Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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678 FXUS62 KRAH 132330 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 725 PM EDT Sat Jul 13 2024 .SYNOPSIS... A front will weaken over the NC Coastal Plain through this evening. A strong subtropical ridge will otherwise remain over the Southeast through early to mid-week. && .NEAR TERM /THROUGH TONIGHT/... As of 310 PM Saturday... Hotter, with widely scattered convection possible in both the Coastal Plain this afternoon and nw Piedmont this evening. An anomalously strong subtropical ridge, one which this morning broke daily 500 mb heights at JAX and MFL and will produce standardized anomalies of 4-5 sigma from the Bahamas to the DR and Cuba, will remain across the Southeast and swrn N. Atlantic. Poleward of the ridge and trailing a prominent but compact MCV over the Chesapeake Bay --one related to convection that prompted the issuance of a Flash Flood Warning over Franklin Co. overnight-- a weak mid-level shear axis will move east across the srn Middle Atlantic coastal region through this evening. At the surface, a front and lingering wind shift extended from near the aforementioned MCV swwd across the NC Coastal Plain and ern Sandhills; and this boundary will move little while becoming increasingly diffuse through this evening. Meanwhile, a weak lee low now developing across the Shenandoah Valley to near ROA, within a broader trough extending swwd along and just east of the NC Blue Ridge, may drift ewd into the nw Piedmont this evening-tonight. Weak to moderate destabilization, slowed by lifting and scattering of morning stratus/stratocumulus, and (albeit weakening) convergence along the front, may yet support the development of widely scattered afternoon showers/storms in the Coastal Plain. Additional, more- isolated cells have developed along the lee trough near UKF and HKY. This regime of isolated cells along the lee trough may drift into the nw Piedmont before dissipating this evening. While HRRR simulated reflectivity also depict what appear to be showers lingering over the nw Piedmont throughout the night, associated point soundings reveal that reflectivity originates from a layer of altocumulus and saturation around 10 thousand ft AGL and would be unlikely to overcome an otherwise dry and deep sub-cloud layer, and should instead evaporate as virga. After a hot afternoon, and a humid one over all but the nw Piedmont where dewpoints have mixed out well into the 60s F, temperatures will slowly settle into the lwr-mid 70s for most by Sun morning, with patches of altocumulus and fair skies likely. && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 257 PM Saturday... Steady warming trend begins Sun with temperatures rising into the mid/upper 90s and heat index values ranging from around 100 to near 105. A lee trough will develop over western NC in between an area of high pressure over the LA riding up into the Ohio Valley and the anchored Bermuda High in the Atlantic. This will prompt mostly southwesterly flow at the surface up through 850mb and advect in warmer temperatures aloft (850mb 19 to 21C). This will support temps rising into the mid/upper 90s through the early afternoon. Point soundings indicate some relatively drier air aloft that will mix down to the surface and keep surface dew points in mid 60s (W) to low 70s (E). This should temper heat indices a bit, but still reach around 100 to near 105 degrees. Isolated locations will likely reach 105 during the afternoon for a brief time, but areal coverage and confidence is low enough to not preclude a heat advisory at this time. Some isolated to scattered showers/storms will be possible Sun afternoon within a hot and humid airmass. Greatest coverage will likely be along the lee trough in the western Piedmont as a low amplitude shear axis sags over the area as well as along the seabreeze, with subsequent showers/storms possible along convective outflows. Severe potential remains low as deep layer shear remains weak (around 20 kts) and warm/dry air aloft will work to combat sustained deep convection. Isolated strong winds cannot be ruled out if deeper convection is able to develop with a deeply mixed boundary layer and DCAPE > 1000 J/kg in place. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 257 PM Saturday... The main weather story for Monday and Tuesday will be the intense heat, given the pattern which features weak ridging and flow aloft, coupled with H8 temp anomalies of 4-6 deg C above normal. This will result in highs in the upper-90s both days, and some low-100s can`t be ruled out. Heat indices of 105+ are expected from the Triangle eastward on Monday, perhaps reaching as far west as the Triad by Tuesday. In terms of precip chances those days... coverage should be isolated at best both days given the overall weak forcing over the region. PoPs will increase on Wednesday as heights begin to fall in advance of a trough moving across the Great Lakes. With increasing flow above the BL, expect to see the Piedmont trough sharpen and improved low level convergence and subsequent outflow boundaries should be the primary lifting mechanisms for increased shower activity. Shower and thunderstorm activity, which may begin by early afternoon, may help keep high temps limited to the lower 90s. Rain chances will continue to increase, with well-above climo PoPs by Thursday and for Friday and possibly Saturday as well as the aforementioned trough pushes a cold front into the Mid Atlantic and Carolinas regions before stalling over us. That boundary, coupled with another plume of deep moisture will likely result in several rounds of heavy rains. However, that will also keep temps limited to near-climo values. && .AVIATION /00Z SUNDAY THROUGH WEDNESDAY/... As of 725 PM Saturday... A few isolated showers along along the slopes of the Appalachian Mtns have been drifting east toward the Piedmont but have been diminishing quickly. One shower popped up SW of GSO earlier, so another shower in the vicinity of INT/GSO cannot be ruled out through around 02Z based on some hires guidance, but after that no showers are expected overnight. VFR will generally prevail everywhere, with the lone and temporary exception most likely being at RWI where some brief MVFR vsbys are more probable (but still low confidence) after 06Z. A similar day is expected on Sunday, with isolated showers and storms developing over western NC and perhaps impacting INT/GSO late in the afternoon. The seabreeze could trigger a storm near FAY but is less likely and will not be mentioned in the TAF for FAY. Outlook: Isolated afternoon storms could result in sub-VFR conditions at TAF sites early this week, but otherwise VFR conditions are expected until the next front settles into the region with higher chances of convection and flight restrictions late Wed-Thu. && .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 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... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...Swiggett LONG TERM...np AVIATION...BLS CLIMATE...RAH