Sunrise 6:35 AM   Sunset 7:52 PM Moonrise 2:07 PM   Moonset 3:17 AM

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FXUS62 KRAH 181338 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 938 AM EDT Thu Apr 18 2024

SYNOPSIS
A weak cold front will move east across the region this morning and off the coast this afternoon. A stronger cold front will move across the area late Friday into Saturday, before stalling near or just to our south. A wave of low pressure will track along the front along the southeast coast late in the weekend.
Much cooler conditions are expected this weekend.

NEAR TERM /THROUGH TONIGHT/
As of 938 AM Thursday...

Little change to the morning forecast update package. Temperatures and other sensible weather remains on track as expected. The previous discussion follows.

* Mainly sunny and quite warm with highs 12 to 16 degrees above average this afternoon.

The latest surface analysis shows a weak area of low pressure across the northern Chesapeake Bay with a weak cold front extending southwest into the southern Appalachians. The cold front will move southeast across VA and the Carolinas this morning and off the Carolina coast this afternoon. A backdoor cold front will drive into far northeastern NC near sunset and drive southwest across central NC tonight. Further aloft, weak troughing extending from the mid- Atlantic southwest across the southern Appalachians early this morning will shift east with a modest and short lived period of northwest flow aloft developing across the region today before short wave ridging moves across the area tonight. The airmass across the region will dry out a bit today with PW values dropping from a little over 1.0 inch to 0.75 inches or so this afternoon. The developing northwest flow aloft and a northwest low level wind behind the front today will result in some downslope drying complimented by mixing up to 5-6kft.

In terms of sensible weather, the band of high clouds extending from southwest to northeast across the eastern Carolinas early this morning will shift offshore this morning with mainly sunny skies today. Some high clouds will move into the region from the west tonight and thicken overnight as the ridge axis shifts east. In addition, a layer of lower clouds will advance into the region from the northeast in the wake of the backdoor cold front across the northern Coastal Plain and northeast Piedmont toward daybreak. Low level thickness values will start off the day in the 1378-1388m range supporting highs in the mid to upper 80s. These highs are about 12 to 16 degrees above average. Lows tonight will range in the mid 50s to around 60. -Blaes

SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/
As of 340 AM Thursday...

* Challenging forecast with considerable temperature contrast and instability that will impact convective coverage and severity.

* Trend for a somewhat more limited coverage and intensity to storms, greatest threat across the southern areas.

A general west to northwest flow aloft is expected across the Carolinas on Friday and Friday night as the Carolinas are on the southern periphery of strong mid and upper level jet across the Midwest and the Great Lakes. At the surface, a frontal zone will be in place across southern NC on Friday morning marking the leading edge of a cooler and more stable airmass that moved into the region from the northeast on Thursday night. This front will lift northeast as a warm front on Friday afternoon as a stronger cold front approaches from the west on Friday afternoon and moves into central NC late Friday night. The airmass across central NC will vary considerably with the frontal zone lifting northeast across the area. Highs across the north will range in the upper 70s to near 80 but south of the front, highs will reach the mid to upper 80s. These temperatures combined with dew points in the upper 50s to lower 60s will result in weak to perhaps moderate destablization across the southern areas with a more stable airmass near the VA border and northern Coastal Plain.

This pattern will support the development of scattered showers and thunderstorms on Friday afternoon and Friday night that should shift east and southeast. Deeper convection is favored across the southern areas in the region of greater instability and with 0-6 km shear values of around 25-35 kts, some storms could become organized and possibly severe. SPC has trimmed the marginal risk southwestward given the more stable regime to the northeast. The primary threat will be damaging wind gusts with a secondary threat of large hail.
Limiting factors for severe weather include the amount of destablization and the presence of a capping inversion that could linger across much of central NC, including southern areas into the afternoon and evening. In addition, convection may be limited in coverage during the afternoon and evening with greater coverage overnight during a period of reduced instability.

Highs on Friday will be problematic with the presence of the frontal zone and a good deal of cloudiness. Highs will range from the upper 70s near the VA border and northern Coastal Plain to the lower 80s in the Triad and Triangle to the mid and upper 80s across the southern areas and Sandhills. Lows Friday night will range from the mid 50s near the VA border to lower 60s near the SC border.
-Blaes

LONG TERM /SATURDAY THROUGH WEDNESDAY/
As of 231 AM Thursday...

