textproduct: Raleigh

WHAT HAS CHANGED

As of 317 AM Saturday...

* Marginal risk for a few isolated stronger wind gusts in the southern Piedmont Sunday afternoon.

* Enhanced Risk for severe storms Monday.

KEY MESSAGES

As of 317 AM Saturday...

1) A few organized storms possible Sunday afternoon and evening, with isolated damaging winds possible across the southern Piedmont/Sandhills.

2) Anomalously potent system will spread convection across central NC Monday with increased chances for severe storms Monday afternoon and evening.

3) Cooler than normal temperatures expected Tuesday and Wednesday across central NC, with highs running 1520 degrees below normal.

DISCUSSION

As of 317 AM Saturday...

KEY MESSAGE 1... A few organized storms possible Sunday afternoon and evening, with isolated damaging winds possible across the southern Piedmont/Sandhills.

Strengthening swly flow along the western ridge of an offshore mid- level anti-cyclone will promote increasing moisture advection into the southeast on Sunday. At the sfc, esely flow will persist across central NC for much of the day as a sfc wave/low ride along the Carolina Coast. Forcing from this feature will likely spread showers and storms inland Sunday afternoon and evening.

Forecast soundings in the Southern Piedmont/Sandhills region indicate some support for potential mini supercells Sunday afternoon and evening. The 00Z RREFS contained a clustering of mid-level helicity swaths in this general vicinity. SBCAPE should be limited, and as such think stretching rotation to the sfc would be difficult. Additionally, CAPE profiles would not largely support hail. However, if a stronger storm or two develops, would not be surprised if a stronger gust mixes down from the stronger flow just above the sfc. As such, can't rule out an isolated damaging wind gust in the southern Piedmont/Sandhills region Sunday afternoon.

KEY MESSAGE 2... Anomalously potent system will spread convection across central NC Monday with increased chances for severe storms Monday afternoon and evening.

There continues to be good agreement amongst deterministic and ensemble guidance in simulating the eastward ejection of a potent mid-level trough and sfc cold front across the east coast Monday into Tuesday. Ahead of the front, central NC will be firmly in the warm sector Monday morning characterized by dew points in the mid to upper 60s. While initial morning convection and cloud cover could dampen downstream instability some, massive forcing aloft and associated very strong kinematics will likely support continued pre- frontal convection and convection along the front Monday afternoon and evening.

Sfc flow will pick up early Monday morning ahead of the approaching cold front supporting gradient wind gusts of 30 to 35 mph (perhaps some higher gusts with morning showers/storms mixing down stronger flow aloft). Guidance is in general agreement pumping at least ~500 J/kg of MLCAPE into central NC by early Monday afternoon. In the most bullish case (the NAM), upwards of 750 to 1000 J/kg of MLCAPE could plume up into our southern areas. Regardless, bulk-layer shear of 50 to 60 kts will spread east with time and easily support the potential for widespread strong to severe storms Monday afternoon and evening.

Forecasted shear-vectors early Monday afternoon may be oriented at 45 degrees wrt to the boundary. If so, this would support discrete supercells capable of isolated tornadoes. This scenario would be especially concerning if the more bullish MLCAPE scenario depicted by the NAM unfolds (latest runs of the NAM depict concerning STP values (~2 to as high as 4 in some runs) across much of central NC).

As the afternoon progresses, guidance supports a transition of the shear vectors to more-so boundary-parallel along the advancing front. Given how strong the shear is forecasted to be, a QLCS appears possible along the frontal passage which would favor potentially wide-spread damaging wind gusts with an embedded tornado risk through Monday evening.

Any lingering convection should move east of central NC by early Monday night.

KEY MESSAGE 3... Cooler than normal temperatures expected Tuesday and Wednesday across central NC, with highs running 1520 degrees below mid-March averages.

In the wake of Mondays cold front, cooler and drier air will filter into central North Carolina late Monday night into Tuesday. A broad upper-level trough settling over the eastern US will reinforce cold air advection through the day Tuesday, keeping temperatures below mid-March climatology.

High temperatures are expected to reach only the upper 40s to near 50 across the region Tuesday, which is roughly 15-20 degrees below normal for this time of year. Gusty west to northwest winds may also persist through much of the day Tuesday, with early morning wind chills in the 20s. Tuesday night lows will be in the mid to upper 20s with some cooler spots in the low 20s.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

As of 150 PM Saturday...

24 hour TAF period: High confidence VFR conditions will prevail through this evening. Northwesterly winds, with some gusts to around 20 kts, will veer around to more sely this aft. High clouds should move ewd across the area, becoming sct to bkn this aft/eve (highest coverage north). The biggest uncertainty is timing the development of MVFR cigs Sun morning. Most, if not all, terminals should be MVFR by the end of the TAF period. Ely winds may become gusty toward the end of the TAF period, mainly at the ern terminals.

Outlook: Cigs should lower to IFR and perhaps LIFR Sun eve through Sun night, with periods of rain/showers possible (highest chances in the Triad) as low-level moisture increases in a return flow pattern. Some gusty winds will be possible with showers where they occur. A strong cold front will bring showers and thunderstorms along with gusty winds (potentially strong) on Monday, accompanied by the usual cig/vsby restrictions where storms impact a terminal. Showers and storms should move out of the area Mon eve/early Mon night, with dry weather and VFR conditions expected thereafter.

RAH WATCHES/WARNINGS/ADVISORIES

None.