textproduct: Raleigh

KEY MESSAGES

As of 116 PM Sunday...

1) A Heat Advisory may be needed for the Sandhills and southern Coastal Plain Monday.

2) A Marginal to Slight Risk of severe storms remains for Monday, along with a heavy rainfall threat.

3) Continued periods of unsettled weather this week as a stalled front lingers across NC.

DISCUSSION

As of 116 PM Sunday...

KEY MESSAGE 1... A Heat Advisory may be needed for the Sandhills and southern Coastal Plain Monday.

A Heat Advisory may be needed Monday, but for a smaller area of the eastern Sandhills into the southern Coastal Plain. As dewpoints remain high in the mid 70s and temperatures warm into the low 90s, heat indices will certainly get close to advisory criteria.

KEY MESSAGE 2... A Marginal to Slight Risk of severe storms remains for today and Monday, along with a heavy rainfall threat.

A slight risk of severe storms remains in place through tonight for all of central NC and a marginal risk of storms is in place Monday.

As for storm coverage, it appears isolated to scattered activity this afternoon and early evening could become widespread over portions of the region late tonight and overnight. A surface boundary is evident on satellite and surface obs along the northern Piedmont, between the Triad and north of RDU. At the same time, a cold front across the lower OH valley and VA will gradually approach from the north. Storms have already formed along the surface boundary, in a region of a CAPE gradient and may additionally track south of the front in VA. A heavy rainfall threat will exist this afternoon but especially tonight. As the front approaches later tonight and early Monday, there remains a threat of heavy rainfall as the low to mid- layer flow is nearly parallel to the boundary to support training storms. The HREF/REFS differ on this potential, with the HREF showing more of a signal from Raleigh east and south into the Coastal Plain. The 12z HREF/HRRR appear to be coming in line with this scenario as well, given weak upwind propagation vectors. A swath of 2-4 inches is possible in these areas, though confidence on exact location is not great.

The front and/or remnant outflows will stall along or near the US-64 corridor on Monday. Additionally, it appears the sea-breeze may be an additional focus for storms Monday afternoon and evening, suggested by a few HREF members. Moisture values remain high, with again the low to mid-layer flow parallel or slightly southwest of the boundary, favoring again training storms for heavy rainfall. Both the HREF/REFS show this heavy rainfall signal Monday along the US-64 corridor, but the threat could be anywhere storms train and move slowly.

KEY MESSAGE 3... Continued periods of unsettled weather this week as a stalled front lingers across NC.

Broad and weak troughing over the eastern CONUS on Mon will become reinforced by a more vigorous shortwave trough pivoting across the Great Lakes and southern Quebec on Tues. A low-amplitude likely convectively altered perturbation rippling through the basal portion of the trough is forecast to shift across the Ohio Valley Tues morning before potentially shifting across the southern Mid- Atlantic during peak heating. There are some notable timing differences with the low-predicitability feature, but nevertheless, enhanced westerly winds of > 30 kts are forecast to sink south and into North Carolina and overlap a continued moist and unstable environment. Although flow throughout the troposphere is not particularly strong, consistently veering winds with height will support curved hodographs capable of producing transient supercells and bowing segments. Any right-moving storm will have a storm motion of southeast and increase the likelihood that storms may drift into our region from VA. All hazards will be on the table for Tuesday, although damaging straight-line winds will be the most likely primary and more widespread hazard.

An upstream shortwave trough is forecast to cross the mountains Wednesday with an attendant surface cold front in tow. With PW's still at or near 2" and nearly 2000 J/KG of MLCAPE available, strong to severe storms are more than plausible with the front. Significantly lower PW's will follow the front with substantially lower precip chances Thursday through Saturday, although model inconsistencies regarding how far south the front and drier air push south results in an lower forecast confidence in a dry spell; especially with such a weak and progressive surface high and climatologically approaching the window when it is difficult for fronts to progress all the way through the Carolinas.

AVIATION /00Z MONDAY THROUGH FRIDAY/

As of 730 PM Sunday...

TAF period: Scattered showers and thunderstorms will continue through the evening into the overnight hours, and these are generally covered by PROB30 groups, except for FAY where thunderstorms are more imminent. After precipitation decreases in coverage, a nearly stationary front in southern Virginia is expected to drop far enough south into North Carolina to allow for low level moisture to move into the region and bring widespread IFR/LIFR stratus. Confidence is highest that the stratus will reach RDU and RWI, and models have been trending farther west with the coverage towards INT/GSO - lowered the height of the ceiling in those airport's TAFs. The stratus is not expected to reach as far south as FAY. More showers and thunderstorms are expected Monday afternoon, with -SHRA and VCTS mentions at all sites.

Outlook: Additional showers/storms are expected Monday through midweek with associated sub-VFR conditions. There will also be low stratus and fog during the morning hours through midweek.

CLIMATE

Record High Temperatures:

July 19: KFAY: 101/2002

Record High Minimum Temperatures:

July 19: KGSO: 75/2016 KRDU: 80/1942 KFAY: 77/2023

July 20: KGSO: 75/2019 KRDU: 76/2025

July 21: KGSO: 76/2011 KRDU: 78/1932 KFAY: 80/2017

July 22: KGSO: 77/2011 KRDU: 78/2011 KFAY: 82/2017

RAH WATCHES/WARNINGS/ADVISORIES

None.