Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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695 FXUS62 KRAH 070731 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 330 AM EDT Sun Jul 7 2024 .SYNOPSIS... A weak frontal zone will remain stalled just east of the Appalachians through early Monday. This front will weaken further and dissipate Monday, as mid level high pressure builds over the Southeast states and Carolinas Monday through Tuesday. && .NEAR TERM /TODAY AND TONIGHT/... As of 255 AM Sunday... Fairly high coverage of convection is expected once again today. A very warm and deeply moist air mass remains over central NC, east of a diffuse frontal zone stretching SW-NE over the E slopes of the Appalachians, according to the latest surface analysis. The vast majority of the area saw rainfall yesterday (much needed, given the ongoing dry/drought conditions, although a bit too much/too fast in some spots). This ground moistening has led to some light/isold fog/stratus development early this morning, although this should be limited by both considerable higher debris clouds (esp in the W) and by relatively dry air just off the ground, noted on 925 mb progs. Persistence will largely be the rule today: The weak surface front should hold in place while slowly weakening, with weak low level flow to its east over central NC and anomalously high PWs (150-175% of normal) likely to linger across the area. Central NC will also remain within weak mid-upper level flow, in a col area between SW steering flow from the S Plains across the Ohio Valley and an upper low spinning well off the Carolina coast, while through the lower levels, the subtle trough noted on the 07/00z 925-850 mb UA analyses across GA and the Carolinas will likely hold in place with no mechanisms to dislodge it. All told, today`s convection pattern should behave much like yesterday, except perhaps a bit earlier initiation. Moderate SBCAPE is again expected, but with modest deep layer shear, so we may again see a few strong cells with the potential for downbursts, and the slow-moving water-laden cores will present a threat of heavy downpours and localized flooding as well. Recent CAM runs from various modeling systems have frankly been rather poor, fairly to accurately depict current/00H precip over its last several runs, going back to last evening, and they aren`t in very good agreement with each other. As such, have gone with a precip pattern not far off Saturday`s, most closely replicated by the 00z HREF mean. Expect coverage to peak at numerous/likely pops mid afternoon into early evening, with again a slow decline in coverage through tonight as elevated CAPE very slowly wanes, similar to last evening/early this morning. Expect highs today in the upper 80s to mid 90s, with clouds tempering heating a bit amidst thicknesses near to just slightly above normal. This will also keep heat index values below heat advisory criteria, although areas south and east of the Triangle may still see a few hours of 100-104F. Lows in the low-mid 70s. -GIH && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 330 AM Sunday... Our overall pattern remains much the same, although there are signs that convection coverage may be a bit lower than Sat and today. The frontal zone to our NW will have largely dissipated or morphed into a very weak lee trough, keeping high surface dewpoints and near to above normal temps over the area. Models generally agree in taking the mid-upper low off the Carolinas slowly SSW toward the N Bahamas Mon/Mon night with rising mid level heights over GA/SC/NC, while the high PW axis sitting across central NC decreases about a quarter to a third of an inch. SBCAPE is again expected to peak in moderate territory but with the higher values shunted to our NW. The mid- upper level flow remains quite weak, yielding poor deep layer shear, hindering storm organization once again. Will have pops just slightly under today, peaking at good chance to likely in the afternoon and decreasing in the evening. Once again expect highs in the upper 80s to mid 90s, followed by lows in the 70s. -GIH && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 255 AM Sunday... Tuesday and Wednesday: Beryl is forecast to become ingested within a trough digging into the central/southern Plains Tues and lift into the Mid-MS Valley Wed evening with a transition into an asymmetric cold core cyclone. Closer to home, a continued hot/humid airmass will be in place as central NC is situated within a weakness in the mid-level flow with little synoptic forcing for ascent. This will favor near climo rain/storm chances with pulse, classic summer-type, storm mode. Storm depth/strength may be less than previous days with less instability (500-1500 J/kg SBCAPE) and an upper level anticyclone centered over central NC. Well above normal deep layer moisture and slow storm motions will still pose an isolated risk for flash flooding, mainly in urban and poor drainage locations Tue and Wed. Temperatures will remain hot/humid and average 5-10 degrees above normal. Highs with range from the low/mid 90s with lows in the mid/upper 70s. With heat indices still expected to reach 100-105 and with little recovery overnight, anyone without effective cooling and/or adequate hydration may experience heat related illnesses. Wed night through Friday: The extratropical cyclone associated with Beryl merging with the synoptic trough is forecast to lift through the Mid-MS Valley through the Ohio Valley and towards the Great Lakes region by Wed night into early Thurs morning. Ensemble guidance suggests a unseasonably deep cyclone should evolve (40-60% of members indicating < 1010mb and 20% < 1005mb) by early Thurs with a low-level convergence axis and surface cold front should push into the central Appalachians, and perhaps the Piedmont of central NC into the mid week, which will provide a focus for showers/storms. This should favor rain/storm chances continuing through Wed night and above normal precipitation chances heading into late week. There remains some important along-track inconsistencies on how quickly this area of low pressure shifts northeast, so confidence on timing and eastward extent of the pressure trough and/or effective cold front is lower than normal during this time. Mostly cloudy conditions and above normal chances for rain will temper highs towards below normal by late week, but overnight lows will likely remain around 5 degrees above normal (low/mid 70s). && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 1230 AM Sunday... Adverse aviation conditions are likely to dominate across the Piedmont terminals (INT/GSO/RDU) through mid morning, with scattered showers and isolated storms expected to persist here through around 09z, with just isold showers thereafter through the morning. These sites will also see variable sct-bkn IFR/LIFR cloud bases topped by bkn-ovc VFR decks through mid morning, although the highest chance of IFR/LIFR cigs will be 09z-12z. There will be less of a chance of IFR/LIFR cigs at FAY/RWI. Any fog this morning should be MVFR at worst and focused in the SW Piedmont, S and W of INT/GSO/RDU. As cloud bases rise slowly this morning, VFR conditions should return by 15z areawide, but redevelopment of scattered to numerous showers and storms is expected by 16z-18z starting first in the W Piedmont before quickly expanding across all of central NC, lasting through the afternoon and evening, and aviation interests can expect a risk of storms, with periods of sub-VFR cigs/vsbys and gusty/erratic winds, across all terminals during this time, although coverage should begin to decrease toward 04z. Outside of any storms, surface winds will be light and variable, mainly from the SW at RDU/FAY/RWI. Looking beyond 06z Mon, there is a high chance of IFR cigs and MVFR vsbys in fog developing areawide shortly after 06z, forming first at INT/GSO then expanding E. VFR conditions should return by 15z. Another round of scattered showers and storms is expected Mon, with coverage slightly lower than today. The general pattern of scattered to numerous showers and storms each afternoon through evening will continue through Thu, with at least some chance of early-morning sub- VFR clouds/fog each day. -GIH && .CLIMATE... Record High Minimum Temperatures: July 7: KGSO: 73/2019 KRDU: 77/1900 KFAY: 78/2017 July 8: KGSO: 76/2010 KRDU: 78/1986 KFAY: 79/2012 July 9: KGSO: 76/1987 KRDU: 74/2014 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Swiggett AVIATION...Hartfield CLIMATE...RAH