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FXUS62 KGSP 210549 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 149 AM EDT Tue May 21 2024

SYNOPSIS
Warm high pressure will persist across the region through the middle of the week. A cold front approaches from the northwest on Thursday, bringing a chance of showers and storms mainly to the mountains. The front will stall over the area Friday, keeping rain chances through weekend and into early next week.

NEAR TERM /THROUGH TODAY/
As of 145 AM EDT Tuesday: Given cloud cover across the mountains and foothills is being more stubborn than the models suggest, sky cover was bumped up thru daybreak and fog largely removed. Still some patchy fog may form in any valleys that can manage to stay clear for a while before sunrise. The I-77 corridor is mostly clear, but drier BL should limit any fog potential there.

Otherwise, persistence looks like a really good forecast over the next 24 hours as the salient features don't change much. We continue to enjoy a positively-tilted mid/upper ridge that supports weak high pressure to our northeast. As a result, expect another round of mountain valley low stratus/fog late tonight, with some locally dense. Once that mixes out in the middle-part of the morning, the day should be quiet again east of the mtns, but ridgetop showers can be expected in the mid/late afternoon. High temps will nudge upward a bit, maybe a category above normal Tuesday afternoon.

SHORT TERM /TONIGHT THROUGH THURSDAY/
As of 130 AM Tue: Upper ridge will persist over the Southeast coast Wednesday. Cold front will push slowly past the Ohio River, having limited dynamic support with parent low occluding north of Lake Superior. The front looks to remain west of the Appalachians thru Wed night. Max temps will trend warmer, both at the sfc and at around 700 mb. Any uptick in low level instability looks to be stifled despite good lapse rates developing above 700 mb; we also lack much of a trigger, so deep convection looks questionable even over the mountains.

Vort lobe encircling the Canadian low will rotate past the Great Lakes Wednesday night, and RR quad of associated jet streak will promote development of a weak, possibly convectively enhanced shortwave. This may result in some convection in East TN and remnants thereof could reach the mountains in the very early morning. The shortwave itself is likely to push across the Appalachians near peak heating Thursday, flattening the ridge a bit.
700mb temps cool slightly and although this may not totally erode the inversion it makes convection more likely than Wednesday. Storm motion will be a bit faster and steering flow westerly, so small PoPs are warranted in the upper Piedmont in addition to the high chance to likely values over the mountains. The better flow will also translate to a bit better deep layer shear, perhaps above 30 kt. However the column may be too moist for the level of severe threat than we would typically see with convection this time of year, or for strong cold pool generation, thus not especially concerned for severe. Locally heavy rain may be of greater concern.
Although increased cloud cover may knock temps back a little in the higher terrain, the Piedmont will trend a little warmer Thursday.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
As of 215 PM EDT Monday: An active pattern returns for this period as a series of short waves move east across the area. These will push a series of low pressure/frontal systems across the area as well. Expect good to numerous, mainly diurnal, convective coverage each day, with the highest PoP favoring the mountains. Still to early to be certain on the severe storm chances given the potential for limited instability, even though forcing and shear will be decent. Heavy rain potential may eventually creep up as well, especially if the better coverage hits the same areas day after day.
Highs will drop a few degrees on Friday then remain nearly steady through the period. Lows rise a few degrees then remain nearly steady.

AVIATION /06Z TUESDAY THROUGH SATURDAY/
At KCLT and elsewhere: High-based stratocu continues to expand across the NC mountains and south into the Foothills and much of the Upstate. Guidance seems to be too quick to dissipate the clouds, and so will keep more clouds in the TAFs thru daybreak. This results in much less fog potential than previously thought. Have opted to remove fog mention with the 06z TAFs, as a result. AT KCLT, despite clear skies, fog is not expected there, as air mass looks too dry. Otherwise, today looks similar to yesterday. Another round of VFR cumulus should develop by midday and persist thru the afternoon and evening. Isolated to widely scattered convection is expected across the mountains again today. With decent confidence of SHRA never KAVL, will add a PROB30 for mid to late aftn. The rest of the TAF sites are expected to be dry. Wind will be light thru the period, favoring a S/SE direction, and not expected to be above 5 kt this aftn.

Outlook: High pressure remains over the terminals through Wednesday but isolated mountaintop convection is expected in the aftn.
More numerous showers and thunderstorms, along with restrictions, may return with a cold front late Thursday into Friday. A more active pattern may persist into the weekend.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.

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