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WHAT HAS CHANGED

A Heat Advisory will be in effect from 11am to 8pm for Chesterfield and Lancaster Counties today. Uncertainty remains in convective coverage and timing Saturday. Aviation discussion updated for 06z TAF issuance.

KEY MESSAGES

- 1. Heat Advisory in effect from 11am until 8pm for Lancaster and Chesterfield Counties today.

- 2. Heat Index values from 105 to 110 possible Saturday.

- 3. Severe storms possible Saturday afternoon or evening.

DISCUSSION

KEY MESSAGE 1. Heat Advisory in effect from 11am until 8pm for Lancaster and Chesterfield Counties today.

The ridge will slowly begin to retrograde through the day today, but 850mb temperatures near the NAEFS 99th percentile and robust heating should once again yield temperatures in the mid to upper 90s. Dewpoints are expected to mix out again toward the low 70s, but a few locations could stick toward the mid 70s. Overall, this should yield heat indices between 105-108. A few areas near Chesterfield and Lancaster Counties could briefly reach Heat Advisory criteria and due to this, a Heat Advisory will be in effect today from 11am until 8pm this evening for these counties.

KEY MESSAGE 2. Heat Index values from 105 to 110 possible Saturday.

The forecast remains on track with the upper ridge expected to retrograde through the day Saturday as a fairly strong trough digs into the eastern US. This should bring northwesterly downsloping flow that will aid in bringing temperatures into the upper 90s despite the ridge moving westward. Moisture is also expected to slightly increase ahead of a front moving in from the north through the day where surface dewpoints could stick toward the mid 70s for much of the area, though deeper mixing may aid in lowering these slightly. Overall, heat indices between 105-110 could be possible Saturday afternoon and the need for a Heat Advisory will continue to be monitored. Besides the potential for slightly lower dewpoints from mixing, any convection that could develop earlier in the afternoon would throw a wrench in this. The 00z suite of models continues to favor any convection holding off until later in the day at this time however, which is reasonable as the upper wave and front are not progged to near until then. Either way, another hot/humid day is expected and heat safety will need to be exercised with any outdoor activities.

KEY MESSAGE 3. Severe storms possible Saturday afternoon or evening.

The 00z suite of guidance remains fairly insistent that the majority of convection is expected to hold off until the late afternoon to early evening hours Saturday as seen in the mean HREF solution. The cold front and shortwave mentioned in Key Message 2 are expected to spark convection north of the CWA through the day that should persist in the strongly unstable and moisture rich environment. The degree in which this activity holds together as it moves toward the FA remains uncertain depending on timing, but MLCAPE values on the order of 2500 J/kg should be in place with steep low level lapse rates and around 20-25 kts of effective shear. These parameters suggest a damaging wind threat could be seen as convection pushes in, especially toward the northern FA and the Pee Dee with greater uncertainty further south. A few instances of sub-severe hail cannot be ruled out either given large CAPE profiles in the hail growth zone and some mid-level dry air. Overall, timing trends will need to be monitored, but an isolated severe threat is possible given the environment.

The cold front is forecast to remain near the region on Sunday so we can expect at least a chance of showers and thunderstorms with moisture still in place and some shortwave activity rounding the base of the trough. The trough is expected to persist into early next week, bringing temperatures closer to normal and at least isolated diurnal rain chances before global models and ensemble guidance indicate the ridge to our west should slowly work back in. This should bring back drier conditions and warming temperatures.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

VFR conditions for much of the period with near sunrise restrictions possible.

Guidance continues to trend towards the potential for restrictions at all terminals near daybreak, mainly from low ceilings, although some visibility restrictions will be possible as well. There remains a question whether the clouds that develop, which will likely be below 1000 feet, will be high enough in coverage to lead to ceilings or remain scattered. Confidence is highest in at least a brief period of IFR ceilings at all terminals. VFR conditions should return mid to late morning through the rest of the TAF period. Winds will remain out of the southeast tomorrow.

EXTENDED AVIATION OUTLOOK...Chances for restrictions and thunderstorms increase this weekend as a cold front approaches.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ016-115-116. GA...None.