Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 151839 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 239 PM EDT Tue Aug 15 2017 .SYNOPSIS... A moist and unstable airmass will persist today. A drier airmass will advect into North Carolina tonight and Wednesday as a back-door cold front progresses southward into the Mid-Atlantic. Moisture will return by Thursday as southerly flow strengthens in advance of a cold front progressing east toward the Ohio valley. && .NEAR TERM /THROUGH TONIGHT/...
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As of 239 PM Tuesday... At 16Z, observations indicated an atypically moist airmass in place across central NC, with surface dewpoints in the mid/upper 70s and PWAT values ranging from 2.00-2.25". Diurnal heating is expected to yield moderate to strong instability (MLCAPE 1500-2500 J/kg) this afternoon. Low-level forcing will be virtually absent this aft/eve. Central NC remains at the southern fringe of the westerlies. At 16Z, several small amplitude waves were noted upstream of central NC, the closest of which was located in northeast TN (invof the Tri-Cities). With the above in mind, expect convection to develop by mid aft in the W/NW Piedmont as the aforementioned wave progresses east into northwest NC. Convection should build E/ESE across the area in advance of the wave late this afternoon and evening. Despite marginal DCAPE and weak (5-10 knot) low-level flow, 15-25 knot westerly mid-level flow and moderate to strong instability should be sufficient for activity to increase in coverage along/ahead of the wave as it tracks E along the NC/VA border this aft/eve. Convection is expected to end from WNW-ESE or NW-SE between 03-06Z as the upper wave progresses east of central NC toward the OBX. Low-level flow is expected to veer to the north overnight in the wake of the wave, advecting a drier low-level airmass southward through central NC. As a result, early morning fog/stratus is unlikely to develop on Wed. Expect highs ranging from the mid 80s (north) to lower 90s (south), with lows tonight in the lower/mid 70s, warmest S/SE. Wet downbursts cannot be ruled out in assoc/w the deepest cores this aft/eve given moderate to strong instability, deep moisture, and 0-6 km shear supportive of multicellular organization, though weak low- level flow and weak DCAPE should preclude anything more than brief/isolated instances thereof. -Vincent
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&& .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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As of 239 PM Tuesday... Subsidence in the wake of shortwave energy progressing ESE of central NC tonight and early Wed will result in weak pressure rises over the central Appalachians, aiding the southward advection of a drier low-level airmass into central NC. A drier low-level airmass combined with warmer mid-level temperatures should act to mitigate diurnal destabilization and, most likely, preclude convective development. Will indicate dry conditions with highs in the upper 80s (N) to lower 90s (S). Lows Wed night in the low/mid 70s, warmest S/SE. -Vincent
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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As of 239 PM Tuesday... Thursday and Friday...the risk for scattered showers/tstms remains in the forecast as a series of weak short waves move across in the wsw flow aloft. A more robust short wave trough is progged to approach on Saturday and lift by to our north on Sunday, and pushing a cold front down into the Carolinas in the process, and providing the synop scale support for additional rounds of scattered showers/tstms both Saturday and Sunday. With the upper trough pulling away and zonal or broad cyclonic flow left in its wake, the sfc boundary and moisture pool gets left behind across the Carolinas for early next week, thus continuing the daily risk for showers/tstms Monday and perhaps Tuesday, and also elevating the risk for the presence of clouds during the eclipse. Temps will run at or above normal through the period with no signif airmass changes.
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 1230 PM Tuesday... MVFR ceilings are expected to lift to borderline MVFR/VFR or low-VFR (3000-4000 ft AGL) by mid/late afternoon. However, sub-VFR conditions associated with convection will be possible at all terminals late this afternoon and evening, primarily between 18-03Z. Light/variable winds are expected to veer to the north at 5-10 knots after midnight. A drier low-level airmass advecting into the region from the north should preclude fog/stratus development late tonight/early Wed, though some uncertainty persists, primarily at the FAY terminal. Looking Ahead: Moisture will return to the region Wed night, and sub- VFR ceilings /low stratus/ will be possible once again during the early morning hours Thu. Expect a potential for aft/eve convection and early morning stratus each at all terminals Friday through the upcoming weekend. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...np AVIATION...Vincent

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