Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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524 FXUS62 KRAH 261703 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 100 PM EDT TUE JUL 26 2016 .Synopsis... Strong high pressure aloft will extend across the region through Wednesday, bringing continued hot and humid conditions to central NC. The chance for afternoon storms will increase toward the end of the work week. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 AM Tuesday... Late today into this evening may bring our best chance for rain in several days, with good chances for scattered showers and storms across the northern half of the forecast area. Latest surface analysis shows the offshore-centered ridge extending across the Southeast states with weak lee troughing over our west and the synoptic front to our N/NW along the OH valley. While the mid and upper level ridge will hold across the region, the axis will shift a bit southeastward later today as shortwave energy over the lower Midwest tracks eastward across the OH valley and mid-Atlantic, nudging the westerlies slightly to the south and inducing sufficient acceleration aloft to boost deep layer bulk shear to around 20 kts across northern NC. This, along with a corresponding slight increase in previously-meager mid level lapse rates along and north of the NC/VA border, will create an environment that will be more conducive for convection to initiate and grow upscale. MUCAPE is expected to peak at 1000-2000 J/kg today, highest near the border and over NE NC, and this is where the convection-allowing models (CAMs) show the most long-lived activity today. But the HRRR/HRRRX/RAP, WRF-NMM/ARW, SSEO, NSSL WRF, and NCAR ensemble neighborhood probabilities all indicate at least some convection over the remainder of the western Piedmont as well, warranting at least isolated coverage there, with warmer/drier air aloft limiting coverage. Scattered coverage is anticipated over northern NC, and this activity may congeal into clusters over our NE sections this evening -- fueled by better deep layer bulk shear and slightly greater instability in this area - - before gradually diminishing overnight. The only notable changes to the existing forecast will be to delay convection onset a couple of hours over all but the NW, raise pops a tad over all of the western Piedmont, and retain pops in our eastern sections later into the night as suggested by the NSSL WRF, HRRRX, and others. High-res guidance still supports highs in the mid-upper 90s, and with a mixing/lowering of dewpoints with heating likely to follow a pattern similar to yesterday, we should reach dewpoints from the upper 60s NW to lower 70s SE this afternoon, equating to heat index values easily peaking at or above 105 over the advisory area. -GIH Previous discussion as of 305 AM Tuesday: Today: Mid/upper level ridging continues over the area this morning with the mid level high centered across the Carolinas. Weak disturbances aloft continue to track around the mid/upper level ridge to the west and north of central NC. The center of the mid/upper level ridge is forecast to shift slightly to the southeast today, which will allow for a better chance of weak disturbances tracking around the ridge to affect northern portions of central NC this afternoon/evening. Once such disturbance is helping to support and area of showers drifting northward across northern GA/AL. This weak energy coupled with another weak disturbance located over the lower OH/TN valley region this morning will combine along with a weak surface trough across the area to produce isolated to widely scattered showers and storms this afternoon/evening (with better coverage likely to the north of our area). Given strong heating during the morning into the early afternoon hours we will likely see at least 2000 to 2500 J/KG of MLCAPE across the area today. Deep shear however looks fairly weak, with maybe 15 to 20 kts of westerly flow at 500 MB. This environment will be supportive of wet downbursts, with perhaps a few clusters of storms possible. Thus, the latest day one convective outlook from SPC has our far northern counties in a marginal risk for severe storms with possibly a few damaging wet downbursts. The main story today though will again be the relentless heat, with high temps expected to again range from the mid to upper 90s and heat index values ranging from near 100 NW to 104-107 elsewhere. Thus, will continue the heat advisory today from noon to 8 PM for all but the far Western Piedmont. Tonight: Most convection will generally die off by late evening with another warm night expected. Expect lows temps tonight to generally be in the mid to upper 70s. Can`t completely rule out additional weak disturbance tracking across northern portions of the area overnight, possibly sparking a shower or storm, though think any activity will be quite isolated as we should still be under the general influence from the nearby mid/upper level ridge.-BSD && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 325 AM TUESDAY... Persistent mid/upper level ridge located just to the south/southeast of central NC will continue to provide the region with hot and humid conditions with another day of highs in the mid to upper 90s and heat index values in the 100-107 degree range (highest east and south again). Thus, another heat advisory will likely be needed again on Wednesday afternoon/evening. With a similar pattern to today, we will again see the best chance of scattered showers and storms across the northern half of the area, with less across the south (closer to the center of the ridge). Deep layer shear is a bit stronger with around 20-25 KTS of 500 MB westerly flow. Thus, think we could see a few more clusters of storms across northern portions of the area. In addition a weak cold front will stall across southern VA on Wednesday afternoon, helping to increase coverage near the VA/NC border as well. More of the same is expected on Wednesday night, with warm lows in the mid to upper 70s and generally dry conditions. However, as will be the case tonight, we can`t completely rule out isolated showers/storms associated with possible weak disturbance(s) tracking across northern portions of the area. Confidence is too low to include any mention of precip in the forecast at this time though. && .LONG TERM /Thursday through Monday/... As of 300 AM Tuesday... Persistent upper level high over the Southeast U.S. will maintain hot conditions over central NC Thursday and Friday. Heating of the moist and moderately unstable air mass will support the development of isolated-scattered late afternoon-evening convection, mainly north of highway 64 where subtle height falls and presence of surface trough will occur. Low level thicknesses Thu still support max temps in the mid/upper 90s, and with sfc dewpoints in the low/mid 70s, potential for the continuation of heat advisory very possible. Thicknesses Fri lower 15-18m as the upper high begins to weaken, though this may be too aggressive as history suggest that the thicknesses may only lower 5-8m. Thus expect highs Friday back into the mid/upper 90s. Potential for more appreciable change in the weather pattern expected by Saturday-Monday as center of upper ridge shifts southward. This will allow weak upper disturbances to skirt across our area, especially across the north. This should lead to an uptick in the coverage of afternoon-evening convection. In addition, with more clouds/convection, should see max temps lower a few degrees with max temps generally in the 90-95 degree range. Presence of the surface trough and available moisture and instability will support additional convective development early next week. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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As of 100 PM Tuesday... VFR conditions are likely to dominate through Wed afternoon, although scattered storms may produce localized enhanced wind gusts and brief sub-VFR conditions late today through this evening, mainly at INT/GSO/RDU/RWI. Strong, dry, and deep ridge of high pressure in the middle and upper levels of the atmosphere will hold overhead for the 24 hours and beyond. Any cloudiness will be VFR, mostly scattered except for a period of broken clouds late today into tonight at INT/GSO/RDU/RWI, as well as in/near any storms. Light fog (MVFR) is possible late tonight into Wed morning, mainly at RWI/FAY, and isolated banks of shallow, more dense fog may occur, mainly near RWI. The overall threat of sub-VFR fog is low, but places that see a shower or storm later today will have a better chance of seeing fog late tonight into Wed morning. Surface winds will be light from the southwest at 6-10 kts through Wed. Looking beyond 18z Wed: Mostly VFR conditions are anticipated, although late night and early morning MVFR fog is possible each day through Fri, with a better chance of sub-VFR fog/stratus Sat/Sun. Scattered showers/storms are again expected Wed afternoon, mainly at the northern TAF sites. Storm chances will drop once again for Thu and Fri, before rising again over the weekend. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon today to 8 PM EDT this evening for NCZ007>011-024>028-040>043-074>078-083>086-088-089. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/BSD SHORT TERM...BSD LONG TERM...WSS AVIATION...Hartfield

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