textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes from the earlier forecast.

DISCUSSION

As of 320 AM Thursday...

KEY MESSAGE 1... Unsettled weather and above-normal rain chances are expected through Sat evening, with isolated heavy downpours possible. A few strong storms also possible on Fri.

We will stay in a moist and unsettled pattern through late Sat, as baggy mid level troughing holds from the E Great Lakes/SW Quebec down through W NC/AL/GA, sandwiched between a strong anticyclone centered over AZ/NM and another anticyclone centered offshore SE of Bermuda. Yesterday's below-normal PW (~0.75-1.1") has already been supplanted by values of 1.5-2.0" as a deep wet flow through the column continues on the E side of the mid level trough. These anomalous PWs (110-130% of normal, highest along/E of Hwy 1) combined with periodic upper level speed maxes rotating through the trough base to the E side of the trough (yielding modest DPVA) and the passing bouts of RRQ upper divergence will act on this moisture to squeeze out scattered showers across our area, with a few mainly afternoon and evening thunderstorms possible. Dewpoints returning to the low-mid 70s and partial heating through a mix of sun and clouds will help push daily SBCAPE to peaks of 1500-2500 J/kg each day through Sat, highest mid-late afternoon, although the deep layer bulk shear stays quite borderline at around 20 kts and mid level lapse rates are likely to hold at 5.3-5.9 C/km, which should limit storm organization and strength respectively. But the elevated PW values especially along/E of Hwy 1 along with expectations of a deep warm cloud layer over 4 km favoring warm rain processes and the potential for slow storm motion and training will support pockets of heavy downpours and high localize rain totals. The expected limited coverage of heavy rain clusters precludes consideration of a flood watch, but at least a few flood advisories may be needed. Rain chances will head back down late in the weekend as the upper level shear axis pivots clockwise to a W-E orientation and pushes to our S, allowing mid-upper ridging to build from the mid Miss Valley and lower Ohio Valley through the Mid Atlantic.

Regarding the potential for strong storms, a few wet microbursts will be possible each afternoon/evening, with the highest risk for strong storms on Fri, when SPC has us in an area of Marginal Risk (level 1 of 5) for severe storms. Again, the bulk shear won't be especially strong, but the moderate CAPE and possible dynamic contributions from upstream MCVs and RRQ upper divergence could tip the scales to more mature and long-lived storms on Fri.

KEY MESSAGE 2... Above-normal temperatures likely to end August and persist into early September.

The persistent anomalous mid/upper lvl ridge and anticyclone over the Four Corners region will be displaced by a series of shortwave troughs progressing through the PacNW and northern/central Intermountain West. This process will gradually build mid/upper lvl heights over the Deep South and TN Valley early next week and likely persisting into early September.

This height pattern will be favorable for positive H850 temp anomalies to spread into the region and favor well-above normal temperatures. Although the temperature forecast will naturally be complicated by late morning and afternoon convective chances, deep layer of anomalous lower/mid tropospheric temps, and close proximity with the deep subtropical ridge may help mitigate the widespread convective chances. As a result, temperatures in the mid/upper 90s will be possible Tues onward with the experimental HeatRisk having a 40-70% chance of reaching the Major risk category.

The European model suite and related AI guidance holds this pattern well into the first full week of September while the GFS model suite shows the potential to break down the ridge and retrograde it westward as early as late next week.

AVIATION /12Z THURSDAY THROUGH MONDAY/

As of 650 AM Thursday...

In addition to streams of mid and high level cloudiness passing over our region this morning, areas of bkn MVFR to IFR clouds have developed across NC, with pockets of IFR/LIFR conditions across our extreme east and south, including IFR conditions at RWI/FAY and MVFR at INT/GSO over the last few hours. These low clouds and fog are expected to break up and lift by 15z, although the very light winds over the area may result in a slower improvement in isolated locations. Then starting late morning, VFR conditions should dominate across central NC terminals for much of today, although isolated to scattered showers/storms are expected to develop during the early-mid afternoon, with the highest coverage expected in the SE (FAY), and brief MVFR conditions could occur in and near and showers/storms. Coverage of any rain will diminish from late evening into the early overnight hours, then there is a chance for MVFR cigs/vsbys at all sites early Fri morning, especially in areas that see any rain. Surface winds will be under 8 kts mainly from the S and SW through tonight.

Looking beyond 12z Fri, any sub-VFR conditions should improve to VFR by late morning Fri. The chance of showers and storms and associated periodic sub-VFR conditions will remain high through Sat evening, with highest chances from mid afternoon through early evening Fri and Sat. Morning sub-VFR fog/stratus can't be ruled out 08z-14z at any site Fri and Sat. Rain chances should then decrease for Sun onward as ridging builds aloft, and chances for early-morning sub- VFR fog/clouds will also decline.

RAH WATCHES/WARNINGS/ADVISORIES

None.