Upper pattern through the extended: An upper trough will move across the Great Lakes/northeast Saturday into Sunday promoting primarily wnwly flow over central NC Saturday. Flow will turn more swly over central NC Sunday into Monday as a low-amplitude short-wave moves through the deep south. A more vigorous short-wave will drive through the southeast Monday into Tuesday. Wnwly flow will then persist into Wednesday.

Saturday: A sfc cold front will sag south into our area on Saturday.
The NAM and GFS move the front south of our area by Saturday afternoon. The Euro and NBM are a bit slower and allow some decent warming to occur across our southern areas Saturday afternoon. The latter scenario would suggest some instability could develop ahead of the advancing cold front. This would promote the potential for some showers/storms to potentially form Saturday afternoon/evening.
Decided to lean on the slower solutions and maintain chance POPs across southern areas (where dew points may reach the lower 60s)
Saturday afternoon and evening. Temps on Saturday will largely depend on the evolution of the front, but generally expecting mid 70s to lower 80s from north to south.

Sunday through Tuesday: Flow aloft turns swly Sunday and Monday increasing low-level moisture advection into the southeast. While guidance is in good consensus generally pinning the cold front along the coast (and shunting most instability to our south), ensembles are suggesting a decent soaking may still be possible for some of our southern areas Sunday evening. The highest QPF amongst ensembles (GEFS/EPS), some deterministic guidance (ECMWF, CMC), and machine learning guidance (EC-AIFS) is generally from our Sandhills southeast across the Coastal Plain/Coastline. Alternatively, the deterministic GFS and GEPS ensemble suggest some higher QPF spreading further north into our Piedmont. Regardless, it looks wet in this period, especially across our southern areas. Thunder chances should be minimal as temps cool off into the lower to mid 60s and dew points drop into the mid to upper 40s. However, some instability could develop over the southern Coastal Plain and perhaps support some higher rain rates in these areas Sunday evening. It's worth noting that WPC has introduced a marginal risk for excessive rainfall over the southern two thirds of our CWA for Sunday into Monday. However, unless instability can indeed promote higher rain rates in these areas, the current QPF would likely negate much of a flash flooding threat.

Any lingering rain Monday morning should largely pull off to our north by early afternoon. A few additional scattered showers may be possible Monday afternoon/evening with the passing of the upper feature, but overall Monday should largely be dry. Tuesday will follow suit under nwly flow aloft.

Temperatures Sunday and Monday will be cool in the mid 60s. Temps will rise into the mid 70s Tuesday and Wednesday.

AVIATION /10Z THURSDAY THROUGH MONDAY/
As of 545 AM Thursday...

24 hour TAF period: VFR conditions are generally expected through the 24-hr TAF period. A shield of mid and high clouds extending from southwest to northeast across the Carolina coast will continue to shift east early this morning. Otherwise, generally clear skies are expected into this evening. Areas of high clouds will begin to spread east into central NC this evening and then thicken with SCT-BKN cirrus clouds expected across the area by daybreak Friday. In addition, areas of MVFR stratus will move into central NC from the northeast late tonight spreading into the northern Coastal Plain and northeast Piedmont early Friday morning impacting the KRWI and KRDU terminals toward and especially after 09Z.

Light southwest to west winds at 3 to 7 kts early this morning will gradually veer around to westerly to northwesterly shortly after daybreak. A weak cold front will move across the area today and winds will shift to northwest at 8 to 12 kts with a few gusts over 15 kts during the afternoon. Winds will decrease late this afternoon with winds becoming northeast at 4 to 8 kts between 03 and 09Z tonight.

Outlook: A period of MVFR cigs are expected around daybreak Friday morning across the northeast including KRWI and perhaps KRDU. An approaching cold front will trigger scattered showers and thunderstorms Friday afternoon into Saturday morning with sub- VFR cigs/vsbys. Another round of sub-VFR conditions is possible Sunday into Monday as a wave of low pressure travels along the front that will stall to our south. -Blaes

RAH WATCHES/WARNINGS/ADVISORIES
None.

Bannermans Branch
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Thu -- 12:13 AM EDT     1.24 feet High Tide
Thu -- 04:12 AM EDT     Moonset
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Thu -- 07:45 PM EDT     Sunset
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