Area Forecast Discussion
Issued by NWS Memphis, TN
Issued by NWS Memphis, TN
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868 FXUS64 KMEG 222021 AFDMEG Area Forecast Discussion National Weather Service Memphis TN 321 PM CDT Sun Sep 22 2024 ...New SYNOPSIS, DISCUSSION... .SYNOPSIS... Issued at 320 PM CDT Sun Sep 22 2024 An approaching cold front will bring scattered showers and thunderstorms to the Midsouth on Monday. A few of these storms may reach severe limits north of Interstate 40 during the late afternoon and evening. Damaging winds will be the primary severe weather threat. This front will eventually stall over north Mississippi on Tuesday, as a deep upper level low pressure system approaches. This upper low will remain near the Midsouth through much of the week, as a tropical system likely develops in the Gulf of Mexico. && .DISCUSSION... (This evening through next Saturday) Issued at 320 PM CDT Sun Sep 22 2024 Another day of summer temperatures on this first day of autumn. Isolated showers were noted on radar this afternoon, aided by lower 70s dewpoints, cooler midlevel temps a weak midlevel shortwave evident on GOES water vapor imagery. Deep layer shear will increase on Monday, as an approaching positively-tilted midlevel trough dampens the upper ridge that has brought mid-summer heat over the past few days. A belt of stronger midlevel southwesterly flow will overspread the Midsouth Monday afternoon, with 0-6km bulk shear increasing to around 40 knots. HREF ensemble mean surface-based CAPE is around 1100 J/kg late Monday afternoon, with 25th and 75th quartiles of 800 to 1500 J/kg respectively. The take-away: instability should be adequate for severe storms, even if cloud cover results in realized CAPE near the low end of the ensemble spread. Regarding storm timing, CINH should weaken sufficiently for storms by midafternoon Monday, but the severe threat will likely be focused just ahead of a midlevel trough passage Monday evening. A cold frontal passage will follow the passage of the midlevel trough late Monday night. This front will likely stall over north MS on Tuesday. A belt of strong midlevel flow will overspread much of the Midsouth, as a closed upper low drops into western MO. The stalled front will provide focus for storms on Tuesday, particularly south of I-40. Modest instability should limit Tuesday`s severe storm threat. The closed low will deepen over the Ozarks through late Wednesday night. By this time, 12Z global consensus develops what could become Hurricane Helene over the central/eastern Gulf of Mexico, lifting it rapidly north ahead of the mid-latitude closed low over AR. GFS, ECMWF and Canadian model deterministic solutions all depict the midlevel upper low and remnant tropical system congealing into one large low pressure system over the mid- MS River valley by Saturday. With so many moving parts, it`s too early to say with confidence how this pattern will evolve through the course of the week. While the mid-latitude closed upper low appears a good bet, important details of tropical development over the gulf remains uncertain. For that, be sure to follow the latest forecasts and discussions from the National Hurricane Center. PWB && .AVIATION... (18Z TAFS) Issued at 1235 CDT Sun Sep 22 2024 VFR conditions will prevail across much of the airspace. JBR is expected to lower to MVFR around sunrise tomorrow with the movement of a cold front. VCTS with a PROB30 for -TSRA looks to impact JBR late this evening through around 08Z. Guidance is in decent disagreement on timing and coverage of convection with the cold frontal movement tomorrow. Confidence was too low to include in TAF at other terminals, though potential exists for convection at MKL/MEM/JBR tomorrow afternoon, though best coverage looks to occur after the TAF period. South/southwest winds sub 8 kts will remain across all sites. AEH && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...None. TN...None. && $$ PUBLIC FORECAST...PWB AVIATION...AEH