textproduct: Raleigh

SYNOPSIS

A warm front will remain over northwest North Carolina through Thursday morning. The front will resume its northward motion late Thursday, lifting well north of the area and leading to a strong warm air flow into the region through Sunday. A cold front will approach from the west Sunday evening, then slowly move through the region through Monday.

NEAR TERM /THROUGH TONIGHT/

As of 836 PM Wednesday...

Overview: Early evening radar and satellite imagery reveals abundant cloud cover across much of NC, with a few showers and isolated non- severe storms moving through the western Piedmont. The showers developed following the passage of a warm front that has mostly made it through the forecast area as of 00Z...with the only site remaining on the cool/stable side of the front being INT with a dewpoint of 51 whereas all other sites have dewpoints in the upper 50s to mid 60s. This is all setting the stage for a cloudy/mild night tonight.

Precip chances: PoPs will be maintained across the western Piedmont through the remainder of the evening hours with a mention of showers and thunderstorms mainly from the Triad south to the SC state line. Several consecutive runs of the HRRR and other hi-res models insist that these showers will maintain themselves as they move northward. Instability is forecast to increase a bit through midnight per SPC mesoanalysis page, but a lack of strong forcing should keep them below severe thresholds. Eventually after midnight the BL should stabilize and these showers should dissipate, but quickly be replaced by areas of drizzle as strengthening isentropic ascent overspreads much of NC tonight. Drizzle may be seen as far east as the Triangle before daybreak, and a 15-20 percent mention of precip will be maintained in these areas as well.

Temperatures: Expect lows to range from the low/mid 60s in the north, to the upper 60s in the south. It's entirely conceivable that a few spots in the southern Coastal Plain may stay above 70 tonight. See climate records section below, including record warm minimum temperatures which could be jeopardized tomorrow morning.

SHORT TERM /THURSDAY AND THURSDAY NIGHT/

As of 205 PM Wednesday...

* Thursday will begin a stretch of anomalously warm conditions with little overnight relief.

Widespread low overcast, and perhaps some light drizzle, Thur morning will gradually lift/scatter from southeast to northwest through the morning into the early afternoon.

Continued strengthening/expanding of the anomalous sub-tropical ridge over the southwest N. Atlantic, scattering cloud cover, and 12z low-level thicknesses 40m above normal for early April, will result in the first of several days of abnormal heat for central NC as temperatures rise into the upper 70s to mid/upper 80s. Warmest temps will likely be across the Sandhills into the eastern Piedmont and Coastal Plain where erosion low overcast occurs first.

In the wake of the low overcast, diurnal heating of the already warm/moist airmass in place will result in moderate instability (1000-2000 J/kg of MLCAPE) mainly over the Piedmont. Proximity to the strong sub-tropical ridge may prevent much or even any deep convection, but isolated showers will be possible during the afternoon into the early evening hours. Among the latest 12z Hi-Res guidance, only the HRRR develops any deeper convection, likely since it has surface dew points closer to 70 degrees while mean 12z HREF dew points are closer to mid 60s during the afternoon. Light stirring southwesterly flow and potential redevelopment of some low overcast will result in another unseasonably warm night as temperatures only dip into the mid 60s.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

As of 335 PM Wednesday...

High chances for showers and isolated storms late Sun into Mon will be bookended by near-record warmth on the front end and cool temps with a freeze potential on the back end.

Fri/Fri night: Generally dry and very warm conditions are expected, but there remains a chance for a few showers and perhaps a storm in the far N, near the VA border, associated with a backdoor front. This frontal approach will be largely driven by a fast polar shortwave trough crossing E Quebec and the Canadian Maritimes, allowing a progressive 1030+ mb high to briefly nose down the Mid Atlantic coast. This cooler air should be fleeting and shallow this far S, as the strong low-mid level anticyclone just off the Southeast/FL will persist. The ens output shows a pretty small spread with this frontal feature, and the output mean takes the front just to the NC/VA border Fri evening before dissolving or lifting the surface front back northward by daybreak Sat. The ens members favor at least isolated convection Fri evening into the overnight hours, particularly in our far NE over and E of Kerr Lake, in conjunction with a ribbon of ~1.25" PW near the front. Will maintain the previous chance pops late afternoon through evening, with isolated thunder given a short period of 500-1000 J/kg projected. If we can manage to get any CAPE, given the shallow strongly veering profile near the surface near and just N of this boundary on forecast hodographs, a quick spinup of a landspout could occur, but this potential is very low, given the poor CAPE and lack of other strong lift. With thicknesses likely to be 50-60 m above normal with decent sunshine (after a little morning stratus) and deep mixing, highs in the 80s to around 90 are likely (see climate section below for record temp info). Lows mostly in the low-mid 60s.

