textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes from the previous forecast.

DISCUSSION

As of 310 AM Saturday...

KEY MESSAGE 1... Isolated pockets of heavy rainfall are possible once again this afternoon into early evening, mainly over the S and E. Drier weather starts Sun and lasts through much of next week.

A diffuse surface boundary remains over the region, running NE to SW through central NC, with dewpoints mostly in the 60s to its NW and 70-75 to its SE. In the mid levels, a baggy shear axis to our W has been steadily drifting ESE toward our area while weakening, and early this morning this shear axis extends through the NC Foothills, keeping us on the weakly perturbed SSW mid level flow on its east side. PW values were around 110%-125% of normal NW-SE Fri but are projected to decrease to 90%-110% of normal NW-SE today, as both the surface boundary and the stream of deeper moisture shift gradually to our SE, and as the shear axis weakens further while maintaining an ESE drift. Observational trends and the latest model and ensemble output still show sctd showers and storms developing today, primarily S and E of the Triad, fueled in part by passing weak mid level perturbations yielding modest DPVA, upper divergence in the right rear jet quad, and SBCAPE peaking around 1000-1500 J/kg this afternoon. Drier air in our NW Piedmont and lesser dynamic contribution to lift will mean lower coverage there, perhaps just isolated at best. The weakening deep layer bulk shear and modest CAPE should keep the severe threat low today, but the continued slow cell motion will bring about another risk for locally excessive rainfall, primarily across our S and E where the PW will be greater. Most of the forecast area is under a Marginal risk (level 1 of 4) for excessive rainfall (excluding the Triad) Saturday. Convective activity should dwindle with loss of heating by mid evening, leading to fair to partly cloudy skies overnight.

As the shear axis weakens further and settles to our SSE with strong ridging building in from the W, PW will plummet further, with a loss of low level access to Gulf and Atlantic moisture as surface ridging spreads E-W to our S. As a result, rain chances will become quite low Sun through at least Wed, with building heat.

KEY MESSAGE 2... A hot start to September is expected across central NC.

After one near to slightly cooler than normal day today (highs in the lower-to-mid-80s), a warming trend will commence on Sunday that continues into late next week. This is due in large part to a strong ~595 dam mid-level ridge initially centered over the Southern Plains that shifts east into the lower MS and TN Valleys and eventually the Carolinas. At the surface, a Bermuda High will bring warm SW flow to the region through the period. With mostly sunny skies and very low (if any) precipitation chances, excessive heat will be a concern across central NC as we start the workweek and especially by mid to late week.

By Monday, forecast highs are in the lower-to-mid-90s, with mid-to- upper-90s by Tuesday that last into Friday. The hottest days look to be Wednesday and Thursday when isolated 100F readings can't be ruled out. The one silver lining is dew points don't look overly oppressive through the period and are forecast to mix out to the upper-60s to lower-70s each afternoon (other than perhaps the far SE). Still, with the exception of the far northern and northwestern Piedmont, this is enough for heat indices in the lower-to-mid-100s from Tuesday through Friday. The WPC Experimental HeatRisk is in the Major to Extreme categories for much of the region during this period. This means the heat is expected to affect anyone without adequate cooling/hydration. Heat Advisories may eventually be needed for a portion of the area, especially given the expected prolonged nature of this heat and overnight lows only dropping into the lower- to-mid-70s.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

As of 645 AM Saturday...

VFR conditions will dominate across central NC this morning, however areas of MVFR to IFR cigs are possible through 16z, mainly at RWI and FAY. Otherwise, mainly sct mid and sct-bkn high clouds will continue to stream over central NC today, especially over the SE half. VFR conditions are expected to dominate after 16z, although sctd showers and storms are possible this afternoon into early evening (17z-23z), mainly at FAY with a lower chance at RDU/RWI and lower still at INT/GSO, and brief MVFR conditions may occur in and near any such showers/storms. After 07z tonight, there is another chance for MVFR to IFR clouds, lasting through the end of the period. Surface winds will remain light, under 8 kts, mainly from the NE and E but shifting to be from the SE and S.

Looking beyond 12z Sun, sub-VFR conditions will remain possible through 13z early Sun morning. Otherwise, as mid level high pressure begins to build over the area with drier weather, VFR conditions are likely to dominate from Sun through Wed.

CLIMATE

Record High Temperatures:

September 1: KRDU: 101/1932

September 2: KRDU: 99/1912

September 3: KRDU: 99/2010 KFAY: 101/2010

September 4: KRDU: 100/1925 KFAY: 100/1944

Record High Minimum Temperatures:

August 31: KGSO: 73/2012

September 1: KGSO: 74/2012 KRDU: 76/1932 KFAY: 77/2021

September 2: KGSO: 73/1912 KRDU: 75/1912 KFAY: 75/2020

September 3: KGSO: 73/2020 KRDU: 78/1933 KFAY: 77/2020

September 4: KGSO: 72/2018 KRDU: 74/1921 KFAY: 75/2020

RAH WATCHES/WARNINGS/ADVISORIES

None.