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Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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526 FXUS62 KRAH 200216 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1016 PM EDT Fri Jul 19 2024 .SYNOPSIS... A series of convectively-amplified disturbances in moist, southwesterly flow aloft will overspread and interact with a surface front that will remain nearly stationary over central NC through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1015 PM Friday... Amid swly flow downstream of a shortwave perturbation that will pivot from sern MO/nrn AR newd and across the mid-South, a series of convectively-amplified disturbances will be directed from the lwr MS and TN Valleys to the srn Middle Atlantic. The most notable and probably influential of these features for the sensible weather in cntl NC was well-defined in regional radar data over n-cntl SC this evening, including in KCAE velocity data that depict a deep circulation from around 3 to 25 thousand ft ARL in wrn Chester and Fairfield Co. SC. This feature will continue to move generally newd and across cntl NC overnight. As it does so, it will encounter an environment characterized by only weak instability from widespread outflow and surface cooling from prior convection and otherwise weak, 5-5.5 C/km lapse rates upward through 500 mb. As such, it seems most likely that a mix of stratiform rain immediately surrounding the approaching MCV, and occasional weak cellular development preceding it, will spread newd into/across cntl NC overnight. Hourly rainfall amounts in the stratiform rain have generally been light, from several hundredths to a quarter inch over nrn SC in the past couple of hours. Given that the stratiform rain shield will likely continue to diminish in the absence of additional, concentrated deep convection, beyond the sporadic/ isolated cellular development like that which has recently developed from near FAY to CTZ to GSB, the risk of flooding overnight appears low. .PREV DISCUSSION... /ISSUED 318 PM EDT Fri Jul 19 2024/ The cold front is now a stationary front as it has moved little since this morning. The best estimate position of the front, mindful of an outflow boundary sagging south from the boundary, stretches from Davidson/Randolph east into southern Wake and into Wilson County. An outflow boundary exists south of this tied to convection from Wayne to Lee counties. The front arcs to the southwest to near CLT and into northern SC/GA/AL. Since the front has not made any southward progress the main showers and storms have occurred along and south of the boundary, along US- 64. Storm chances are thus highest over the next few hours in this area. With time, southward movement of the outflow from convection should aid increased coverage of storms in the southern Piedmont, Sandhills, and southern Coastal Plain by early evening. While convection along and north of the boundary should weaken near sunset with loss of heating, additional convection is forecast to move into the southern and western Piedmont later tonight and overnight into early Sat. This would be tied to mid-level energy from MS/AL and upstream convection that may congeal over GA/SC and track ENE. Isentropic ascent could also favor showers over the Triad and western Piedmont overnight. Guidance also suggests perhaps an MCV may track into the Triad early Sat, which could also touch off a few isolated showers/storms along and north of the boundary in the Triangle and northeast Piedmont early Sat morning. How much of this convection survives with nocturnal stabilization is unclear, but have 30-60 percent PoPs mainly US-1 westward. Outside of convection, low stratus is forecast to envelope the area overnight, especially along and north to northwest of the boundary. Overnight lows are expected to be in the upper 60s to low 70s, coolest across the north. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 230 PM Friday... The damp pattern will persist through the weekend, including above- normal cloud cover and rain chances, and near to slightly below normal highs. A marginal severe threat persists for Sat, and locally heavy rainfall will remain possible throughout the weekend. Sat/Sat night: Rain chances will be high amidst PWs of 2.0-2.3", but the highest pops are likely to be skewed to earlier in the day than usual, morning through mid afternoon, as indicated by the HREF local probability matched mean output. Southwesterly mid level flow over the region will draw MCVs from the current Gulf Coast convection northeastward across the western and central Carolinas starting Sat morning. It`s tough to tell exactly where the weak surface boundary will be, but the latest RAP runs depict it sitting nearly W-E over NC as the low-mid level perturbation lifts northeastward. Light low level winds will limit mass convergence, but this may still play a role in focusing locally heavy downpours and slow-moving storm clusters. The RAP output also favors warm rain processes, with an LCL-0C depth over 4 km, and slow MBE movement will increase the risk of localized flooding. The risk of strong to severe storms is supported by an uptick in mid level flow from 15-20 kts to 25-35 kts Sat, within persistent moderate SBCAPE and beneath a modest upper divergence max. After high morning-through-midday pops, we may have a relative lull period for a portion of the afternoon until we see a redevelopment of scattered convection late in the day and into the evening, perhaps lasting into the early overnight with at least marginal elevated CAPE lingering amidst growing CINH. Expect highs to range from the 80s to lower 90s, with lows in the upper 60s to mid 70s. Sun/Sun night: Attempting to pin down convection details (both location and timing) becomes more difficult by Sun, but we`ll still be in a regime featuring weak Gulf-source southwesterly low-mid level flow, between baggy troughing over the E Plains/Miss Valley and a strong NW Atlantic ridge extending WSW toward FL. Both PWs and the vertical thermal/moisture profile will likely exhibit little to no change, although mid level flow will once again weaken, leading to a reduced threat of strong storms. See no reason to change from the good chance/likely pops, with continued variably to mostly cloudy skies. We should see highs in the 80s to near 90 and lows mostly in the low-mid 70s. -GIH && .LONG TERM /MONDAY THROUGH FRIDAY... As of 300 PM Friday... ...Above normal rain chances will lead to seasonable to slightly below normal temperatures next week... Sandwiched between persistent upper level troughing that stretches south from the Great Lakes to the southern US Plains and a strong subtropical ridge that extends over the western Atlantic and SE US, deep SW flow will keep moisture-laden plume of 120-140% percent of normal PWATs entrenched across the region all next week. DPVA via shortwave impulses embedded in the SW flow, in tandem with daytime heating and interaction with seabreeze/outflow will lead to high/likely chances of showers and storms each day. The above normal rain chances and associated increase cloud cover and will result in seasonable to slightly below-normal high temperatures and mild above normal min temps. Highs generally 85-90. Lows in the 70s. The super ensemble mean average cumulative rainfall during the long term period is between 1-2", with higher amounts possible within any heavier convection. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... As of 820 PM Friday... Generally VFR conditions are expected to start the TAF period. A stationary front is draped along/south of the northern terminals (RDU/RWI). As the front is progged to lift slowly northward or remain stationary across central NC, the best chance of showers/storms overnight would be at GSO/INT/RDU, where lift and instability is more focused. Most high-res guidance suggests this, but uncertainty in the coverage means that it cannot be ruled out at FAY/RWI early Sat. Outside of storm chances overnight, CIGs are expected to lower to LIFR, with conditions slowly rising to MVFR to VFR midday Sat. Outlook: Showers and storms will continue into this weekend and early next week as a front stalls over the area and several impulses track through in the moist flow. Early morning fog and stratus will be possible each day as well. && .CLIMATE... Record High Minimum Temperatures: July 19: KGSO: 75/2016 KFAY: 77/2023 July 20: KGSO: 75/2019 KRDU: 76/2020 July 21: KGSO: 76/2011 KRDU: 78/1932 KFAY: 80/2017 July 22: KRDU: 78/2011 July 23: KRDU: 78/2011 July 24: KRDU: 79/2011 KFAY: 79/1945 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS/Kren SHORT TERM...Hartfield LONG TERM...CBL AVIATION...Badgett/Kren CLIMATE...RAH