Area Forecast Discussion

WHAT HAS CHANGED

Minimal change to Key Messages. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Above average temperatures and increased chances for showers and storms continue into early next week.

- 2. Cooler and drier air returns by the middle of next week but forecast uncertainty remains.

DISCUSSION

KEY MESSAGE 1: Above average temperatures and increased chances for showers and storms continue into early next week.

A diffuse frontal boundary has sank near the Pee Dee early this afternoon, characterized by a very subtle wind shift and slightly enhanced moisture convergence. As temperatures continue to warm toward the low to mid 90s and surface dewpoints remain in the upper 60s to lower 70s, around 1500-2500 J/kg of MLCAPE should develop. Overall forcing remains weak and due to this, both the 12z HREF and REFS keep diurnally driven convection fairly isolated to widely scattered (mainly after 19-21z). Overall, the severe risk with any storm this afternoon and evening is low, but a few efficient downpours will be possible and perhaps some gusty winds in the strongest storms.

This chance for isolated to scattered diurnal convection continues Sunday and into early next week, where coverage has trended slightly higher on Tuesday. Slightly above normal temperatures and PWAT's remaining above 1.75" will likely drive seasonable instability, but with weak forcing, activity Sunday and Monday will likely be more diurnally driven. Come Tuesday, the upper air pattern begins to shift with the mid level low currently over the far eastern Gulf, drifting northward along the eastern seaboard. This feature along with developing troughing moving in from the Midwest could bring increased synoptic forcing, aiding in increasing coverage of showers/storms. Overall, the severe weather risk through the early week is on the lower end, but cannot rule out periods of heavy rainfall, especially into Tuesday.

KEY MESSAGE 2: Cooler and drier air returns by the middle of next week but forecast uncertainty remains.

There is better agreement that troughing from the Midwest will generally shift eastward through the week, with the aforementioned mid level low continuing to glide northward, eventually generating a surface response off the East Coast. The main surface feature of note will be the robust area of high pressure that builds into the Quebec, ridging down into the Mid- Atlantic during the mid to late week. This high is expected to be near the NAEFS climatological max. Generous uncertainty remains in the degree of surface ridging that reaches the CWA, which is displayed well across the spread of ensemble membership in LREF clusters. The degree of moisture advection atop the potential surface wedge will likely be modulated by the timing and strength of the troughing mentioned above. The latest ECMWF run keeps the trough a bit weaker and slower, keeping a bit more southwesterly flow aloft with increased moisture overriding the surface wedge, while the GFS and NAM are favoring a stronger trough, more northwesterly to northerly flow aloft, and thus drier air atop the wedge. The EOF patterns from the LREF cluster analysis really highlight the importance the strength and timing of troughing will have on potential CAD conditions. Due to the uncertainty that remains, there is fairly low confidence Wednesday into the late week in terms of temperatures and PoP's. The potential for below normal temperatures exists, but nearly 10 degree IQR ranges remain during this period. Widespread precipitation seems fairly low, but if moist isentropic lift can ride over the potential wedge, cannot rule out typical CAD conditions with light stratiform rain or drizzle, acting to reinforce the wedge.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Mid and upper level cloud cover earlier this morning has thinned out, giving way to scattered and agitated Cu with heating early this afternoon. Isolated to scattered showers and thunderstorms developing again this afternoon necessitates maintaining PROB30 groups from 20-02z across CAE, CUB, and OGB, and 21-03z across AGS, DNL, and AIK, with greater coverage possible across the latter 3 terminals. Recent GFS-MOS and LAMP guidance has shown consistency in recent runs in developing low cigs and possible vis restrictions by 08-09z Sunday, particularly across the western half of the FA per 12z HREF guidance. Have included TEMPO groups for 09-13z for the potential for IFR conditions with SCT clouds below 1000ft at all terminals, as well as potential for IFR vis down 1-2 SM at more fog-prone AIK, AGS, and OGB terminals. Will continue to monitor later near term guidance and adjust these values as necessary, especially following rainfall with convection this afternoon and evening. Any low cigs and/or vis should lift/improve by late morning tomorrow with heating.

EXTENDED AVIATION OUTLOOK...Chances for showers and/or thunderstorms will continue through early next week. Morning cig/vsby restrictions are possible as well.

CAE WATCHES / WARNINGS / ADVISORIES

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