textproduct: Raleigh

WHAT HAS CHANGED

* An Excessive Heat Watch was considered for the Triangle and Coastal Plain Wednesday into Friday. It appears that we will fall a bit short of the criteria of 110+ heat index values.

KEY MESSAGES

As of 215 AM Tuesday...

1) The Heat Wave will peak with Heat Advisories likely for a good portion of the area from Wednesday into Friday.

2) Labor Day weekend through Monday gradually trends cooler along with highest thunderstorm chances on Saturday.

DISCUSSION

As of 215 AM Tuesday...

KEY MESSAGE 1... The Heat Wave will peak with Heat Advisories likely for a good portion of the area from Wednesday into Friday.

The high heat and humidity will really get going this afternoon when highs will top out in the 90s. Heat indices are expected to fall just short of the Heat Advisory criteria of 105 degrees for several hours. Most areas from the Triangle east and south will have heat indices of 100 to 104, thus it would still be a good idea to prepare for the day as if an advisory is in effect.

The heat will peak this week from Wednesday into Friday. This is when the upper ridge will park overhead at 595dm overhead of the TN valley to the mid-Atlantic coast. This is slightly lower heights than what was observed during the early July heat wave. Other than an isolated thunderstorm, chances less than 15 percent at any one point, expect mostly sunny hot days and very warm and humid nights from tonight into Friday. Highs should be hottest Wednesday and Thursday (mid 90s to near 100), with Friday potentially as hot.

Even overnight lows will be in the mid to upper 70s for many areas. An Excessive Heat Watch was considered for the Triangle and Coastal Plain for Wed-Fri (as overnight lows will struggle to fall below 80 and heat indices potentially approach 110 during the peak of the afternoon heat each day). We held off for now - but it will be considered in later shifts.

Heat index values in the upper 90s to around 105 degrees are expected each day with areas from Raleigh east and south will be most likely to surpass 105 degrees. Some areas may approach 110 degrees during peak heating. Heat advisories appear likely.

There is a chance of mainly PM thunderstorms Friday and Saturday as the upper ridge begins to break down and shift back to the west for a time. Temperatures will back off some, especially Saturday and Sunday when mostly mid to upper 80s are expected.

KEY MESSAGE 2...Labor Day weekend through Monday gradually trends cooler along with highest thunderstorm chances on Saturday.

Ensemble guidance continues to show a gradual westward shift of the upper ridge this weekend, allowing troughing and an approaching cold front to bring a cooler pattern change to central NC by later in the weekend. Temps still expected to trend slightly downward Saturday, but still remaining well above normal with highs in the lower to mid 90s. A more substantial cooldown is expected Sunday into Labor Day with highs in the mid 80s. High pressure building in behind the front may also bring a reduction in humidity by Monday.

Shower and thunderstorm chances should increase Friday into Saturday as the front approaches, with the best opportunity for convection Saturday. Scattered showers or storms could potentially linger into Sunday, but the best chances will be particularly south and east of Raleigh. Overall, the trend toward cooler and drier conditions for Sunday and Labor Day is becoming increasingly well supported. While a severe threat cannot be ruled out Saturday, predictability remains too low to determine the magnitude or coverage of any severe weather threat at this time.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

As of 640 AM Tuesday...

Generally VFR conditions are expected through 12z/Wednesday as high pressure strengthens over the region.

Looking beyond 12z Wed, VFR conditions should dominate into Friday. The chance of PM thunderstorms will increase Fri/Sat as deep low pressure and troughing over the Northeast states nudges the ridge westward, thus the chance for sub-VFR conditions will rise starting late Fri.

CLIMATE

Record High Temperatures:

September 1: KGSO: 99/1932 KRDU: 101/1932

September 2: KGSO: 101/1921 KRDU: 99/1912

September 3: KGSO: 101/1921 KRDU: 99/2010 KFAY: 101/2010

September 4: KRDU: 100/1925 KFAY: 100/1944

Record High Minimum Temperatures:

September 1: KGSO: 74/2012 KRDU: 76/1932 KFAY: 77/2021

September 2: KGSO: 73/1912 KRDU: 75/1912 KFAY: 75/2020

September 3: KGSO: 73/2020 KRDU: 78/1933 KFAY: 77/2020

September 4: KGSO: 72/2018 KRDU: 74/1921 KFAY: 75/2020

September 5: KGSO: 73/2018 KRDU: 74/2012 KFAY: 74/1935

RAH WATCHES/WARNINGS/ADVISORIES

None.