textproduct: Raleigh

WHAT HAS CHANGED

* Isolated showers are possible over the NW Piedmont this evening. A better chance will exist area-wide Friday into Saturday ahead of a cold front.

* The extended forecast period could bring more seasonable temperatures with unsettled weather early to middle of next week.

KEY MESSAGES

As of 115 AM Thursday...

1) A few frontal systems will bring isolated to scattered storms Thursday through Sat.

2) An unsettled pattern with more seasonable temperatures may return early to middle of next week, though details are unclear at this point.

DISCUSSION

As of 115 AM Thursday...

KEY MESSAGE 1... A few frontal systems will bring isolated to scattered storms Thursday through Sat.

The anomalous upper ridge over the TN valley is forecast to gradually shift west toward the lower MS valley late this week and weekend. As that happens, northwest flow around the periphery of the ridge may direct a few convectively-induced disturbances into the region today through early Sat ahead of a few frontal systems. Moisture levels will correspondingly increase to well above seasonable normals with precipitable water values around 1.7 to 2 inches during this period.

Ensemble and deterministic guidance shows isolated showers or storms developing over the lower OH valley into the Appalachians of NC/VA this afternoon and evening in association with a convectively-induced disturbance in the developing NW flow aloft. Instability today will be confined west of central NC in VA and far western NC. Any showers that do develop, albeit minimal, are only expected to briefly impact the Triad and along the VA border of the northern/northwest Piedmont.

A better chance of showers and storms will exist Friday into Saturday as a more prominent lead trough and backdoor cold front move south from the northeast late Friday through early Saturday. Instability increases to 1000-1500 J/kg, though lapse rates and shear will limit storm intensity. Storms will maximize during the early to mid evening Friday over central NC. On Saturday, as the front moves through, the best chance of storms will focus over the southern Piedmont, Sandhills, and southern Coastal Plain along residual instability and any lingering convergence if the front is slow to move through. Either way, NE flow should favor lower temperatures in the mid 80s Saturday, contrasted with lower 90s Friday. We cannot rule out some stray isolated storms Sunday, but that part of the forecast appears to be trending drier.

KEY MESSAGE 2... An unsettled pattern with more seasonable temperatures may return early to middle of next week, though details are unclear at this point.

From Sunday onward, ensemble guidance continues to show a potentially unsettled pattern, albeit with low predictability. Regardless of which ensemble cluster solution you examine, they all appear to agree that northeast flow will re-exert itself Tuesday into mid-late next week as a 1035-mb high over eastern Canada noses down into the Mid-Atlantic. This is evident after a brief warm and humid pattern Sunday and Monday in the 80s to around 90. Ahead of the cooler and potentially more seasonal pattern will be a cold front, sometime Monday or Tuesday, that could bring showers/storms. Coupled to this will be a closed upper-low over the NE Gulf that could ride up the SE US in response to troughing over the MS/OH valley. If that were to happen, suggested by some ensembles, as well as the EC-AIFS and AI-GFS, a surface low could develop along a frontal zone along the Carolina coast, to favor isentropic rain or showers early to middle of next week. All of this is unclear given the spread in the guidance, though there are signals for more seasonable temperatures in the 70s to low 80s in a CAD-type regime if that were to materialize.

AVIATION /16Z THURSDAY THROUGH TUESDAY/

As of 1140 AM Thursday...

Scattered showers/storms are expected to develop from wrn through Southside VA through this afternoon; and a couple of isolated ones may drift generally swd and into the INT/GSO vicinity mainly between 22Z-01Z, before dissipating. VFR conditions are expected otherwise and elsewhere until just beyond the 18Z TAF period, when Friday afternoon through night a couple of cold fronts will trigger scattered to locally numerous showers and storms over cntl NC.

Outlook: A risk of convection will linger along the passing fronts on Saturday, especially over the srn half of NC and including at FAY. Nely flow behind the fronts will otherwise increase the likelihood of IFR-MVFR ceilings, lowest and most prolonged over the Piedmont (especially at INT/GSO), both Saturday and Sunday mornings. Stronger nely flow, and an increasing likelihood of cold air damming, will favor additional sub-VFR conditions and periods of light rain during the middle of next week (as early as Tue).

RAH WATCHES/WARNINGS/ADVISORIES

None.