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FXUS62 KRAH 050135 AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 935 PM EDT Wed Oct 4 2023

SYNOPSIS
High pressure will extend through our area from the northeast through early Thursday. This high will weaken Thursday and Friday, as an increasing onshore flow brings Atlantic moisture westward into the Carolinas. A cold front will move in from the west early Saturday, ushering in cooler air late Saturday through Sunday.

NEAR TERM /THROUGH TONIGHT/
As of 930 PM Wednesday...

The Rex Blocking H5 pattern over the eastern seaboard of the CONUS will begin to break down in advance of the mid/upper trough digging into the central CONUS. As the eastern edge of the mid/upper ridging extending over the Northeast strengthens and shifts east tonight, the surface response builds high pressure over the Canadian maritimes to 1030mb. Surface ridging will extend its influence down through the southern Mid-Atlantic while increasing easterly flow helps shift an inverted trough off the NC coast westward into the Coastal Plain by 12z Fri.

Ahead of the westward advancing pressure trough, a 925mb moisture gradient has spread into the Coastal Plain and has resulted in the nocturnal development of patchy stratus with bases between 3500 and 5500 feet AGL. As the boundary layer continues to cool, this area of stratus is expected to expand over the Coastal Plain and portions of the Northeast Piedmont providing a nocturnal blanket and preventing otherwise excellent radiational cooling over these areas. Farther to the west of the developing stratus deck, locations that are able to go calm will otherwise experience excellent radiational cooling regime and allow lows to crash into the low 50s, while areas with light stirring as well as urban areas only fall into the mid/upper 50s. Low-level thickness are forecast to bottom out in around 1375m suggesting some patchy upper 40s can't be ruled out in outlying rural areas that are able to remain calm through the night.

Fog potential will also be possible west of the developing stratus deck as mostly calm conditions and crossover temperatures in the mid/upper 50s will be challenged with temps falling into the mid/low 50s. Latest 00z guidance does indicate mostly patchy fog, but locally dense fog will be possible, mainly over portions of the northeast Piedmont.

SHORT TERM /THURSDAY AND THURSDAY NIGHT/
As of 203 PM Wednesday...

At the mid-levels of the atmosphere the shortwave trough circulating off the SE coast and the ridge off the NE US will slowly slide to the ENE Thu night and Fri morning. This will be in response to a deep trough over the northern Great Plains that will dive into the upper Mississippi Valley. At the surface, high pressure extending into the area from the Canadian Maritimes will exert less influence with time as it also slides to the east through the day/night.

Morning low stratus/fog will be possible across central NC, especially along/east of US-1, tied to onshore easterly flow between the the trough to our SE and the ridge to our NE. This moist flow appears confined to the 925-850 mb layer. This morning/fog stratus should lift through the mid/late morning but generally be mostly cloudy through much of the afternoon with redevelopment of afternoon stratocumulus in the moist flow. Highs should range from the upper 70s to lower 80s, tempered slightly by cloud cover. The 12Z HRRR/HRRR develop some very isolated spotty showers across the Coastal Plain with a westward moving inverted trough. The NAM soundings show a weaker cap aloft but other models show less instability. For now, just have a slight chance of a shower in Sampson County. Dewpoints will be elevated in the 60s Thu night with increased onshore easterly flow. This should favor another night of stratus/fog, especially along/east of US-1. The increased clouds should favor lows on the warmer side in the low to mid 60s.

LONG TERM /FRIDAY THROUGH WEDNESDAY/
As of 220 PM Wednesday...

