textproduct: Raleigh

KEY MESSAGES

As of 300 AM Saturday...

1) Unseasonably hot, near record temperatures today - but with very low humidity

2) Noticeably cooler Sunday - cloudy with light stratiform rain in the morning, then clearing through the afternoon-evening

3) Patchy frost possible Tuesday morning

DISCUSSION

As of 300 AM Saturday...

KEY MESSAGE 1... Unseasonably hot, near record temperatures today - but with very low humidity

Shortwave ridging, poleward of a sub-tropical high over the ern Gulf, will progress across and offshore the South Atlantic states today and ahead of a shortwave trough that will progress into the OH/TN Valleys by 12Z Sun. That trough will be preceded by a convectively-amplified mid-level trough, related to an extensive band of upstream convection now extending from the upr Great Lakes to the srn Plains, which will progress into the Middle Atlantic and wrn NC tonight-Sun morning.

At the surface, a front now draped across Southside and Tidewater VA will retreat slightly nwd ahead of a frontal wave forecast to develop in the lee of the Appalachians and across nrn VA and the Delmarva this evening. A trailing cold front will move across the Appalachians and into the nrn Piedmont of NC by 12Z Sun. Cntl NC will consequently be in the warm sector and a regime of swly flow between the approaching cold front and sub-tropical high pressure from the w-cntl N. Atlantic to the South Atlantic coast.

While mid and high clouds will thicken with the approach of the convectively-amplified mid-level trough tonight, moisture will otherwise remain limited. In fact, surface dewpoints are likely to mix out into the 40s F over most of the Piedmont and Sandhills again today. So while warm sector temperatures will likely reach the upr 80s and lwr 90s this afternoon, low humidity values in the 20s percent will help take the edge of the unseasonably hot, mid-April temperatures.

KEY MESSAGE 2... Noticeably cooler Sunday - cloudy with light stratiform rain in the morning, then clearing through the afternoon- evening

The cold front noted above will progress across cntl NC Sun morning. Its passage will be marked by the arrival of markedly cooler air and nwly winds that will gust up to 30-35 mph for a few hours immediately post-frontal passage. A band of light, anafrontal rain and widespread clouds will also follow the front, with both expected to move east and yield afternoon through evening clearing. Rainfall amounts are expected to be very limited: an average of a few hundredths of an inch over srn zones ranging to a tenth of an inch or so over the ne Piedmont and nrn Coastal Plain. Strong radiational cooling of the post-frontal airmass will favor low temperatures in the mid-upr 30s over rural Piedmont locations to lwr-mid 40s elsewhere Sun night - 50 F colder than high temperatures of recent days.

KEY MESSAGE 3... Patchy frost possible Tuesday morning

A 1028+ mb high will slide sewd from the Great Lakes across the mid- Atlantic Mon night into Tue before shifting offshore. Low-level thicknesses vary amongst the available guidance, ranging anywhere from 1300 m to 1330 m across central NC. The winds may remain stirred early until the high ridges across the area. The other question is whether high clouds will spread across the area and how thick they might be. For now, expect that coverage to be limited if they do develop. Combined with the light winds early Tue, temps could drop into the low-mid 30s across the VA border counties and some of the usual cold spots. However, with dewpoints in the low-mid 20s, RH values should max out in the 50-60 percent range by daybreak Tue, which may limit actual frost formation.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

As of 750 AM Saturday...

Continued influence from a continental/dry airmass will favor VFR conditions until of a cold front, and following band of low VFR to briefly MVFR ceilings and patches of light rain, moves across cntl NC Sunday morning - including at INT/GSO as early as 10-12Z Sun. Calm to very light/variable surface wind this morning will become swly and strengthen with daytime heating, with gusts to around 20 kts this afternoon.

Outlook: The aforementioned strong cold front will move southeast and across RDU, FAY, and RWI between 12-16Z Sun. A band of post- frontal ceilings, some as low as MVFR, and light rain, will result for a few hours behind the front, as will strong nwly surface winds that may gust up to 25-30 kts.

CLIMATE

All-Time Records for April:

KGSO: 95 on 4/28/1915 KRDU: 95 on 4/23/1980 and 4/18/1896 KFAY: 96 on 4/12/1930

Record High Temperatures:

April 18: KGSO: 90/1976 KRDU: 95/1896 KFAY: 93/1941

RAH WATCHES/WARNINGS/ADVISORIES

None.