textproduct: Raleigh

WHAT HAS CHANGED

* Weather parameters will be supportive of Increased Fire Danger and possible Red Flag conditions Monday.

KEY MESSAGES

As of 540 AM Sunday...

1) It will be noticeably cooler and breezy behind a cold front today, with a chance of light, stratiform rain in the morning and clearing through the afternoon-evening.

2) Patchy frost will be possible over rural nrn Piedmont locations tonight, then again over most of cntl NC (except perhaps the srn Sandhills and srn Coastal Plain) Tue morning.

3) Weather parameters will be supportive of Increased Fire Danger and possible Red Flag conditions Monday.

4) Aside from Tuesday, temperatures will be above normal through the extended forecast period. Dry through the end of the work week, with the next chance of rain over the weekend.

DISCUSSION

As of 540 AM Sunday...

KEY MESSAGE 1... It will be noticeably cooler and breezy behind a cold front today, with a chance of light, stratiform rain in the morning and clearing through the afternoon-evening.

A couple of shortwave perturbations, evident in GOES-E water vapor satellite data over the mid and upr MS Valley this morning, will pivot across the Great Lakes and upr OH Valley today and nrn Middle Atlantic and srn QC tonight. Glancing but seasonably strong 500 mb height falls of 60-100 meters will result across cntl NC today. A strong low-level frontal zone, strongest along and nearest the upr feature's path across the Middle Atlantic, will progress across the Carolinas and offshore by mid-afternoon.

The passage of the surface cold front, which at 07Z stretched from ern NY and cntl PA swwd through ern WV, swrn VA, and along the TN/NC border, will be marked by the arrival of markedly cooler air and nwly winds that will gust up to 30-35 mph, strongest for a few hours immediately post-frontal passage. A band of light, anafrontal rain and widespread clouds will also follow the front, with both expected to move east and yield afternoon through evening clearing. Rainfall amounts are expected to be spotty and very limited: a Trace to a few hundredths over srn zones to perhaps a tenth of an inch or so over the ne Piedmont and nrn Coastal Plain.

KEY MESSAGE 2... Patchy frost will be possible over rural nrn Piedmont locations tonight, then again over most of cntl NC (except perhaps the srn Sandhills and srn Coastal Plain) Tue morning.

Following today's cold frontal passage, Pacific high pressure will briefly extend across the Southeast through Monday. A reinforcing, polar cold front will settle swd and across cntl NC late Mon afternoon through evening. Canadian high pressure will then build across and offshore the Middle Atlantic Monday night and Tuesday.

Strong radiational cooling of the post-frontal airmass tonight will favor low temperatures in the mid-upr 30s over rural Piedmont locations to lwr-mid 40s elsewhere, supportive of patchy frost in typically cooler, rural locations over the nrn Piedmont. The colder, Canadian high will become centered around 1030 mb over VA by 12Z Tue and support even chillier temperatures over cntl NC Tue morning, with lows likely to range from around freezing over the far nrn Piedmont and nrn Coastal Plain to upr 30s to around 40 F along the SC line. Although surface (2-meter) dewpoints will likely be in the 20s F during that time, with associated marginal RH values for frost development, ground-level RH should be higher and adequate for at least patchy frost development.

KEY MESSAGE 3... Weather parameters will be supportive of Increased Fire Danger and possible Red Flag conditions Monday.

Wly to nwly flow, within a deep, well-mixed boundary layer of 7-9 thousand ft AGL, will result both ahead of and behind a cold front forecast to settle south across cntl NC during the afternoon- evening. With that strong and deep mixing, and momentum transfer of 30-35 kts at its top, related surface winds will likely average mid to upr teens mph, with frequent gusts of 25-30 mph and infrequent peaks to around 35 mph. Given the already dry airmass that will have been deposited behind today's cold front, RH will likely reach critical values of 25% during the morning (probably by ~10 AM) over the srn Piedmont and Sandhills, then elsewhere over cntl NC by afternoon, when widespread 15-25% minimums will be likely. Confidence is above average on these criteria being met, with maximum temporal overlap and duration across the srn Piedmont and Sandhills. A band of altocumulus along the front may locally and briefly limit otherwise strong insolation and dry adiabatic mixing and peak gust potential over the nrn Piedmont and nrn Coastal Plain, such that the temporal overlap of critical wind and RH there may be limited to just a couple or so hours. Coordination of possible fire weather headlines will likely be needed with NCFS and surrounding WFOs later today.

KEY MESSAGE 4... Aside from Tuesday, temperatures will be above normal through the extended forecast period. Dry through the end of the work week, with the next chance of rain over the weekend.

Aloft, the longwave trough will shift ewd and offshore Tue/Tue night. The ridge will progress ewd across the CONUS through the week, to over the region by the end of the week. At the surface, the ~1030 mb high over the mid-Atlantic Tue morning will move ewd across the region and offshore by Tue night. A low may track ewd across the Northeast or nrn mid-Atlantic Wed/Thu, but should stay north of NC. Uncertainty increases beyond Thu as model spread increases. Highs Tue will still be below normal, mid 60s NE and east to low 70s SW. Above normal temperatures may return by Wed, with a moderating trend through the work week. The weather should largely remain dry through the week, however the guidance still shows a signal for some rain over the weekend, though timing and amounts are uncertain.

AVIATION /10Z SUNDAY THROUGH THURSDAY/

As of 540 AM Sunday...

A cold front and following band of low VFR ceilings and patches of light rain will move across cntl NC this morning, during which time ceilings may briefly lower to MVFR near and northeast of RWI. Generally light sswly surface winds ahead of the cold front will veer sharply to nwly and become strong and gusty behind it, strongest in the first few hours immediately following its passage.

Outlook: Shallow radiation fog will be possible over ern NC, including near and probably just east of RWI, late tonight-Mon morning, where low level moisture characterized by surface dewpoints in the 30s to around 40 F will linger.

RAH WATCHES/WARNINGS/ADVISORIES

None.