textproduct: Raleigh

SYNOPSIS

A front will become quasi-stationary over NC through tonight, then retreat north into VA as a warm front on Sunday. A stronger, polar front will sweep across the region early Sunday night. A vigorous mid and upper-level trough and Arctic cold front will then move across the region late Monday into Monday night.

NEAR TERM /THROUGH TONIGHT/

As of 400 AM Saturday...

* Unseasonably mild, with elevated convection tonight

A couple of closely-spaced shortwave perturbations now evident in GOES-E WV data over the srn Middle Atlantic and OH Valley will lift newd along the Middle Atlantic and New England coasts today, then offshore tonight. Between that trough and another forecast to amplify across the Midwest and mid MS Valley, low amplitude ridging and rising heights will migrate across and offshore the Middle Atlantic. A sswly low-level jet will develop and migrate across the Carolinas tonight, within a broader regime of low to mid-level WAA.

At the surface, a somewhat diffuse front now stretching from the Middle Atlantic coast swwd to the lwr MS Valley will settle sewd and across NC this morning, where it will become quasi-stationary through Sun morning, or perhaps retreat slightly nwd ahead of a weak frontal wave tonight.

A band of weakening convection and trailing stratiform rain will continue to weaken with time and ewd extent as progresses across e- cntl NC this morning, as it moves away from the aforementioned lifting shortwave troughs and forcing for ascent that will be moving away from the region. Partly to mostly sunny conditions will follow for today, in subsident influence from the progressive, low amplitude ridging aloft.

Isentropic lift will then develop and strengthen tonight, as the aforementioned low-level jet intersects the quasi-stationary surface front over cntl NC, amid broader but strong low/mid-level WAA. Associated lift, beneath modest mid-level lapse rates around 6 C/km, will contribute to the development of scattered to locally numerous, elevated convection tonight, within an environment characterized by ~50 kts of wswly mid-level flow and MUCAPE of a few hundred J/kg across the nw Piedmont to 750-1000 J/kg over the Sandhills and srn Coastal Plain. CAM solutions indicate elevated supercells, with a primary risk of hail, may result where that instability maximizes across the Sandhills, and adjacent Piedmont and Coastal Plain counties. Locally heavy rainfall will also be possible, as PWs increase to around 150-175% of normal; and there may be some tendency for cells to regenerate along the quasi-stationary front. That risk also appears greatest over the Sandhills per 00Z HREF LPMM fields, which indicate 2-4" will be possible locally.

It will otherwise remain unseasonably mild and in the 70s this afternoon and 50s overnight, or about 10-20 F above average.

SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/

As of 215 AM Saturday...

* Strong Arctic cold front moves through Sunday evening, with a drastic change in temperatures

* Conditional severe threat remains ahead of the front, mainly along/east of US-1/I-95

A deep and vigorous upper trough will dig southeast into the OH valley and SE US Sunday night into Monday, with core of the trough reaching portions of the OH/TN valley region Monday morning. Tied to the trough will be the well advertised Arctic cold front that will stretch from the western OH to TN valley region Sunday morning, with an area of low pressure over OH. The Arctic front is forecast to move through central NC late Sunday afternoon over the NW Piedmont and mid to late evening across the central and SE portions of central NC.

A warm front near southern VA early Sun will continue to lift north into MD during the late morning and afternoon. Some lingering showers or isolated storms may still be around Sunday morning over our NE sections, but most CAM solutions have this activity into VA by the morning hours. Otherwise, morning clouds should give way to partly sunny skies and one last mild day ahead of the front with low 70s NW to upper 70s SE.

The position of the trough Sunday afternoon results in a fair bit of dry air over the area during the day in the wake of the departing warm front. As such, the amount of deep moisture decreases relative to Sat night. This appears to be the main limiting factor in redevelopment of isolated or scattered showers/storms Sunday evening ahead of the Arctic cold front. HREF members suggest a conditional threat given more than sufficient deep-layer shear of 50+ kts, but marginal instability of 250 to 500 J/kg, focused mainly along/east of US-1/I-95. SPC has maintained a marginal severe risk in our far eastern Coastal Plain, but how much coverage we will see remains unclear.

The passage of the front will bring a drastic change in temperatures, with lows by Mon morning in the upper 30s NW to low/mid 40s SE.

LONG TERM /MONDAY THROUGH FRIDAY/

As of 215 AM Saturday...

* Below normal temperatures are expected behind behind a strong Arctic cold front to start the next week. A hard freeze Monday night is expected with lows mostly in the 20s across central NC.

* Dry weather and warming temps are expected for mid to late week.

The coldest air of the season is expected to surge into central NC behind the strong Arctic cold front that is expected to move across the area on Sunday afternoon/evening, propelled by a strong highly anomalous trough moving across the region early next week. The anomalously deep trough will shift to the east of the area by mid week, with west to southwesterly low level return flow expected by mid week.

Low temperature Monday night will be the big story during this period, with low temperatures expected to fall into the mid/upper 20s to near 30 degrees across the across central NC, likely resulting in a hard freeze for most locations. Otherwise, dry weather is generally expected with well below normal temps to start the week, warming to near normal by mid/late week. This will result in highs ranging from the mid 40 to lower 50s early next week, before warning into the upper 50s to 60s by mid/late next week. Low temps will follow a similar trend, with lows in the lower to mid 30s Tuesday night to around 40 for Wednesday night and Thursday night.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

As of 700 AM Saturday...

Very low stratus and fog at INT/GSO, and near and especially just west of RDU, will disperse through 13-14Z. Another area of MVFR ceilings will probably affect FAY for at least a few hours around midday. Lift will strengthen atop a stalled frontal zone over NC by this evening, such that LIFR-IFR conditions will develop over cntl NC and be accompanied by scattered to locally numerous, mostly elevated convection tonight.

Outlook: Strong and gusty swly surface winds will result ahead of a polar front on Sun, followed by similarly strong and gusty nwly ones behind it Sun night into early Mon. A vigorous trough aloft and accompanying Arctic, surface cold front will move across the region late Mon and Mon night, with a renewed surge of even stronger nwly gustiness and virga.

RAH WATCHES/WARNINGS/ADVISORIES