textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes to the forecast at this time.

KEY MESSAGES

1. A cold front will bring spotty showers, and possibly a thunderstorm, Wednesday afternoon and evening. 2. Briefly cooler Thursday and Thursday night as dry high pressure builds into the area, which also leads to low relative humidity Thursday and Friday afternoons. Temperatures trend well above normal over the weekend.

DISCUSSION

Key message 1: A cold front will bring spotty showers, and possibly a thunderstorm, Wednesday afternoon and evening.

An upper speed max will dig from the upper Midwest this afternoon, across the Ohio Valley late tonight, and into the Mid-Atlantic by Wed afternoon. Low level flow with a southerly component will be established across our area in advance of the cold front attending these height falls. However, moisture is already meager across the CWA, and moisture flux into the area will remain virtually non-existent, as northerly flow and well-below normal PWATs are forecast across the Gulf for much of the next 24-36 hours. Therefore, elevated moisture and weak instability adequate for deep convection is therefore forecast to be limited to a narrow zone within the frontal circulation zone itself. Showers are expected to be quite spotty Wed afternoon/evening, warranting PoPs only in the 20-40% range, mainly along/north of I-40. Can't rule out a stray thunderstorm over the mans, but instability is forecast to be quite weak.

Min temps tonight are forecast to again by a solid 5 degrees below climo owing to below-normal levels of low-level moisture, and development of ideal radiational cooling conditions. Otherwise, temps are forecast to be very close to normal Wed/Wed night.

Key message 2: Briefly cooler Thursday and Thursday night as dry high pressure builds into the area, which also leads to low relative humidity Thursday and Friday afternoons. Temperatures trend well above normal over the weekend.

Under confluent upper flow between the Northeast CONUS cutoff low and a ridge moving into the Mississippi Valley, dry surface high pressure will shift across the southern Appalachians Thursday, centering east of the CWA by late Friday. Max temps look to trend cooler across the area Thursday, as much as 10 degrees cooler across the mountains and northern foothills, but with downslope NW winds offsetting the CAA across most other areas for a less noticeable drop. Gusts of 30-35 mph are possible much of the day in higher mountain elevations, with peak gusts in the gap-wind prone areas of the Piedmont near 25 mph. RH should dip to the 25-30% range in the Piedmont. Winds relax Thursday evening as the high centers over the CWA. Winds may still be enough to maintain mixing but any sheltered areas should experience good radiational cooling. Mins Thu night into Fri morning will be around 10 below normal, with upper 30s possible in the northern mountains. Southwest flow is restored over the region Friday as high shifts to the Carolina coast and as we enter the broad warm sector of a low north of the Great Lakes. Temps moderate and trend a few degrees warmer; despite some moisture return low RH below 30% is still forecast once again, especially in the French Broad and Toe valleys and downwind of the northern Blue Ridge Escarpment.

Upper pattern turns quasi-zonal over the Southeast Saturday and the Bermuda High strengthens its influence over the region; we thus begin a stretch of typical late spring weather, with temperatures trending several above normal Saturday and more so Sunday and Monday. Still expecting max temps near 90 in spots those days. Models and ensemble members generally depict a front stalling in the Ohio Valley Saturday, and related perturbations in the 500mb flow approaching our CWA from the west. Any convection that develops across TN/KY may be directed toward the NC mountains Saturday, and possibly Sunday as well. Model QPF response varies widely and the setup still only supports small PoPs those days, still confined to the mountains. As Bermuda ridge continues to build, by Monday we no longer look to be in the path of convection emanating from the MS/OH valleys, but still could see a few ridgetop, nonsevere pulse showers/storms develop. Small mountain PoPs are again forecast.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR conditions are expected through this forecast cycle. FEW/SCT cumulus in the 050-070 range are possible this afternoon, while high clouds are forecast to continue clearing, and mostly SKC conditions are expected for much of the period. Winds are expected from the SE at 5-7 kts this afternoon before becoming light/variable or calm this evening. Winds are then expected to pick up from the SW at 5-10 kts by early Wed afternoon.

Outlook: A cold front may bring a few showers/possibly a thunderstorm later Wed afternoon into the evening, mainly across western NC. Otherwise, VFR and quiet weather the rest of the week.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.