textproduct: Raleigh

SYNOPSIS

A wedge front will develop and become quasi-stationary over the western Piedmont of the Carolinas and Virginia today and tonight, then be overtaken by a cold front that will sweep across the region Friday morning. Following high pressure will migrate quickly eastward and across and offshore the Southeast through Saturday.

NEAR TERM /THROUGH TONIGHT/

As of 245 AM Thursday...

* Increasing rain chances this evening and overnight, with rainfall of 0.25-0.50". * Winds gusts of 25-35mph this evening, with some sporadic gusts to 40mph possible later tonight and early Friday. * Locally dense fog possible around the Triad this evening and overnight.

At 06Z surface analysis showed high pressure east of NC extending across the south east US. Water vapor imagery shows a southern stream shortwave lifting across the lower Mississippi River Valley and a northern stream shortwave digging into the central Plains. High clouds are spreading across the southeast US in association with the southern stream wave and there are even a few light radar returns across north west NC associated with a weak disturbance crossing the Ohio Valley.

Moisture will increase today ahead of the approaching short waves, with a shield of rain and some embedded showers associated with the lead southern stream wave initially expected to break out across Georgia and upstate South Carolina and move north through the western Piedmont by late morning and this afternoon. A more robust area of precip should develop this evening with increasing influence of the northern stream trough, followed by a band of showers along the cold front more towards daybreak Friday morning. Overall rainfall amounts are expected to be 0.25 - 0.75 inch range, with the locally highest rain rates between 00-06Z based on current guidance.

Temperatures will range from the upper 60s in the southeast to upper 40s in the north west where a strong wedge front will develop. The current forecast leans heavily on MET guidance, which is much more reliable in CAD patterns. On the cooler western side of the wedge front, locally dense fog is possible by this evening, particularly across Forsyth County, although confidence in whether that fog will cover the entire Triad area is still a little uncertain.

The other concern with the system will be winds, which will initially be focused aloft with an increasing low level jet, but will gradually mix to the surface as dew points increase tonight. Gusts should generally be in a 20-30mph range with some sporadic gusts to 35mph or even 40mph in isolated showers and especially with those along the cold front Friday morning.

Thunderstorm potential is generally low as overall instability looks very limited and focused across areas east of I-95 where perhaps MLCAPE of 100 200 could materialize.

SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/

As of 230 AM Thursday...

Friday and Friday night: The strong cold front associated with the potent northern stream trough is forecast to move through central NC on Friday morning, ending in lingering threat of showers. The main weather impacts on Friday will come from windy conditions generally along and behind the cold front (possibly enhanced by any lingering showers too). Winds will become west to west-northwesterly behind the front, with wind gust up to 30 to 35 mph possible, with even a few stronger wind gusts possible. High temps are expected to range from the lower to mid 50s in the far northwest Piedmont to the mid 60s across southeast/eastern portions of central NC (with some locations not seeing much of a diurnal recovery, rather holding steady in the afternoon or falling).

Chilly high pressure will quickly build into the area Friday night. This coupled with the loss of diurnal mixing will allow for winds to decrease and temperatures to fall into the upper 20s to around 30 by Saturday morning, under clear skies.

Saturday and Saturday night: High pressure will shift to the east of the area and offshore on Saturday, allowing for a southerly return flow. Expect dry weather will continue under a general westerly flow aloft. High temps Saturday will be near normal, generally in the lower to mid 50s, with lows Saturday night expected to be in the mid to upper 30s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

As of 1140 PM Wednesday...

* Dry (mostly), with unseasonably mild conditions Sun and Wed that will bookend a couple of days of unseasonably cool ones Mon-Tue

An amplified but moisture-starved shortwave trough will progress from the lwr Great Lakes to Atlantic Canada Sun-Sun night. A prolonged period of wnwly flow will follow and prevail around a sub- tropical high and low amplitude ridge that will progress from Baja CA to the nrn Gulf and Gulf Coast states through mid-week. Within that regime, a mid-level frontal zone and band of WAA and lift will progress across the Appalachians and Middle Atlantic on Tue.

At the surface, cntl NC on Sun will likely be between a couple of frontal zones that will progress across the OH Valley/Middle Atlantic and Southeast, respectively, with the former a moisture- starved one that will likely move south and across cntl NC Late Sun into early Sun night. Following, continental Polar high pressure, strong and near 1040 mb over OH/WV at the start of the period, will weaken while building across and offshore the srn Middle Atlantic Mon-Tue, then settle into the Southeast on Wed. The presence and influence of the cP high and associated dry air will favor both cooler than average temperatures and mainly dry conditions, with the exception to the latter being a chance of light rain or sprinkles accompanying the aforementioned mid-level WAA regime and ceilings over the far nrn NC Piedmont on Tue. Return flow around the high will favor moderating/milder temperatures for Christmas Eve.

AVIATION /12Z THURSDAY THROUGH MONDAY/

As of 640 AM Thursday..

VFR to continue at GSO/INT through 15-18Z and RDU/FAY/RWI through around 18-21Z

Low level moisture will increase rapidly today ahead of a strong system approaching from the west. Expect to see low clouds and showers increasing from CLT to GSO/INT this morning by 15-18Z, with ceilings falling to IFR this afternoon widespread rain sets in several hours. In addition, fog is expected to develop and could become dense around INT and GSO this evening and overnight.

To the east, the lowering of ceilings will be a little slower with a few scattered showers late this morning and this afternoon, followed by a trend towards IFR tonight by around 00Z.

The system will also bring strong winds, initially aloft in the form of low level wind shear this evening, but with time we expect southerly wind gusts to around 25kt to more frequently reach the surface, and more isolated 30kt to 35kt gusts will possible later tonight and early Friday as the cold front moves through the area.

Outlook: A cold front will sweep across the area early Friday. Wind gusts of 20 to 25 kts will be possible Friday afternoon especially at KRDU/KRWI. VFR conditions will then persist through the remainder of the extended period.

RAH WATCHES/WARNINGS/ADVISORIES

None.