textproduct: Raleigh

SYNOPSIS

A vigorous mid and upper-level disturbance will move across VA and NC through this evening, then offshore. Arctic high pressure will follow and build across the region through Tuesday. The high will settle across the Southeast ahead of a strong, clipper low pressure system that swing across the Great Lakes Tuesday night and Wednesday. A moisture-starved cold front trailing the clipper low will move across NC Wednesday night.

NEAR TERM /THROUGH TONIGHT/

As of 245 PM Sunday. . .

*A Winter Weather Advisory in effect through 12pm Tuesday for portions of the northern Piedmont and northern Coastal Plain of central NC.

*Up to an inch of snow accumulation is possible, highest along the immediate NC/VA border, with lesser amounts south. Isolated areas near the VA/NC border could receive up to 2 inches of snow.

*Any leftover moisture on surfaces are expected to freeze Monday night resulting in areas of black ice Tuesday morning, thus the extension for the Winter Weather Advisory through noon on Tuesday.

We are currently seeing a rain/snow mix line extending from just south of Roanoke Rapids down towards Asheboro. Drying has already begun across the western Piedmont with lingering snow showers across the Northwest Piedmont. Expect these snow showers to taper off this afternoon, over the next few hours. For the Triangle region many surface reports have been mainly rain-snow around the Durham area with a slow change over expected across the Raleigh/Wake County area in the next hour or so. Since there is drying aloft and the dry air within the column is making its way to the surface quickly, I would not expect a long lived all snow event for the Triangle area but as mentioned in previous discussions a quick burst of light snow before the end of the event. If any snow does fall, accumulations shouldn't be an issue for the Triangle region as temperatures are still just above freezing and wet snow flakes are expected to melt on contact with the warmer surfaces. However motorists should use extra caution with wet slippery roads this afternoon/evening. To the north of the Triangle, near the VA border we continue to see snow coming down with reports from Roxboro and Henderson of light snow falling across the region with accumulations only occurring on grassy and elevated surfaces. This band is expected to move across the northern Piedmont and into the Northern Coastal Plain over the next few hours, continuing as all snow. Latest model data shows a slight increase in amounts across the Northern Coastal Plain and areas along the VA border with this band as rates are expected to slightly increase the last few hours as it exits the area. All the precip is expected to exit the western portion of CWA over the next hour or so, and continue to clear the region through late evening. Temperatures are expected to crash as the cool dry air moves into the region with overnight lows in the mid to upper teens across the north to low/mid 20s US-64 south. As the shortwave exits the area later this evening, winds are expected to pick up as precip moves out with gusts up to 25 mph. Winds will calm down before sunrise as high pressure settles overhead.

SHORT TERM /TUESDAY AND TUESDAY NIGHT/

As of 335 PM Monday...

* Arctic cold, and dry

Behind the vigorous shortwave trough that will have moved off the Middle Atlantic coast by the start of the period, heights aloft will rise across the Carolinas on Tuesday. Meanwhile, another shortwave perturbation now over the far nern Pacific, and dominated by shear vorticity and with model-analyzed upper-level winds of 150-175 kt, will dig sewd across the nrn Plains, then amplify sharply across the upr Midwest Tue night. Associated strong subsidence over cntl NC early Tue will weaken with time, but it will have a lasting dry influence through the lwr/mid-levels through Tue night. There will, however, be periods of considerable cirrus and cirrostratus that may become orographically-enhanced and regionally-maximized over the srn Middle Atlantic Tue afternoon through early Wed.

At the surface, Arctic high pressure now centered at 1029 mb over MI will weaken while migrating swd and across the middle Atlantic and Carolinas Tue, then into nrn FL by 12Z Wed. It will do so downstream of a clipper low that will deepen into the 980s millibars over MI, 3- 4 sigma below average, by 12Z Wed. After light and variable winds within the Arctic surface ridge Tue, the MSL pressure gradient will tighten markedly over cntl NC between the ridge and the anomalously deep clipper low and favor the development of a swly breeze Tue night.

After a very cold start to the day, and an icy one where snow accumulated and/or the ground was adequately soaked by rain (eg. at least several hundredths of an inch), temperatures will only rise to afternoon highs in the mid/upr 30s across the nrn Piedmont and nrn Coastal Plain to lwr-mid 40s elsewhere. Then despite the presence of the Arctic airmass, the aforementioned developing swly surface wind, and also high clouds that will probably thicken and lower with time through Wed morning, will keep overnight lows within a category or two of climo - mostly mid-upr 20s.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

As of 230 AM Monday...

* Gusty winds Wed with winds up to 30 mph possible

* Precipitation chances somewhat limited with a few moisture starved frontal systems.

* Well below normal temperatures favored for the late weekend

High pressure will shift offshore Wed. A fast-moving low pressure system tracking across the Lower Great Lakes will create a tightened pressure gradient across the region. Southwest winds could gust up to 30 mph or so at times during the afternoon hours as guidance depicts a strong low-level jet upwards of 50-kts. The pressure gradient relaxes Wed night as a moisture starved cold front advances through by early Thu. Precipitation chances appear very limited with this front. Temperatures should moderate closer to average with highs in the 50s and lows in the 30s.

Cool high pressure settles over the region Thu, with highs below normal generally in the mid 40s to near 50.

Our next system looks to arrive sometime Fri/Fri night when a warm front lifts north across the Carolinas. This will be ahead of another potentially strong Arctic cold front that tracks through sometime Sat-Sun, ushering in much below normal temperatures with highs possibly in the upper 30s to low 40s and lows in the teens to low 20s. For the warm front Fri, ensemble guidance is largely dry, with moisture and lift somewhat lacking. However, if it were to trend wetter, we could not rule out a rain/snow mix. Confidence in that scenario, however, is not high at the moment. The Arctic front Sat into Sun appears right now as a dry passage, with impacts mainly centered around very cold temperatures as wind chills could be in the lower teens Sun morning.

AVIATION /18Z MONDAY THROUGH SATURDAY/

As of 110 PM Monday...

A precipitation shield now blossoming across cntl and ern NC will include ongoing snow at INT/GSO and a transition to snow at RDU and RWI in the next couple of hours. While the predominant precipitation type at FAY will be a cold rain, a mix with snow will be possible for a few hours around and shortly after sunset. Otherwise, a mix of IFR-MVFR restrictions in both ceilings and visibility restrictions will lower a category on average through late this afternoon-early this evening, lowest and longest at RWI, then gradually lift through MVFR overnight and scatter to VFR Tue morning. Nely surface winds will also be at least occasionally gusty, as the MSL pressure gradient tightens between deepening low pressure off the coast of the Carolinas and Arctic high pressure that will build south across the region tonight.

Outlook: VFR. Low-level wind shear will be possible, especially over the Piedmont, Wed morning, followed by the development of a strong and gusty swly surface wind with daytime heating/mixing through Wed afternoon.

RAH WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 7 AM Monday to noon EST Tuesday for NCZ007>011-021>028-041>043.