textproduct: Wakefield

WHAT HAS CHANGED

Confidence has increased with respect to the development of coastal low pressure Sunday into Monday. However, confidence remains low with regard to sensible weather impacts.

KEY MESSAGES

1) A back door cold front drops south and southwestward across the mid-Atlantic coast Thursday. Developing onshore winds will bring lower temperatures for much of the area, especially across the VA/MD Lower Eastern Shore, and areas along the western shore of the Chesapeake Bay through Hampton Roads.

2) Several disturbances bring the chance for rain back to the area tonight through Saturday.

3) Stronger coastal low pressure potentially impacts the region Sunday into early Monday.

DISCUSSION

As of 320 PM EST Wednesday... KEY MESSAGE 1...A back door cold front drops south and southwestward across the mid-Atlantic coast Thursday. Developing onshore winds will bring lower temperatures for much of the area, especially across the VA/MD Lower Eastern Shore, and areas along the western shore of the Chesapeake Bay through Hampton Roads.

Surface high pressure is centered off the Southeast coast this afternoon. Meanwhile, the flow aloft is quasi-zonal on the northern periphery of a broad flat ridge over the Deep South, which is flattened by vigorous troughs over the Midwest and Atlantic Canada. Mostly cloudy, mild, and breezy this afternoon. Temperatures range from the upper 50s/lower 60s from central VA to the Eastern Shore, to the upper 60s/around 70F across far SE VA and NE NC where the high clouds are thinner. The wind is SW 10-15 mph gusting to 20-25 mph, and locally gusting to 25-30 mph across far SE VA and NE NC.

Weak low pressure slides across southern NY and and southern New England tonight, which allows for a backdoor cold front to slide across the area Thursday as high pressure builds across New England. Low clouds and onshore flow will keep high temperatures in the upper 40s to mid 50s from central VA to the Eastern Shore (coolest over the Eastern Shore), with upper 50s/lower 60s across southern/SE VA and coastal NE NC, and milder with lower to mid 60s for interior NE NC.

KEY MESSAGE 2...Several disturbances bring the chance for rain back to the area tonight through Saturday.

A weak cold front aloft drops into the area tonight and settles in vicinity of the VA/NC border early Thursday. This has the potential to bring some light rain tonight, with PoPs generally 20-30% this evening, and then 30-40% in vicinity of the VA/NC border later tonight. By Thursday, the aforementioned backdoor cold front drops through the area, and overrunning/WAA aloft improves with widespread steady light rain developing across the area Thursday. Deeper moisture diminishes Thursday night. However, the low-level cool airmass lingers as the backdoor boundary begins to lift N as a warm front. This should result in persistent areas of light rain and drizzle through early Friday morning. QPF through 12z Friday is mainly 0.1-0.25" S to 0.25-0.5" N.

Another cold front aloft slides across the area Friday morning. This will bring additional rain to the area, and should act to scour out the low-level moisture by afternoon, with milder temperatures arriving from SW-NE. This boundary stalls across the Carolinas Friday night into Saturday with another wave tracking along the boundary. This will bring additional rain chances to southern VA and NE NC. QPF after 12z Friday is limited, generally 0.1-0.25", with total QPF 0.25-0.5" S to 0.5-0.75" N through 00z Sunday (7PM Saturday).

KEY MESSAGE 3...Stronger coastal low pressure potentially impacts the region Sunday into early Monday.

By Sunday through early Monday, most model guidance continues to depict a vigorous upper trough and strengthening coastal low pressure off the Mid-Atlantic coast impacting the region. Confidence in the storm developing is high. However, there remains uncertainty in the timing, track, and resultant sensible weather impacts. The 18/12z run of the GFS/CMC each brought precipitation back closer to the coast Sunday night/early Monday, with substantial QPF that shows rain to snow as cold air is pulled into the system. Meanwhile, the 18/12z ECMWF has has a coastal low, but is flatter, weaker, and slower to pull cold air into the system. The associated EC AIFS now is more amplified and has more wintry potential than the dynamical model.

