textproduct: Raleigh

WHAT HAS CHANGED

As of 320 PM Wednesday...

* No appreciable changes were noted with this forecast update. Latest guidance still shows the potential for localized rainfall amounts of 2+ inches somewhere along the US-64 corridor Thursday

KEY MESSAGES

As of 320 PM Wednesday...

1) A period of unsettled weather develops late tonight and continues into Friday.

2) Another period of cool and wet weather expected Monday into Tuesday.

DISCUSSION

As of 320 PM Wednesday...

KEY MESSAGE 1: A period of unsettled weather develops late tonight and continues into Friday.

A southern stream jet streak will strengthen along and just off the Delmarva Peninsula late tonight through Thursday. This will leave central NC in the rear-right entrance region with divergence increasing aloft with time Thursday. Simultaneously, vorticity perturbations upstream of an approaching short-wave will spread east across central NC starting tonight. At the sfc, a cold front currently draped over the Midwest will progress southward tonight but get slowed by the Appalachians. Ahead of the front, a sfc trough (marked by wind shifts and a bit of a dew point/theta-e gradient) will strengthen early Thursday somewhere along the western/southern Piedmont northeast through the central Coastal Plain. With time tonight/early Thursday, forcing along this boundary and from the mid-upper forcing discussed earlier will produce a good swath of rainfall across central NC through early Friday. Initial precipitation tonight/early Thursday will focus along and north of the sfc boundary (northern Piedmont/Coastal Plain) before spreading sse with time as the boundary collapses southward through Thursday evening. The bulk of the heaviest rain should move out of here by Thursday night. The trailing shortwave and sfc cold front will dive south of us early Friday into Saturday, with latest guidance trending most appreciable rainfall Friday to our south in SC/GA. Here locally, a few lingering pockets of rain may amount to trace to a few hundreds of an inch through Saturday morning.

The last several runs of the HREF/REFS are showing the potential for some west-east training along the sfc boundary Thursday morning/afternoon. The LPMM output has shown a consistent swath of 1.5 to 2 inches across the southern/western Piedmont east to the Coastal Plain (with some localized 2+ inch amounts). Guidance only really shows weak MUCAPE, if any, and as such any higher amounts would largely be jet-driven but not out of the realm of possibility. Regardless, given the drought conditions, even if realized these amounts would not lead to flooding concerns.

Warm sly flow south of the sfc boundary could gust a bit Thursday morning/early afternoon mainly across the southern Coastal Plain/Sandhills. Although, clouds should persist there so not sure how much mixing will be realized but forecast sounding mean layer momentum transfer values indicate upwards of 25 to 30 mph gusts could be possible. Any linger gusts should diminish with time Thursday evening/night.

Lastly, as the boundary sags south Thursday afternoon, if more instability can be realized than guidance currently shows, there is a low-end chance for small hail given favorable shear and cooler temps aloft along the NC/SC border. Think this is more likely further into SC (HREF minimum helicity swaths cluster more-so in SC) where instability is likely to be higher. Still, wanted to at least mention this possibility.

A marginal temperature gradient looks likely Thursday with high temps peaking in the mid 60s across the south to mid 50s across the north. While a weak CAD signal should lock in nely flow Friday, the sfc high over New England should slide offshore rather quickly, and with less rain to promote in-situ CAD conditions in the forecast, not expecting a crazy classic CAD temperature gradient Friday. Highs should peak in the mid 50s across central NC Friday afternoon.

A coastal low will develop along the cold front Saturday but should keep any weather to our east through the weekend.

KEY MESSAGE 2: Another period of cool and wet weather expected Monday into Tuesday.

A 1040 mb surface high shifting across the Great Lakes and building into New England will wedge southward into the Mid-Atlantic Monday and Tuesday. Temperatures will largely depend on the strength of the CAD signal, with a notable gradient Monday ranging from the mid to upper 40s across the NW Piedmont to near 60 across the Sandhills and Coastal Plain. By Tuesday, the high will slowly shift offshore, though CAD influence will persist, keeping highs in the mid 40s NW to mid/upper 50s SE.

Meanwhile, a frontal boundary extending from TX/LA through the Deep South and Tennessee Valley into the Carolinas will increase precipitation chances across central NC Monday into Tuesday. Latest guidance suggests the highest PoPs Monday, especially across the northern Piedmont. Precipitation may linger into Tuesday but should become more isolated and scattered as drier air filters in from the strengthening surface high.

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 745 PM Wednesday...

A frontal zone, initially focused between 2500-5000 ft AGL, will strengthen from TN to NC tonight. Associated intense lift along it will promote the development and ewd expansion of rain and flight restrictions along it and into cntl NC tonight-Thu morning. Additionally, the redevelopment of a low-level jet in the lee of the Appalachians, one which produced a secondary peak in 20-30 kt surface winds over the Piedmont in the past hour or two, will contribute to the redevelopment of LLWS until the aforementioned band of rain arrives over the Piedmont and RWI and causes low-level jet winds to decelerate there. The low-level jet will otherwise progress ewd and persist to the south of the area of rain and flight restrictions, including at FAY, where LLWS wind shear will become likely late tonight, through the onset of stronger daytime heating and turbulent mixing of the stronger flow aloft to the surface by ~14-15Z. The aforementioned front, initially focused aloft, will develop down to the surface and strengthen during the day Thu, which will both maintain rain and overcast on its cool side and also favor the development of a line of heavier showers along the front as it settles sewd and across cntl and sern NC through Thu afternoon- evening.

Outlook: Rain and flight restrictions may linger or develop at FAY through Fri-Fri night, while lingering low-level moisture will maintain a chance of especially overnight-early morning fog and stratus otherwise and elsewhere through Sat morning. Another chance of flight restrictions and rain will result in cold air damming early next week.

RAH WATCHES/WARNINGS/ADVISORIES

None.