Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220544 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 144 AM EDT Sat Jul 22 2017 .SYNOPSIS... Hot and mainly dry sub-tropical high pressure will expand across the mid-South and southern Appalachians through the weekend, then gradually weaken by early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 905 PM Friday... Scattered storms across eastern portions of the CWA have died off owing to loss of heating with no significant upstream convection to worry about that could move into the area. Thus it appears it will be dry for the remainder of the night. That leaves us with another very warm night ahead. Some of the earlier storms did manage to cool things off, with current readings in the east running a good 5 to 10 degrees cooler than this same time last night. Lows 75 to 80. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 335 PM Friday... ...Excessive Heat Watch for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) 1100 AM Saturday through 700 PM Sunday... Heat advisory in effect for the rest of our region including all the Piedmont, Sandhills, and Coastal Plain 11 AM Saturday through 700 PM Saturday. The big story will be the heat and humidity, but there will be a slight chance of thunderstorms as well. The Excessive Heat Watch is for the Fayetteville/Cumberland and Raleigh/Wake urban areas. The Heat Advisory is in effect for the rest of the counties in our region. The Watch is driven by the potential for excessive heat with heat indices of 108 to 113 for several hours both Saturday and Sunday in the Watch area. Highs near 100 with dew points in the mid 70s are expected. Just as importantly, the night time temperatures tonight through Saturday night will remain in the 80s for all but an hour or so. This will not give time for those outdoors to cool down without fans or air conditioning. The accumulative affects of 3 or more days with heat index values near or above 110 in the cities of Fayetteville and Raleigh combined with the failure of temperatures to fall below 80 at night will create excessive stress. If these readings are still expected in later forecasts, these two counties/cities will be upgraded to an Excessive Heat Warning. The Heat Advisory is in effect elsewhere for heat indices of 105+ for several hours time Saturday afternoon. Highs should top out in the mid to upper 90s again Saturday. In the NW and W Piedmont, heat indices may not reach 105; however criteria allows for the issuance of advisories if the heat index values are 100+ for several days in a row. The urban areas in the Triad cities will also have nighttime temperatures slow to fall below 80, making the advisory needed as well when combined with the consecutive days of high heat. Convective chances should improve late Saturday from the north. However, not all models are in agreement. Several CAMS runs do have MCS activity rapidly moving ESE from the Ohio Valley to VA late Saturday and Saturday night. Some of the MCS activity or associated outflows may drive thunderstorms into the northern Piedmont, yet this will have to be watched closely due to the high variability in the current forecasts. Some severe storms will also be possible, mainly after 500 PM Saturday into Saturday night. Lows 70s to near 80 Saturday night, with some potential for cooling north if storms make the run into that region. && .LONG TERM /SUNDAY THROUGH FRIDAY/... As of 225 PM Friday... ...Excessive Heat Watch for Raleigh and Fayetteville through Sunday at 700 PM... Hot and humid airmass will remain over central North Carolina Sunday as a ridges remain centered near Bermuda and in the lower Mississippi Valley. Meanwhile a shortwave moving across Great Lakes Sunday into Tuesday will deepen a trough over the Northeast and mid Atlantic states allowing a cold front to move south into the North Carolina area. Temperatures will lower to near seasonal averages by mid week with additional cloud cover and convection. Another shortwave will move across the Great Lakes Thursday and Friday keeping the eastern trough in place. Maximum temperatures on Sunday are expected in the mid to upper 90s with heat indices approaching or exceeding 105F to 110 in many locations. However there is a possibility that some MCS related clouds/rain may affect portions of the region, which would help out and lower temps a bit. Chances appear to increase late Sunday with the potential for strong to severe storms in the north late day. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 140 AM Saturday... Aside from a small chance of showers and storms, and associated gusty winds and brief sub-VFR conditions, VFR conditions with a mainly light, 7-12 kt surface wind, are expected through the TAF period. The relative highest probability of convection will be at INT and GSO, where 1) showers have recently developed from near KMWK to KFVX and may skirt the Triad vicinity this morning, and 2) upstream convection and associated outflow may propagate late this afternoon and this evening. Otherwise and elsewhere, an isolated "pop-up" storm will be possible, but predictability and timing of any such occurrence is too low to include for any other TAF site at this time. Outlook: Mainly VFR conditions will continue through the middle of next week, with the primary sub-VFR risk coming courtesy of showers and storms that will grow in coverage each successive day through Tue. && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 22 July | 103 2011 | 78 2011 23 July | 105 1952 | 78 2011 24 July | 101 2011 | 79 2011 GSO Records: Date | High Year | High Min Year ------------------------------------------ 22 July | 101 1926 | 77 2011 23 July | 99 1952 | 78 2010 24 July | 99 1914 | 78 2010 FAY Records: Date | High Year | High Min Year ------------------------------------------- 22 July | 107 1932 | 79 2011 23 July | 103 2011 | 79 1998 24 July | 105 1952 | 79 1945 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM to 7 PM EDT Saturday for NCZ007>011- 021>028-038>040-042-043-073>078-083>086-089. Excessive Heat Watch from Saturday morning through Sunday evening for NCZ041-088. && $$ SYNOPSIS...MWS NEAR TERM...CBL SHORT TERM...BADGETT LONG TERM...JF AVIATION...MWS CLIMATE...RAH

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