####018009598#### FXUS62 KRAH 070043 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 840 PM EDT Mon May 6 2024 .SYNOPSIS... A series of mid to upper-level disturbances will interact with an unseasonably moist airmass as they move across NC through Thursday, while sub-tropical high pressure will otherwise extend across the South Atlantic states. A cold front will move across the region on Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 405 PM Monday... Continued unseasonably humid conditions, with above average chances of showers and storms --with heavy downpours and water-loaded wind gusts up to 45 mph-- will continue through tonight. Regional satellite and radar data depict multiple MCVs stretching from, the most pronounced one along the KY/IN border, sewd and across the srn Appalachians and Carolinas. Each will continue to move generally ewd across the srn Middle Atlantic, with associated 30-40 meter 500 mb height falls over cntl NC, through tonight. At the surface, a well-developed cold pool and outflow boundary stretched at 1945Z from near MTV to INT to SVH and was moving eastward at its leading edge at close to 30 kts. This feature should continue ewd across the nrn Piedmont with an accompanying risk of wind gusts of 30-40 mph through ~22Z, before probably weakening as it encounters rain-cooled and more-stable conditions from around HBI to RDU. The swrn flank of this boundary has slowed and nearly stalled across the srn Appalachians and Middle TN. Upstream convection may track along at boundary and move into the srn NC Piedmont this evening. A separate outflow boundary and ongoing, bowing convective cluster was moving across the ern Sandhills and srn Coastal Plain, where it will soon merge with the sea breeze and outflow convection, and a maximum in instability driven by surface temperatures in the mid 80s, through the remainder of the NC Coastal Plain. Continued unseasonably humid and weakly unstable conditions will otherwise favor a continued slight to small chance of showers/storms overnight, and also the likely redevelopment of areas of low stratus late tonight-Tue morning. Lows will be in the 60s. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 340 PM Monday... Tuesday and Tuesday night: Aloft, as the s/w moves east and off the mid-Atlantic coast, a brief period of omega blocking will set up as the sub-tropical ridge builds northward through the Southeast US, central Appalachians, OH Valley and western Great Lakes. To the east of the block, a low will progress eastward through Quebec and Newfoundland Tue, then out over the northern Atlantic Tue night. To the west, a large low will sit over the northern Plains as several s/w disturbances rotate around it. The eastern low progressing eastward Tue night will weaken the block, allowing a leading s/w moving through the OH Valley around the western low to push the ridge slightly eastward and suppress it southward. At the surface, a warm front will lift newd through the area early Tue, with a Piedmont trough setting up east of the mtns and strengthening through Tue night as a low develops over the southern Great Lakes. Expect continued advection of warm, moist air into the area, with PWATS starting the day around 1.7 inches, decreasing slightly with daytime mixing, but remaining largely in the 1.4-1.6 inch range. The 12Z NAM and 12Z GFS both have MLCAPE values of about 1000-2000 J/Kg (GFS lower than the NAM) across all of central NC Tue aft/eve, with effective shear around 30 kts. The SPC has included just about all of central NC in a marginal risk for Tue. The big question will be the presence of a forcing mechanism to get storms firing. Look for showers/storms to largely form along the developing lee trough and/or differential heating boundaries if they are present. An isolated strong to severe storm is possible, with the primary threat of damaging wind gusts and possibly hail. As for temperatures, highs should top out in the mid to upper 80s, while lows in the mid 60s to around 70 degrees are expected. Wednesday and Wednesday night: Aloft, the leading s/w will continue eastward through the Northeast US toward the eastern low, while the western low finally begins to migrate slowly eastward. A second s/w will swing through the Plains and the MS Valley Wed/Wed night. At the surface, the surface low will move slowly eastward through the Northeast US Wed and offshore Wed night. Another low will develop along the front over the southern Plains early Wed, lifting newd into the upper MS Valley through Wed eve before drifting eastward into the OH Valley Wed night. The trough over central NC will weaken and lift northward out of the area as the low move east and offshore Wed night. The frontal zone between the two lows should generally remain north of the area through Wed night, with continued swly flow over the area. Expect continued advection of warm, moist air into the area, with PWATS largely in the 1.4-1.7 inch range. The 12Z NAM and 12Z GFS both have MLCAPE values of about 1500-2500 J/Kg across all of central NC Tue aft/eve, maximized over the eastern Piedmont and Coastal Plain, with effective shear again around 30 kts. The SPC has included all of central NC in a marginal risk for Wed. The forcing mechanism will likely be the lee trough as it moves eastward through the area. An isolated strong to severe storm will once again be possible. As for temperatures, highs should be about a category higher than Tue, topping out in the upper 80s to low 90s. Lows should be in the upper 60s to low 70s. