textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes from earlier forecasts. Aviation discussion updated.

KEY MESSAGES

As of 155 PM Thursday...

1) There is a marginal (level 1 of 5) risk for severe thunderstorms from damaging wind gusts this afternoon, primarily west of US-1, as well as a marginal (level 1 of 4) risk for excessive rainfall across the area.

2) Risk for hot temperatures and dangerous heat increase early next week, but many failure modes exists within the expected forecast pattern Wednesday onward.

DISCUSSION

As of 155 PM Thursday...

KEY MESSAGE 1... There is a marginal (level 1 of 5) risk for severe thunderstorms from damaging wind gusts this afternoon, primarily west of US-1, as well as a marginal (level 1 of 4) risk for excessive rainfall across the area.

With the 12:30pm update from the Storm Prediction Center, the western half of the forecast area (generally west of US-1) has been added to a marginal (level 1 of 5) risk for severe thunderstorms this afternoon, with the threat coming from damaging wind. Vertical wind shear over the area is minimal today, meaning that it will be hard for storms to become organized, and wind speed through the vertical profile is low, meaning that storms will have a slow storm movement. With the amount of moisture that is present, cannot rule out some water-loaded downdrafts to produce some isolated damaging winds. The threat should last primarily through sunset, which is when the bulk of the rainfall should come to an end. However, locations in the western Piedmont could see some thunderstorms continue through midnight. In addition, with the slow storm movement, any locations that does receive multiple rounds of showers/storms could receive heavier amounts of rainfall due to training, which may result in localized flash flooding.

KEY MESSAGE 2 ... Risk for hot temperatures and dangerous heat increase early next week, but many failure modes exists within the expected forecast pattern Wednesday onward.

Strong sub-tropical ridging parked over the western Atlantic is expected to be suppressed south this weekend before retrograding and elongated westward across FL and into the northeast Gulf into early next week. Flow through the lower troposphere will remain relatively weak over the Carolinas as seasonably stronger zonal flow will remain confined to the northern Mid-Atlantic into early next week. Heat building over the Mid-Atlantic and into the Carolinas into early/mid week will certainly be possible, but will likely be complicated by convective debris within the westerly to northwesterly flow aloft.

In the absence of convection, building sub-tropical ridge to our south and warming H850 temperatures to around 20C will support low- mid 90s as early as Sun, and as high as upper 90s possible Tues through the remainder of the forecast period. Moisture and associated heat index values during peak heating will largely depend on the position/location of a persist Piedmont trough, with drier downsloping flow to its west and more humid conditions to its east. Locations east of this feature, and that remain void of convection, will likely reach Moderate HeatRisk and eclipse 105 degree heat indices during peak heating.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

As of 745 PM Thursday...

A cluster of storms east of GSO and around RDU will continue to the northeast this evening, likely exiting the RDU vicinity by 01-02Z VFR is then expected through 06Z. Some LIFR/IFR low cloud cover is possible by 09Z, with highest confidence at FAY but possible everywhere with a relatively unchanged airmass and pattern. VFR is then expected during the day Friday, with some scattered storms possible around INT/GSO later in the day.

Outlook: Isolated to scattered thunderstorm coverage is forecast again Saturday afternoon, with minimal coverage expected Sunday through Tuesday afternoons. With no change in the muggy airmass, cannot rule out restrictions around dawn each morning at any terminal.

RAH WATCHES/WARNINGS/ADVISORIES

None.