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FXUS62 KRAH 131852 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 250 PM EDT Mon May 13 2024

SYNOPSIS
A warm front over the deep south will lift into the region Tuesday afternoon and evening. An area of low pressure over the Midwest will bring a cold front through Wednesday night to early Thursday, followed by high pressure for the end of the week Friday.

NEAR TERM /THROUGH TONIGHT/
As of 250 PM Monday...

Afternoon surface and satellite imagery analysis reveals high pressure offshore of NC/VA. A stationary front continues to be present across the deep south, stretching from southern TX into the FL panhandle. Along this boundary are two convective complexes, the first from this morning now into the northern Gulf and over FL to southern AL/GA. A secondary convective complex is just starting to develop over southern TX. Both of these convective systems will not impact us tonight, though the latter will influence us directly or indirectly tomorrow. Both of these are tied to a mid-level shortwave trough over the midsection of the country that will reach east- central MO early tomorrow morning. Clouds will continue to be in place tonight, increasingly lowering in bases as low-level WAA increases as the trough shifts eastward. Isentropic ascent and some weak elevated instability will favor isolated/scattered showers developing overnight, spreading in from SW to NE. There could be a few brief isolated showers over the west/southern Piedmont this evening with activity upstream in western SC/NC, but most CAMs dissipate this as it moves east in the more stable air. Lows tonight will dip into the upper 50s to mid 60s.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
As of 250 PM Monday...

A difficult forecast is in store Tue/Tue night, with uncertainty in regards to timing, duration, and intensity of showers, as well as severe potential. Synoptically speaking, the shortwave trough from Mon over the Midwest is forecast in most of the guidance to reach the southern Appalachians by early Wed, weakening as it moves east.
At the surface, the stationary front over the deep south Mon will likely move north as a warm front into central GA and SC. The area of convection presently over southeast TX is forecast in much of the guidance to become a convective MCS somewhere over the deep south of LA/MS or western FL. Several of the models, including the high-res HRRR/ARW, indicate that as this convective MCS reaches the SE US Tue morning and afternoon, a remnant MCV could remain and possibly impact our SE counties Tue aftn/eve period. This remains to be seen and is uncertain. Nevertheless, the aforementioned storm complex could influence how much rain showers we get Tue morning, with the HRRR/ARW, for example, indicating scattered showers in the morning and the better chance of storms in the aftn/eve with the remnant MCV. The NSSL CAM, on the other hand, suggests stratiform rain in the morning, which could stabilize the atmosphere and limit convection later in the day. This certainly makes for a difficult forecast.

Our current thinking favors isolated/scattered showers in the morning given lesser forcing aloft during this period. Better chances of showers and even some storms would be favored in the aftn/eve period as the mid-level trough inches closer and PW's increase along with the 850 warm front getting into the Carolinas.
As for the severe potential, SPC maintains a marginal risk across the southern Piedmont and Sandhills, but perhaps the better risk area could be from SW to NE over the eastern Sandhills to southern Coastal Plain to capture any remnant MCV and possible gravity wave favoring damaging wind potential or an isolated tornado. The NCAR Neural Network favors this region as well. Highs are tricky but we kept highs in the upper 60s to mid 70s.

There could be a lull in showers and storms by the late evening, though guidance continues to hint at some storms over the higher terrain and over eastern TN possibly impacting the western Piedmont late Tue night in association with the trough and an attendant front/trough in the TN valley. This will also be near nocturnal stabilization so most activity would be isolated in nature. Lows in the 60s.

LONG TERM /WEDNESDAY THROUGH MONDAY
As of 225 PM Monday...

...Unsettled Weather Pattern Potentially Continues Into the Weekend...

Wednesday and Wednesday night: A compact shortwave trough centered over the TN Valley will progress slowly eastward through the region through Wednesday night. In the wake of the secondary/triple point sfc low and attendant warm front lifting north and east of the area, a lull in precip is looking increasingly probable through mid day, with a noticeable reduction in PWATs noted across the area during this time.

However, favorable diurnal timing of the upper trough dynamics and surface front into the area from the west, should lead to a ramp up of convective rain chances during the afternoon and evening.
Expected moderate destablization with deep layer shear of 30-40 kts would be sufficient to support a few strong to severe storm clusters, with the FV3/GFS ML probabilities maximized along and east of US 1 from 3-9 PM. Damaging wind gusts and large hail will be the primary threat. Rain chances will taper off west to east during the late evening and overnight hours.

High will depend on breaks in cloud cover and timing of convective Wednesday afternoon; ranging from mid/upper 70s north to lower/mid 80s south. Lows in the upper 50s to lower 60s.

Thursday and Thursday night: Drier conditions are expected on Thursday, through weak perturbations on the back-side of the exiting shortwave trough could result in some isolated showers and perhaps a rogue thunderstorm Thursday afternoon. Temps should be very comparable to Wednesday. Highs in the mid/upper 70s north to lower/mid 80s south. Lows in the upper 50s to lower 60s.

Friday through Monday: Significant timing/phasing discrepancies persist wrt the eastward ejection of a southern stream shortwave trough from the SW US Thursday and into the SE US sometime during the second half of the weekend, or possibly delayed until early next week. Until the timing can be resolved, will advertise scattered showers and storms each day with a decent chance that we could see some convectively enhanced vorticity disturbances impacting the area, well in advance of the synoptic scale trough. Seasonable highs 80-85. Lows in the lower to mid 60s.



AVIATION /18Z MONDAY THROUGH SATURDAY/
As of 112 PM Monday...

There is high confidence that VFR conditions will start the TAF period. A few stray isolated showers could reach the terminals early this evening, mainly at GSO/INT, but confidence is too low that any sub-VFR conditions could develop given the dry air over the area currently. A better chance of sub-VFR conditions will arrive during the overnight period and into Tue morning/afternoon as a batch of showers move in from the southwest tied to a warm front and low pressure. Guidance, including high-res models, are not in agreement on the timing, placement, and intensity of showers starting early Tuesday morning and continuing into the afternoon. Therefore, confidence lowers toward the end of the TAF period. As such, the main change with this forecast was to slow the onset of IFR conditions given the model spread/uncertainty. More widespread IFR could develop after the TAF period with models showing a better signal at this time.

Outlook: IFR/MFR conditions in showers and storms are favored Tue afternoon and evening, with the best storm chance at FAY/RWI/RDU.
Sub-VFR conditions and possible fog is then possible early Wed.
Another period of showers or storms are possible Wed aftn/eve, along with a chance of sub-VFR clouds early Thu. VFR should return Thu aftn, with the next chance of showers possibly Sat.

RAH WATCHES/WARNINGS/ADVISORIES
None.

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