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 202 PM Monday... Thursday/Friday: There is good consensus amongst models supporting an upper trough moving east from the Great Lakes/Midwest across the eastern seaboard Thursday into Friday. This feature will promote increasingly swly flow and deep moisture advection into the southeast with PWAT rising to 150 to 200 % of normal. At the sfc, a weak low initially over IN/OH Thursday morning, will deepen some as it progresses east into the Mid-Atlantic through Thursday night. An associated cold front will approach the Southern Appalachians Thursday night, before passing through central NC on Friday. Given high humidity and temperatures reaching the upper 80s/lower 90s on Thursday, moderate instability is expected to develop across our area ahead of the approaching front. Aloft, increasing mid-level height falls and associated perturbations will help to generate widespread pre-frontal showers and storms which should grow in coverage/intensity Thursday afternoon. Additionally, severe parameters including bulk-layer shear (30 to 40 kts), 0-1 km shear (15 to 25 kts), mid-level lapse rates (>7 C/km), and even helicity (200 to 300 units) will all be elevated. As such, there still appears to be a good chance for severe weather (potentially widespread) Thursday and Thursday night. Damaging wind gusts, large hail, and isolated tornadoes would all be possible. The SPC has outlined our entire area with a 15% chance for severe storms four days in advance, increasing confidence that Thursday could be a complex severe weather day. Depending on the eventual evolution of the cold front, some guidance does show instability forming ahead of the front as it moves through our area on Friday. As such, maintained thunder in the forecast for those south of Raleigh on Friday. Additionally, the upper trough will swing through on Friday which could generate additional showers/storms into the evening period. Highs on Friday may be a bit tricky given uncertainty wrt to the advancing cold front. For now, highlighting mid to upper 70s north to lower to mid 80s south. Saturday through Monday: The cold front will have pushed east of the area by Saturday morning, behind which considerably drier and cooler air will filter across central NC. An additional weak perturbation aloft will pass over later Saturday which may generate a few showers across our northern areas, but overall the area should stay mostly dry. Similar conditions are expected Sunday through Monday, with dry and cooler temps in the upper 70s. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... As of 235 PM Monday... There is a chance of showers/storms overnight, with mostly associated MVFR to IFR CIGS/VSBYS with a disturbance arriving from the west. Otherwise, continued unseasonably humid air will also favor the redevelopment of areas of IFR-MVFR stratus late tonight- Tue morning. Associated ceilings should then lift and scatter and yield to a gusty swly surface wind by ~14-16Z Tue. Outlook: There will be a chance of mainly afternoon-evening showers and storms throughout cntl NC through Thu, then ahead of a passing cold front, mainly at FAY, on Fri. && .CLIMATE... Record High Minimum Temperatures: May 8: KGSO: 66/1938 KRDU: 68/1930 KFAY: 70/2003 May 9: KGSO: 68/2002 KRDU: 70/1936 KFAY: 71/2009 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...KC LONG TERM...Luchetti AVIATION...pwb/MWS CLIMATE...RAH ####018008091#### FXUS64 KBMX 070043 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 743 PM CDT Mon May 6 2024 ...New SHORT TERM, AVIATION... .SHORT TERM... (Tonight through Wednesday) Issued at 720 PM CDT MON MAY 6 2024 Clouds will form late tonight as southerly, moist flow continues. Additionally, a brief period of patchy fog is also possible around sunrise. The best chances for fog will be south. The lower clouds will increase in height and thin somewhat by afternoon. Scattered thunderstorms will develop mainly during the maximum heating of the day. The discussion below still applies for Tuesday afternoon. 75 Previous short-term discussion: (This afternoon through Tuesday) Issued at 103 PM CDT MON MAY 6 2024 A cold front moves into the Mid-South region tomorrow, and a very subtle weakness in the low to mid-level flow will move across the Lower MS River Valley and towards the Tennessee Valley during the afternoon. Although forcing will be very weak, the airmass will quickly destabilize during peak heating. MUCAPE is progged to rise to around 3000 J/kg across the west where dewpoints will stay near 70F, and eff. shear of 40 kts will support some scattered strong to severe thunderstorm potential. Stronger storms will be capable of producing damaging winds up to 60 mph and quarter size hail with highest thunderstorm coverage expected along and north of I-20. 