textproduct: Raleigh

SYNOPSIS

A cold front will move south through North Carolina tonight. High pressure will build in from the north Sunday and Monday, then move off the Mid Atlantic coast Monday night.

NEAR TERM /THROUGH TONIGHT/

As of 355 PM Saturday...

As of 18Z, showers associated with the s/w aloft were sliding ese across the nrn Piedmont and nrn Coastal Plain. The showers should continue ese and out of the area during the next few hours. Meanwhile, the cold front, draped wswwd from a low over s-central VA, was still north and west of the area. A pre-frontal trough should move across central NC this aft/eve, as the surface low drops southward over the NC Coastal Plain, dragging the cold front with it. However, the arrival of cooler air will be delayed until the surface low moves swd out of the area this evening and cooler air advects in (backdoor style) from SE VA late evening/early tonight. A second s/w aloft should track sewd across the area in the wake of the surface cold front tonight.

Precipitation: From the SPC mesoanalysis page, MLCAPE was maximized across the southeast half of central NC, generally 500-1000 J/Kg, while Effective Shear ranged from around 55 kts across the north to 40-50 kts where the MLCAPE was highest. Low-level lapse rates were about 7 C/Km. Showers and storms have developed as of 20Z, along the pre-frontal trough near the Triangle, and should continue ewd within a good convective environment for the next hour or so. Additional showers and storms have also developed over the srn Piedmont, and may continue spreading ewd across the Sandhills and srn Coastal Plain tonight, possibly increasing in coverage and intensity as the front approaches later this evening.

Temperatures: Temperatures could drop some behind the front this aft/early eve, but the cooler air will arrive from the NE later this eve/tonight, with lows bottoming out in the mid 40s north to low/mid 50s south by 12Z Sun.

SHORT TERM /SUNDAY AND SUNDAY NIGHT/

As of 145 PM Saturday...

Overview: In the wake of the s/w aloft, nwly flow will prevail over central NC Sun/Sun night. A nrn stream s/w will track ese across the Northeast, while the sub-tropical ridge approaches from the west ahead of the next low pressure system. At the surface, high pressure will remain over the Midwest on Sun, finally building into the region in the wake of a dry, reinforcing cold front Sun eve/night. Dry weather will prevail, with highs mainly in the 60s and dewpoints in the 40s. Winds could get a bit breezy with the dry cold fropa Sun eve and remain a bit stirred Sun night. Cloud cover will decrease Sun morning, with sunny/clear skies Sun aft through Sun night. Lows Sun night may depend on how much stirring there is and for how long, with otherwise excellent radiational cooling conditions. For now, lows in the mid 30s to low 40s expected.

LONG TERM /MONDAY THROUGH SATURDAY/

As of 105 PM Saturday...

* Quiet and seasonable Mon, then unsettled Tue through Wed night, although no significant hazards are currently expected.

* Dry and colder Thu through Sat.

Mon/Mon night: Mild continental surface high pressure centered to our N Mon morning will push E and offshore through Mon evening, while slowly flattening mid level ridging shifts from the Gulf/Mid South E into the Southeast US. High clouds will gradually increase Mon, esp over the NW, as our upper level flow accelerates from the SW. And with the low level flow becoming more SE and S yielding increasing moist upglide at around 290-300K over the Piedmont Mon night, lower level clouds will also increase Mon night, again mainly over the NW half. Low level thicknesses will be just slightly above normal Mon with decent insolation early in the day, supporting highs in the 60s to near 70, followed by lows Mon night in the upper 30s to mid 40s.

Tue-Wed night: This period is still likely to be somewhat active, and models are coming into better agreement on timing of the incoming mid level trough and surface cold front. The surface high pushing further out over the NW Atlantic will put NC in a deepening return flow pattern, with falling heights aloft as the mid level ridge flattens and pushes off the Southeast coast, in response to a trough digging over the Dakotas and Upper Midwest. Looking at the ensemble cluster analysis, the variation among members can be explained by differences in both timing and amplitude of this trough and the upstream ridge, although these differences have decreased from yesterday's runs. The most likely time of cold front passage is Wed evening or early overnight, although there remains a decent spread of several hours either side of this timing. Will retain above-climo pops through this period, although it likely won't be raining this entire time. It appears that the better pops will be focused Tue night, highest in the NW where jet-induced upper divergence is projected to be maximized. There still appears to be chance for at least isolated prefrontal thunderstorms Wed, with somewhat low CAPE (mean SBCAPE of just 200-400 J/kg) but high deep- layer bulk shear with long and generally straight hodographs, so we could get a storm with strong winds and/or small hail, esp along and E of Hwy 1 where surface dewpoints and CAPE should be greater. Expect highs Tue in the lower 60s NW (with greater cloud cover and the potential for a rain-induced stable pool) ranging to low-mid 70s elsewhere. Wed highs should be mostly in the 70s.

Thu-Sat: We may see some lingering clouds E Thanksgiving morning, but otherwise expect increasing sunshine, with fair, dry, and cool conditions through Sat as the mid level trough shifts over E NOAM. Despite the abundant sunshine, since the incoming surface high will be of Canadian/Arctic origin, the CAA will keep temps below normal, esp Fri through Sat as the surface high settles overhead and just to our N. Expect highs in the 50s Thanksgiving Day (about 5 degrees below normal) and upper 40s to mid 50s Fri/Sat (about 6-12 degrees below normal), with lows in the upper 20s to lower 30s Thu night and in the 20s Fri night. -GIH

AVIATION /00Z SUNDAY THROUGH THURSDAY/

As of 745 PM Saturday...

The last in a series of a few segments of a fractured cold front now moving through cntl NC will move south and across RWI and RDU through ~02Z, GSO and INT between 03-04Z, and FAY around 05-06Z. Ahead of that cold frontal segment, light wind and an unseasonably moist airmass will support the development of areas of pre-frontal fog. Behind the front, areas of IFR-MVFR stratus now over nern NC and sern VA will develop in the post-frontal regime swd and across RWI, RDU, and FAY tonight, where the strongest post-frontal push of nely flow will result and also favor a short period of nely surface winds at or above 10 kts. Meanwhile at INT and GSO, where the aforementioned push of nely flow will be weaker, areas of fog will be favored in the several hours surrounding 12Z. Lastly, altocumulus ceilings between 6-9 thousand ft may produce patches of very light rain or sprinkles overnight, but no flight restrictions or operationally significant weather are expected to be directly related to that light precipitation.

Skies will clear and be accompanied by a wly surface wind that will develop and strengthen to around 10 kts with afternoon heating on Sunday.

Outlook: IFR-MVFR ceilings and patchy light rain will likely overspread the Piedmont ahead of a retreating warm front Tue morning. A chance of rain, increasingly convective in nature, and also flight restrictions, are expected later Tue through Wed, as a strong frontal system traverses the region.

RAH WATCHES/WARNINGS/ADVISORIES

None.