textproduct: NWS Wilmington

SYNOPSIS

Rain chances will increase later today and tonight ahead of a cold front that will move off the coast Friday. Canadian high pressure will build across the area Saturday. A dry cold front arriving Sunday will bring chilly weather for Monday, but a warming trend is expected to begin later next week with above normal temperatures by Tuesday and Wednesday.

UPDATE

Aviation discussion updated for 12Z issuance.

NEAR TERM /THROUGH FRIDAY/

Southeasterly flow increases today as high pressure slides offshore. A coastal trough will push onshore this morning and could produce a few isolated showers. The chance of precip will be low, highest in northeastern SC and the Grand Strand. Behind the initial surface trough, warm, moist air advection will push temperatures into the upper 60s to near 70. Mostly cloudy skies this morning will become overcast during the afternoon.

A pre-frontal shortwave will bring showers across the region later today and tonight. Light rain will spread SW to NE across the region by early or mid afternoon. The Cape Fear region should stay dry until after sunset, but points southward will see intermittent showers after 2 PM. Shower coverage becomes more uniform after sunset as the pre-frontal shortwave slides overhead.

Maximum synoptic lift and saturated atmospheric profiles will produce moderate to heavy rain this evening. An approaching upper level trough to our west will gradually bring lower heights during this time as well. This should produce some elevated instability near the coast leading to heavier rain rates. HREF guidance continues to suggest that the bulk of this instability will remain offshore. Regardless, I have maintained the mention of a few localized thunderstorms from Georgetown to Surf City. A briefly enhanced gust would be possible near the coastline, if anything materializes, but severe weather is not expected.

The actual cold front will lag the end of the precip by several hours late tonight and Friday morning. This should maintain low clouds and humid conditions until the frontal passage around noon on Friday. The surface gradient should prevent the development of fog across the region, but Friday will start with mostly cloudy or overcast skies and mild temperatures in the lower 60s.

SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/

A shortwave extending across the central Appalachians Friday morning will attain a slight negative tilt as it lifts across the northeastern U.S. Friday night. Right entrance region effects from the jet streak should remain to our north. However there is a narrow window of time during the morning where residual low level moisture and steepening low level lapse rates could coexist, allowing some fast-moving convective showers to develop especially across southeastern North Carolina.

These steepening lapse rates have a high probability of producing widespread gusty winds on Friday. NAM and GFS forecast soundings show winds only 1000 feet AGL could exceed 30 knots (35 mph) during the morning, diminishing to 25 mph during the afternoon as winds veer westerly behind the actual surface cold front. This is a good approximation for expected wind gusts at the surface.

Surface high pressure will build eastward Friday night, reaching North Carolina on Saturday. The high will slip off the coast Saturday night with light return flow developing.

NBM temperatures look acceptable during the period. Radiational cooling both nights could knock typical cold spots on peat/pocosin soils 10 degrees F below nearby cities.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Another shortwave moving through the Great Lakes and the northeastern U.S. on Sunday will support sub-1000 mb surface low pressure moving eastward over southern Quebec. This low will drag a dry cold front through the eastern Carolinas during the day. Behind it, a chilly airmass will build across the area for Monday with daytime highs only anticipated to reach the lower 50s. Canadian high pressure following behind the front should reach the area Monday night.

As the shortwave clears off to the east, the upper air pattern should change across North America as ridging develops along the Gulf Coast and northward through the Mississippi Valley. An average of the GFS, ECMWF, and Canadian suggests our 1000-500 mb thicknesses will rise almost 100 meters between Monday and Wednesday as the airmass warms. Daytime highs could poke back toward 60 on Tuesday and into the mid 60s by Wednesday (Christmas Eve) as dry weather continues.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Isolated showers are possible this morning as a coastal trough moves inland. Obs near the coast indicate that restrictions associated with these showers will be unlikely. Gusts increase to around 15-20 knots in the increasing SE gradient today. Showers spread SW to NE across the region after 18Z-20Z. Showers should be light at first, with increasing intensities toward Thursday evening. IFR likely after sunset.

A few thunderstorms are possible near the coast after 00Z, but the best instability should remain just offshore. Regardless, rainfall intensities should increase. Most areas will see IFR decreasing to LIFR/VLIFR as low level inversions are reinforced. This inversion should also produce fairly strong wind shear through sunrise.

Extended Forecast... High confidence in IFR on Friday morning with gradual improvement to VFR throughout the day. VFR conditions continue into early next week.

MARINE

Through Tonight...Onshore flow will increase today ahead of an approaching cold front and leading mid level shortwave. With a gradually increasing gradient, warm advection during the daylight hours should limit mixing efficiency with gusts generally around 20 knots. Seas build to 3-4 feet by mid afternoon with a rapid increase in wind energy thereafter.

The strengthening gradient will become maximized during the late afternoon and evening. Surface winds should exceed SCA thresholds by 00Z for all nearshore waters with wind waves quickly responding to 4- 6 feet during that time. Heavy rain and isolated thunderstorms will limit visibility and lead to locally higher winds and seas. Winds turn S and SSW overnight as the cold front approaches the coast. Ongoing SCA gusts will continue through the end of the period. A SCA remains in effect starting at 23Z Thursday.

Friday through Tuesday...A cold front extending southward from Canadian low pressure will push off the Carolina coastline Friday. SW winds near 25 kt in the morning will veer westerly 15-20 kt in the afternoon. Small Craft Advisory conditions may continue through early evening due to lingering 6 foot seas.

High pressure will build across the area late Friday night. The center of the high will reach coastal NC Saturday afternoon, pushing offshore Sunday night. This will be quickly followed on Sunday by the arrival of a dry cold front. Models show a rather impressive surge of northerly winds developing Sunday night, veering northeasterly and lasting through Monday and perhaps into Monday night. This surge has a good chance of forcing another Small Craft Advisory due to 25 knot winds and 6 foot seas. Lighter winds appear likely for Tuesday as high pressure builds across the area.

ILM WATCHES/WARNINGS/ADVISORIES

NC...None. SC...None. MARINE...Small Craft Advisory from 6 PM this evening to 9 PM EST Friday for AMZ250-252-254-256.