textproduct: Raleigh

WHAT HAS CHANGED

As of 325 PM Thursday...

* Scattered showers and perhaps an isolated storm will accompany a pre-frontal trough/confluence axis across cntl NC on Fri. They will be followed by a dryline that will move across wrn NC and likely into the srn and wrn NC Piedmont by late afternoon. Swly winds will gust between 25-35 mph ahead of them, followed by equally gusty wly ones behind them. Critical fire weather conditions may briefly result over the wrn/srn Piedmont by late Fri afternoon.

KEY MESSAGES

As of 325 PM Thursday...

1) A front, and focus for rain along and to its north, will waver over northern NC through Fri morning, with continued unseasonably mild/warm and near record temperatures to its south and throughout most of cntl NC.

2) A pre-frontal trough/confluence axis and focus for scattered showers and perhaps an isolated storm will move across cntl NC on Fri. Meanwhile, a dryline will likely move across wrn NC and into the srn and wrn NC Piedmont by late afternoon. Critical fire weather conditions may briefly result over the wrn/srn Piedmont Fri afternoon.

3) Continued forecast uncertainty Friday night through Monday, with details dependent upon the track, timing, and strength of a low as it moves across the Southeast US/Carolinas and off the East Coast.

4) Below normal temperatures expected early to middle of next week.

DISCUSSION

As of 325 PM Thursday...

KEY MESSAGE 1... A front, and focus for rain/drizzle along and to its north, will waver over northern NC through Fri morning, with continued unseasonably mild/warm and near record temperatures to its south and throughout most of cntl NC.

1020 mb high pressure now centered over srn new England will probably cause the backdoor front now over nrn NC to settle slightly swd into cntl NC tonight. The associated low overcast, rain/drizzle, and mist/fog now over VA will consequently edge swd and across the nrn NC Piedmont and nrn Coastal Plain overnight. While rainfall amounts from this regime in cntl NC will be very light and just a few hundredths of an inch, with heavier amounts nwd into VA, some briefly heavier showers may also launch along the boundary through tonight. Those showers, like the few now over the nrn Coastal Plain, will likely be surface-based ones with afternoon heating and elevated ones overnight, with both supported by weak CAPE through an uncapped thermodynamic profile with modest, ~6C/km mid-level lapse rates sampled by the 12Z GSO RAOB. Forecast low temperatures will be above the average high temperature for mid Feb and near daily record high mins.

KEY MESSAGE 2... A pre-frontal trough/confluence axis and focus for scattered showers and perhaps an isolated storm will move across cntl NC on Fri. Meanwhile, a dryline will likely move across wrn NC and into the srn and wrn NC Piedmont by late afternoon.

A mid-level cyclone will deepen while progressing from the cntl Plains this afternoon to the Great Lakes by Fri, with associated height falls and forcing for ascent that are forecast to only glance the srn Middle Atlantic (mostly north of cntl NC). At the surface, the backdoor front will likely retreat nwd across nrn NC and srn VA with daytime heating through midday Fri. Meanwhile, a pre-frontal trough and dryline will move across NC Friday afternoon and be followed by a cold front Friday night. Given the only glancing forcing for ascent at the latitude of cntl NC, lift will likely be shallow and confined to the surface features, with only scattered showers and/or an isolated storm along the pre-frontal trough. The moist sector ahead of them will be characterized by unseasonably warm, humid, and weakly unstable air, with swly winds that will gust between 25-35 mph. A sharply drier, but still unseasonably warm and deeply mixed boundary layer, with equally strong wly wind gusts, will follow them and likely reach the srn and wrn Piedmont by late afternoon. Near record temperatures will result, as will critical or nearly so fire weather conditions over the wrn/srn Piedmont, briefly, Fri afternoon.

KEY MESSAGE 3... Continued forecast uncertainty Friday night through Monday, with details dependent upon the track, timing, and strength of a low as it moves across the Southeast US/Carolinas and off the East Coast.

