NW-to-SE beginning early Thursday afternoon. Although redevelopment of a few showers and thunderstorms will be possible along the actual cold front Thursday afternoon, widespread overturning in the wake of the morning MCS should limit concern for severe weather. The cold front is predicted to be shifting southeastward and out of the region early Thursday evening, but with a separate complex of convection expected to spread eastward along the central Gulf Coast Thursday night, we have maintained a low POP for light rain on the northern fringe of this system early Friday morning. && .LONG TERM... (Friday through Monday) Issued at 427 AM CDT Tue May 7 2024 Prevailing NW flow aloft will exist across the region for much of the extended period, allowing a cooler and drier Canadian airmass to be advected deep into the southeastern CONUS. Highs will be in the 70s, with lows in the 50s, and although conditions will remain dry for most of the region, at least a couple of well- defined vorticity lobes will track southeastward across the TN Valley on Friday/Saturday, warranting a very low POP for light showers. && .AVIATION... (12Z TAFS) Issued at 644 AM CDT Tue May 7 2024 Multi-layered clouds have begun to spread across the TN Valley this morning ahead of a weakening QLCS well to the NW of the region. Based on latest satellite data and sfc obs, we will indicate broken MVFR stratus, along with layers of As/Cs thru 16Z, before the clouds disperse. As the local airmass begins to destabilize early this aftn, scattered thunderstorms will develop invof a trailing outflow boundary, impacting MSL/19-23Z and HSV/20-24Z. Large hail, damaging winds and frequent CG lightning may occur with the strongest cells, perhaps warranting AWWs at both terminals. After a brief period of clearing early this evening, low stratus clouds will return around Midnight, with another episode of showers/storms expected between 8-12Z Wednesday. Sfc winds will remain from the SSW for much of the period, with speeds increasing to 12G20 kts by 16Z. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...17 SHORT TERM....70 LONG TERM....70 AVIATION...70