textproduct: NWS Wilmington

WHAT HAS CHANGED

Diurnal shower chances have been reduced each day through Saturday due to limited boundary layer moisture and a capping inversion aloft. Forecast rain chances Sunday into Sunday night have been increased with the arrival of the next cold front.

KEY MESSAGES

1) Summerlike Bermuda high pressure will maintain southerly winds and unseasonably warm weather throughout the week.

2) The next cold front should arrive late Sunday accompanied by an increased chance of showers or t-storms.

DISCUSSION

KEY MESSAGE 1: Summerlike Bermuda high pressure will maintain southerly winds and unseasonably warm weather throughout the week.

Models have been fairly stable over the past few days with their depiction of an amplifying upper ridge along the Southeast Coast through the remainder of the week supporting Bermuda high pressure at the surface. Using Hysplit to view back-trajectories from the GFS reveals the incoming airmass is not of tropical origin, but instead is Canadian air that moved off the New England coast 3 days ago and has ventured no farther south than about 30 degrees latitude across the subtropical Atlantic. For this reason low level moisture should not increase substantially and daytime dewpoints should mix down into the 50s each afternoon away from the beaches.

This also nudges the forecast chances for diurnal showers downward slightly by eroding what was already marginal CAPE below the subsidence inversion aloft. If we get an isolated daytime shower Thursday through Saturday, it's most likely to be inland where surface temperatures will be higher and the capping inversion aloft slightly weaker.

Forecast highs each day through Sunday are in the 80-84 range inland, with mid to upper 70s expected at the beaches. This is due to synoptic onshore flow supplemented each day by the seabreeze circulation. Both day and nighttime temperatures should run about 10 degrees above seasonal norms through Sunday.

KEY MESSAGE 2: The next cold front may arrive late Sunday accompanied by an increased chance of showers or t-storms.

Models continue to show surprising agreement with timing of the next cold front, still anticipated to reach the area Sunday night.

The persistent upper level ridge will erode along its western periphery as a shortwave moves eastward across the Great Lakes on Sunday. Mid level flow should veer southwesterly which will advect a stream of Gulf moisture across the eastern Carolinas during Sunday's afternoon and evening hours. With the capping inversion aloft gone, this is our best chance of seeing more widespread shower and thunderstorm activity across the eastern Carolinas. GFS MOS agrees with NBM guidance with 50-70 percent chances for measurable rain as this system crosses the area Sunday into Sunday night. Two week-observed rainfall has ranged from 0 to 10 percent of normal across the area (1.3 to 1.6 inches below normal) since March 17 so we would dearly like to see some rain from this system.

It's still too early to read too much into severe weather chances on Sunday. Forecast 700 mb wind speeds Sunday afternoon and evening vary from 25-45 knots between the ECWMF and Canadian (the GFS is in between) which implies very different values of 0-6 km bulk shear. We'll hopefully get a clearer picture over the next few days.

The post-frontal airmass Monday and Tuesday looks significantly cooler with highs in the 60s and diminishing rain chances.

AVIATION /18Z TUESDAY THROUGH SATURDAY/

The area remains in a very summer-like pattern with Bermuda High Pressure keeping a south to southwesterly flow across the area. Such a pattern can leave terminals susceptible to fog development, not unlike what was experienced this morning at CRE. Guidance has just about unilaterally agree that there is no repeat tonight. There was concern earlier that stratus development may occur but this too is not portrayed in much guidance and the ones that do have 2-4kft cigs are not typically the more reliable ones so confidence is a bit lowered at this time.

Extended Forecast... Mainly VFR conditions are expected, although the potential exists for early morning fog/stratus Thu/Fri. Sea fog may become an issue beginning for the coastal terminals toward the end of the week and weekend.

MARINE

Through Wednesday...Bermuda High will keep conditions relatively unchanging with S to SW flow as is typical most of the summer. Waves will run about 3 ft and right near the wind wave/swell cusp of 7 seconds though the very small power bump seen in spectral plots at 10 seconds could linger.

Wednesday Night through Sunday...Although centered hundreds of miles east of the Carolinas, a ridgeline extending westward from the Bermuda High will sit across the Cape Fear area through Saturday. This should ensure light southerly winds 5-10 kt each day with nearshore bumps to 10-15 kt each afternoon due to local seabreeze effects. Seas should average 3-4 feet mainly in a 7-8 second southeasterly swell.

Winds should begin to increase in speed and veer southwesterly ahead of an approaching cold front Sunday. Despite being 5 days in advance, there is good model agreement on the front arriving at the coast Sunday night accompanied by a chance of showers or thunderstorms.

CLIMATE

Both January and February ran 2 to 4 degrees F below normal across eastern North and South Carolina. March has reversed that trend and heading into the last day of the month March's average temperature has run 3 to 4 degrees F above normal.

Assuming daily temperatures through the coming weekend run 8-10 degrees above normal, we should completely eliminate the remaining accumulated temperature "deficit" since January 1.

Location Current YTD Departure Forecast YTD Departure April 5 Wilmington -0.1 F +0.6 F N Myrtle Beach -0.2 F +0.3 F Florence -0.6 F +0.1 F Lumberton -0.3 F +0.3 F

ILM WATCHES/WARNINGS/ADVISORIES

NC...None. SC...None. MARINE...None.