textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

More detailed information on potential gusty winds and heavy rainfall Thursday and Friday.

KEY MESSAGES

1. Mild and relatively dry through the first half of the workweek, with temperatures comfortably below normal Tuesday. Rain chances remain low overall, but a few showers are possible in the lower Piedmont Tuesday evening through Wednesday. 2. Humidity and rain chances increase Thursday, with periods of rain and gusty winds likely at times between Thursday evening and late Friday night. Locally heavy rainfall and stronger, damaging winds cannot be completely ruled out either of those days. Drier air is expected to return for the weekend.

DISCUSSION

Key message 1: Mild and relatively dry through the first half of the workweek, with temperatures comfortably below normal Tuesday. Rain chances remain low overall, but a few showers are possible in the lower Piedmont Tuesday evening through Wednesday.

A front will remain stalled across south GA and the SC Lowcountry into Tuesday, but is reactivated late Tuesday as a pronounced shortwave rotates into the longwave trough across the Great Lakes and St Lawrence Valley. We should remain on the cool side of the front, and following a cool start Tue morning, temps top out 5-9 below normal, with relatively low humidity represented by dewpoints in the 50s to around 60. Warm upglide over the boundary could result in light precip for parts of the southern CWA as soon as Tuesday evening, especially S and SE of I-85. The chances peak as the shortwave passes by to our north early Wednesday. The actual front begins to shift northward that day, so an unstable subtropical airmass looks to return to the southern zones, resulting in small convective PoPs Wed afternoon, at which time temps trend back to normal if not slightly above.

Key message 2: Humidity and rain chances increase Thursday, with periods of rain and gusty winds likely at times between Thursday evening and late Friday night. Locally heavy rainfall and stronger, damaging winds cannot be completely ruled out either of those days. Drier air is expected to return for the weekend.

Moisture flux increases Wednesday night as the stalled front over the Deep South again reactivates, in response to shortwave and sfc cyclone over the Upper Midwest but also possibly influenced by the inland track of the disturbance near the western Gulf Coast. This frontal reactivation alone warrants a gradual increase in PoPs Thursday. The Gulf disturbance itself continues to be a point of contention among the global models, though the majority of guidance appears to favor a solution similar to the last couple runs of the GFS, showing that system opening into a wave along the Deep South front which advects over our area by Thursday night, at which time we also experience height falls as the Midwest system advances. Recent runs of the ECMWF AIFS favor this type of solution, and the GDPS has trended toward this type of solution as well, though it is still more amplified with its frontal wave. PWATs are elevated in these solutions, but not terribly unusual for early summer; heavy rain threat could still result if we manage some instability Thursday or Friday afternoons, with steering flow roughly parallel to the front. Even a weak wave like the GDPS's depiction could lead to locally enhanced rainfall. We'll be under an unusually strong height gradient for this time of year and gusts of 25-35 mph may occur Thursday and/or Friday even if the Gulf wave dampens out. The ECMWF remains a relative outlier in showing the Gulf low remaining a distinct cyclone which is picked up by the Midwest trough which does not reach our area Friday, and would result in enhanced low-level shear and instability over the area which could result in a severe weather threat, mainly of the gust front variety, but with a tornado or two not out of the question.

Temps look to rise back to near 90 Thursday over the Piedmont with heat indices in the upper 90s in spots, unless rain and clouds spread in more quickly than currently expected. Rain is most likely overall Thu night or early Fri over the mountains and foothills, and Fri afternoon over the lower Piedmont. As the Midwest front pushes out of the area Friday night, dewpoints and PoPs decline for the weekend although temps remain near normal.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions will prevail through the TAF period at all terminals. High clouds will continue to increase in coverage as moisture returns from the southwest. Ceilings will remain well above restrictions through the period. Light and variable winds overnight will increase to 6-12kts out of the southwest by tomorrow afternoon.

Outlook: Mostly quiet conditions expected through midweek. MVFR to IFR stratus may form across GA and expand NE into the Upstate and western NC mountains as soon as Tuesday evening, and could remain through Wednesday morning before scattering out. A similar setup may occur again Wednesday night into Thursday morning. Diurnal convection and associated restrictions will likely return Thursday and Friday.

GSP WATCHES/WARNINGS/ADVISORIES

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