Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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360 FXUS62 KRAH 031818 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 217 PM EDT Wed Jul 3 2024 .SYNOPSIS... Canadian high pressure centered just offshore the Middle Atlantic coast will linger over the Carolinas through tonight. A subtropical ridge will otherwise extend across the South Atlantic states through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 217 PM Wednesday... Latest satellite observations show cumulus developing across the region as high pressure is centered off NJ coast. Upper level ridge over the Mid-Atlantic will slowly shift offshore by Thursday. Increased moisture levels moving into the region will result in dew points in the mid/upper 60s later this evening and into the low 70s by Thursday morning. Temperatures across the region this afternoon are in the mid to upper 80s with expectations for most areas to hit 90 degrees. Lows overnight will 3-6 degrees above average 68-71. Light southeast surface winds will slowly shift to SW by early Thursday morning. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 420 AM Wednesday.. Much hotter, but with seasonable humidity characterized by mixed/afternoon surface dewpoints in the upr 60s to around 70 F. A subtropical ridge over the Deep South will weaken and retreat slightly, as a mid-level cyclone develops and deepens from the nrn Plains to the upr MS Valley. In the intervening wswly flow between the two, a corridor of convectively-amplified disturbances will sag sewd and extend from the Middle Atlantic to the srn Plains by 12Z Fri. Weak mid-level height falls and associated adiabatic cooling will cause initially weak mid-level lapse rates to steepen to 5.5 to 6 C/km over the srn Middle Atlantic by Thu afternoon. At the surface, very warm-hot sswly flow will expand throughout the Southeast, equatorward of a convective outflow-modulated frontal zone that will settle to a similar position as the corridor of mid- level disturbances noted above (ie. from the Middle Atlantic to the srn Plains). Meanwhile, an Appalachian-lee trough will become established across the Foothills and wrn Piedmont of the srn Middle Atlantic/Carolinas. The influence of the subtropical ridge and sswly low-level flow will allow heat to expand newd and across cntl NC once again, with forecast high temperatures in the mid 90s to around 100 F and around daily records at all three climate sites. Mixed/afternoon surface dewpoints mostly in the upr 60s will somewhat temper associated heat index values that are expected to peak in the upr 90s to near 105. Thu night will be very mild and muggy, with lows centered in the middle 70s. While the intersection of the lee trough and convectively-modulated frontal zone will likely focus the greatest concentration of diurnally-maximized convection across n-cntl VA, isolated cells will be possible swwd in the vicinity of the lee trough over the wrn NC Piedmont during the afternoon. Additionally, some outflow from upstream convection may outpace the main baroclinic zone and move into the nrn NC Piedmont during the evening, during which time scattered, multi-cell development will be possible. An isolated strong to damaging wind gust will be possible with any afternoon cells owing to strong diabatic cooling potential in the strongly- heated boundary layer characterized by 9.5 C/km lapse rates and 25- 30 degree dewpoint depressions, after which time nocturnal cooling and stabilization will limit convective intensity. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 225 AM Wednesday... Aloft, a potent northern stream s/w will move through the Great Lakes Fri/Fri night, as the longwave trough amplifies southward through the Plains and MS Valley. As the trough amplifies, the high over the Southeast US will be gradually pushed southeastward off the Southeast US coast Fri night/Sat. Another northern stream s/w will drop into the northern Plains and track eastward along the US/Canada border Sat/Sat night as the initial s/w lifts newd into Canada. As this second s/w moves through the Great Lakes Sun/Sun night, another disturbance will quickly drop ssewd through the northern Rockies and into the central Plains, helping further amplify the longwave trough through the southern Plains/lower MS Valley by Mon morning. All the while, central NC will remain situated between the trough to the west and the high to the east, with deep southwesterly flow prevailing. The fly in the ointment is the medium-range guidance picking up on a possible tropical low approaching the Carolina coast over the weekend. There is some uncertainty wrt this feature for Mon and Tue. Also on Sun/Sun night, Beryl is expected to make landfall along the western Gulf Coast, however exactly where that happens and when will determine what happens to the system as/where it moves inland early next week. There is still a lot of uncertainty in the forecast for Mon/Tue, but for now, it appears the longwave trough axis will generally remain west of the Appalachians through Tue, while s/w disturbances move through it. At the surface, a lee trough will remain in place through Sat, when a cold front will approach from the west. As of the latest model solutions, the front still appears to get hung up and generally wash out along the Appalachians Sat night, as Bermuda high pressure ridges westward. An area of low pressure will sit off the Southeast US coast Fri/Fri night, then weaken on Sat before the remnants of the low lift newd off the Carolina coast Sat night/Sun. possibly laying W-E through WV/VA Sun as high pressure lifts newd through the OH Valley and Northeast, but the front appears to stay north of central NC. Expect swly flow and the advection of warm, moist air into the area to take over once the ridge moves out Thu morning and prevail through at least Sat. The lee trough should once again strengthen over the area early next week. Temperatures will be above to well above normal through Tue. Latest forecast heat index values of 100-106 are expected across much of central NC for Fri and Sat. Sun and Mon heat index values max out around 100, mainly across the south, but may creep upward again on Tue. As for rainfall, the weather seems to be turning a bit wetter. As the mid-level ridge gradually gets suppressed south and the lee trough strengthens, expect more diurnally driven convection Fri through Tue, with higher chances/amounts as s/w disturbances clip the area. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 120 PM Wednesday... VFR conditions expected for the 24 hour TAF period as high pressure dominants the region. While high pressure is centered just of the NJ coast, onshore flow is helping produce a nice Cu field across much of North Carolina. No restrictions are expected with a more widespread development of clouds across the area later tonight and into tomorrow morning. Winds will be overall light and variable, with onshore SE flow this afternoon slowly swinging to a SW flow by Thursday afternoon. Outlook: Sub-VFR conditions are possible in the NW by Thursday afternoon ahead of a tough moving into the region. Also, showers and storms will be possible Thursday afternoon in the NW with increasing chances spreading across Central NC Friday through early next week. && .CLIMATE... Record High Temperatures: July 4: KGSO: 98/1970 KRDU: 101/2012 KFAY: 98/2019 July 5: KGSO: 98/2012 KRDU: 102/1999 KFAY: 101/2002 July 6: KRDU: 102/2022 KFAY: 99/1990 Record High Minimum Temperatures: July 4: KGSO: 73/2018 July 5: KGSO: 74/1999 KRDU: 78/1902 KFAY: 77/2005 July 6: KGSO: 76/1999 KRDU: 79/1900 KFAY: 76/2017 July 7: KGSO: 73/2019 KRDU: 77/1900 KFAY: 78/2017 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...CA SHORT TERM...MWS LONG TERM...KC AVIATION...CA CLIMATE...RAH