textproduct: Raleigh

WHAT HAS CHANGED

* Updated Aviation discussion

KEY MESSAGES

As of 235 AM Wednesday...

1) Heat index values will rise above 100 degrees in some Piedmont areas today, with 100-105 degree values expected area-wide on Thursday.

2) It will become progressively hotter through at least Fri-Sat, then at least a little less so with increasing chances of convection by early next week.

DISCUSSION

As of 235 AM Wednesday...

KEY MESSAGE 1... Heat index values will rise above 100 degrees in some Piedmont areas today, with 100-105 degree values expected area- wide on Thursday.

The strong mid and upper-level high/anticyclone, centered over the the TN/OH Valley as of 00Z, will build ewd across the Appalachians and into the mid-Atlantic through Thu.

Temperatures: The upward trend in temperatures will continue, with highs in the mid 90s today increasing into the upper 90s on Thu. Some locations could hit 100 degrees on Thu. For low temperatures, tonight may be the last night for several days where the overnight temperatures drop below 70 degrees.

Heat Index: With dewpoint temperatures in the mid 60s to low 70s both days, max heat index values today of 97-103 are expected across the Piedmont, with mid-upr 90s over the Coastal Plain. Max heat index values on Thu of 100-105 are expected area-wide. Based on the latest forecast, a Heat Advisory may be needed on Thu for areas expected to hit 105 or higher.

KEY MESSAGE 2... It will become progressively hotter through at least Fri-Sat, then at least a little less so with increasing chances of convection by early next week.

Criteria and issuance times for heat-related products, per NWS Directive 10-515 and accompanying ER Supplement 02-2011, are as follows:

Excessive Heat Watch: 110 F or more for at least two consecutive days and intervening MinT of 77 F or more, typically issued at 36-72 hours

Excessive Heat Warning: 110 or more for at least two consecutive days and intervening MinT of 77 F or more, typically issued 1st or 2nd period, or at 12-36 hours

Heat Advisory: 105 F or more for two consecutive hours, typically issued for 1st or 2nd period (ie. today, tonight, etc), or at 12-36 hours

An already strong mid and upper-level high/anticyclone, centered over the TN and OH Valleys with observed 500 and 700 mb heights of 596 and 325 dam, respectively, will progress slowly across and offshore the southern Middle Atlantic through the holiday weekend, while weakening.

Historically, the most significant heat waves in cntl NC occur when the position of the ridge is centered from the TN Valley to the srn Appalachians, immediately upstream of, and at a similar to slightly lower latitude than cntl NC. In this case, the position of the anomalously strong ridge from the lwr OH Valleys to the Virginias will favor the hottest temperatures to the north of cntl NC, from VA and NJ to the srn New England coast, while mostly ely flow equatorward of the high will prevail over cntl NC.

It will nonetheless be hot through the holiday weekend, with temperatures in the upper 90s to lower 100s. Heat index values will generally range between 100 and 110 but not become too excessive given only modest afternoon humidity levels during the period, regulated by mixed dewpoints in the 60s, to even 50s possible over the wrn Piedmont Fri and Sat. Although the ridging aloft is forecast to weaken and break down over the Carolinas by Independence Day, then drift offshore and across the swrn N. Atlantic, the underlying airmass will probably not cool much until convection and diabatic cooling are introduced Sun and especially Mon. If shower/storm coverage remains limited through Sun, temperatures could be comparably as hot as previous days, thereby prolonging the hottest conditions through the entirety of the weekend.

With the above criteria in mind, and with official forecast heat index values remaining sub-110 F through the entire forecast period, except for a few pixels in the Coastal Plain and at RDU this weekend, indications are that this will probably be a multi-day Heat Advisory event, with such Advisories probably issued a day in advance.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

As of 645 AM Wednesday...

24 hour TAF period: VFR conditions should largely prevail through the TAF period. Winds will generally be light and sly (sswly to sely) through the period.

Outlook: VFR conditions will largely prevail through at least Sat. A potential return to more unsettled weather is expected late this weekend with localized reductions in cigs/vsbys where storms develop.

CLIMATE

All-time High Temperature Record and Most Recent Date of Occurrence:

KGSO: 104/1914-07-27 KRDU: 106/2024-07-05 KFAY: 110/1983-08-21

Record High Temperatures:

July 1: KGSO: 99/2012 July 2: KGSO: 98/1954 KRDU: 101/1954 July 3: KGSO: 98/1911 KRDU: 101/2012 KFAY: 102/2019 July 4: KGSO: 98/1970 KRDU: 101/9999 KFAY: 98/2019 July 5: KGSO: 98/2012 KRDU: 106/2024 KFAY: 101/9999

All-time High Minimum Temperature Record and Most Recent Date of Occurrence:

KGSO: 80/2007-08-09 KRDU: 80/2025-07-18 KFAY: 84/1928-06-22

Record High Minimum Temperatures:

July 2: KGSO: 76/2018 KRDU: 78/1931 KFAY: 77/1931 July 3: KGSO: 76/2018 KRDU: 79/2023 KFAY: 76/2023 July 4: KGSO: 73/2018 KRDU: 79/1902 KFAY: 78/1913 July 5: KGSO: 74/1999 KRDU: 78/2024 KFAY: 77/2005

RAH WATCHES/WARNINGS/ADVISORIES

None.