textproduct: Wakefield

WHAT HAS CHANGED

06z Aviation discussion updated. Updated Discussion. 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 today. 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 periods of rain back to the area through Saturday.

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

DISCUSSION

As of 258 AM EST Thursday... 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 now well offshore of the SE coast east of Bermuda early this morning. Aloft, vigorous upper troughs over the Upper Midwest and Atlantic Canada has flattened the east coast ridging a bit more, and is now quasi-zonal. High pressure nudging south out of ON/QC into New England has begun to push a nearly stationary frontal boundary over the northern mid- Atlantic south as a cold front, and that front has begun to drop south across the Delmarva coast in "backdoor" fashion.

Low clouds and the cool, damp maritime airmass behind that front will continue to spill south and southwest across the Eastern Shore early this morning, and much of the rest of the area through the day. In so doing, the front 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 low to mid 60s across interior NE NC, where they will remain in the quasi- warm sector, but will nevertheless remain mostly cloudy.

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

The latest in a series of weak shortwaves riding upper level flow from the southern plains/mid-south into the area is bringing showers to south central and SE VA early this morning. As that activity wanes later this morning, the aforementioned backdoor cold front drops into the area, with overrunning/WAA aloft allowing showers to re-develop, with widespread steady light rain/drizzle developing across the area today into tonight. 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 of US-460 to 0.25-0.75" N of US-460 and over to the Eastern Shore.

Another cold front aloft slides across the area Friday morning, bringing another round of rainfall to the area, and should act to scour out the low-level moisture by afternoon, with milder temperatures arriving from SW-NE. However, this boundary stalls across the Carolinas Friday night into Saturday with another wave tracking along the boundary. This will bring yet another round of rain to southern VA and NE NC. QPF after 18z 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 and amplifying upper level 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 finer details (i.e. timing, track, and resultant sensible weather impacts). In terms of track, there remains quite a bit of variability model solutions. The deterministic runs of the 00z/19 ECMWF and the UKMET remain flatter/farther south and offshore as the coastal low exits the Coastal Carolinas. The GFS/CMC are more amplified and closest to the coast, and therefore have the greatest impacts to the region. Each of these solutions bring substantially more precipitation back closer to the coast Sunday night/early Monday, with enough phasing of northern and southern stream that a deeper mean H5 trough develops over the eastern CONUS, allowing cold air to be pulled into the system such that precipitation ends as snow over central VA over to the VA northern neck and Eastern Shore (The ECMWF/UKMET solutions, being flatter, are slower to pull cold air in, and are therefore less bullish on winter wx potential). 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 from the previous cycle, with the GEFS still showing the highest probabilities for accumulating snowfall over the northeastern third of the area. While this is still best characterized as a rather low-probability (albeit 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 (i.e. lack of cold air in place antecedent to the event), the most likely scenario remains additional rainfall and a period of gusty winds later Sunday/Sunday night, and potentially strong winds along the coast. That said, given the trends toward a more amplified upper level system, 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 /18Z THURSDAY THROUGH TUESDAY/

As of 1255 PM EST Thursday...

A backdoor cold front has pushed through most sites as of 18z with the exception of ECG. Cigs are primarily IFR/LIFR behind the backdoor cold front, with vsby generally 2-5sm in areas of light rain, and locally 2sm or less along the coast where some marine fog has pushed onshore. The front becomes stationary in northern NC by tonight, then slowly lifts northward as a warm front Friday morning. LIFR conditions are expected to prevail tonight into early Friday morning, and then IFR/LIFR lingering through much of Friday morning. Areas of light rain/drizzle persist tonight, with reduced vsby possible with areas of fog developing (especially along the coast). The wind will remain easterly this aftn through tonight, before shifting to SE early Friday morning, and then S later Friday morning. A cold front will cross the area Friday aftn, and this should lead to slowly improving conditions from SW-NE.

Outlook: 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. Drier air and high pressure will bring a return to VFR conditions later Monday into Tuesday.

MARINE

As of 530 AM EST Thursday...

Key Messages:

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

- Patchy to Dense Fog is possible across the waters this morning and potentially lasting through Friday morning.

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

Early morning analysis shows high pressure far off the SE coast and a backdoor cold front draped across the Eastern shore. The pressure gradient ahead of the cold front remains week and winds are around 10 kt out of the SW. Behind the front winds have shifted out of the NE and are around 10 kt. Seas remain low this morning with 3 to 4 ft seas across the coastal waters and 1 to 2 ft across the bay. Dense marine fog continues to push out of the north reducing visibilities of less than 1 NM. A Marine Dense Fog Advisory has been issued through this afternoon for the ocean zones north of the Capes as the fog continues to push south. The Marine Dense Fog Advisory may need to be expanded depending on how far south and west the fog pushes. Through the rest of the morning and through today the front will continue to push south and winds will begin to shift out of the NE or ENE between 5-15 kt. Behind the front onshore flow is expected to persist and could cause seas to rise between 4 to 5 ft across the northern waters by late this evening . No SCA have been issued at this time due to low confidence in the wave heights. Sub-SCA winds are progged through Friday into Saturday as the frontal boundary continues to linger across the area. Confidence for hazardous marine conditions slowly increases for late this weekend and into early next week. The 00z guidance still shows potential for a strong coastal low to develop off the coast Sunday into Monday. Potential for Gale conditions increase as local winds probs have risen and show 50 to 70% of gusts >= 34 kt across all waters.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Dense Fog Advisory until 1 PM EST this afternoon for ANZ630>638-650-652-654-656-658.