992 FXUS62 KRAH 031752 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 150 PM EDT Thu Jun 3 2021 .SYNOPSIS... A very moist air flow will continue across North Carolina through Friday, ahead of an approaching cold front and upper trough. The front and upper trough will shift east to the coast late Friday before weakening and dissipating. Upper level high pressure will develop across the region early next week, resulting in above normal temperatures. && .NEAR TERM /THROUGH TONIGHT/... As of 955 AM Thursday... Forecast is in good shape, and just a few tweaks were needed this morning. Still looking like a multi-hazard day, with the potential for flooding along with damaging winds and marginally severe hail. After the rains of yesterday through mid morning, most areas along and E of I-95 saw 1-5" of rain in the last 24 hrs, with spots of street flooding and high water on smaller creeks reported. Any additional rainfall is apt to run off quickly, and the ongoing flash flood watch remains valid. With MLCAPE already at 1000-1500 J/kg and no cap with a very damp column, the showers and isolated storms will have little to no impediment to development. Effective deep layer shear is marginal at just 20-25 kts this morning, but will be improving slowly today with the approach of the mid level trough from the WNW, producing a risk of a few strong to severe storms esp as the larger scale forcing for ascent strengthens later today. The deep moisture plume into the area will persist, esp over the E half of NC, and this is illustrated well by the MIMIC-TPW2 imagery showing a swath of 1.75-2.0" PW streaming into E NC from the Bahamas and E FL, with an area of 2.0-2.25" PW just off CHS/SAV which is poised to stream northward over our E sections through today. We're already seeing a rapid increase and expansion of convection upstream over SE SC. Will maintain high pops, highest E with highs in the upper 70s to lower 80s. -GIH Earlier discussion from 345 AM: Latest surface analysis shows a warm front lifting north across VA and WV with a moist southerly flow across the Carolinas. Surface dew points currently range in the upper 60s to lower 70s. SPC mesoanalysis shows PW values ranging from 1.5 inches across the western Piedmont to around 1.9 inches across the Coastal Plain. An upper trough across the western Great Lakes extending into the Missouri Valley this morning will slowly shift east, reaching the western slopes of the southern Appalachians by Friday morning. The air mass across central NC will remain moist with PW values actually increasing to around 2 inches this afternoon and evening and with greatest values shifting west slightly. In addition, the air mass will remain weakly to moderately unstable through tonight with MLCAPE values averaging between 500 and 1000 J/Kg. The greatest instability and moisture will be focused on our eastern locations in the Coastal Plain. With multiple disturbances moving across central NC in the moist southwesterly flow ahead of the trough, numerous to widespread showers and storms are expected. The greatest storm coverage and intensity will be across the eastern Piedmont, Sandhills and Coastal Plain during the afternoon and early evening. Given good storm coverage yesterday with 1 to 2 inches of rain observed in several locations in the eastern Piedmont and Sandhills and another 1 to 3 inches of rain expected today and tonight, have coordinated with neighboring offices and opted to issue a Flash Flood Watch for locations near and east of US route 1 from noon through 6am Friday. Many high res convection allowing models note the potential for localized amounts of 2 to 5 inches of rain in these areas which supports the threat for flash flooding. WPC has outlined eastern parts of central NC with a slight risk of excessive rain. In addition, SPC has outlined all of central NC in a marginal risk of severe thunderstorms. With weak to moderate instability and a strengthening southwesterly flow aloft resulting in effective 0-6km shear of 30 to 40kts, a limited severe weather threat will be present through the evening, mainly from damaging winds. With some suggestion of locally backed southeast surface winds and low LCLs across the east, a limited tornado threat is also present. Expect lots of clouds today with temperatures slowly climbing into the upper 70s to around 80 before areas of showers and storms knock temperatures back. Muggy lows in the upper 60s are expected tonight. -Blaes && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 405 AM Thursday... The upper trough axis will push slowly east on Friday and Friday night with a lead short wave axis pushing across central NC on Friday afternoon. The deep moisture will shift east during the day and by late afternoon PW values will drop off into the 1.0 to 1.25 inch range across the western Piedmont with PW values of 1.5 inches across the Coastal Plain. Despite the drying, there will be sufficient low level moisture for MLCAPE values to reach the 1000 to 2000 J/KG range during the afternoon. High res guidance shows a signal for a line of showers and storms to move across central NC during the afternoon and evening along with a rogue shower or storm storm during the morning or outside of the line. Despite an increasingly westerly flow aloft, a southwesterly low level flow in a region of steep low level lapse rates combined with 25 to 35kts of mid level flow will result in the some storm organization with 0-6km shear values of 20 to 40 kts. SPC has outlined most central NC to the coast in a marginal risk for severe storms. The majority of the convection should dissipate by midnight although the presence of the upper trough could support an isolated overnight shower or storm. Highs on Friday will range in the lower to mid 80s with lows in the lower to mid 60s. -Blaes && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 330 AM Thursday... In the upper-levels, the trough will continue to exit east into the Atlantic Saturday, then a ridge will build north from the Southeast into the OH Valley on Sunday. By late Monday, the ridge will build east into the Mid-Atlantic, and then slightly west again by the middle of next week, centering across the TN Valley/Carolinas. At the surface, a Bermuda high will remain anchored to our east throughout the period, with a Piedmont trough developing across the region most days. Precipitable water values will lower slightly behind the cold front this weekend, then increase again early to mid next week to between 1.50-1.75". With high pressure building aloft and a slightly drier atmosphere, this weekend will likely be the driest in the long term, with only isolated showers and thunderstorms expected for the southern half of the region. Surface dewpoints will increase next week to near 70 degrees, and with increasing moisture and sufficient daytime heating, afternoon scattered thunderstorms will develop once heating is strong enough to overcome any capping aloft. Highs will be mostly in the mid-80s to near 90, with lows in the mid to upper 60s. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 150 PM Thursday... Low confidence in the temporal details of the aviation forecast, as we'll see mostly prevailing MVFR to VFR conditions dropping periodically to IFR with passage of showers and storms through this evening. The most numerous storms will be E (RDU/FAY/RWI), but they could occur anywhere bringing a short period of adverse aviation conditions. Gusty and shifting winds are possible in and near any storms as well. The storm threat will persist through the evening, then we'll see lower coverage after midnight with a trend to prevailing IFR cigs and MVFR to IFR vsbys and scattered showers, lasting through daybreak Fri. Conditions should improve slowly to MVFR by 15z then to VFR by 18z, with scattered to numerous showers and storms once again with coverage increasing by early afternoon. Surface winds will be from the SE or S, mostly 10 kts or less but with sporadic gusts to 15 mph. Looking beyond 18z Fri, the chance for sub-VFR conditions within numerous showers and storms will dominate through Fri afternoon before pushing east. Storm chances may linger into Sat near FAY. Otherwise, improvement to VFR and lower precipitation chances are expected Sat, lasting into Tue, as the front shifts to the coast and dissipates, although sub-VFR fog and patchy stratus is possible in the early-morning (08z-13z) all three days. An isolated storm or two is also possible Mon and Tue afternoons. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through late tonight for NCZ009>011-026>028- 041>043-077-078-085-086-088-089. && $$ SYNOPSIS...Blaes/GIH NEAR TERM...Hartfield/Blaes SHORT TERM...Blaes LONG TERM...JT AVIATION...Hartfield