Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | 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
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
495 FXUS62 KRAH 231805 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 210 PM EDT Mon Oct 23 2017 .SYNOPSIS... A potent upper level trough and accompanying surface front will approach from the west this afternoon, then surge through the region this evening. A secondary dry cold front will follow and cross our region Tuesday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1110 AM Monday... ...Slight risk of severe storms late this afternoon and evening... Current conditions... Cloudiness has become extensive across the western and central portions of NC this morning, with the only residual partly sunny skies from the Coastal Plain eastward, where the high pressure and dry air were slower to give way to the approaching storm system. Radar indicated occasional showers tracking north or north-northwest over the western Piedmont which actually was keeping this region a bit more stable near the surface. Temperatures were holding in the 60s over the Piedmont where at least an In-Situ CAD event is developing. Temperatures at late morning were warming through the 70s over the SE zones and dew points were rising to near 70. An onshore SE flow has been increasing across the region, with even more backing to the east over the far NW Piedmont and Foothills. Aloft, the flow veers to the SW and was increasing out ahead of the approaching strengthening storm system. Water Vapor imagery continued to show a the deepening closed mid level low becoming more negatively tilted with time as it moves NE toward the Tennessee Valley. The surface storm system was located over central Indiana and was also deepening rapidly as it moves NNE. The trailing cold front extended SSE through eastern TN and far western NC, with a strong line of convection noted surging eastward into the Mountains of NC. A secondary meso-low was located over north GA and it is this secondary low that is expected to move NE through western NC later this afternoon, tracking along the low level boundary set up by the developing In-Situ Damming over the NW Piedmont. The developing severe threat... The extensive cloudiness and showers over the western Piedmont will keep things more stable, lessing the severe threat over that region by a category (more marginal than a slight risk for the Triad Region may be more appropriate). However, along and east of the In-Situ wedge there will be more instability - especially from Raleigh and Southern Pines eastward where some sun will send temperatures well into the 70s (even some lower 80s SE). 500 to 1000 J/KG CAPES are expected by mid to late afternoon. The current line of showers and thunderstorms racing into the NC Mountains from the west is expected to surge east into our region mid to late afternoon in the Yadkin River Valley region, likely strengthening as it moves into the more unstable environment over central and eastern NC late afternoon and evening. The previous timing still looks to be on target, maybe a bit slow. Therefore, we expect the line to reach the Triad and southern Piedmont between 3 and 5 PM, then the Triangle and Fayetteville areas around dinner time, and the Interstate 95 corridor by mid evening. A 3-4 hour period of significant weather is expected as the lines of storms push through. The line itself should be accompanied by a few damaging wind gusts and possibly isolated tornadoes. A few supercell storms may develop out ahead of the line main line of convection in the south and east, with the threat of damaging wind gusts, hail, and isolated tornadoes. Minor urban or small stream flooding will be possible during the height of the event, with 2+ inch per hour rainfall rates generally lasting 30 to 45 minutes at any given spot. Very dry antecedent conditions and the quick movement of the system overall should keep the flash flood threat low. Clearing behind the convective line, with the passage of the cold front, will spread west to east overnight. Areas of low clouds and fog may redevelop over the srn/wrn piedmont, where clearing will occur first, and lessening winds between this lead cold front, and a trailing one scheduled for a late Tue-Tue night passage, will favor modest-strong radiational cooling. Lows are expected to range from the upper 40s west to lower-mid 60s east. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 310 AM Monday... Tuesday morning, precipitation associated with a cold front moving through central NC will be in the vicinity of the eastern edges of the CWA and heading eastward with time. Since the low pressure system associated with this front will be located well to the northwest of the area over the Great Lakes, it will take some time for the colder airmass to filter in behind the front. Therefore high temperatures will remain fairly high on Tuesday with upper 60s to mid 70s expected across the area from NW to SE. Lows Tuesday night will be in the low 40s across the NW Piedmont to near 50 degrees in eastern counties. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 210 PM Monday... Cooler and dry weather continues into the latter half of the week with highs in the upper 50s to mid 60s Thursday and near 70 degrees for the end of the week. Lows will remain in the 40s for the majority of the week and then climb back into the upper 40s to lower 50s for the weekend. The next chance for rain comes from a frontal system that will move through the area next weekend. There is uncertainty with regards to timing and also the evolution of a low pressure system riding up the southeast coastline prior to the arrival of the cold front that could cause a chance of precipitation earlier in the weekend. && .AVIATION /12Z MONDAY THROUGH SATURDAY/... As of 800 AM Monday... In strengthening and increasingly moist east to sely low level flow off the Atlantic ocean, an axis of IFR-MVFR ceilings and showers will continue to move across wrn portions of the forecast area/mainly at Triad TAF sites this morning, then continue, with periods of IFR ceilings, today through this evening. Aside from a brief instance of an IFR-MVFR ceiling and/or a shower at RDU/FAY/RWI this morning, generally VFR conditions are expected to persist at those locations until this evening. An approaching frontal system will then result in the ewd progression of a band of IFR-MVFR ceilings, heavy showers and isolated storms with strong and gusty sly to sswly winds --including some severe with isolated tornadoes and straight line wind gusts aoa 50 kts-- between 22Z/23rd and 05Z/24th. Sely surface winds will otherwise increase and become strong and gusty by late morning to midday, ahead of the expected line(s) of convection. West to east clearing will occur with the passage of the associated cold front this evening-early tonight, with a period of enhanced swly winds in the hour or three immediately following the frontal passage. Lessening winds and lingering low level moisture late tonight may result in the development of fog and low stratus primarily at INT and GSO between 08-12Z/24th, though the latest model guidance has backed off on this potential. Outlook: VFR conditions are anticipated for at least the next several days. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett/MWS NEAR TERM...Badgett/MWS SHORT TERM...Ellis LONG TERM...Ellis/Franklin AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.