Model ensemble (GEFS/EPS/GEPS) snow probabilities for >1" of snow (at 10:1 SLR) have increased slightly, or remained similar over central/eastern VA and the Eastern Shore. While this remains a rather low-probability (and higher impact) scenario, it is somewhat more feasible given the trend toward a stronger upper low, which is modeled to briefly close off this weekend over the interior Northeast. Given the marginal thermal profiles, the most likely scenario remains additional rainfall and a period of gusty winds later Sunday/Sunday night, and potentially strong winds along the coast. Given the more amplified upper level trends, this scenario of precipitation ending as some light snow early Monday, particularly across the Delmarva and peninsulas of eastern VA, and potentially back into central VA should be watched over the coming days. Also of note, models continue to show increased blocking in the northern Atlantic, which indicates a chilly start to next week before the Canadian surface high modifies into the latter half of next week.

AVIATION /20Z WEDNESDAY THROUGH MONDAY/

As of 100 PM EST Wednesday...

VFR under BKN-OVC mid and high clouds as of 18z with a SW wind of 10-15kt gusting to 20-25kt, and locally 25-30kt at ORF. Primarily VFR through this evening with a SW wind diminishing to 8-12kt and becoming less gusty after 21-22z. A 20-30% chc of light rain arrives this evening, but should initially have little impact on cigs and vsby. A backdoor cold front crosses the area early Thursday. IFR cigs are expected to arrive behind the front, with light rain and reduced vsby developing Thursday morning into the aftn. The wind veers to NE behind the boundary.

Outlook: The boundary lifts back N as a warm front Thursday night. LIFR conditions are possible with areas of light rain and drizzle lingering across the region. Another front brings a chc of showers Friday morning, and cigs should lift in the wake of this boundary by Friday aftn. This front lingers S of the area Saturday, with rain chances lingering across southern VA and NE NC (mainly at ORF, PHF, and ECG). Stronger low pressure develops off the coast Sunday into Monday and this has the potential to bring another period of rain, gusty winds, and flight restrictions to the region Sunday into early Monday. Precipitation could end as a rain/snow mix or all snow at SBY and RIC.

MARINE

As of 320 PM EST Wednesday...

Key Messages:

- Small Craft Advisories continue into this evening for all area waters.

- A backdoor cold front drops southward on Thursday with winds turning onshore behind the boundary.

- A stronger system potentially impacts the waters Sunday into early next week.

Surface high pressure continues to move farther offshore with a strong occluded low over the upper Midwest. The gradient between these features forces broad SW flow over the region. Afternoon observations show gusty W/SW winds, mainly near the land/water interface with relatively warm air and cool waters impeding mixing away from shore. The highest gusts observed through the day have been in the tidal rivers, near-shore portions of the western Chesapeake Bay, and along the immediate coast. Waves/seas have underperformed considerably today with waves generally 1-2 ft and seas 3-4 ft offshore. With continued westerly flow this evening, not overly confident in seeing 5 ft seas so have SCA headlines ending at 10PM/03z (this timing may even be generous). SCAs for the bay/rivers/sound end at 7PM/00z. There is increasing potential for marine fog tonight with warm air interacting with relatively cold waters. Fog could become dense and a Marine Dense Fog Advisory is possible tonight ahead of the backdoor front. The front drops south late tonight into Thursday with winds becoming NE or ENE 5-15 kt behind the boundary. Exactly how far south the boundary gets before stalling is still somewhat in question. Onshore flow behind the front may allow seas to build into the 4-5 ft range (well offshore) for the northern coastal waters but will hold off on any additional SCA headlines with marginal seas and relatively low confidence. Sub- advisory winds of varying direction are expected Friday into Saturday as the front meanders near the region. 12z guidance continues to show the potential for a stronger system to develop near the coast Sunday into Monday before moving offshore. There remains considerable disagreement from run-to-run and between models during this period but the potential for SCA or Gale conditions is increasing.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ630>638. Small Craft Advisory until 10 PM EST this evening for ANZ650- 652-654-656-658.