Sunrise 6:16 AM   Sunset 8:05 PM Moonrise 3:14 AM   Moonset 3:18 PM

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FXUS62 KRAH 050120 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 920 PM EDT Sat May 4 2024

SYNOPSIS
A series of mid and upper-level disturbances will overspread and interact with a front that will remain quasi-stationary over central NC through early Sunday, then weaken and move northward into VA later Sunday and Sunday night.

NEAR TERM /TONIGHT/
As of 920 PM Saturday...

The models and recent trends in water vapor satellite data indicate an upr-level, srn stream shortwave perturbation may amplify slightly as it moves east and across the srn Appalachians and wrn-cntl Carolinas through early Sunday. Preceding this feature, a long-lived MCV from convection that developed across LA Fri morning was evident in regional radar data over the Upstate of SC this evening. This mid- level feature is forecast to track generally newd, in ~15 kts of mean swly 700-500 mb flow, and into the srn and wrn NC Piedmont through early Sunday. It may be preceded by smaller-scale and weaker MCVs from small convective clusters ongoing from near CLT to CAE to AGS. The net result will be mid through upr-level forcing for ascent that will edge newd and across the srn and wrn NC Piedmont (the wrn half of cntl NC) late tonight-early Sunday.

At the surface, a quasi-stationary front extended at 01Z from near ECG in nern NC wswwd to near PGV, where it intersected a nne to ssw- oriented outflow boundary extending through the cntl and srn Coastal Plain. To the west of that outflow boundary, the front, masked and modulated by associated rain-cooled air over the rest of cntl NC, extended across srn NC to a weak mesolow in the Upstate of SC near GSP. The mesolow will follow a similar path as the parent MCV above and reach the nw Piedmont/Triad region by 12Z Sun.

While a shallow frontal inversion and weakly stable layer, with a surface temperature of 60 F, were evident in the lowest couple of thousand ft AGL in the 00Z-observed GSO sounding, a deeply moist (PW of 1.5"), saturated, and conditionally-unstable profile was otherwise present throughout the troposphere. Even slight modification of observed surface parcels with representative mid/upr 60s preceding the mesolow yields up to several hundred J/kg of SBCAPE. Associated weak instability, and forcing for ascent as the mid/upr-level features noted above overspread and interact with the surface frontal zone, should cause showers and isolated storms to become increasingly numerous over the srn and wrn NC Piedmont overnight-Sunday, where a continued Marginal risk of excessive rain (ie. isolated instances of flash flooding) will remain possible. It will otherwise be unseasonably mild and muggy, with lows in the 60s.

SHORT TERM /SUNDAY AND SUNDAY NIGHT/
As of 215 PM Saturday...

Aloft, the sub-tropical ridge will shift offshore and breakdown Sun/Sun night as the increasingly sheared shortwave disturbance moves through the mid-Atlantic and Northeast US. Another southern stream s/w will strengthen over the southern Plains on Sun, then move eastward into the lower/mid-MS Valley through Sun night. At the surface, high pressure will move off the New England coast and eastward over the northern Atlantic as a low moves through the Great Lakes and into the Northeast Sun/Sun night. An attendant cold front draped swwd from the low will become more W-E oriented through the OH Valley by Sun night. Meanwhile over central NC, the quasi- stationary front that had lingered over the area will lift northward as a warm front, with warm, moist southerly return flow over the are in its wake.

Precipitation/Convection: Showers and storms will likely still be ongoing Sun morning, most prevalent over the Piedmont. PWATs will remain anomalously high, in the 1.6 to 1.8 inch range, through the afternoon. Surface-based instability should increase with daytime heating, although the latter may be somewhat inhibited by the ongoing convection and extensive cloud cover. Bulk shear is also expected to be weak again on Sun. As a result, slow-moving, widely scattered showers and storms will be possible through the aft/eve Sun, with the main threat of some isolated heavy rainfall and localized flooding, although most locations may only receive a few hundredths of an inch of rain.

Temperatures: Widespread overcast skies and ongoing convection should somewhat limit heating early, but temps could recover during the afternoon. For now expect highs to range from the mid 70s along the NC/VA border to around 80 degrees SE. Lows Sun night mainly in the low to mid 60s expected.

LONG TERM /MONDAY THROUGH SATURDAY/
As of 415 PM Saturday...

The extended forecast will feature a continued chance of unsettled weather to start the week Mon, followed by somewhat drier and hot temperatures by the middle of the week. Energetic wswly flow aloft will increase shower/storm chances again mid-late week, followed by milder, stable, and less humid conditions by Sat.

The models remain in relatively good agreement regarding a srn stream shortwave trough forecast to pivot across the TN Valley and srn Appalachians Monday and srn Middle Atlantic and Carolinas Monday night-early Tuesday, during which time above average chances of showers/storms will result over cntl NC. Shortwave ridging will follow and migrate across and offshore the South Atlantic with drier conditions favored Tue-Wed. Associated subsidence, on the wrn periphery of sub-tropical high pressure that will extend across the swrn N. Atlantic, will also result in unseasonably hot and humid conditions extending over cntl NC Wed-Thu. Increasingly-energetic wswly flow, and at or above climatological chances of convection, will otherwise prevail across the Southeast, within closely-spaced srn and nrn stream branches of the westerlies, through early next weekend. An associated synoptic cold front will move across cntl NC Fri or Sat.

While the models are in relatively good agreement regarding the pattern described above, they also depict the development of a couple of rex blocks over n-cntl NOAM during the middle of the week and over wrn NOAM late week into next weekend. With those blocking developments in mind, model guidance may trend slower with the progression of the cold front and following milder and more stable conditions by early next weekend.

AVIATION /00Z SUNDAY THROUGH THURSDAY/
As of 825 PM Saturday...

LIFR ceilings are expected at most sites through 15z/Sun. There is also a good chance of MVFR to IFR vsbys with showers and fog.
Showers and thunderstorms are expected Sunday morning (south and west) into the afternoon (east), with associated IFR to LIFR conditions.

Outlook: MVFR to IFR ceilings are likely to sock back in Sunday and Monday night with additional scattered showers/storms possible.

RAH WATCHES/WARNINGS/ADVISORIES
None.

Bannermans Branch
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Sat -- 12:33 AM EDT     1.42 feet High Tide
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