Key MESSAGE 1, In the wake of the rain, very moist bndry layer remains in place. With light to calm nrly flow tonight and building high pres, a subsidence inversion will develop and produce ideal conditions for fog and very low stratus. There is a potential that some locally dense fog will develop, witht the best chances for this to happen in the coastal plain counties of interior ENC. If lower and mid clouds can scour out, this threat should materialize. For now, have inc covg and intensity of fog, adding 1/2 mi vsbys for interior zones.
KEY MESSAGE 2, In the wake of today's cold front, an anomalously deep upper trough is forecast to develop off the Mid-Atlantic Coast to the east of a dome of hot and humid air over the Central U.S. This will setup an elevated thermal gradient oriented NW to SE across the Mid-Atlantic and Carolinas. Increasing moisture and instability along this boundary will combine with various shortwaves dropping SE along the periphery of Central U.S. Ridge, supporting scattered clusters of thunderstorms from Sunday night through Monday night. Southerly low-level flow beneath NW flow aloft will support increasing deep layer shear on the order of 30-40kt. There is some uncertainty regarding how much instability will develop locally along the boundary. However, the increased deep layer shear and a favorable NW flow convective pattern appears supportive of a few rounds of strong to potentially severe convection. Of note, some of this convection may even occur at night thanks to a continued influx of moisture and instability into the thermal gradient.
While instability may be on the lower side for this time of year, ECMWF's EFI guidance suggests the presence of stronger deep layer shear may setup a notable shear/instability combo for this time of year. While this doesn't guarantee severe weather locally, it's a scenario that bears watching.
KEY MESSAGE 3, Anomalous upper troughing is forecast to remain in place across the Mid-Atlantic and Carolinas through at least the middle of next week. Within this regime, a convectively active NW flow pattern appears likely, and this is supported by deterministic, analog, and machine learning guidance. The signal is the strongest on Tuesday, and this is the day that the Storm Prediction Center has outlooked a portion of our area in a Slight Risk of severe thunderstorms. Synoptically, the overlap of building instability and notably strong deep layer shear for this time of year certainly appears favorable for severe thunderstorm development.
In addition to the potential convective hazards, there will also be a risk of dangerous heat. This risk also looks to be focused on Tuesday when dewpoints and air temperatures are forecast to be the highest, with heat indices of 100-105 degrees.
00z Sunday through Thursday Widespread IFR cont with ENC locked under an unusual (for this time of year) frontal inversion. Overnight tonight, it appears that it will be mostly a very low stratus setup. However, periods of reduced VIS in low end BR and FG are expected. Best chance of seeing some dense fog are ISO and PGV where vsbys may drop to 1/2 mi or lower. Of note, the latest ensemble guidance suggests a 20- 40% chance of dense FG development for most TAF sites tonight. Cigs and VIS are expected to gradually improve through the morning hours on Sunday, with VFR conditions expected to return by the afternoon hours.
Outlook (Sunday night through Thursday): Despite a drier airmass moving in Sunday night, there may be just enough moisture and instability to support a risk of scattered SHRA and maybe a storm Sunday night. Moisture and instability will remain in place to support a continued risk of scattered TSRA, esp late Tue afternoon into the evening ahead of a strong cold front.
Low pressure will move off the coast of ENC this evening, likely in the vicinity of Cape Lookout and Cape Hatteras. As the low moves offshore it is forecast to deepen some, supporting a period of moderate northeast to north winds of 15-20kt. Guidance suggests the risk of frequent 25kt gusts is low, therefore no marine headlines are planned at this time. Seas of 3-5ft are expected along and north of the low track, with 2-4ft seas to the south. The risk of thunderstorms will end from west to east across all waters as the low pulls away.
Outlook: Northerly flow will lay down and become southerly by Sunday night. Southerly flow then continues through the middle of next week. Winds are expected to build Tuesday and Wednesday, offering the next chance of 25kt winds and hazardous conditions for small craft. Occasional gale-force gusts will be possible for the outer coastal waters during this time. Seas will build to 3-7ft by the middle of the week as the winds build. Occasional rounds of thunderstorms will be possible through the middle of the week as well.
Nc, none. Marine, none.
