Area Forecast Discussion
Issued by NWS Huntsville, AL
Issued by NWS Huntsville, AL
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381 FXUS64 KHUN 041754 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1254 PM CDT Sat May 4 2024 ...New AVIATION... .NEAR TERM... (Rest of Today) Issued at 1011 AM CDT Sat May 4 2024 Temperatures are currently in the upper 60s to lower 70s primarily. A good deal of cloud cover is in place over portions of Jackson and DeKalb counties and also from Limestone into Colbert counties. In between, a substantial amount of sunshine is in place. Precipitation is mainly confined to near a weak surface low that currently is in place over north central Georgia. The forcing with this feature should remain far enough to the east to keep it from producing activity in our area. One additional area of scattered showers is also present in central Tennessee that is associated with a weak upper level trough axis extending southwest from a weak low at 700 mb over southern Indiana. Expect this to be the main driver of additional showers and possible thunderstorms this afternoon into the early evening hours. However, models don`t really move this trough axis much to the south this afternoon, so confidence in even scattered coverage has lessened near and south of the Tennessee River overall. The exception to this could be northeastern Alabama into portions of southern middle Tennessee, where a higher chance (30 to 50 percent) may occur this evening, as a diurnal heating boundary sets up from north to south through the area. We should see cloudy conditions return fairly quickly towards into the early afternoon hours over much of the area, except maybe portions of Cullman county and further south. Lowered temperatures overall today given current temperatures and expected cloud cover through the day. Highs should make it into the lower 80s in locations that are currently seeing more sunshine (mainly near and south of the Tennessee River). Elsewhere, expect highs to be cooler, only reaching the mid to upper 70s. && .SHORT TERM... (Tonight through Monday night) Issued at 418 AM CDT Sat May 4 2024 The general synoptic pattern across the TN Valley will remain largely unchanged tonight and Sunday, with light/moist southerly flow expected to persist in the low-levels beneath a zonal flow regime aloft. There are some indications that another weak mid- level vort max (perhaps convectively-induced) may track eastward across our region late this evening, and with some agreement from the 00Z CAMs on an increase in convection, we have included a low- medium chance POP between 3-9Z. This activity will in all likelihood exit the region prior to sunrise on Sunday, with a warm/humid but dry start to the day followed by development of isolated afternoon showers and storms as temps rise into the m-u 80s. Over the course of the day tomorrow, another shortwave trough is predicted to lift northeastward from the Red River Valley of OK/TX within the flow around a strong upper low tracking east- northeastward from the Great Basin into the central Rockies. Due to the motion of the upper low, a well-defined lee cyclone will evolve across eastern MT throughout the day, forcing a warm front to spread northeastward across the TN Valley late Sunday night/early Monday morning. Deep lift generated by the warm front and approaching shortwave trough will produce a fairly widespread coverage of rain and storms that may begin across our western zones as early as 00Z Monday before spreading further northeastward. Although mid-level winds will back to SW and increase to 15-25 knots preceding the arrival of the trough, shear does not appear strong enough at this point to warrant concern for organized storm structures. Most NWP guidance suggests that the effective warm front will lie across the OH Valley by 12Z Monday, with remnants of nocturnal precipitation expected to spread northeastward and out of the region during the late morning. A 500-mb shortwave ridge to the east of the upper low (discussed in the paragraph above) will translate across the region, yielding a lower but non-zero coverage of showers and storms Monday afternoon and night. Low- level SW flow will strengthen in the wake of the warm front, with dewpoints expected to rise into the u60s-l70s. && .LONG TERM... (Tuesday through Friday) Issued at 418 AM CDT Sat May 4 2024 Latest long range guidance from the global models suggests that the presence of a mid-level ridge will continue to limit the coverage of warm sector showers and thunderstorms across the TN Valley on Tuesday, with a breezy, warm and humid day expected as highs rise into the m-u 80s. However, by Tuesday night, we will need to keep a close eye on thunderstorm activity to our northwest that should develop along a Pacific cold front/dryline that will surge eastward ahead of an occluding cyclone across eastern MT/western ND. There are some indications that frontal convection across southern portions of MO/IL may evolve into a broken MCS Tuesday evening that could potentially track southeastward into the local area early Wednesday morning and may feature a risk for strong-severe storms as mid-level westerly flow will likely increase to 35-40 knots prior to its arrival in our region. However, a more reasonable scenario is that the initial MCS will not reach our region due to the development of another weak area of low pressure across the southern High Plains that should eject northeastward into MO by Wednesday evening. In this case, redevelopment of thunderstorms would occur along the path of the surface low (across MO) early Wednesday afternoon that could potentially grow upscale into a larger and more significant MCS that would reach our region late Wednesday night/early Thursday morning. This convective system would be entering an environment of even stronger deep-layer shear (with WSW flow aloft of 45-50 knots) and moderate-high levels of instability driven by surface dewpoints in the lower 70s beneath a plume of steep lapse rates aloft. Thus, a notable risk of severe thunderstorms producing large hail and damaging winds may materialize during this timeframe. A third and final round of storms may occur on Thursday night/Friday morning prior to the eventual passage of a cold front that should bring a drier/cooler airmass into the region by next weekend. && .AVIATION... (18Z TAFS) Issued at 1247 PM CDT Sat May 4 2024 Primarily VFR CIGS are expected through 22Z. However, some MVFR CIGS could occur, so a tempo group for that was included. A low chance (PROB30) for -TSRA exists from 22Z through 03Z at KHSV. Not expecting this possibility further west at KMSL. Fog may be a possibility at both terminals, but left out for this issuance. Some may be added in subsequent issuances. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...KTW SHORT TERM....70 LONG TERM....70 AVIATION...KTW