textproduct: Raleigh

SYNOPSIS

Arctic high pressure will migrate across the Southeast ahead of a strong, clipper low pressure system that will swing across the Great Lakes later tonight and Wednesday. A moisture-starved cold front trailing the clipper low will move across NC Wednesday night. Another area of high pressure will follow and build across the Southeast Thursday and Thursday night.

NEAR TERM /THROUGH TONIGHT/

As of 355 PM Tuesday...

* Unseasonably cold, with refreezing of melting snow cover that will lead to a risk of black ice near the VA border

Within a broad trough encompassing ern NOAM, a low amplitude shortwave perturbation now over the srn Appalachians, and preceding plume of cirrostratus, will progress ewd and across cntl NC through early this evening, then offshore. Meanwhile, a more vigorous and highly amplified shortwave trough will dig from the nrn Plains this afternoon to the mid MS Valley by 12Z Wed. After a short period of relatively clear between the two this evening over cntl NC, additional mid and high-level moisture will be enhanced downstream of that trough, with a gradual thickening and lowering of associated ceilings to around 15 thousand ft, through Wed morning.

At the surface, Arctic high pressure now centered at 1023 mb over the ern Carolinas will continue to weaken while settling across the South Atlantic states, to the vicinity of nrn FL by 12Z Wed. It will do so downstream of a now 989-990 mb clipper low that will migrate from ern ND to MI through the same time. The MSL pressure gradient and height fields between the two will tighten markedly over cntl NC overnight, with the development of a swly breeze that may gust at times into the 20s mph over the srn and nw Piedmont around sunrise, when an intense, 60-70 kt low-level jet will be in the process of progressing across the Appalachians. That low-level jet may also contribute the maintenance of an area of stratocumulus ceilings that has been slow to disperse today beneath a strong, subsidence inversion over the wrn Carolinas, as the associated shearing deformation acts upon a zone of pre-existing 925 mb Fgen and frontal lift inferred by the strong 925 mb temperature gradient evident there in 12Z-observed upr air data.

The Arctic airmass overhead, which has supported temperatures this afternoon only in the mid 30s to lwr 40s, will have an opportunity to radiationally cool this evening, between the aforementioned areas of high clouds and prior to the strengthening of the swly breeze. Quick cooling into the 20s to lwr 30s will probably result, before temperatures steady or rise after midnight. Lastly, visible satellite data this afternoon depict a shrinking area of snow cover confined to the far nrn reaches of the nrn Piedmont and nrn Coastal Plain, such that refreezing and black ice concerns Wed morning will be too spatially-limited for any additional Winter Weather Advisory issuance.

SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/

As of 221 PM Tuesday...

A potent mid-level short wave will dive southeast through the Ohio Valley early Wednesday before pushing across the Southeast US Wednesday evening. While mid-level height falls will accompany this feature, mid to upper flow should be relatively wly, and as such, most moisture associated with the feature should ring out on the western slopes of the southern Appalachians.

At the sfc, pre-frontal swly flow will pick up early to mid Wednesday morning, allowing temperatures to rebound to near normal (highs in the lower to mid 50s.

Forecast soundings from various models continue to depict the potential for strong momentum transfer if we can mix deep enough. Gusts of 30 to 35 mph may be possible late Wednesday morning through sunset. Otherwise, a dry cold front will pass through central NC Wednesday night. Overnight lows will be a bit warmer though as winds stay stirred behind the front and we only radiate down into the upper 20s/lower 30s.

LONG TERM /FRIDAY THROUGH TUESDAY/

As of 1255 AM Wednesday...

* Main story in the extended is much below normal temperatures Sun night and Mon, with wind chills early Mon in the single digits to teens

On Fri, a clipper system will track across the lower OH valley and into VA during the afternoon and evening. Pretty good WAA will build over the region as a warm front lifts north. We would not be surprised if some virga or light precipitation exists across our far northern counties. But as the system looks right now, most of the energy is situated in VA so the main influence we will see is increasing cloud cover. Highs should top out in the mid 40s N to low 50s S.

More seasonal temperatures arrive on Sat in the wake of the Fri system with low 50s N to upper 50s in the south.

A strong Arctic cold front is still forecast to advance through the region Sunday evening, with cold high pressure in its wake on Mon. This front will largely pass through dry as NW downslope flow favors the best rain chances on the windward side of the Appalachians. However, the AI-GFS and AI-ECMWF are wetter than most ensemble members. For now, we kept a dry forecast in line with the model consensus, but would not be surprised if some isolated showers were around during the day Sun.

Well below normal temperatures will build behind the Arctic front, with mid teens to low 20s Mon morning and highs then in the mid 30s to around 40. Wind chills Mon morning could dip into the single digits to teens. Temperatures should moderate by Tue with highs back into the 40s.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

As of 1220 AM Wednesday...

Predominately VFR conditions are expected through the period, with occasional broken to overcast mid/high clouds streaming across the region.

There remains a low probability that shallow low-level moisture trapped beneath an inversion could result in brief MVFR ceilings around the Triad around daybreak, though guidance support has continued to diminish.

A 35-45 kt SW low-level jet will overspread the area tonight, likely resulting in low-level wind shear late tonight and mechanical turbulence after daybreak. This will transition to strong gusty winds at the surface as momentum mixes down with daytime heating. Expect sustained SW winds of 15 to 20 kts, gusting up to 25-35 kts from mid morning into the afternoon, decreasing after sunset.

Outlook: VFR conditions are expected to dominate through the weekend.

RAH WATCHES/WARNINGS/ADVISORIES

None.