textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes.

KEY MESSAGES

As of 205 PM Friday...

1) Marginal (level 1 of 5) risk for severe thunderstorms both Friday and Saturday afternoons.

2) Isolated to scattered storm chances continue into Monday with a backdoor cold front.

3) After a reprieve from the heat Sun through Tue, hot temperatures expected to return mid-late next week.

DISCUSSION

As of 228 AM Friday...

Key Message 1: Marginal (level 1 of 5) risk for severe thunderstorms both Friday and Saturday afternoons.

The persistent hot and humid airmass continues today across central NC. Despite the potential for scattered afternoon convection, strong insolation through early afternoon should support highs in the mid to upper 90s, with a few locations near 100 degrees across the southern Coastal Plain and Sandhills. With sfc dewpoints expected to remain in the lower to middle 70s, peak heat index values of 105 or more are expected this afternoon, particularly south and east of Raleigh where convective development will hold off until later in the day (compared to locations farther north and west where showers/thunderstorms may occur earlier). Confidence remains high that Heat Advisory criteria will be met across Scotland, Hoke, Cumberland, and Sampson counties, thus a heat advisory has been issued for those four central NC counties from 11 AM until 8 PM today. While thunderstorms may provide localized relief later this afternoon and evening, they will arrive too late to significantly limit daytime heat stress, particularly in the advisory counties. Residents with prolonged outdoor exposure should take frequent breaks, remain hydrated, and seek air-conditioned environments whenever possible.

KEY MESSAGE 2... Isolated to scattered storm chances continue into Monday with a backdoor cold front.

An area of low pressure and mid-level disturbance currently across the Mid MS valley will slowly reach the TN valley by Sunday. As that happens, a backdoor cold front will gradually approach from the northeast. Depending on the ensemble or deterministic model one looks at, the front may move through Sunday or early Monday. Regardless, it looks as though the front settles south of the region Monday as cool 1024-mb high pressure builds down from the northeast.

Ahead of the front, we will continue to be in that isolated to scattered afternoon and evening storm regime. That storm risk appears more focused over the western and southern Piedmont and Sandhills of central NC Sunday, in line with the latest SPC marginal risk southwest of the Triangle. Increased mid-level flow of 25-35 kt will support a risk of damaging straight line winds.

As the boundary shifts south Monday, stability should favor reduced storm chances, though diabatic precipitation will be possible in any CAD-type regime. Overall subsidence should favor dry weather Tuesday into most of next week.

KEY MESSAGE 3... After a reprieve from the heat Sun through Tue, hot temperatures expected to return mid-late next week.

A backdoor cold front will approach Sunday and settle south of the region Monday. The latest model and ensemble guidance shows a rather strong high for this time of year extending down into the region Monday at around 1024-mb. In addition, with a trailing low pressure over the TN valley, there is the potential for a CAD-type wedge to develop Sun into early next week. Whether or not that develops in mid-July remains to be seen. Regardless, ensembles do indicate anomalously cool 850-mb temperatures during this time. This along with increased cloud cover should favor a reprieve from the heat with largely middle 80s, perhaps some low 80s Sunday and Monday.

Most ensemble scenarios indicate that troughing over the TN valley next week retrogrades westward into the middle to latter part of next week. As that happens anomalously ridging over the Upper MS valley will build in from the northwest. The 850-mb temperatures Wed through Fri are currently projected to range from 20-22 degC, approaching near-max values for mid-July. That should propel the area to see a return to the heat with mid and upper 90s to near 100 in spots. The HeatRisk currently is forecast to reach a level 3 of 4, especially Thu onward.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

As of 810 PM Friday...

TAF period: Isolated to scattered showers/storms will gradually decrease over the Piedmont through late evening; otherwise, expect generally VFR conditions after midnight.

Outlook: A cold front will move through the region Saturday night. Scattered thunderstorms Saturday afternoon will become more numerous Saturday night, and continue Sunday, Sunday night, and across the south on Monday. Conditions should finally dry out by Monday night. Flight restrictions will be possible in the showers/storms with additional widespread MVFR/IFR beginning to move in from the north Sunday morning.

CLIMATE

Record High Temperatures:

July 10: KRDU 99/1993 KFAY 103/1986

Record High Minimum Temperatures: July 11: KGSO 75/1992 KRDU: 77/1981 KFAY: 77/2024

RAH WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT this evening for NCZ085-086-088-089.