Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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894 FXUS62 KRAH 112338 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 735 PM EDT Thu Jul 11 2024 .SYNOPSIS... A nearly stationary front over the Coastal Plain today will pivot westward and stall over the Piedmont tonight through Friday night. && .NEAR TERM /THROUGH TONIGHT/... As of 348 PM Thursday... A Flood Watch has been issued for most of central NC except those in the far western Piedmont starting midnight tonight and extending through midnight Friday night. Convection thus far today has largely remained just east of our CWA and near the coast as convergence tended to backbuild ese, as opposed to retrograde west. However, some convection is slowly approaching the northern Coastal Plain currently. The sfc boundary remains east of our area, but should begin to ease westward through later tonight. The associated instability axis will start to pivot inland as well, and thus still expecting scattered showers and storms to migrate into our Coastal Plain/Sandhills through this evening. As we enter the overnight period, onshore moisture flux, as noted in IVT model fields, should increase for those east and southeast of the Triad. Additionally, weak mid-level impulses will pivot across these areas near sunrise Friday morning. As such, scattered to numerous showers and storms will likely increase in coverage early Friday morning, and blossom across the Piedmont/Sandhills/Coastal Plain through Friday afternoon. the 12Z HREF LPMM QPF guidance continues to paint the highest QPF potential for those east of I-95, and a secondary axis of higher amounts somewhere between the Triad and the Triangle. The latter of which, may mostly materialize early Friday morning. While instability will wane some overnight, PWAT will remain 120 to 150 % of normal (>2 inches) area wide. Given forecasted freezing levels >15,000 feet, tall-skinny CAPE profiles, warm-cloud layer depths > 12,000 feet, and very slow mean-cloud layer flow (~5 kts), any convection that develops tonight could be capable of producing highly efficient downpours. Despite quite dry soils, this type of atmospheric environment could easily encourage efficient warm-cloud processes and rain rates capable of producing flash flooding. Biggest concerns would be over urban areas, but any efficient, slow- moving storm could produce localized flooding even in rural areas. Highs today will still push the upper 80s/lower 90s but with lower humidity for much of the day. Overnight lows will dip into the lower to mid 70s. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 400 PM Thursday... ..Flash Flood Watch in effect through Friday evening. On the wrn periphery of an expansive and anomalously strong 500 mb high, with simulated heights up to 602-603 dam centered over the cntl N. Atlantic, a convectively-amplified mid-level trough/banner of vorticity will likely have developed across the e-cntl Carolinas and cntl VA by Fri morning. That trough, associated MCVs, and corridors of mesoscale forcing for ascent, should then drift newd and reach the srn Middle Atlantic coast by 12Z Sat. Rising heights aloft will otherwise result across the swrn N. Atlantic and South Atlantic states, as the aforementioned mid-level high expands swwd, with an area of ~5 sigma standardized height anomalies forecast to become centered over the Bahamas through the same time. At the surface, a quasi-stationary front, now extending along a line from EDE-OAJ-ILM, will retreat wwd and reach the RAH Coastal Plain and ern Sandhills (invof I-95) by 12Z Fri. The front should then drift wwd and waver over the NC Piedmont through Fri night. Anomalously high PWs that set a daily record in excess of 2.3" at MHX this morning will spread wwd generally in tandem with the mid- level trough and surface front and become centered over e-cntl NC Fri, then edge ewd Fri night. While widespread clouds will limit insolation and destabilization, deep, moist thermodynamic profiles will become uninhibited with even weak heating into the upr 70s to lwr 80s. As such, convection, probably ongoing over e-cntl NC at the start of the period, will likely grow in both coverage and intensity through early-mid afternoon, then linger particularly through early Fri night. Slow storm motions (10-15 kt steering flow at 850-500 mb) and very deep warm cloud layers of over 4 km will support efficient, slow-moving convection capable of locally very heavy rain and flash flooding. Convective coverage should gradually diminish from west to east with the passage of the mid-level trough and waning instability overnight-Sat morning. After high temperatures in the upr 70s to middle 80s, muggy and mild lows in the lwr-mid 70s are forecast for Fri night. && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 330 PM Thursday... Much needed shower/storm chances lower as wet system moves away Saturday. Another heat wave expected to develop Sunday and last into mid-week. Showers and thunderstorms are expected to become widely scattered through the day Saturday as the wet system over eastern NC pulls away. It will continue warm and humid with highs returning into 90- 95 range. Heat indices should reach/return 100 to 104 in the eastern Piedmont and Coastal Plain. Heights continue to rise Monday and Tuesday. The low level flow is also more westerly. Heat Advisory criteria looks likely to be met in the southern and eastern areas where index values should reach and exceed 105 Sunday and Monday even with some mixing out of the dew points in the afternoon, then possibly Excessive Heat Warning criteria of 110 on Tuesday and Wednesday as the heat wave peaks. Actual highs should reach the mid 90s to lower 100s Tuesday and Wednesday. Lows in the mid 70s to lower 80s. Both could challenge daily records. There is only a small chance of isolated storms Sunday and Monday. The chance of mainly afternoon and evening thunderstorms returns Tuesday especially in the west. All areas have a chance by Wednesday afternoon and evening. The chance of showers and thunderstorms will increase on Thursday as a cold front will approach from the NW. Highs will "cool" into the lower to mid 90s. A potential wet period with less heat late next week into the weekend. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 735 PM Thursday... TAF period: Although all terminals will begin the period with VFR conditions, showers and restrictions will eventually overtake all airports from east to west. Eastern sites such as RDU/FAY/RWI will have scattered showers develop this evening with MVFR ceilings developing around midnight along with a several hour period of IFR ceilings before returning to MVFR for Friday afternoon. Have also included VCTS at RDU/FAY, as models are showing the greatest likelihood of thunderstorms occurring across the central portion of the forecast area overnight. Meanwhile, at western sites such as INT/GSO, it appears those sites should remain VFR through the night, with MVFR ceilings and widespread showers developing Friday morning. Did not have enough confidence in thunderstorms to include at INT/GSO or RWI, although thunderstorms are certainly a possibility. The wind will have an easterly component throughout the period, remaining less than 10 kt. Beyond 00Z Saturday: Additional showers and storms are likely through late Friday night as an area of low pressure lifts through eastern NC. A strengthening low-level jet will pivot over eastern TAF sites Friday, but the strongest LLWS will reside east over the Outer Banks. Rain chances (and perhaps morning stratus/fog as well) will largely remain across the east this weekend. Convection Monday/Tuesday should be fairly isolated in nature. && .CLIMATE... Record High Temperatures: July 15: KGSO: 97/1974 KRDU: 99/1997 July 16: KGSO: 99/1915 KRDU: 101/1887 KFAY: 103/1937 Record High Minimum Temperatures: July 11: KGSO: 75/1992 KRDU: 77/1981 KFAY: 76/2019 July 12: KGSO: 76/2011 KRDU: 78/2011 KFAY: 80/1935 July 13: KGSO: 75/2017 KRDU: 78/2017 KFAY: 78/2017 July 14: KGSO: 77/1981 KRDU: 77/2017 KFAY: 80/2017 July 15: KGSO: 74/2019 KRDU: 76/1992 KFAY: 78/2015 July 16: KGSO: 75/2010 KRDU: 77/2010 KFAY: 78/1992 && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch from midnight EDT tonight through Friday evening for NCZ007>011-022>028-039>043-074>078-083>086-088-089. && $$ SYNOPSIS...MWS NEAR TERM...Luchetti SHORT TERM...MWS LONG TERM...Badgett AVIATION...Green/Luchetti CLIMATE...RAH