textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes from the previous forecast. Confidence is increasing that Thu afternoon through Sat will contain the highest rain chances of this next 7 days. Hottest weather likely Mon through Wed.

DISCUSSION

As of 335 AM Tuesday...

KEY MESSAGE 1... Unsettled weather and above-normal rain chances are expected late this week, with isolated heavy downpours possible.

Our current setup featuring surface high pressure nosing into NC from the N within below-normal PW will undergo a transition to a wetter pattern with increasing rain chances and higher humidity by Thu. The surface high will push E off the Mid Atlantic coast this morning, allowing a diffuse stalled surface frontal zone stretching from IA/MO SE and E through AL/GA/SC to off the S NC coast to lift back northward through NC today. The ensuing increasing low level southerly-component flow will draw higher dewpoints into central NC, while aloft, above-normal PW now over the central Plains and mid Miss Valley will swing SE and E into the Carolinas. Our mid level flow will be gently cyclonic as a baggy trough holds just to our W, reinforced by digging shortwave energy through S Ont/N MI, and nestled between two strong ridges over the Atlantic and the Desert Southwest. As periodic upper level speed maxes rotate through the trough base to the E side of the trough, the bouts of RRQ upper divergence, modest DPVA, above-normal PW, increasing surface dewpoints, and moderate SBCAPE will all contribute to increased rain chances for central NC, particularly late Thu through much of Sat. Given expected PWs over 2", deep warm cloud layer over 4 km favoring warm rain processes, and potential somewhat slow storm motion and training, pockets of heavy downpours and high rain totals will be possible. Limited coverage 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 through the Mid Atlantic.

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 Corner region will be displaced by a series of shortwave troughs progress 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 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.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

As of 650 AM Wednesday...

VFR conditions are generally expected to dominate central NC terminals for the next 24 hours, as high pressure centered to our north holds over NC, and a frontal zone remains to our south. But isolated IFR/LIFR conditions in the NE (including RWI) will persist until lifting between 13z and 14z. Otherwise, mostly sct VFR cumulus and sct-bkn high thin clouds are anticipated through this afternoon. Arrival of a weak disturbance from the NW and W this evening will bring increasing clouds with a trend toward VFR cigs based at 5-6kft through the end of the TAF period, and a few showers are possible after 22z, moving W to E. With these showers will come an increased chance for brief MVFR cigs after 06z. Surface winds will be under 10 kts from the S and SW during the daylight hours and light/variable pre-dawn and from dusk through nighttime.

Looking beyond 06z Thu, any patchy sub-VFR conditions near the end of the TAF period should improve by mid morning Thu. A higher chance of showers and storms and associated sub-VFR conditions is expected Thu afternoon through early Fri, with another high chance late Fri through midday Sat Rain chances should then decrease for late Sat through Sun as ridging builds aloft.

CLIMATE

Record High Minimum Temperatures:

August 31: KGSO: 73/2012

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

RAH WATCHES/WARNINGS/ADVISORIES

None.