textproduct: Raleigh

SYNOPSIS

A cold front will move across central and eastern NC, then offshore, this morning. Cold high pressure will migrate quickly across and offshore the Middle Atlantic today and tonight, ahead of low pressure that will develop and rapidly strengthen from the Southeast to the Middle Atlantic coast on Tuesday.

NEAR TERM /TODAY THROUGH TONIGHT/

As of 245 AM Monday...

* Dry through the day, with rain chances returning late tonight.

* Below normal high temperatures, with near normal lows.

A cold front will continue to push through central NC overnight, exiting the region by daybreak this morning. This will allow for high pressure to pass north of the region through the Great Lakes region and into the northeast US, setting up another wedge airmass by afternoon/evening. At the same time, a trough and associated cold front will start to approach from the west late tonight as a low pressure system starts to form and moves up the southeast coast. This will allow for a soaking rain to start spreading into the region from the west shortly after midnight. The HREF 6 hour local probability matched mean shows generally 0.15 to 0.75 inches of rain between 1 and 7am for central NC, with the greater values to the west. Widespread rain will continue into Tuesday.

High temperatures should be about 10 to 15 degrees below normal this afternoon. This will equate to highs in the mid 40s north to around to slightly above 50 in the south. Overnight lows will dip to near freezing in the north to low 40s in the south. Temperatures look to be above freezing when and where rain will fall late tonight.

SHORT TERM /TUESDAY AND TUESDAY NIGHT/

As of 340 AM Monday...

* A cold, soaking rain early Tue will yield to west to east drying and clearing during the afternoon and especially Tue night

A shortwave trough comprised of a couple of perturbations now stretching across the Four Corners and Southwest will have reached the OH to lwr MS Valleys by 12Z Tue and lift across and offshore the Middle Atlantic and Carolinas late Tue-Tue night. A strong low through mid-level WAA regime, and plume of anomalous moisture characterized by PWs around 200% of normal, will precede the trough and be swept across and offshore the Carolinas through early Tue afternoon.

At the surface, the center of a 1035 mb, Arctic high now centered over IA will migrate quickly ewd and reach Nova Scotia by 12Z Tue, while steadily weakening to near 1025 mb. A narrow, in-situ cold damming ridge will extend swwd from the transitory and weakening high and across the favored cold air damming region across the Carolinas and neighboring VA and GA on Tue, while coastal low pressure will rapidly deepen from around 1010 mb along the coast of the Carolinas Tue morning to around 980 mb off the Nova Scotia coast Wed morning. Through the same time, a weaker high than the first, centered around 1025 mb over the srn Plains Tue morning, will migrate ewd and into the OH and TN Valleys, with associated cold and dry air advection that will spread east of the Appalachians and across cntl NC Tue afternoon and night.

The transitory and weakening nature of the Arctic high is not favorable for wintry precipitation in cntl NC, where forecast partial thickness and surface wet bulb freezing values, and the top- down approach from point soundings, all indeed suggest just a cold rain. Storm total rainfall amounts are expected to range from around 0.75" over the nw Piedmont to around 1.5" in the Coastal Plain, the latter where where low-level Fgen and weak elevated instability nearest the deepening cyclone will probably yield a swath of highest totals.

It will be a cold and raw morning amid widespread rain and peak cold air damming, when temperatures will be in the mid/upr 30s over the nw Piedmont to lwr 40s in the Coastal Plain. However, the departure of the rain shield, and downslope flow and CAA in the stable CAD layer, will likely yield east to west erosion of the CAD airmass behind the coastal low (a CAD erosion scenario) during the afternoon and evening, when temperatures will moderate through the 40s, to perhaps lwr 50s over the srn/wrn Piedmont. A clear and colder Tue night will follow, with temperatures mostly in the 20s.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

As of 400 AM Monday...

Downstream of a positive tilt trough that will extend from Four Corners and Southwest, swwd through a cyclone over the sern N. Pacific, fast/quasi-zobnal flow will prevail across the Southeast and Carolinas. To what degree and how quickly shortwave energy from that positive tilt trough ejects ewd will have ramifications on downstream vertical motion and contribution to cyclogenesis near the coast of the Carolinas Fri-Sat. While forecast confidence is below average in that regard, the trend in model guidance has been toward generally more suppressed and drier solutions, driven mostly by a plume of mid-level WAA and Fgen, and such that precipitation centered around Fri-Fri night will very likely be much lighter than this Tuesday's system.

At the surface, high pressure will weaken while migrating across and offshore the Southeast Wed-Thu, ahead of a dry cold front that will lead an Arctic high across the Middle Atlantic and into the Carolinas Thu night-early Fri, then quickly offshore by Fri night. A wavy frontal zone draped from the nrn Gulf to just offshore the Southeast coast may allow for at least a couple of episodes of, as it appears at this time, weak cyclogenesis Fri-Sat.

The fast and progressive nature of the pattern described above will favor a continuation of transitory and weakening Arctic highs as they migrate across the Great Lakes and Middle Atlantic, then offshore, which is not favorable for more than nuisance wintry precipitation mostly at onset in cntl NC. Indeed, the aforementioned mid-level WAA regime would support adequate lift when partial thicknesses are initially supportive of snow if the precipitation were to arrive early in the day Fri, but with subsequent warming that would favor a relatively quick transition to rain. While there could also be an intervening, short period of light freezing rain over the nw Piedmont before surface temperatures rise above freezing, that too would be short-lived, self-limiting in the absence of a more favorably located and anchored surface high, and low impact.

Forecast confidence is even lower for Sun, but with a general signal for drier and less chilly conditions behind whatever transpires from the mostly light precipitation Fri-Sat.

AVIATION /12Z MONDAY THROUGH FRIDAY/

As of 645 AM Monday...

Last night's cold front has moved out of the region, leaving VFR conditions everywhere in the CWA. VFR conditions will prevail through the day today. Periods of gusty winds look possible this morning through early afternoon. It appears that FAY/RWI the best chance of gusting up to 20-22 kts, with INT/GSO/RDU having the potential for gusts in the teens. MVFR ceilings and light rain look to start moving into central NC around 06Z from the west and south, spreading over the region by 08Z. Ceilings look like they could drop quickly, with LIFR ceilings potentially covering the CWA by 12Z.

Outlook: Widespread rain will continue through Tuesday evening, bringing sub-VFR ceilings and visibilities. VFR returns Wed and Thu under high pressure. Another late-week system may bring rain/showers late Fri-Sat.

RAH WATCHES/WARNINGS/ADVISORIES

None.