textproduct: Raleigh

SYNOPSIS

A cold front will move south and across the Carolinas today, then stall near the Savannah Basin tonight, when high pressure will migrate across the Middle Atlantic. The front will return north across the Carolinas as a warm front Christmas Day, only to move south as a cold front again Thursday night. Cold high pressure will follow and ridge across the Middle Atlantic on Friday.

NEAR TERM /THROUGH TONIGHT/

As of 340 AM Wednesday...

* An unseasonably mild Christmas Eve, with patchy light rain possible over w-cntl NC Thu morning

A 590 dam sub-tropical high at 500 mb, extending across the upr TX Coast and nwrn Gulf, will remain. A ridge extending from the high and nwd across the Plains --one that broke monthly record 500 mb heights across several upr air sites over the cntl Plains and mid MS Valley on Tue, and with underlying record warmth at the surface-- will be briefly dampened by a shortwave perturbation that will progress around it and into the srn Middle Atlantic by 12Z Thu. Accompanying and slightly preceding that shortwave perturbation, a zone of relatively strong and deep lwr/mid-level WAA will progress across the Appalachians late tonight-Thu morning. The models depict a relative maximum of this WAA over w-cntl NC and srn VA at 925 mb around 12Z Thu.

At the surface, the frontal zone that retreated nwd and across cntl NC on Tue, now located over e-cntl VA and which separated at 08Z 30s F from the ern part of the Commonwealth from rather remarkable lwr 60s (~30 F above average) at ROA and CHO, will return swwd and across cntl NC as a backdoor cold front today. The front will stall near and probably just northeast of the Savannah Basin tonight. Following and forcing that front swwd, ~1025 mb high pressure now over OH/IN will migrate quickly sewd and across and offshore the srn Middle Atlantic through 12Z Thu.

Despite the progression of the backdoor front across cntl NC today, temperatures will remain mild given more dry air advection than cold behind it, nnwly downslope flow that will weaken from ~40 kts this morning to 15-20 kts by sunset, and mostly sunny skies that will be interrupted by a short period of orographic cirrus over the wrn Piedmont this morning and another plume of high-level moisture around sunset. Temperatures will consequently be well above average and range from mid-upr 60s across the nrn Piedmont and Coastal Plain to lwr 70s elsewhere. Low temperatures tonight will range from mid/upr 30s in the nrn Coastal Plain and ne Piedmont to mid/upr 40s over the srn and wrn Piedmont, with the latter regulated by MVFR range ceilings and an associated chance of patchy, light rain that will progress with the aforementioned 925 mb WAA regime across w- cntl NC after 06Z.

SHORT TERM /THURSDAY AND THURSDAY NIGHT/

As of 400 AM Wednesday...

* Continued unseasonably mild on Christmas, but with warming slowed through the morning by multi-layered ceilings and patchy light rain that will progress ewd and out of cntl NC through the afternoon

A shortwave perturbation in nwly flow aloft, and preceding low/mid- level WAA regime, will progress across and offshore the srn Middle Atlantic early Thu. A sub-tropical high over the Gulf, and ridge initially extending across the Plains and MS Valley, will otherwise break down and yield increasingly-zonal flow across the mid- latitudes by Thu night.

At the surface, the wavering frontal zone that will have settled to near and northeast of the Savannah Basin Wed night will retreat newd and across the Carolinas as a warm front Christmas Day, only to move south as a cold front again Thursday night. Cold high pressure will follow and ridge across the Middle Atlantic Thu night-Friday.

Multi-layered ceilings and patchy light rain/sprinkles, accompanying the aforementioned low/mid-level WAA regime, will progress ewd and out of cntl NC through early afternoon. Associated clearing, and deepening of the boundary layer/mixing, will cause swly surface winds to strengthen and gust up to 20-25 mph during the afternoon, with nearly persistence high temperatures ranging from upr 60s ne to lwr-mid 70s sw. Low temperatures will be equally persistence in the upr 30s ne to mid/upr 40s sw, with a short period of nely gustiness in CAA behind the backdoor front overnight, along with areas of post- frontal low overcast.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

As of 139 AM Wednesday...

Upper pattern: An anomalous ridge will de-amplify late Thursday as a short-wave moves east across the Ohio Valley Friday into Saturday. The ridge will briefly re-establish itself over the Deep South on Saturday ahead of a deeper trough will dig down from Canada and move across the eastern US late Sunday into Tuesday. Nwly flow and rising mid-level heights aloft will spread east across central NC Wednesday.

Friday: Guidance continues to trend colder with a potential short- lived wedge and associated nely flow on Friday. Rain chances are limited as the main forcing and anomalous moisture will remain north of us, but areas along the NC/VA border may see some light rain Friday. Regardless, persistent nely flow and cloud cover will keep temps down in the lower 40s (NE) to mid 50s (SW). Any lingering rain should erode and exit to our east Friday night as sly flow re- establishes over our area. Overnight lows in the mid 40s are expected friday night.

Saturday through Wednesday: After a dry and warmer Saturday (highs in the upper 60s to lower 70s), a more amplified system will push across the eastern US Sunday into early next week. Guidance has trended slower with the arrival of a strong cold front and associated CAA. Most guidance now has the front moving across central NC early Monday, with CAA ramping up later during the day. As such, highs on Monday will likely by higher than previously thought, reaching the upper 40s to mid 50s. Still expecting some stronger post-frontal nwly gusts of 20 to 30 mph Monday afternoon into the early overnight period Monday night. Temps will drop into the lower to mid 20s early Tuesday morning. Highs on Tuesday will struggle to reach the upper 30s while overnight lows drop into the mid to upper teens.

Rain chances will peak Sunday night into Monday morning with the frontal passage. Overall though ensembles continue to highlight low QPF with this system (95th percentiles amongst ensembles peak around a few hundreds to a few tenths of an inch of rain).

Low-level thicknesses remain lower through the end of the week with a potentially re-enforcing cold front Thursday into Friday. As such, current signs show the potential for a chilly start to the new year.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

As of 730 AM Wednesday...

VFR conditions, with mainly just periods of cirrus and cirrostratus, are expected through most of the TAF period. However, an area of mostly MVFR ceilings are forecast to develop across the NC Foothills and wrn Piedmont after 06Z, with an associated likely probability of those ceilings reaching INT and GSO around 09-10Z Thu, along with an accompanying small chance of patchy light rain. A dry cold front will otherwise move south across cntl NC today and cause initially light wswly surface winds to veer to nly and strengthen/briefly gust into the teens kts between 15-18Z, before continuing to gradually veer through nely, while weakening, through the afternoon-evening.

Outlook: A cold front and band of post-frontal, MVFR ceilings, to perhaps IFR ones at its leading, will move swwd and across cntl NC Thu night. The frontal zone will continue to waver across NC through the weekend, with related periods of mostly MVFR ceilings most likely on Fri and again Sat night-Sun.

RAH WATCHES/WARNINGS/ADVISORIES

None.