Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 281921 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 320 PM EDT THU JUL 28 2016 .Synopsis... An upper level disturbance will track just to the north of the region today and tonight around the hot high pressure over the Southeasten US. A surface trough of low pressure will stall across the area through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 320 pm Thursday... ...Have upgraded the Heat Advisory to an Excessive Heat Warning for areas along and east of I-95... ...Heat Advisory continues for all of the Piedmont counties... The Subtropical ridge in place over the SE U.S. will continue to produce very warm and humid conditions across Central NC today. A mid-level shortwave trough, currently over the TN Valley, will skirt the NW periphery of the subtropical high in place over the region and will track newd across the southern and central Appalachians this evening, shearing along the way before reaching the Northern Mid-Atlantic States by Friday morning. In response to the approaching trough, the persistent lee side surface trough in place east of the Appalachians will sharpen with a weak surface wave expected to develop invof of Virginia/DC later this evening. Dangerously high dew points in the mid 70s to upper 70s has and will continue to pool on the east side of the sharpening surface trough. As of 10 am, heat indices along and east of the I-95 corridor are already in the 100 to 105 range. When combined with afternoon temperatures in the upper 90s to 100 F range, heat indices of 110 to 115 F are expected and thus have upgraded the heat advisory to a heat warning for areas along and east of the I-95 corridor. Elsewhere across the western and central piedmont will leave heat advisory in place with heat indices expected to range between 103 to 109 F. As far as rain/convective chances: Regional mosaic radar shows a band of showers and storms across eastern KY/TN that has developed along ahead of the approaching trough. While the bulk of the convection is expected to affect TN/KY/WVA/VA, associated outflow boundaries may set off new convection, at least on a scattered basis, over much of the northern tier into the mid-evening hours. While the stronger mid-level flow is expected to be just north of the region, 20 to 25 kts of deep layer shear bordering the northern counties combined with moderate to strong instability of 2500 to 3000 J/KG of mlcape will yield a threat for one or two severe clusters to develop, with damaging wind the main threat. The threat will diminish rapidly this evening as is typically the case with strongly diurnally driven storms. We will carry 30 to 40 POP across the N, with only 10 to 15 POP SE. Lows tonight 70-76. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 320 PM Thursday... Low-level thicknesses and heights aloft fall slightly on Friday as the subtropical high shifts just east of the area and broad troughiness begins to settle into the area from the west. However of more significance, is the potential for dewpoints to mix out into the upper 60s and lower 70s Friday afternoon owing to the low-level westerly flow that develops in the wake of the surface low exiting off the Mid-Atlantic Coast. So despite similar afternoon temperatures in the lower 90s NW to upper 90s SE, the drier air will suppress heat indices with current forecast grids showing only the far SE zones close to advisory criteria. Confidence is too low at this time to warrant the issuance of an advisory with this package so will let midnight shift re-evaluate. Expect the westerly low-level flow east of the mountains to also suppress convection Friday afternoon, maintaining isolated/slight chance of diurnally driven convection. Lows Friday night in the lower to mid 70s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 250 PM Thursday... The pattern for the long term period will feature a low amplitude but broad trough across much of the eastern third of the country. With our area on the eastern side of the trough axis during the weekend, look for above normal temps to continue (low-mid 90s) during that time, but daily diurnal rain chances should be at or above normal (30-40% each day) given more abundant deep layer moisture and a series of passing short waves embedded in the sw flow. Perhaps the increased rain chances and assoc cloud coverage may help mitigate the oppressive heat somewhat compared to what we`ve seen the past few days. For the early part of next week, the aforementioned trough axis is progged to cross the eastern seaboard. The assoc sfc cold front may attempt to move across our area, setting up increased rain chances for Monday. Assuming the front does indeed push south of our area, we may see at least a brief return to normal temps (highs in the upper 80s and lows in the upper 60s) during the mid-week period with lower humidity and at or below climo pops. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 140 PM Thursday... Isolated to widely scattered strong to severe storms are possible, mainly across northern portions of the forecast area through the early evening. Otherwise generally VFR conditions are expected with some patchy early morning ground fog possible Friday morning. Outlook: Outside of isolated to scattered storms each afternoon/evening and some patchy early morning fog, expect predominately VFR conditions through Friday. Rain chances are expected to increase by the weekend and into early next week. && .RAH WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 8 PM EDT this evening for NCZ011-027- 028-042-043-077-078-085-086-088-089. Heat Advisory until 8 PM EDT this evening for NCZ007>010-021>026- 038>041-073>076-083-084. && $$ SYNOPSIS...BADGETT NEAR TERM...CBL SHORT TERM...CBL LONG AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.