####018008879#### FXUS62 KRAH 031549 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1149 AM EDT Fri May 3 2024 .SYNOPSIS... Sub-tropical high pressure will extend across the South Atlantic states today, while a backdoor cold front will move through eastern VA and northeastern NC. The front will settle southwestward and into north-central NC tonight, where it will stall through Saturday night, then weaken and move northward into VA on Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 1145 AM Friday... A mid/upr-level ridge centered near the srn Middle Atlantic coast will remain so through tonight, while a mid-level trough and embedded, weak MCVs now over the ern OH and TN Valleys will be directed around the ridge and into the cntl Appalachians. At the surface, a 1019-1020 mb sub-tropical high will remain situated off the coast of the Carolinas. Meanwhile, a backdoor cold front, now stretching from the mouth of the Chesapeake Bay nwwd to a 1014 mb frontal low over OH, will merge with a developing bay breeze and move swwd to the vicinity of the Roanoke River between 22Z-00Z. A separate, srn stream front extending from cntl TX enewd and across the lwr MS and TN Valleys, to a 1013 mb frontal low over Middle/wrn TN, then ewd across nrn GA and the Piedmont of the Carolinas, will move little through the period. With no airmass change from Thu and continued influence of ridging aloft, today will be persistently, unseasonably warm, with temperatures continuing at 10-15F above average - mid 80s to around 90. Showers and isolated storm will focus today along both fronts noted above, including into the NC nrn Coastal Plain and far ne Piedmont early this evening and also with diurnal heating along a differential heating zone evident in late morning visible satellite and surface observational data along the srn stream front from AGS to HKY. The latter activity, should it indeed develop, would then be steered in weak wswly steering flow and into the srn and wrn NC Piedmont late this afternoon-evening. Areas of persistence fog and low stratus will likely redevelop into the srn-cntl Coastal Plain and ern Sandhills tonight, while a separate area of post-frontal, very low stratus will develop behind the backdoor front across the ne Piedmont and nrn Coastal Plain. Temperatures tonight will remain unseasonably mild and mostly persistent in the upr 50s to mid 60s. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 225 AM Friday... Confidence is high on increasing chances for showers and a few storms, although no one will see rain the entire day, and pinpointing the location and motion of what should be shower/storm clusters is challenging. PWs will continue to rise, with models indicating a swath of 1.5-1.75" values surging up through central NC, in the 90th percentile and even nearing daily records. This will occur in tandem with increasing low level moisture flux drawing Atlantic moisture into our area. As the backdoor front settles further into the area Sat morning, followed by a very gradual weakening and washing out, the considerable stratus over much of the area, esp N and W sections, will hinder heating and destabilization until it retreats and breaks up later in the day. And our large scale dynamic forcing for ascent will be poor, given the weak mid- upper level flow, but we may still feel the effects of MCVs emanating from today's Plains convection as it shifts into our area late Sat through Sat night. All of this supports scattered to numerous clusters of showers and storms, particularly in areas W of I-95 where moisture will be deepest, with the highest pops in the Triad and perhaps a secondary focus along the weakening backdoor frontal zone. The storm threat will be limited, given the weak deep layer bulk shear and modest CAPE, but a few storms will remain possible mainly in the afternoon and evening. Rain chances will persist overnight with further moistening of the low levels with confluent 925 mb southerly flow strengthening to 15-25 kts with both Atlantic and Gulf taps. While areally averaged rainfall amounts aren't likely to be high, given the anomalously high PW and somewhat slow storm motion with cell mergers possible, isolated areas could see local rainfall totals that could present minor urban flooding issues, esp in the Triad region, despite the