Friday and Saturday: An upper level trough will amplify as a s/w moves within it. The trough will move eastward through the western Great Lakes and mid/upper MS Valley on Fri. It should then continue eastward through the central Great Lakes and OH/TN Valleys Fri night, extending southward almost to about the Gulf Coast by Sat morning. Meanwhile over the Atlantic, a low should lift generally northward well off the Carolina/mid-Atlantic coast Fri/Fri night. As the upper trough shifts eastward from the eastern Great Lakes into the Northeast on Sat, a low may close off within the trough invof NY. The trough should then broaden, covering much of the eastern US by Sat night. At the surface, a low offshore about halfway between the NC Coast and Bermuda will lift northward off the mid-Atlantic Coast and into New England through Sat night. Meanwhile, a strong cold front will approach from the west as cold Canadian high pressure slides southeast from MT to the central Plains Fri/Fri night. The cold front should push through central NC on Sat. With the offshore low deepening as it moves into New England and the 1030 mb high approaching from the west, the pressure gradient across central NC may increase Sat night. This could keep air temps from dropping more than forecast, low to mid 40s, however wind chill values may be quite chilly, upper 30s to low 40s. As for precipitation, there could be some isolated showers over the area on Fri ahead of the front, however the best chance for rain will be immediately ahead of the front Fri night/Sat. The medium-range guidance is not in good agreement with rain chances as the front moves through central NC. The GFS is mostly dry while the ECMWF holds the rain together. As a result, confidence in rain chances, coverage, and amounts is low at this time. Best chances will be Fri night/Sat. Sat night should be dry.

Sunday onward: Aloft, central NC will remain under the upper trough through the remainder of the extended forecast period as the closed low slowly rotates counter-clockwise from NY, through southern Ontario into Quebec, then back into Ontario and the northern Great Lakes. Several weak s/w disturbances may move through the area as they rotate through the trough, but for now the forecast remains mostly dry. At the surface, the cold Canadian high over the southern Plains Sun morning should shift eastward over the Deep South and into the Southeast through Sun night. A surface trough may move through the area Mon/Tue, flattening the ridge over the Southeast as the high moves well out over the Atlantic. The forecast becomes much more uncertain beyond Tue. Sun/Sun night should be the coolest period of the forecast, with highs in the 60s and lows mainly in the 40s. Some of the usually cooler, sheltered spots could dip into the upper 30s Sun night, but how low will depend on how much the winds decrease overnight. Temperatures should then moderate from Mon to Wed.

AVIATION /00Z THURSDAY THROUGH MONDAY/
As of 740 PM Wednesday...

The latest satellite data indicated a few stratocumulus along the coast, otherwise it was clear across the region. The latest guidance continues mixed on the chance of low stratus later tonight - mainly in the Coastal Plain region. It appears moisture will increase from off the Atlantic later tonight, with favored levels of cloudiness around 2k and 5k feet. Scattered MVFR CIGS are possible, especially around KFAY and KRWI.

Looking beyond 18z Thu, sub-VFR CIG/VIS will be possible Friday morning, especially across the eastern terminals. A few showers will be possible Fri afternoon into Sat afternoon, but coverage looks limited. A cold front sweeping through Sat afternoon will usher in VFR Sat night through Mon.

RAH WATCHES/WARNINGS/ADVISORIES
None.

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Petersburg
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Wed -- 03:30 AM EDT     0.28 feet Low Tide
Wed -- 07:07 AM EDT     Sunrise
Wed -- 08:25 AM EDT     3.07 feet High Tide
Wed -- 01:02 PM EDT     Moonset
Wed -- 03:17 PM EDT     0.36 feet Low Tide
Wed -- 06:48 PM EDT     Sunset
Wed -- 08:38 PM EDT     3.51 feet High Tide
Wed -- 10:17 PM EDT     Moonrise
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Chester
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Wed -- 03:31 AM EDT     0.21 feet Low Tide
Wed -- 07:07 AM EDT     Sunrise
Wed -- 08:38 AM EDT     2.99 feet High Tide
Wed -- 01:03 PM EDT     Moonset
Wed -- 03:18 PM EDT     0.28 feet Low Tide
Wed -- 06:48 PM EDT     Sunset
Wed -- 08:51 PM EDT     3.41 feet High Tide
Wed -- 10:16 PM EDT     Moonrise
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Chester, James River, Virginia, Tide feet

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