textproduct: Raleigh

WHAT HAS CHANGED

* There is a low-end severe risk over the southern Piedmont and western Sandhills tonight.

* The forecast has trended drier for Friday night into Saturday. Meanwhile, the forecast has trended wetter for Sunday and Sunday night.

KEY MESSAGES

As of 110 PM Wednesday...

1) Waves of showers and embedded thunderstorms are expected tonight through through Thursday along/ahead of a cold front.

2) While showers are possible Saturday, the next round of widespread rain is expected Sunday through Monday.

DISCUSSION

As of 110 PM Wednesday...

KEY MESSAGE 1...Waves of showers and embedded thunderstorms are expected tonight through through Thursday along/ahead of a cold front.

This evening and tonight: Waves of showers and embedded storms are expected this evening, tonight, and during the day on Thursday along and ahead of a cold front forecast to push south during the afternoon and evening Thursday. Current radar and satellite imagery reveals several embedded mesoscale convective vortices (MVCs) tracking east along and ahead of the cold front. The front presently stretches from the lower OH valley into the TN valley region. An MCV currently near CLT will bring some isolated to scattered showers this afternoon over the western and southern Piedmont, but will be decaying as it tracks east with limited instability to fuel its eastward progression. While we cannot rule out some isolated showers as far east as the triangle, we should stay dry early this evening along/east of US-1.

The better chance of more widespread showers and embedded storms will be later tonight and overnight. Additional storms with embedded MCVs are expected to reignite over portions of eastern TN and northern AL/GA this afternoon and early evening. This activity is simulated by the latest HRRR/NAM-NEST, tracking east tonight and overnight as large-scale lift increases and precipitable water values reach anomalous values. At this time too, MLCAPE upwards of 500 J/kg combined with 50 kt or greater of deep-layer shear will focus over the southern Piedmont and western Sandhills of central NC. The last few runs of the HRRR have indicated some gusty winds tied to this messy convection tracking east, perhaps related to a possible gravity wave enhancement noted in our prior discussion. SPC does indicate a small area of marginal risk of damaging winds over this area of the western Piedmont given the aforementioned parameters. As such, we will need to keep a close eye on this conditional severe threat from about 22z to 03-04z tonight.

Widespread showers and storms should push east across most of the area overnight and early morning hours of Thursday with the said large-scale forcing. The actual surface cold front will stay pinned to our north and west across VA.

Thursday: Widespread showers and embedded storms will be in place much of Thursday morning and afternoon. Large-scale forcing and height falls will be driven by southwest moist flow aloft with a trough over the Great Lakes. Embedded MCVs are expected to complicate the forecast of the overall orientation of the showers. Some of the 12z CAMs, such as the HRRR and NAM- NEST show morning showers and storms especially across our southeast over the eastern Sandhills and southern Coastal Plain. While the actual cold front will still be to our north at this time, an effective front may set up south of US-64 and any associated MCVs. Along and south of this effective front is where a low-end severe risk cannot be fully ruled out during the morning and early afternoon. Effective shear will still reach over 50-60 kt but instability is somewhat lacking, leading to reduced confidence in the southeast.

By the afternoon and evening, the front is expected to slide south out of VA, earliest across the northern sections of our CWA during the afternoon and over the south in the late-afternoon to early evening. Additional shower activity will still be favored as the mid-level flow is still southwesterly, aiding some isentropic ascent atop the boundary. This shower activity is not expected to be severe as instability is forecast to align south of the front by this time. Showers should come to an end by Thursday evening as the front sags south and forcing wanes. Cool high pressure will favor lows by early Fri in the mid/upper 40s to low 50s.

Rainfall amounts: While embedded MCVs and potential messy convection may alter the orientation and pattern of rainfall, most CAM solutions indicate rainfall totals ranging from a half inch to an inch, with higher end isolated amounts of 1.25 to 1.75 inches of rain. The 00z HREF painted the highest rainfall totals from Charlotte up into the Triangle and Roanoke Rapids, while the 12z HREF shows similar amounts but perhaps slightly shunted a bit northwest of its 00z solution.

KEY MESSAGE 2...While showers are possible Saturday, the next round of widespread rain is expected Sunday through Monday.

The front that will cross the area over the next two days will sink south to the Gulf Coast by Friday, then begin to shift offshore to the east during the beginning of the weekend. While models continue to signal that another wave of low pressure will develop along the front, it now appears that the wave and associated precipitation will remain a little closer to the Carolina coastline than previously forecast, which will reduce the overall chance of precipitation across central North Carolina. The forecast now calls for only a slight chance of showers primarily along and east of I- 95, mainly Saturday morning.

On the other hand, the next cold front that is going to move along the East Coast is now projected to arrive a little more quickly. As a result, the next chance of rain will begin as early as Sunday morning, and with the frontal passage occurring late Sunday night, Sunday night should have the highest chance for precipitation. The chance for showers will linger on Monday, especially east of Interstate 95, but nearly all precipitation will come to an end by Monday evening.

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 814 PM Wednesday...

Through 00Z Friday: The next of several episodes of rain is now moving into the Triad area, but flight conditions remain VFR as rain intensity is mostly light. This rain will gradually move east, and with time overnight flt conditions are expected to fall below VFR as heavier rain moves in and across central NC from the west. Then toward daybreak (sometime between 09-13Z) IFR flight conditions will become more uniform across central NC as the front move south and sfc winds become more N-NE. It's worth noting that until the front moves through (that is, for areas south of the front), there remains the possibility for the precip to be more convective/shower in nature, with perhaps even some tstm activity along with wind gusts up to 25-30kt, but that would be most likely south of RDU between 13- 18Z Thursday and until the front completely clears central NC. Otherwise, even after the front exits, sub-VFR flt conditions will continue through the TAF period everywhere across central NC except KINT/KGSO where some low-level drier air will begin arriving during Thursday afternoon.

Outlook: A favorable pattern may exist for fog/low-stratus in the wake of the departing rain and clearing skies Thurs night into Fri morning. There will be another chance of showers/storms and flight restrictions with the approach and passage of another frontal system Sun-Mon.

RAH WATCHES/WARNINGS/ADVISORIES

None.