Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
331 FXUS62 KRAH 220818 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 418 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/...
-- Changed Discussion --
As of 400 AM Saturday... ...Dangerously hot conditions will expand across central NC today... Excessive Heat Warning now in effect for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) from 11 AM until 7 PM today... Heat advisory in effect for the rest of our region, including all of the Piedmont, Sandhills, and Coastal Plain from 11 AM Saturday through 7 PM today. Excessive Heat Watch remains in effect for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) from 7 PM this evening through 7 PM Sunday. Beneath and downstream of a 321 dm/595 dm sub-tropical ridge at 700mb and 500 mb, respectively, centered from the central Plains to the lower OH and TN Valleys, around persistence high temperatures are expected throughout central NC today - mostly middle 90s to around 100 degrees. A difference between the two days, and an important one, will be that the Appalachian-lee/Piedmont trough is forecast to sharpen over the srn and wrn Piedmont today, as opposed to from near KASJ to KJNX to KMEB like Fri. Consequently, surface dewpoints in the lower to middle 70s are expected to encompass a larger portion of central NC, on the ern side of the trough axis; and associated heat indices should likewise be higher farther nwwd. Observed heat index values from Fri, the ones with a relatively high degree of confidence of reliability, and the idea of a persistence forecast for today, suggest maximum heat index values will be very near 110 degrees across the ern Sandhills and srn and central Coastal Plain, and an upgrade to an Excessive Heat Warning was considered for the counties between the current Warning for just Wake and Cumberland Co., which should be noted was set up and well placed with "outside the box" thinking by the day shift on Fri. This would include Scotland, Hoke, Harnett, Johnston, Wayne, Sampson, and Wilson. Since it appears the handful of sites that reached or exceeded 110 degrees on Fri was for only an hour, and Warning criteria is two hours, we elected to maintain the Heat Advisory as is. Frankly, the difference between a degree or two and an hour or two is more for bookkeeping than actual affects of the heat, so it`s important to not get caught up in criteria and definitions. It will be dangerously hot throughout central NC today. Also like Fri, isolated convection will initially be possible in the vicinity of both the Piedmont trough, likely over the srn and wrn Piedmont, and the sea breeze. Later, upstream convection from the upper Midwest and OH Valley, or at least associated MCV`s and/or outflow, may propagate into the nwrn and nrn Piedmont late this afternoon through this evening - an idea many of the CAM solutions favor. Strong to marginally severe wind gusts will pose the primary hazard owing to a strongly and deeply mixed boundary layer characterized by surface dewpoint depressions of around 25 degrees, amidst a weakly-sheared environment on the srn rim of the belt of westerlies focused over the nrn Middle Atlantic states. It will be mild/warm, and muggy, overnight, with lows mainly 75 to 80 degrees. The associated continued relatively warm and moist boundary layer, and probable remnant outflow over at least the nrn half of the forecast area, will favor a slight chance of a shower or storm all night.
-- End Changed Discussion --
&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
As of 415 AM Saturday... Excessive Heat Watch remains in effect for the cities of Raleigh and Fayetteville (counties of Wake and Cumberland) from through 7 PM Sunday. Generally persistence, though with a higher probability of afternoon convection, as heights aloft fall over the srn Middle Atlantic states and NC consequently becomes increasingly susceptible to passing perturbations, some resulting from upstream convection, in wly to nwly flow. Another Heat Advisory will likely be needed for all of central NC, with a good chance of another Excessive Heat Warning over at least Wake and Cumberland counties once again. The coverage and initiation time of convection, and preceding high level "blowoff" cloudiness from upstream convection, may result in slightly lower high temperatures and associated heat index values, however, but the overall cumulative affects of the heat will persist regardless.
-- End Changed Discussion --
&& .LONG TERM /MONDAY THROUGH FRIDAY/... As of 335 AM Saturday... A weak but fairly progressive upper level trough will move over the area on Monday and then continue eastward, taking a surface low off of the Long Island coast and out to sea. Behind the exiting low, a high pressure system will move over the northeastern CONUS that will eventually drop a cold front through the area and bring some relief to the heat. A general cooling trend will begin on Monday with temperatures easing back into the lower 90s, but dropping further into the mid to upper 80s by Wednesday afternoon, after the passage of the front. Upper 80s to low 90s will prevail through the remainder of the forecast period. The Piedmont trough and a lingering frontal boundary across the southern part of the area will be the focus for convection for much of the work week as a series of disturbances tracks along this boundary. The strongest of these disturbances could come on Tuesday night into early Wednesday morning but will be short lived before either weakening or moving out to sea. Otherwise expect diurnal showers and thunderstorms. The best chance for severe weather may be across the north on Monday as the upper dynamics are more favorable for supporting severe thunderstorms. As such the SPC has included northern portions of the CWA in a marginal to slight risk of severe thunderstorms. && .AVIATION /08Z 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...
-- Changed Discussion --
Heat Advisory from 11 AM this morning to 7 PM EDT this evening for NCZ007>011-021>028-038>040-042-043-073>078-083>086-089. Excessive Heat Warning from 11 AM this morning to 7 PM EDT this evening for NCZ041-088. Excessive Heat Watch from this evening through Sunday evening for NCZ041-088.
-- End Changed Discussion --
&& $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...RE AVIATION...MWS CLIMATE...RAH

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.