textproduct: Raleigh

SYNOPSIS

Surface high pressure over the area will shift offshore this afternoon, as a weakening clipper low and attendant warm front lift north along the SC-NC state line. This lead front will stall across the area Saturday, ahead of an Arctic cold front that will move in central NC late Saturday night and Sunday.

NEAR TERM /TODAY/

As of 250 AM Friday...

* Light snow accumulations possible along the Va border across northern portions of the Piedmont and Coastal Plain this morning with little to no impacts.

Weak, clipper disturbances rotating eastward through the long wave trough in place across the Eastern US will brush northern portion of the forecast area today. At the surface, high pressure over the area will shift offshore this afternoon, as a weakening clipper low and attendant warm front lift north along the SC-NC state line. Driven by these weak disturbances and warm air advection aloft, a narrow stripe of light accumulating snow is possible along the Virginia bordering counties across northern portions of the Piedmont and Coastal Plain counties through mid to late morning, possibly mixing with light rain before tapering off early afternoon. A light dusting is possible across these far northern counties. Otherwise, expect flurries or sprinkles with limited coverage and little to no impacts.

The north-south contrast in cloud cover/thickness and precip chances will yield a sharp temperature gradient, with highs ranging from upper 30s north to lower/mid 50s south.

Mid-level cloud bases should scatter out this evening, periodic broken to overcast cirrus will persist overnight, especially across the northern half of the area. Lows will fall into the mid/upper 20s north to lower 30s southeast.

SHORT TERM /SATURDAY AND SATURDAY NIGHT/

As of 250 AM Friday...

* Seasonable Saturday followed by increasing clouds Saturday evening/night and limited precipitation chances.

Heights aloft will rise Saturday as synoptic scale subsidence briefly takes hold, though this will be short-lived. An amplifying northern stream trough/upper low will dig southeastward into the Eastern US Saturday night into Sunday. At the surface, a lingering frontal zone across southern portions of the forecast area will become increasingly ill-defined through the day, while the leading edge of an Arctic cold front approaches and moves into central NC late Saturday night and Sunday.

Pre-frontal warming ahead of the cold front will support one day of seasonable to slightly above-normal temperatures, with mostly sunny skies and highs ranging from the lower to middle 50s north to upper 50s/near 60 south.

By Saturday evening, strengthening upper jet dynamics--including increasing upper divergence within a 140 kt jetstreak, H5 falls of 60 to 80m, and multi-layer frontogenetic response--will result in increasing cloud cover Saturday evening/night. Precip chances along the front appear quite limited across the area Saturday night/early Sunday morning, with the strongest moisture transport directed across eastern NC. The best precip chances look to be ana-frontal, occurring in the true Arctic air arrives 12-18z Sunday.

For now, a slight chance PoP is maintained for Saturday night, with rain expected to be the predominate precip-type. A brief rain-snow mix cannot be ruled out across the far NW Piedmont towards daybreak. In this cold-air-chasing-moisture set-up, snow accumulations are typically on the low end, resulting in minor to no impacts.

LONG TERM /SUNDAY THROUGH THURSDAY/

As of 250 AM Friday...

* Bitter cold temperatures and wind chills Sunday night through Mon morning behind a strong Arctic cold front

* Moderating temperatures with highs possibly in the 60s by Thu

The main story in the extended continues to be dangerously cold temperatures set to arrive Sunday late afternoon through Mon behind a strong Arctic cold front. The low-level thickness values will be near minimums for mid-December and a strong near 1040 mb Arctic high will settle over the region Mon.

There is a slim chance of some precipitation ahead of the front Sun morning, but guidance has been trending dry - the best chance is along/east of US-1. While the front will move through Sun morning, the Arctic air will likely get hung up until the evening. We should see highs in the upper 30s NW to upper 40s SE. But by Sun evening, temperatures will crash into the teens and 20s, eventually falling into the low to mid teens by Mon morning. NW wind gusts will start to pick up Sun afternoon in the 20 to 30 mph range, but increase Sun night with strong CAA. Gusts Sun night of 30 to 40 mph look quite plausible based on forecast soundings from the NAM/GFS, before weakening early Mon. The combination of very cold temperatures and the winds will make for single digit wind chills area wide. A Cold Weather Advisory will likely be needed.

The upcoming week will start off very cold with only mid/upper 30s for highs and upper teens to low 20s for lows Mon night.

Guidance shows a warming trend Tue through Thu as mid-levels transition from NW flow to a quasi-zonal flow. Return flow sets in at the surface in tandem. Highs should rise from the upper 40s Tue to possibly well above normal in the lower/mid 60s Thu. There is quite a bit of spread in the guidance for our next chance of rain, but the best chance appears on Thu. Confidence remains low such that the extended looks mainly dry.

AVIATION /11Z FRIDAY THROUGH TUESDAY/

As of 600 AM Friday...

24 hour TAF period:

Driven by weak disturbances and warm air advection aloft, intermittent light snow or flurries will overspread mainly northern terminals through mid to late morning, possibly mixing with light rain before tapering off early afternoon. Coverage and intensity appears too limited for any restrictions. Otherwise, VFR ceilings are expected with cloud bases between 5 to 10 kft.

Winds will be light and variable, with dry weather and decreasing mid-level cloud cover during the evening and overnight hours.

Outlook: Patchy fog and/or stratus will be possible Sat morning, mainly at the northern terminals. A warm front and lift will result in a chance of rain and flight restrictions Sat night-early Sun, followed by strong and gusty nnwly surface winds behind a passing, Arctic cold front Sun afternoon into Sunday night.

RAH WATCHES/WARNINGS/ADVISORIES

None.