86/Martin && .LONG TERM... (Tuesday night through next Sunday) Issued at 326 PM CDT MON MAY 6 2024 Not many changes needed in the extended this afternoon, other than minor changes rain chances. Will have more details for the Wed night/Thu system once we are in the time range of CAM models. For now, will continue to highlight the key messages below. Key messages: - The warmest day of the spring so far is expected Wednesday with heat indices in the mid 90s. - One or more rounds of showers and storms will result in a threat of damaging winds, large hail, and localized minor flooding Wednesday night possibly into Thursday, especially across the northern half of Central Alabama. However, confidence on details remains low at this time. Isolated to scattered showers and storms may linger into the evening hours on Tuesday before weakening, though some activity could persist across the far northern counties in closer proximity to a stalled cold front and lingering boundaries. A rex block will be in place to start the period with an upper low over the Northern Plains and an anticyclone over the Canadian Prairies. The upper low will eventually split with the majority of its vorticity going into a trough over the Great Lakes by Thursday and a lesser portion going to an upper low over the Southwest CONUS as part of a developing omega block over the eastern Pacific/West Coast. Meanwhile a strong subtropical ridge will be centered over the Bay of Campeche. At the surface the stalled frontal boundary will lift northward as a warm front across the Ohio Valley in response to a broad but sub-1000mb area of low pressure moving from Missouri to the southern Great Lakes. A fairly strong late spring cold front will eventually move through Central Alabama Thursday and Thursday night. Dry air aloft and weak ridging should keep any diurnal convection isolated to widely scattered Wednesday while strong low-level southwesterly flow results in the warmest day of the spring so far. Those that are especially sensitive to heat impacts may need to take precautions given the lack of acclimation to the heat this early in the season. Robust convection should develop to our northwest ahead of the cold front Wednesday afternoon and evening in a very unstable and sheared air mass, aided by a vort max moving through the Mid-Mississippi Valley. This convection will probably eventually grow upscale into one or more MCSs potentially moving towards our northern counties Wednesday night aided by a modest LLJ. With weak forcing there is quite a bit of model spread regarding timing as is typical in this setup. The ECMWF and its ensembles bring convection in during the evening hours while other guidance holds off until after midnight. An earlier timing would coincide with more instability and a greater threat for severe storms, but given mild overnight lows and steep mid-level lapse rates with an EML there would still be at least an isolated severe threat with the later overnight timing. Damaging winds and large hail will be the main threat. The tornado threat while very low may be non-zero. Some guidance does indicate some marginal SRH developing depending on whether a secondary surface low forms. Given the uncertainty over timing, convective mode, and whether storms will be surface-based, will hold off on any brief tornado mention at this time. Fast zonal flow will be in place Thursday as the cold front moves in, with little in the way of height falls until evening when troughing begins to deepen over the eastern CONUS. An impressive overlap of CAPE and shear may be present, but this will be highly dependent on how much convection occurs Wednesday night and Thursday morning and any leftover cold pools. Additionally, low-level flow will be veering and weakening, limiting convergence, while moisture dries up aloft. There will probably end up being at least an isolated threat of severe storms, but will hold off on messaging past Wednesday night given the limiting factors mentioned above. There is also the possibility for an MCS to move along the Gulf Coast Thursday night which could cause locally heavy rainfall and some stronger storms across our southern counties. Behind the front, a welcomed relief from the heat is expected going into the weekend with highs in the 70s to lower 80s and lows in the 50s. There are some model disagreements regarding potential shortwave activity by Sunday, but ensembles support keeping PoPs at 10 percent or less on Sunday. 32/Davis/14 && .AVIATION... (00Z TAFS) Issued at 720 PM CDT MON MAY 6 2024 The terminal forecast trend was continued this cycle. Some convection will be around this evening but will be isolated enough to leave out for the time being. The activity will dissipate by 3z. Southerly low level flow is quite moist and will become saturated toward daybreak. There is some isentropic lift that will occur and expect MVFR ceilings after 08-10z at all terminals. Several locations will also see IFR ceilings which should be rather brief, 4 hours or less. The MVFR ceilings will rise and become VFR by 16-17z. Scattered thunderstorms will be possible in the afternoon for the northern terminals. Starting off with a PROB30 mention. Winds will be south southwest 5-10kts. 75 && .FIRE WEATHER... Isolated to scattered showers and storms are possible each day through Wednesday, with greater rain chances Wednesday night and Thursday. Rainfall amounts will average 0.5-1.0 inch under heavier storms. Afternoon minimum RH values will be above 40-45 percent each afternoon through mid week. 20-foot winds will average less than 10 mph from the south to southwest Tuesday, increasing to 8-12 mph Wednesday. Wind gusts to around 25 mph are possible near convection. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 64 86 67 89 / 20 50 30 30 Anniston 66 86 68 88 / 20 40 20 20 Birmingham 68 86 70 89 / 20 50 20 20 Tuscaloosa 68 87 70 90 / 20 50 20 20 Calera 67 86 69 88 / 20 40 20 20 Auburn 66 86 70 88 / 20 10 10 10 Montgomery 67 90 70 92 / 20 20 10 10 Troy 66 90 69 91 / 20 10 0 10 && .BMX WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...75 LONG TERM....14 AVIATION...75