textproduct: Raleigh

WHAT HAS CHANGED

* Updated aviation discussion

KEY MESSAGES

As of 128 PM Friday...

1) Isolated showers and storms through early next week as we settle into a typical summertime pattern.

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 128 PM Friday...

KEY MESSAGE 1... Isolated showers and storms through this weekend as we settle into a typical summertime pattern.

Early afternoon water vapor imagery reveals a pair of anomalously strong (nearly 600dm) H5 ridges in place (one off the east coast, one over Utah), with an elongated trough in between them stretching from eastern Canada southwestward into Louisiana. Across NC, deep and broad (albeit weak) southwesterly flow remains in place from the surface well into the upper levels of the troposphere. Surface obs and visible satellite reveal a fairly uniform atmosphere across NC this afternoon with storms developing along the sea breeze along with some clusters of storms along the mountains to our west. In between, conditions remain dry with temps in the mid to upper 80s as of 17Z.

While still higher than normal for early August, we've eroded some of the PW that was in place yesterday (was nearly 1.9", now closer to 1.7"). As such, we have a bit less instability to work with this afternoon with MLCAPES still approaching 2000-2500 J/KG compared to more than 3000 J/KG Thursday afternoon. In an atmosphere with less than 20kts of bulk shear available and little in the way of pre- existing surface boundaries, any storms that develop will struggle to sustain themselves for long and should be very isolated in nature. Sea breeze convection across the Sandhills/southern Coastal Plain is one focal area today, with storms coming off the mountains serving as a secondary area of attention across the western Piedmont. Outflow boundary collisions could spawn a few isolated showers in between along the US-1 corridor but coverage should be spotty at best. Expect any/all storm clusters to dissipate closer to 00Z with the loss of daytime heating.

The offshore ridge will undergo a gradual flattening process tomorrow through early next week, eventually building westward into the Gulf and SE states by Monday. This should help to further suppress deeper moisture returns into the area and overall convective coverage on Saturday. Outside of weak sea breeze convection, the highest chances for storms will be concentrated across the western Piedmont.

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. Central NC is expected to situated between two bands of seasonably anomalous deep-layer moisture Sun through Tues, which should limit widespread convective chances, although isolated showers 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 onward which will complicate the risk for continued dangerous heat beyond Tues.

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 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 /18Z FRIDAY THROUGH WEDNESDAY/

As of 1232 PM Friday...

Convective coverage should be much more limited today as compared to Thursday, with two focal areas of concern. The first is along the sea breeze and we are already seeing isolated storms across the southern Coastal Plain approaching FAY. The other will be the western Piedmont where storms have yet to develop. INT/GSO/FAY all stand the highest chance of seeing a quick storm between 20Z-23Z with brief restrictions, albeit a low chance only around 20-30 percent. Chances are much lower at RDU/RWI and storms will be left out of those TAFs. Outside of storms, expect VFR conditions to prevail through the period although some pre-dawn stratus and fog is possible at FAY.

Outlook: Isolated storms are possible this weekend 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.