Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211937 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 337 PM EDT Fri Jul 21 2017 .SYNOPSIS... A hot upper level high pressure will remain in place from the Plains eastward over our region into the weekend. A cold front will approach from the northwest late in the weekend into early next week as the high pressure breaks down over the region. && .NEAR TERM /THROUGH TONIGHT/... As of 335 PM Friday... ...Heat advisory in effect for the eastern Piedmont, Sandhills, and Coastal Plain through 800 PM... A chance of a few strong thunderstorms this afternoon at 20-30 percent. Heat indices of 110 already reached around Fayetteville and Raleigh, with 100+ in all areas. Caution is advised, even late tonight with temperatures slow to fall through the 80s. The latest data analysis indicated a well defined surface trough stretching SW to NE across the Piedmont, or roughly from near Charlotte to Raleigh. It is along this boundary were isolated thunderstorms are favored to develop this afternoon. MLCapes of 2000+ J/KG and high freezing levels support mainly a gusty wind threat with any storm. Even within this favored zone near the trough, POP is no higher than 20-30 percent for any one given spot for a thunderstorm. The MCS tracking over the central Appalachians is helping initiate or even enhance diurnally driven thunderstorms over SW VA and NW NC Mountains this afternoon. Some of the CAMS indicate the probability (30-40 percent) that the NW Piedmont may get in to some action soon. We are not currently in any outlook by SPC; however, any storms that form or move into the NW have the chance to be locally strong to severe given the available energy to work with. Convection chances are expected to drop off by mid-evening, but we will have to watch the development of upstream MCS activity later tonight. Lows will be in the 70s (80 around KFAY). && .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 /19Z FRIDAY THROUGH WEDNESDAY/... As of 125 PM Friday... 24 hour TAF period: Generally VFR conditions under high pressure will persist through the TAF period. There is a low probability (20- 30) for MVFR thunderstorm conditions between 20z and 00z/this evening. Outlook: Generally VFR conditions are expected Saturday. Scattered mainly diurnally driven convection is possible Saturday and Sunday, with MVFR to IFR conditions. An even better chance of storms are expected by early next week as a cold front moves into the area, along with morning stratus and/or fog. && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 21 July | 102 2011 | 78 1932 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 ------------------------------------------ 21 July | 102 1926 | 76 2011 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 ------------------------------------------- 21 July | 105 1932 | 79 1977 22 July | 107 1932 | 79 2011 23 July | 103 2011 | 79 1998 24 July | 105 1952 | 79 1945 && .RAH WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for NCZ010-011- 025>028-040>043-075>078-084>086-088-089. 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...BADGETT NEAR TERM...BADGETT SHORT TERM...BADGETT LONG TERM...JF AVIATION...BADGETT CLIMATE...RAH

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