textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes, updated Aviation discussion.

KEY MESSAGES

As of 220 PM Saturday...

1) Typical late-summer weather is expected, with mostly isolated late-day showers and storms for the next several days.

2) Risk for hot temperatures and dangerous heat increase early next week.

DISCUSSION

As of 220 PM Saturday...

KEY MESSAGE 1... Typical late-summer weather is expected, with mostly isolated late-day showers and storms for the next several days.

Near-normal deep-layer moisture, proximity to deep sub-tropical ridge in the western Atlantic, and minimal mesoscale forcing mechanisms, should keep coverage of showers/storms to isolated to locally scattered over the next several days. Coverage of showers/storms will be locally greatest each day focused around weak surface pressure trough over the Piedmont, the sea breeze as well as where moderate low-lvl instability develops, which varies by day.

Most showers/storms that are able to develop through the afternoon and evening will remain relatively shallow and consist of mostly showers with isolated/embedded storms with infrequent lightning. Downdrafts will be equally typical for summer-time storms and produce 20-30 mph wind gusts immediately surrounding the locations where they collapse.

Isolated and infrequent strong to locally severe storms can't be ruled out given the moderate to strong instability in place within the hot/humid air mass over the Carolinas (MLCAPE of 2000-3500 J/kg). Clustering storms that collapse along a common cold pool will have the best chance to produce 40-60 mph wind gusts given the lack of deep-layer shear to otherwise organize storms (0-6 km shear < 20 kts). Based on low-lvl shear vector, continued storm development will be most likely along the northeast to easterly quadrant of any outflow boundary each day.

KEY MESSAGE 2... Risk for hot temperatures and dangerous heat increase early next week.

Strong sub-tropical ridging over the western Atlantic will continue to be suppressed south through this weekend before retrograding and elongating westward across FL and into the northeast Gulf into early next week. Central NC is expected to situated between two bands of seasonably anomalous deep-layer moisture Sun into Wed, which should limit widespread convective chances, although isolated showers/storms are still possible. Increasing convective debris and lingering small-scale forcing may couple with a band of deeper moisture from the Midwest and northern Mid-Atlantic as it sags south and into the Carolinas Wed night onward which will complicate the risk for continued dangerous heat beyond Wed.

In the absence of convection, building sub-tropical ridge to our south and warming H850 temperatures to around 20C would support low- mid 90s as early as Sun, and as high as upper 90s possible Tues through Fri. 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 SUNDAY THROUGH THURSDAY/

As of 752 PM Saturday...

24 hour TAF period: Showers and thunderstorms continue this evening along an axis from CLT to RDU. These storms could result in gusts to around 30 kts and IFR vsbys. While convective activity and intensity should begin to wane with loss of heating, showers and storms may persist for the next couple/few hours, mainly at KRDU. Cannot completely rule out a shower at KRWI, but it is looking less likely since TAF issuance. Some trailing rain showers could make it into the Triad before diminishing, but for now prob was too low to include in the TAF. There are mixed signals regarding sub-VFR cig development late tonight into early Sun morn, with the best chance near KFAY, but confidence remains too low to include in this TAF issuance.

Outlook: Isolated storms are possible into early next week, with an uptick in unsettled weather potential on Wednesday. Morning stratus and fog is possible any given morning with brief sub-VFR conditions possible.

RAH WATCHES/WARNINGS/ADVISORIES

None.