textproduct: Raleigh

WHAT HAS CHANGED

* No major changes with the afternoon forecast update.

KEY MESSAGES

As of 230 PM Wednesday...

1) A broken line of decaying showers are expected to shift across the southern Mid-Atlantic this evening into the early overnight hours.

2) Trending hot and humid this weekend into early next week with limited chances of showers and storms

DISCUSSION

As of 230 PM Wednesday...

KEY MESSAGE 1... A broken line of decaying showers are expected to shift across the southern Mid-Atlantic this evening into the early overnight hours.

Surface analysis and satellite imagery over the region show an area of low pressure, in the process of occluding, over the Great Lakes with a trailing cold front extending down through the Ohio and Tennessee Valley's. An area of mixed character precipitation and cloud cover is evident across western VA in association of a band of mid-level moisture which is outpacing the cold front. Convection is expected to deepen along the length of the front down into TN where surface dew points in the 50s are contributing to 500-1000 J/kg of SBCAPE underneath cooler temperatures aloft.

A broad area of low pressure off the SC/GA coast and inverted trough axis extending up to the NC coast will prevent richer low-lvl moisture from advecting into our area and result in a widely stable air mass east of the mountains. Hi-res guidance has been consistent with developing mostly shallow convection in KY/TN that will begin a rapid weakening/decaying trend as they traverse the southern Appalachians and encounters this stable environment.

Most model guidance do develop a weak, shallow, and conditionally unstable saturated layer in the mid-levels post effective front (convective outflow and/or eastward advection of a pre-frontal trough), which may support very light rain or sprinkles for a couple hours. However, given large Td depressions below this saturated mid-lvl layer and weak forcing, accumulations will still only range from trace amounts to as much as a 0.1".

KEY MESSAGE 2... Trending hot and humid this weekend into early next week with limited chances of showers and storms

A somewhat perturbed quasi-zonal flow will take over this weekend in the wake of the departing trough off the Mid-Atlantic coast Fri. By late Sun and especially Mon, an anomalous mid- level ridge will set up off the southeast US coast, reaching 588 dm by the early to middle part of next week. Along with a Bermuda high bringing moist south-southwesterly flow and increasing 60s dewpoints next week, low- level thickness will range from 1415-1420 m, typical for late July. These values are supportive of upper 80s to lower 90s, warmest in the eastern Piedmont, Sandhills and Coastal Plain. The warmest temperatures are currently projected Sunday onward, perhaps persisting well into Wednesday of next week.

While shower and storm chances are not expected to be completely zero, they appear limited at best, focused along mesoscale boundaries of any sea-breeze, Piedmont or lee trough. In the perturbed zonal flow this weekend, models do show a weak upper- trough late Sat and Sun. This could favor some isolated storm activity Sun but as of now those chances are around 20 percent. A better chance of any unsettled weather may have to wait until the middle to latter part of next week, when ensembles are supportive of an approaching trough and front from the west.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

As of 230 PM Wednesday...

Prevailing VFR conditions are expected at all TAF sites through the forecast period. An area of decaying showers may result in VFR light- rain or sprinkles at the Triad terminals and a cig around 5-8 kft from 00-04z; sub-VFR is not anticipated at this time. Low-lvl moisture advecting northward across the Coastal Plain may result in a brief window for IFR/LIFR cigs around RWI/FAY until an area of outflow ahead of the cold front progresses across the area. Latest probabilities from HREF/REFS both indicate better potential south and east of RWI/FAY terminals, but observational trends will need to be watched as slower arrival of drier air at the surface is very common in northwest flow frontal passages. Gusty northwest winds and SCT/BKN 3-6 kft cu should be expected Thurs morning into the late afternoon.

Outlook: VFR conditions prevail through at least Sat. Moisture return into the region Sat night into Sun may bring a risk for early morning stratus, marking the beginning of a brief summertime-like pattern.

CLIMATE

Record High Temperatures:

May 17: KGSO: 94/1915 KRDU: 92/1947 KFAY: 97/1941

May 18: KGSO: 95/1911 KRDU: 95/1906 KFAY: 96/1911

Record High Minimum Temperatures:

May 17: KGSO: 69/1991 KRDU: 71/2025

May 18: KGSO: 70/2015 KRDU: 72/1896 KFAY: 71/2018

RAH WATCHES/WARNINGS/ADVISORIES

None.