textproduct: Raleigh

SYNOPSIS

High pressure will build across and offshore NC through Friday morning. A warm front will develop northward across southern NC Friday afternoon, ahead of a clipper low that will track along it and offshore Friday night. Weak high pressure will follow for Saturday.

NEAR TERM /THROUGH TONIGHT/

As of 330 PM Thursday...

* No impact flurries or patchy light snow late tonight

Heights aloft will rise throughout the South and Middle Atlantic states behind an anomalously strong mid/upr-level cyclone forecast to progress across the Gulf of St. Lawrence. Within that regime of rising heights, intense low/mid-level WAA, now centered with an associated precipitation shield across IA/MO, will progress sewd and across the TN and OH Valleys tonight and into wrn and cntl NC by Fri morning.

At the surface, a 1018 mb high now over the lwr OH and TN Valleys will progress ewd and into cntl and ern NC tonight, downstream of a clipper low that will develop esewd and across the mid MS Valley.

Initially mainly clear skies, and developing calm after sunset, will favor excellent radiational cooling and decreasing temperatures into the upr 20s-low 30s this evening.

Multi-layered ceilings will then overspread cntl NC overnight, lowest and with greatest lift and saturation in a 5-10 thousand ft layer centered around 700 mb, where temperatures will range from around minus 6 C at its base to minus 12 C at its top. The cloud layer should consequently be a precipitation-producing one and with a shallow dendritic growth zone near its top. However, that mid- level-centered lift and saturation will exist above a substantial, ~6-8 thousand ft sub-cloud and deeply dry layer; and as such, mostly virga will result. The exception will be patchy light snow and/or flurries that may reach the ground over the nrn Piedmont, and nrn Coastal Plain around daybreak (roughly north of US 64), where the cloud/precipitation band will be maximized in both (relative) intensity and duration, and where associated top-down moistening will likewise be maximized. While surface temperatures will probably steady or rise slightly as clouds thicken, to around or perhaps just above freezing, partial thickness values and the top-down approach both favor snow as the predominant p-type. Given the expected very light nature of any snow that may reach the surface, little to no snow accumulation is expected.

SHORT TERM /FRIDAY AND FRIDAY NIGHT/

As of 400 PM Thursday...

* No, to very low, impact light snow/flurries possible across the far nrn Piedmont and nrn Coastal Plain Fri morning

The low/mid-level WAA regime described above will continue to translate enewd and across and offshore the srn Middle Atlantic Fri, amid otherwise broadly cyclonic that will remain in place.

At the surface, a warm front will develop northward across southern NC Friday afternoon, ahead of a weakening clipper low that will track along it and offshore through Friday night. Weak high pressure will follow and settle overhead by early Sat.

The cloud and precipitation band forecast to overspread cntl NC tonight, related to the aforementioned strong low/mid-level WAA, will persist especially over nrn NC through midday Fri, then gradually lift newd and across VA and offshore through early Fri night. Even the wetter NWP guidance depict less than 0.05" liquid equivalent precipitation over the far nrn Piedmont and nrn Coastal Plain between 12-18Z Fri. Little to no snow accumulation should result given both very light liquid equivalent amounts and also surface temperatures that will likely be rising through the low-mid 30s through the morning. The reasonable worst case scenario would be a light coating of a tenth on an inch or three mainly on elevated surfaces near the VA border between 7 AM and 11 AM, with probability of occurrence of that worst case only 10-20 percent.

A sharp gradient in both cloud cover, and surface temperatures owing to differential diabatic heating and associated Fgen across the surface frontal zone over srn NC, will result over cntl NC on Fri. Temperatures Fri will consequently display a large range from upr 30s near the VA border to 50-55 F over the srn Piedmont and srn Sandhills.

Deep layer clearing will favor mainly clear skies Fri night; and a plume of high-level moisture along a wnwly upr jet axis will probably produce periods of only thin cirrus and cirrostratus overnight. Strong radiational cooling will consequently be likely, as the aforementioned weak high settles overhead behind the passing and weakening clipper low. Patchy fog and/or low stratus may result Sat morning, with low temperatures in the mid 20s to lwr 30s.

LONG TERM /SATURDAY THROUGH THURSDAY/

As of 138 PM Wednesday...

Saturday through Monday: After a relatively mild (highs in the lower 50s) and dry Saturday under zonal flow aloft, an anomalous upper trough will eject out of central Canada and dive southeast across the eastern US through Monday evening. Associated cold air will spill down the east coast with some of the coldest air of the season (850 mb temperatures will fall into the 1st to 2nd percentile compared to climatology by Sunday night).

At the sfc, models have come into better agreement moving the arctic front into central NC a bit early in the day Sunday. As such, guidance has come in colder for highs on Sunday with highs in the mid to upper 30s across the north, to mid 40s across the south. The CAA will really ramp up Sunday afternoon into early Monday, with lows dropping into the mid to upper teens Sunday night/Monday morning. Forecast soundings still indicate good post-frontal mixing potential through sunrise Monday morning. If the cold air does indeed make it over the mountain early Monday morning, there could be a a brief period where some locations may flirt with Cold Weather Advisory apparent temperatures. Will continue to monitor as we get closer to this weekend, but regardless Monday morning should be quite chilly.

The frontal passage should be accompanied with some anomalous moisture and light precipitation (although the GFS is less bullish on precipitation). Depending on the timing of the precipitation, there could be a transition to wintry ptype on the backside of the exiting light precipitation band across the northern Piedmont/Coastal Plain. However, not confident in 1) how much precipitation will occur, and 2) whether it'll catch the cold air or not. Overall though, qpf amounts are minimal right now.

Highs on Monday will only reach the mid 30s with PWAT dropping to 20 % of normal.

Tuesday through Thursday: After another chilly night Monday into Tuesday (lows into the upper teens/low 20s), return sswly flow will develop pushing highs into the upper 40s Tuesday and mid 50s Wednesday. Another short-wave may approach next Wednesday and Thursday which could be our next shot at any precipitation beyond this coming Sunday.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

As of 1250 AM Friday...

24 hour TAF period:

Driven by weak disturbances and warm air advection aloft, a band of light snow or flurries may clip the nrn terminals between 09 to 15z, possibly mixing with light rain late morning before tapering off early afternoon. Coverage and intensity appears too limited for anything other than brief MVFR VSBY restrictions, mainly at KINT and KGSO. Otherwise, VFR ceilings are expected with cloud bases between 5 to 10 kft.

Winds will be light and variable, with dry weather and decreasing mid-level cloud cover during the evening and overnight hours.

Outlook: Patchy fog and/or stratus will be possible Sat morning, mainly at the northern terminals. A warm front and lift will result in a chance of rain and flight restrictions Sat night-early Sun, followed by strong and gusty nnwly surface winds behind a passing, Arctic cold front Sun afternoon into Sunday night.

RAH WATCHES/WARNINGS/ADVISORIES

None.