Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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644 FXUS64 KHUN 131040 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 540 AM CDT Thu Jun 13 2024 ...New AVIATION... .NEAR TERM... (Today) Issued at 421 AM CDT Thu Jun 13 2024 A mid-level trough (initially centered across the Lower MS Valley) will spread southeastward into the northern Gulf of Mexico today, with northerly flow aloft across our region expected to strengthen due to increasing influence from a strong subtropical high over northern Mexico and the southern Rockies. At the surface, a weak area of low pressure along the northeast Gulf Coast (related to the mid-level trough) will retrograde slowly westward over the course of the day, with lift in the vicinity of a subtle trough extending northeastward from the low currently supporting the development of mid-level stratus clouds across northwestern GA/northeastern AL. Strong diurnal warming of the boundary layer and dewpoints recovering into the l-m 60s may be sufficient to initiate a few showers and perhaps a thunderstorm or two in the vicinity of the surface trough in the 16-22Z timeframe, and for this reason we have included a slight chance POP across portions of northeast AL. The remainder of the CWFA should experience mostly sunny and dry conditions, with afternoon temps in the u80s-l90s. && .SHORT TERM... (Tonight through Saturday night) Issued at 421 AM CDT Thu Jun 13 2024 NWP model consensus indicates that the strong 500-mb subtropical ridge (discussed above) will build progressively eastward, becoming centered directly across the TN Valley by Saturday night, and providing an increasingly favorable environment for hot/dry conditions. At the surface, a cold front (attached to an area of low pressure ejecting northeastward across Quebec) will shift southeastward into the OH Valley by 12Z Friday accompanied by a weakening band of convection that may result in an increase in cirrus debris clouds prior to sunrise. Although diurnal redevelopment of showers and thunderstorms will be possible along the length of the front on Friday afternoon/evening, present indications are that this activity will remain north of the I-40 corridor in Middle TN. A frontal wind shift to NE will arrive in our CWFA Friday evening as the center of a modified Canadian airmass spreads eastward through the Great Lakes, and should lie to our immediate southwest on Saturday/Saturday night. However, cooler/drier air will remain displaced well to our north/east, and with a narrow axis of dewpoints in the u60s-l70s expected to pool in the vicinity of the boundary, heat index readings will climb above 100F across the southwestern half of the region Saturday afternoon as temps warm into the m-u 90s. As a result of the increase in low-level moisture, lows will also warm into the lower 70s for most locations Friday and Saturday nights. && .LONG TERM... (Sunday through Wednesday) Issued at 421 AM CDT Thu Jun 13 2024 The center of the subtropical ridge is predicted to begin shifting slowly northeastward and away from the TN Valley on Sunday, becoming centered across western portions of VA/NC by Monday. This (along with a surface ridge migrating eastward off the coast of New England) will result in a gradual increase in deep-layer SSE flow and atmospheric moisture content, which should support a minor increase in the coverage of diurnal showers and thunderstorms early next week. Although some deterministic and ensemble guidance indicates that this could occur as early as Sunday afternoon/evening, it currently appears as if our best opportunity for rainfall will be Monday afternoon/evening. Afternoon temperatures will peak in the upper 90s for many locations on Sunday (with a 100F reading or two possible), but it still appears as if heat index readings will be slightly below advisory criteria. Highs are currently expected to be several degrees cooler on Monday due to clouds and precip, but if this does not materialize, temps will need to be increased. During the period from Tuesday-Wednesday, global models suggest that our deep-layer SSE flow regime will be disrupted by a developing area of low pressure over the southwestern Gulf/Bay of Campeche, and with more of an influence from the Bermuda ridge to our east, we expect hot/dry conditions to return. Fortunately, it appears as if the westward advection of a drier airmass into the region will limit heat index readings in this regime. Strong warming of lower-levels from Wednesday onward will likely support development of afternoon thunderstorms in regions of enhanced orographic ascent across the central/southern Appalachians on a daily basis, and with deep easterly flow predicted to the south of the subtropical high, some of this activity may eventually spill into northeast AL. However, we have maintained a dry forecast at this point. && .AVIATION... (12Z TAFS) Issued at 540 AM CDT Thu Jun 13 2024 incredibly light variable winds and mostly clear skies will promote VFR conditions at both terminals for the duration of the TAF period. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...70 SHORT TERM....70 LONG TERM....70 AVIATION...RAD