Overview: Aloft, the low over the Great Lakes on Fri will continue ewd across the Northeast US Fri night, getting picked up by a larger area of low pressure moving across/north of the Canadian Maritimes. Meanwhile, another s/w will move off the cntl Rockies and track ewd across the Plains within the broadening longwave trough Fri night. The longwave trough will amplify as the s/w continues ewd across the mid/upr MS Valley Sat/Sat night. The medium-range guidance is in fairly good agreement closing off a low over the Great Lakes Sat night as the leading s/w tracks across the TN/OH Valley. The models are still not in agreement with the evolution of the low, and the embedded s/w disturbances swinging around it, thereafter. Generally expect the parent low to track across the mid-Atlantic (possibly as far south as NC), with one or two shortwaves passing over the area between Sun morning and Mon night/Tue. At the surface, as the low moves ewd and away from the New England coast Fri night, the front will progress ssewd across the area, becoming quasi-stationary and draped generally W-E across the Southeast US/Carolinas. A low is expected to develop along the front over the lower MS Valley Fri night/Sat (timing and location still vary amongst the medium-range guidance), then track ewd or newd along the front, across the Southeast US/Carolinas and eventually offshore through Saturday night/Sun. This low is expected to rapidly deepen once it moves offshore, however the track and strength of the low during that time remain uncertain, resulting in continued low confidence in forecast details (wrt precipitation, winds, etc.).

Precipitation: There will likely be a lull in precipitation in the wake of the front Fri night. Rain chances increase from the south Sat/Sat night as the low tracks along the front. The farther north the low tracks, the higher rain chances will be across central NC and the slower it moves across the region, the longer rain may last. Some additional precipitation will be possible Sun night/early Mon as the low aloft moves across the mid-Atlantic and the surface low deepens offshore, however it will depend on the evolution of both features, which continues to be uncertain.

Temperatures could still be above normal Sat/Sat night, with the front just south of the area (possibly lifting northward back into it) and the coldest air largely staying north of the area. Once the low moves out/away Sun, the front will move ewd and off the Carolina and Southeast US coasts and nwly flow will strengthen over the area, allowing for cold air to finally advect in and temperatures to swing back to near/below normal.

Winds: The pressure gradient will strengthen between the deepening low along/off the coast and the strong Arctic high ridging swd across the Plains on Sunday, and remain quite strong through at least Mon night. Additionally, in proximity to the deepening low, a very strong LLJ may develop, with winds upward of 50 kts at the top of the mixed layer possible over northeast portions of the area. Expect breezy to windy conditions to prevail, with strong gusts possible at times.

KEY MESSAGE 4... Below normal temperatures expected early to middle of next week.

There is relatively high confidence temperatures will be below normal Mon and Tue, with nwly flow in the wake of the front/low and Arctic high pressure building swd across the Plains then progressing ewd. Temperatures could rise back to near normal Wed, while the high gradually modifies as it tracks ewd across and out of the region.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

As of 645 PM Thursday...

The development of IFR ceilings is expected overnight. Those ceilings may be accompanied by visibility restrictions in both drizzle and mist/fog along and north of the front, including at all but FAY, and also low-level wind shear, through around 12z Fri morning.

Flight restrictions will gradually improve with daytime heating and the nwd retreat of the warm front into VA through Friday afternoon. SW winds will increase to 15-20 kt with gusts to 25 kt.

Scattered showers or an isolated storm will accompany a weak cold front as it moves across cntl NC during the midday through afternoon hours, followed by markedly drier air and a high probability of VFR conditions.

Outlook: A cold front will move across cntl NC Fri night and stall over SC by early Sat. That front will be a focus for the development of a couple of areas of low pressure and associated periods of rain and additional flight restrictions over the Carolinas this weekend.

RAH WATCHES/WARNINGS/ADVISORIES

None.

CLIMATE

Record High Temperatures:

February 19: KGSO: 74/1939 KRDU: 76/1939

February 20: KGSO: 74/1922 KRDU: 75/1939 KFAY: 82/2014

Record High Minimum Temperatures:

February 19: KGSO: 55/1961 KRDU: 62/1938 KFAY: 62/1938

February 20: KGSO: 56/1939 KRDU: 62/1939 KFAY: 60/1939