recent dry weather. With mostly cloudy to cloudy skies, expect highs from the mid 70s N and W to lower-mid 80s SE. Lows in the 60s. -GIH && .LONG TERM /SUNDAY THROUGH THURSDAY... As of 250 AM Friday... ...Elevated Rain Chances Will Linger Through Monday... ...Heat Returns Middle Part of Next Week... Sunday and Sunday night: The stalled sfc front sagging across northern portions of the forecast will retreat north early Sunday, leaving all of central NC in the warm sector. Subtle upper disturbances coupled with the development of weak to moderate buoyancy during the afternoon will act upon the elevated PWATS (150- 160% of normal)in place over the region to support afternoon showers and storms. Shear is generally less than 20 kts, so the threat for organized severe storms is near zero. The moist PWATs and associated mostly cloudy skies and rain chances should temper afternoon temps. Highs in the upper 70s north to lower 80s. Convection should largely dissipate as BL nocturnally cools and stabilizes. Under mostly cloudy skies, mild overnight temps in the 60s. Monday and Monday night: A compact shortwave trough over the Mid MS Valley will become increasingly sheared as it crosses the central and southern Appalachians Monday afternoon and through the Mid Atlantic States Monday night. PWATs are forecast to increase to ~200% of normal as the trough and associated DPVA moves through the area. As such, expect another healthy uptick in diurnal coverage and PoPs Monday afternoon and into the evening. Shear remains weak. Thus, the threat for severe storms remains low. Low-level thicknesses are on par or slightly higher than Sunday. Highs 80-85. Lows in the 60s. Tuesday through Thursday: Rain chances will lessen during this period, with weak disturbances moving atop the ridge providing the primary focus for scattered shower and storms, mainly across northern portion of the forecast area. The main weather headlines will be the return of the heat during the second half of the work week. Highs Wednesday and Thursday are expected to top out in the mid/upper 80s north lower 90s over interior and southern portions of the forecast area. Expect very warm nights as well, potentially record warm, with lows 65 to 70. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 645 AM Friday... Except for a chance of MVFR vsbys/cigs in the SE including FAY 08z- 12z this morning, VFR conditions are likely to hold through at least this afternoon across all central NC terminals, but with gradually increasing high and mid clouds. Starting after 21z, an upper level disturbance along with daytime heating will prompt isolated to scattered showers and a few storms pushing into the west (INT/GSO), with these chances lasting through the overnight hours, however VFR conditions will still be dominant. However, starting after 04z tonight, a backdoor front dropping into far N and NE sections will bring a good chance for IFR cigs and MVFR to IFR vsbys into northern areas, along and behind the front. As the backdoor front settles southward well into central NC overnight, sub-VFR cigs/vsbys are expected to spread south through most of the area 06z-12z Sat, with scattered showers. Looking beyond 12z Sat, as the front slowly lifts back north and washes out, conditions will slowly improve back to VFR Sat from SE to NW, with the Triad (INT/GSO) remaining sub-VFR well into the afternoon. But the chance for sub-VFR conditions within scattered to numerous showers and storms will be high, especially at INT/GSO/RDU, Sat through Mon, particularly each afternoon and evening, with locally gusty winds in and near storms, and a chance for patchy early-morning fog areawide. -GIH && .CLIMATE... Record High Temperatures: May 3: KGSO: 92/1959 KRDU: 93/1959 KFAY: 95/1913 Record High Minimum Temperatures: May 4: KGSO: 65/2022 KRDU: 68/1938 KFAY: 68/1942 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...Hartfield LONG TERM...CBL AVIATION...Hartfield ####018004979#### FXUS65 KBOI 031549 AFDBOI Area Forecast Discussion National Weather Service Boise ID 949 AM MDT Fri May 3 2024 .DISCUSSION...Main ideas continue to be sunny and warmer wx today, then increasing clouds and southeast/southwest winds and warmer again on Saturday ahead of an approaching north Pacific cold front. Moderate to heavy rain late Saturday/Saturday