textproduct: Raleigh

WHAT HAS CHANGED

* A backdoor front and post-frontal low overcast has drifted a little farther swwd than previously forecast and will result in LIFR-IFR ceilings at all cntl NC TAF sites except probably FAY this morning.

KEY MESSAGES

As of 325 AM Friday...

1) Record heat today will be swept offshore by a strong cold front and following sharply cooler and wet conditions that will develop tonight into Sat.

2) There is still some potential for patchy frost Sun morning and again Mon morning.

DISCUSSION

As of 325 AM Friday...

KEY MESSAGE 1... Record heat today will be swept offshore by a strong cold front and following sharply cooler and wet conditions that will develop tonight into Sat.

An increasingly-phased and high amplitude trough, apparent in GOES-E WV satellite data from nrn Hudson Bay to the cntl High Plains, will pivot across the ern US through late Sat-Sat night. A vigorous upper jet and front will accompany the trough, with a zone of strong and deep ascent that will overspread cntl NC tonight-Sat.

At the surface, a backdoor front has drifted into the nrn Sandhills and the nw Piedmont this morning, about 20-30 miles farther swwd than previously forecast. While low overcast has developed within the pos-trontal regime and would typically slow/retard subsequent nwd retreat of the front, cooling behind the front and the related frontal inversion are not pronounced. Additionally, the MSL pressure pattern surrounding the front over the srn Middle Atlantic, between a 1021 mb high drifting off the coast of New England and a ~1019 mb one off the South Atlantic coast, appear to be reaching equilibrium this morning. As such, it remains likely that the front will retreat quickly nwd with the onset of diurnal heating, in strengthening flow and mass response ahead of the intense trough aloft and a related surface cyclone now deepening across MI. A pre-frontal, Appalachian- lee trough will sharpen across the nw Piedmont this afternoon and precede a strong cold front that will sweep across cntl NC tonight.

A growing warm sector throughout cntl NC today will yield yet another day of record temperatures mostly between 85-90 F, accompanied by a gusty swly surface wind that will develop with daytime heating/mixing by midday-early afternoon.

Scattered showers are likely to develop along the pre-frontal trough over the nw Piedmont by ~21-22Z, in a regime of weak MLCAPE of generally less than 500 J/kg, but where instability will be relatively maximized as cooling temperatures aloft edge east of the Appalachians. The band of showers will spread ewd and across the remainder of cntl NC this evening, along and immediately following the passing cold front. Anafrontal precipitation character will become increasingly stratiform and probably blossom after midnight, as the intense mid and upper-level trough and jet, and deep zone of Fgen, overspread the Carolinas.

The precipitation band will then edge from west to east across cntl NC during the day Sat, with storm total rainfall amounts mostly between a quarter and half inch. It will otherwise turn sharply cooler, with highs Sat 25-30 F below those of today and about 10-15 F below average. A strong and gusty nly wind will make it feel even cooler.

KEY MESSAGE 2... Cold Saturday and Sunday nights, with some patchy frost Sun morning and again Mon morning.

Aloft, it is looking increasingly likely a low will close off within the parent trough as it tracks sewd across the region and offshore Sat/Sat night, though there remain differences wrt where and when that will occur. The low will likely sit/meander near or just off the Carolina/mid-Atlantic coast through much of the week. At the surface, the ~1036 mb high should lift newd from the OH Valley to the Canadian Maritimes Sat night through Sun night, while the ridge continues to extend swwd across the region. A low is expected to develop offshore, along the front, on Sat before cutting off from the parent trough and deepening as it meanders off the Southeast US/Carolina coast through at least Sun night, possibly through much of the week. However, a good bit of uncertainty remains wrt to this low and its impacts for central NC. Expect breezy conditions on Sun, with a strong pressure gradient between the deepening low offshore and the ridge over the area. The LLJ could remain quite stout on the back (NW) side of the low offshore through Sun night, with gusts of 25-35 kts possible with mixing on Sun, highest east. The jet may be stronger overnight (25-40 kts) both nights and over a much larger area, but those stronger winds are generally not expected to mix down to the surface. Still, some gusts of 15-25 kts cannot be ruled out Sun night given the latest guidance showing a little mixing overnight.

There remains a fair amount of spread in the statistical guidance between high and low members for temperatures from Sat night onward, given the uncertainty wrt the low offshore and subsequent impacts. For highs, Sunday should be the coolest day, with highs in the mid 50s to around 60 degrees expected. Highs should rebound a bit on Mon, but still remain below normal, with low to mid 60s forecast. For lows, with continued breezy conditions, generally decreasing cloud cover, and low-level thicknesses around 1320 dam Sat night, will err on the mean for lows, ranging from mid-upper 30s NW to mid 40s SE. With partly cloudy skies, perhaps slightly less breezy conditions, and low-level thicknesses increasing to around 1335 dam Sun night, expect similar lows ranging from upper 30s NW to mid 40s SE Mon morn. With the expected winds overnight/early morning, wind chill values in the low-mid 30s expected across much of the area Sat night, increasing slightly SE into the low 40s SE for Sun night.

There could be some mid 30s lows in the usual cooler, sheltered areas of the Piedmont Sun and Mon mornings, especially if the skies clear out, possibly resulting in some patchy frost.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

As of 735 AM Friday...

LIFR-IFR restrictions should disperse and lift through 14Z, probably last at RWI, with the nwd retreat of a front draped from northwest to southeast across cntl NC this morning. VFR conditions will follow, as will gusty swly winds that will develop with daytime heating/mixing by early this afternoon. Scattered showers are likely to develop along a pre-frontal trough invof INT/GSO by ~21-22Z, then linger as a cold front and gusty nwly surface winds surge sewd across cntl NC tonight. The front will focus showers along and immediately behind it as it moves through. Precipitation character will become increasingly stratiform and probably blossom early Sat morning --with related IFR-MVFR restrictions-- as an intense upper- level trough and jet streak pivot toward the Carolinas.

Outlook: Rain and related flight restrictions will edge from west to east across cntl NC during the day Sat. Surface winds will veer to nly and remain strong and gusty especially during the daytime through the weekend, in a tight MSL pressure gradient between strong high pressure that will build in from the west and coastal low pressure that will deepen and meander of the coast of the Carolinas. Should surface winds diminish as expected each night, a risk of low- level wind shear will exist both Sat and Sun night.

CLIMATE

Record High Temperatures:

October 16: KGSO: 85/1953 KRDU: 86/1925 KFAY: 90/1925

Record High Minimum Temperatures:

October 16: KGSO: 66/1947 KRDU: 69/1919 KFAY: 69/1919

Latest 90 F days:

GSO: 10/12/1904 RDU: 10/14/2026 FAY: 10/26/1940

RAH WATCHES/WARNINGS/ADVISORIES

None.