textproduct: Raleigh

WHAT HAS CHANGED

* Minor tweaks to highs and heat index values through Wednesday, although the message remains the same.

KEY MESSAGES

As of 1240 PM Sunday...

1) Hot and mainly dry through Wednesday.

2) Increasingly unsettled starting Wed night, with more seasonable temperatures.

DISCUSSION

As of 1240 PM Sunday...

KEY MESSAGE 1... Hot and mainly dry through Wednesday.

An unseasonably strong mid/low-level anticyclone and steep mid- level lapse rates (associated with a modified EML) sampled in the 12z RAOB data over Carolinas and portion of the Southeast, will keep conditions capped and void of precipitation amidst unseasonably moist deep-layer moisture in place. Warm temperatures though the mid/low-lvls will exceed the 90th percentile through at least Wednesday and support several days of hot conditions at the surface when temperatures should regularly eclipse 90 degrees by mid- afternoon.

Given central NC's position within the described weather pattern above, there are minimal failure modes and reasonably high confidence in the forecast high temperatures through Wed. However, forecast confidence on mixing out of dew points in the afternoon is slightly lower and will result in fluctuations in the daily maximum heat index values. Leaning on experimental HeatRisk, widespread and prolonged Moderate Risk (level 2 out of 4) is expected through Wed. This level and duration of unseasonably warm temperatures will primarily affect anyone sensitive to the heat, but any outdoor activities in the sun during peak heating should be monitored closely for signs of heat exhaustion. Take breaks in the shade/indoors often and make sure adequate hydration is available.

Reminder, the temperature forecast is the expected temperature in the shade and does not account for additive affects from direct sunlight. Wet-bulb globe temperature (WBGT) does take this into account, but is sensitive to incoming solar radiation, and wind speed. If you would like to know more, please see weather.gov/rah/wbgt for more information.

KEY MESSAGE 2... Increasingly unsettled starting Wed night, with more seasonable temperatures.

The unseasonably strong ridge will gradually weaken and lose its grip on the Carolinas and portions of the Southeast as the mid/low-lvl anticyclone settles back over Bermuda by mid-week. The mid/upper level trough axis well become elongated across the CONUS as the northern wave progressively rides the International Border to the north and a southern portion gradually pinches off over southern Plains into the weekend.

Our first chance for rain may come as early as Wed evening in the northwest Piedmont, but more likely Thurs into Fri as a weak to moderately unstable airmass will precede a backdoor cold front as it shifts across the area Thurs afternoon/evening. Showers and some isolated storms will be possible along the front, given favorable diurnal passage as of the latest forecast, with weak 925mb FGEN and low/mid-lvl WAA atop the front should support a period of light stratiform rain in its wake into Fri, potentially setting up a brief classical-CAD into Fri.

The surface high will be very transitory across the northern Mid-Atlantic and should not sustain classical CAD into the weekend. Fri afternoon/night should see a transition back to a southerly flow regime. This should set the stage for a more typical early summertime pattern for diurnal showers/storms during the afternoon/evening focused around the sea-breeze and terrain circulations.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

As of 1220 PM Sunday...

There is high confidence in VFR conditions through this evening at all terminals. Moisture has increased south and west of the terminals across GA/SC. Isolated to scattered storms are expected to develop in that vicinity this afternoon and evening, but remain well west of the terminals in central NC. A stray shower cannot be fully ruled out near GSO/INT this evening, but that chance is very low at the moment. Moisture levels will continue to increase tonight as dewpoints rise, especially across the eastern Sandhills and Coastal Plain. Morning stratus or sub-VFR visibilities are again possible at FAY on Mon. These conditions could briefly influence RWI but confidence on it getting that far north is too low.

Outlook: Morning stratus and fog will be favored each morning Tue and Wed as return flow strengthens, most probable at FAY/RWI. An increasingly unsettled pattern will set up late Wed through Fri with the approach of a cold front. Sub-VFR restrictions continue to be favored with scattered showers and storms forecast during this time.

CLIMATE

Record High Temperatures:

May 18: KGSO: 95/1911 KRDU: 95/1906 KFAY: 96/1911

May 19: KGSO: 96/1911 KRDU: 95/1962 KFAY: 96/2022

May 20: KGSO: 95/1917 KRDU: 96/2022 KFAY: 99/2022

Record High Minimum Temperatures:

May 18: KGSO: 70/2015 KRDU: 72/1896 KFAY: 71/2018

May 19: KGSO: 68/2018 KRDU: 70/2022

May 20: KGSO: 68/2022 KRDU: 69/2019 KFAY: 71/2022

May 21: KGSO: 67/2022 KRDU: 71/1898 KFAY: 71/2025

RAH WATCHES/WARNINGS/ADVISORIES

None.