Area Forecast Discussion
Issued by NWS Columbia, SC
Issued by NWS Columbia, SC
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333 FXUS62 KCAE 171026 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 626 AM EDT Sat Aug 17 2024 .SYNOPSIS... A cold front approaches the Southeast US this weekend along with increasing moisture and rain/thunderstorm chances. A few strong storms are possible each day this weekend, with higher chances on Sunday. Drier air and cooler temperatures are then on tap for early to mid next week. The next chance of rain arrives for late week. && .NEAR TERM /THROUGH TONIGHT/... Key Message(s): - Scattered thunderstorms late this afternoon and evening focused in the west and north Midlands/CSRA. A few storms may be severe. Deep upper trough over the Great Lakes region will be moving slowly east today and amplifying across the Tennessee river valley. The upper ridge that has been in place across the area will retrograde and resulting heights aloft will be falling although short wave energy moving thru the trough appear to be weak and mainly north of the area. Upper divergence does increase across the area, especially north and west late in the day. At the surface, expect Piedmont trough to set up and strongest low-level convergence will be in the Upstate. Moisture flux increases this afternoon with southwest low-level flow with an axis of 2.00 inch or slightly higher precipitable water values across the area around 00z Sunday. Weak warm advection/some downslope flow so forecast high temps in the low 90s, a little higher than guidance. Model soundings show moderate instability with surface based CAPE 1000-2000 J/kg. CAPE appears "long and thin". HRRR model shows moderately strong deep layer shear approaching 30 kts. The GFS shows stronger shear. So, some potential for organized strong convection late in the afternoon and evening especially across the Piedmont into the north Midlands. Soundings do not show inverted V, but some precip loading/wet microburst potential. CAMS show scattered convection moving southeast out of the Upstate into the west/north Midlands during the late afternoon/evening period then weakening late in the evening. Other storms may develop in the CSRA from north Ga. So a few strong to severe thunderstorms possible given possible higher CAPE than models indicating as temperatures rise into the low 90s and clouds delayed. A few lingering showers overnight, low temps in the low 70s. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... Key Message(s): - Scattered afternoon thunderstorms expected, a few of which could produce damaging wind gusts. Upper trough over the Great Lakes region continues to trek eastward through the day, amplifying as it does. An embedded shortwave is forecast to move through the area during the afternoon timeframe. Meanwhile at the surface, a cold front is expected to pass through the forecast area during the day. Ahead of the front, southerly flow reinforces low-level moisture flux into the area, particularly the eastern half of the state. Behind the front, drier air begins pushing into the western portions of the state, causing a fairly tight moisture gradient across our area. Latest guidance suggests the front and associated moisture gradient sets up along I-20. Some of this location is dependent exactly where the front and moisture gradient set up. Expect thunderstorms to develop along area and push southeastward as the front progresses in that direction. Hi-res guidance indicates that areas in the eastern Midlands are forecast to see mixed layer CAPE values over 2000 J/kg along with 0-6 km bulk shear values in the 25-35 kt range. In addition, low-level lapse rates are forecast to be high, around 9.0 degrees C/km. These parameters suggest there is a risk for severe weather with some of the activity Sunday afternoon into the evening, with damaging winds being the primary threat. && .LONG TERM /MONDAY THROUGH FRIDAY/... Key Message(s): - Dry through midweek before rain chances return for the end of the week. Upper level trough remains over the Atlantic seaboard through midweek while the surface front is forecast to remain offshore. This is expected to allow cooler and drier air to settle into the area for the first half of the week. Ensembles then indicate a surface high building over the Mid-Atlantic to Northeast, which could aid in pushing the surface front back toward the area, leading to slight chances for rain to end the week. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... VFR Conditions expected through at least 18z. Scattered thunderstorms in the late afternoon and evening may result in brief restrictions, but confidence low at this time. Mid level clouds spreading into the region. There is some weak convection in north Georgia moving east. Latest guidance suggest showers will dissipate west of the terminals this morning. High pressure has shifted to the coast. The upper ridge over the area will be weakening today as an upper trough over the Great Lakes region amplifies. At the surface a Piedmont trough will set up and provide some weak low level convergence. The air mass is expected to become moderately unstable in the afternoon and moisture appears high. The high resolution models suggest scattered convection will develop in the afternoon, after 18z. A few storms may impact terminals primarily during the 18z Saturday to 04z Sunday, but confidence low at this time. So, scattered to broken VFR cumulus expected especially during this period. Winds will be southwest 5 to 10 knots with a few higher gusts in the afternoon. EXTENDED AVIATION OUTLOOK...Scattered showers and thunderstorms are expected Sunday afternoon and evening, possibly strong to severe and restrictions possible. && .CAE WATCHES/WARNINGS/ADVISORIES... SC...None. GA...None. && $$