textproduct: Raleigh

WHAT HAS CHANGED

As of 205 PM Wednesday...

* Increased magnitude of winds and wind gusts ahead of and behind the strong cold frontal passage Friday through Saturday. Further increase will likely be needed in subsequent updates as the forecast enters the high-res model range.

KEY MESSAGES

As of 205 PM Wednesday...

1) A strong cold front will bring mostly light rain, seasonably gusty winds, and a sharp drop in temperatures Friday into Saturday.

2) Adverse fire weather conditions possible Friday and again on Saturday around the cold frontal passage.

3) Widespread frost conditions likely with localized freeze possible Sun morning.

DISCUSSION

As of 205 PM Wednesday...

KEY MESSAGE 1... A strong cold front will bring mostly light rain, seasonably gusty winds, and a sharp drop in temperatures Friday into Saturday.

Latest guidance remains in good agreement of the synoptic pattern through mid-week with the main highlight coming from another strong cold frontal passage Fri through Fri night. Amidst mostly zonal flow over the CONUS, mean troughing over the Gulf of Alaska will continue to shed lobes of weak mid-level disturbances, one of which is expected to amplify as it progress into the Eastern CONUS by this weekend.

The next chance for measurable precipitation comes late Fri afternoon into Fri night. Central NC will be displaced south of the better DPVA over the Mid-Atlantic and only experience meager H5 height falls. Primary forcing will come from a combination of low-level FGEN and weak perturbations rippling through a seasonably moist band of moisture along and behind the front. This should result in a medium-high probability of light rain behind the front, but low rainfall amounts (< 0.5"). Showers and some isolated storms can't be ruled out along the front as 700-500mb lapse rates increase to > 7C/km from a remnant/modified EML over the High Plains advects over the Carolinas, but with the lack of Gulf moisture influence in the boundary layer, the base of the EML may act to cap deep convection. Point soundings adjusted surface conditions from the GFS and NAM suggest temperatures in the mid 80s and surface dew points in the upper 50s could substantially weaken SBCIN and result in 500-1000 SBCAPE immediately ahead of the front within a kinematic environment of 30-45 kts of deep-layer shear. This combination would be supportive of a conditional risk for a marginally strong storm or two, but lack of more substantial instability, convective temps unlikely to be met ahead of the front, and storm motions keeping convection elevated behind the front, will all greatly limit the risk.

KEY MESSAGE 2... Adverse fire weather conditions possible Friday and again on Saturday around the cold frontal passage.

Despite marginal meteorological parameters on Friday, daily record warmth, a marginally dry air mass, seasonably breezy southwest winds, and bordering historic dryness within 100hr- fuels may allow for fire behavior to become especially hazardous. Additionally, dry post-frontal northeasterly winds with widespread MinRH less than 30% will likely enhance fire weather concerns, especially across the Piedmont where RH will be closer to 20%.

KEY MESSAGE 3... Widespread frost conditions likely with localized freeze possible Sun morning.

A modified Canadian high will slide across the Ohio Valley Sat and briefly settle over the southern Mid-Atlantic Sun morning, strengthening to +1035mb. Low-level thicknesses slightly compared to Sat morning (behind the frontal passage), but a more favorable surface high location should provide more optimal radiational cooling potential Sun morning. Leaning into statistical guidance during this time supports widespread sub- freezing conditions outside of urban city centers with mid/upper 20s possible in the coldest locations of the eastern Piedmont. These temperatures would be especially hazardous to any early budding plants/vegetation that are sensitive to the cold. The Frost/Freeze program for central NC will begin the morning of April 1st which will resume the issuance of Frost Advisories, Freeze Watches/Warnings. Until then, will continue to highlight this risk in the HWO and gridded weather forecast.

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 740 PM Wednesday...

VFR conditions are likely to hold over central NC terminals for the next 24 hrs. Periods of mostly bkn high and mid clouds will dominate this evening, then sct-bkn clouds based at 5-6kft AGL will develop over the area, lasting through much of Thu. INT/GSO/RDU have a good chance for low level wind shear conditions tonight into early Thu (around 04z-14z), as surface winds from the SSW at 3-6 kts are topped by a SW low level jet at 30-35 kts with an inversion at 1200- 1400 ft AGL. The LLWS will dissipate with mixing by mid morning Thu, when SW winds 9-14 kts will gust up to 18-24 kts through the day.

Looking beyond 00z Fri, another round of LLWS is possible again Thu night 04z-12z, for SW surface winds under 10 kts topped by an inversion with SW winds at 35-45 kts at 1500-1800 ft AGL. An approaching cold front will bring a likely trend to sub-VFR conditions in rain from N to S late Fri afternoon through much of Fri night, with the highest rain chances at RDU/RWI/FAY. VFR conditions should then return Sat, lasting through Mon.

CLIMATE

Record High Temperatures:

March 27: KGSO: 86/1921 KRDU: 87/2007 KFAY: 87/1946

Record High Minimum Temperatures:

March 27: KGSO: 60/2007 KRDU: 65/1949 KFAY: 65/1949

RAH WATCHES/WARNINGS/ADVISORIES

None.