night as the cold front moves through, then gusty west winds and much colder wx Sunday with lighter showers of rain and snow. Also, a 20 percent chance of thunderstorms in eastern-most Idaho zones Saturday afternoon and again Sunday afternoon. We're considering a Wind Advisory for the central Snake Basin and southeast Oregon on Saturday, otherwise current forecast is on track. See "Prev Discussion" (below) for details. && .AVIATION...VFR. Local valley fog/stratus has mostly cleared, but IFR conditions may still exist in isolated mountain valleys through Fri/18Z. Mountains will see scattered to broken cumulus field with bases 3500-5500ft AGL. Surface winds: variable or NW 5-15 kt, then S to SE 10-20 kt this afternoon. Winds aloft at 10kft MSL: Variable <10 kt, becoming S 10-20 kt Fri afternoon. KBOI...VFR and clearing Friday. Light NW winds, becoming SE 10-15 kt Friday afternoon. Winds are set to increase significantly early Sat morning to SE 20-25 kt with gusts to 30-40 kt. Weekend Outlook...Widespread precipitation moves into SE Oregon mid- morning Saturday, then into SW Idaho Saturday afternoon and will continue across the region through Sunday. A 20% chance of thunderstorms Saturday afternoon in s-central Idaho. Snow levels 6000-7000 ft MSL, lowering to 4000-5000 ft Sunday. IFR and widespread mountain obscuration Saturday night and Sunday. Surface winds: SE 15-25 kt with gusts 30-40 kt Saturday afternoon, W 5-15 kt with gusts to 20-30 kt Sunday. && .PREV DISCUSSION... SHORT TERM...Today through Sunday night...Any lingering showers wrapping around an exiting upper trough will dissipate by mid- morning. The exiting trough is replaced by an upper ridge this afternoon, resulting in dry weather and temperatures 5-10 degrees warmer than yesterday. Upstream, a deep Pacific low will approach the NW coast on Saturday. This system will be punctuated by heavy precipitation and gusty winds as it pushes into the region late Sat/Sun. The winds will increase out of the S-SE on Saturday in advance of the low. Widespread sustained winds of 20-30 mph with gusts to 40 mph are expected. Locally stronger winds could set up over SE Oregon Saturday and in portions of the Snake Plain east of Boise that would require headlines. A band of heavier precipitation will form ahead of a cold front that will push into SE Oregon Saturday afternoon, then cross into SW Idaho by evening. Marginal instability and surface energy will support a 15% chance of thunderstorms over s-central Idaho Saturday. Storms that do form will have a favorable shear profile and could become strong. The front will bring a wind shift to the NW Saturday night that will be reinforced by flow aloft on Sunday. Precipitation will continue on Sunday as it wraps around the low center which is forecast to track through northern NV. The probability for precipitation totals of over 0.25" has increased to greater than 80% across SE Oregon and SW Idaho through Sunday. The axis of heavier precipitation remains near the OR/ID border where the chance of exceeding an inch of liquid through Sunday is 15-30%. Snow levels ahead of the front will rise to 6-9kft Saturday evening, falling quickly behind the front Sunday morning. This could bring accumulating snow to SE Oregon as snow levels briefly drop to around 3000 feet early Sunday. Otherwise much of the accumulating snow is above 5500 after the frontal passage. Precipitation continues in the mountains through Sunday night while valleys trend drier. LONG TERM...Monday through Friday...Northwest flow continues in the wake of the exiting trough on Monday. Models show trailing shortwave energy that will keep a chance of showers over the region through Tuesday. An upper ridge will build along the coast Wednesday, gradually folding inland through Friday. Deterministic and ensemble solutions are in good agreement with with this pattern change. Afternoon instability will support a 15-30% chance of showers over the mountains while lower elevations remain dry. Temperatures through Wednesday are 10-15 degrees below normal, warming to near normal Thur/Fri. && .BOI WATCHES/WARNINGS/ADVISORIES... ID...None. OR...None. && $$ www.weather.gov/Boise Interact with us via social media: www.facebook.com/NWSBoise www.twitter.com/NWSBoise DISCUSSION...LC AVIATION.....JM SHORT TERM...DG LONG TERM....DG