Sat/Sat night: Dry and continued quite warm, with the strong subtropical ridge holding firm and keeping us stable and capped aloft, and strong WAA in the low levels. We again may see areas of stratus early Sat and again late Sat night, with partly cloudy skies between, and with thicknesses staying anomalously high, temps should again peak in the mid 80s to around 90, perhaps some lower 90s, with mild lows in the 60s.

Sun through Mon: Best chance for prefrontal convection still looks to be Sun evening and night, with chances shifting to along/E of Hwy 1 Mon. The surface cold front is expected to be situated from the central Gulf up through central and E TN and central PA to New England early Sun. Strengthening and flattening SW steering flow from the TX Gulf coast through the Mid Atlantic region and Northeast will tamp down the subtropical ridge and suppress it SE, and as the correlated prefrontal ribbon of 1.5-2.0" PW is nudged eastward by digging troughing in the polar stream with southern stream phasing, we should see an increase in both thick cloud cover and rain chances from the west late in the day, with models pointing to Sun evening and overnight for the peak coverage, and will maintain high pops, likely to categorical, during this time window. The front should slow for a time or even stall out briefly into Mon as we await southern stream sheared energy to help kick the front to our east, and will slowly decrease and exit rain chances W to E Mon into the evening. Ens probabilities of more than a couple hundred J/kg of CAPE is pretty low, so have held onto lower thunder coverage, isolated to scattered at most, likely embedded within the showers. Still expect plenty of highs in the 80s to near 90 Sun, then mostly 70s Mon.

Tue/Wed: Dry and much cooler, with a freeze still possible in some areas Tue night. The secondary/reinforcing cold front is expected to be over far W NC early Tue, pushing SE through central NC during the day and settling well S across FL as cool high pressure builds in from the Ohio Valley and Midwest and mid level polar stream troughing shifts through the E CONUS, features with which the ens output shows very good agreement. Thus, confidence is high in dry conditions with below normal temps, culminating in low level thicknesses projected to be 50-60 m below normal Wed morning. Freeze conditions may occur, esp if we can decouple Tue night. Expect highs in the upper 50s to mid 60s. -GIH

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 715 PM Wednesday...

Mainly VFR conditions across the area at the moment, but conditions will rapidly deteriorate to IFR or lower between 00Z and 06Z as onshore flow and weak isentropic ascent support the development of widespread stratus later tonight. All sites should see several hours of low ceilings through daybreak, after which time clouds will gradually break up and return to VFR before noon. Weak ascent should also support widespread drizzle across the western Piedmont in particular, although likely not enough to restrict vsbys. The weak ascent may also result in a few hours of LLWS at INT, but likely not strong enough to warrant inclusion elsewhere.

Something else worth monitoring tonight is the potential for isolated shower development across the far western Piedmont, including near INT. Showers have formed south of the CLT metro and are making their way northward. Several runs of the HRRR are insistent that these will maintain themselves as far north as the NC/VA border, moving through INT in the process. I'll maintain a few hours of PROB30 for a brief shower there, but leave the remainder of the area shower free.

Outlook: IFR ceilings are likely again Thursday night and Friday night, despite the meager precipitation chances, due to moist/humid low-level flow. A strong cold front will bring showers and possibly a thunderstorm along with flight restrictions as early as Sunday afternoon at INT/GSO and continuing at all sites Sunday night and Monday.

RAH WATCHES/WARNINGS/ADVISORIES

None.