####018006374#### FXUS61 KCTP 040307 AFDCTP Area Forecast Discussion National Weather Service State College PA 1107 PM EDT Fri May 3 2024 .SYNOPSIS... -Noticeable cool down over the weekend with overcast skies and periods of rain -Remaining unsettled next week with a gradual warming trend && .NEAR TERM /THROUGH SATURDAY/... Radar loop at 03Z shows dwindling, diurnally-driven convection over the NW Mtns. The focus for the rest of the night shifts to the potential of additional showers linked to a mid level vort max lifting into Southwest PA from the Ohio Valley. Surging pwats, combined with the arrival of this feature will bring an increased chance of showers over primarily the southwest portion of the forecast area late tonight. An increasingly moist east/southeast flow off of the Atlantic, combined with upslope flow, will likely yield developing stratus along the spine of the Appalachians late tonight. Low temps will be above early May climo and range between 45-55F from the southwestern Poconos/Coal Region to Warren County. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... Model guidance supports developing rain Saturday across Central PA from south to north ahead of an upper level shortwave lifting out of the Tennessee Valley. The associated southerly low level jet and plume of higher pwats overrunning a dome of cool/stable air across Central PA should result scattered showers giving way to a steady rain early Sat morning over the southern tier counties and by late in the day over the northern tier. The upper level shortwave should begin to lift out of the area Sunday, resulting in rain tapering off from west to east. Scattered late day convection appears possible late Sunday over the Allegheny Plateaus associated with an approaching warm front over Western PA. Ensemble plumes support rain totals by late Sunday in the 0.5 to 0.75 inch range for most of the area. Hires models show CAD pattern firmly entrenched over CPA Saturday, and therefore we continued to trim max temps vs. NBM, due to thick cloud cover, easterly flow and arriving rain. We have blended the cooler NAM surface temps with those of the NBM, resulting in expected max temps in the mid to low 50s for much of the area. No risk of thunder on Saturday, so removed from wx grids and changed character of precip to rain from showers. Sunday looks to be another cool day for May, due to a persistent southeast flow off of the Atlantic. However, a slight rebound is expected over the western counties, due to rain tapering off the chance for a bit of afternoon brightening. Subsidence behind the departing shortwave should result in a mainly rain-free Sunday night. However, a lingering upsloping southeast flow will likely yield lingering low clouds/patchy drizzle. Fcst lows Sunday night are +10-15F above climo for early May in the 50-60F range. && .LONG TERM /MONDAY THROUGH FRIDAY/... Monday should feature much warmer and drier weather, as high pressure builds southeast from the Grt Lks behind a Sunday night cold/occluded front passage. However, the approach of an upper level shortwave appears likely to produce scattered PM convection in the vicinity of the stalled front along the Mason Dixon Line. Highest POPs are placed over the southern tier, with only slight chc POPs across the north. The return of sunshine and 850mb temps near 12C translates to expected highs in the 70s most places. Upper level ridging over PA indicates warm and generally dry conditions are likely Tuesday. However, a warm front lifting out of the Ohio Valley could result in increasing clouds with a PM shower/tsra, primarily across the southwest counties. The bulk of medium range guidance supports a very warm Wednesday with scattered convection, as the area briefly breaks into the warm sector ahead of a cold front pushing in from the Grt Lks. Model consensus supports a better chance for a more widespread rainfall Thursday, associated with a deepening upstream trough and wave of low pressure riding along the stalled cold front just south of PA. The surface low and deepest moisture is progged to shift east of the area by Thursday night. However, falling heights ahead of the upper trough will likely support scattered, diurnally-driven convection Friday, along with a downward trend in temperatures. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Scattered SHRA across western PA has largely stayed east of all airfields in central PA. Some light SHRA passed over JST/AOO although relatively dry air in the lower-levels made for very little in the way of rainfall. Some light showers are still in the vicinity so have outlined VCSH for these airfields for the next couple of hours. The best chance of SHRA at either airfield will come in the very near-term (00Z-01Z) although showers continue to break apart. Chances of TSRA are low (< 30%) and have kept them out of the TAFs for this cycle, with any TSRA occurring at BFD/JST. Chances for TSRA after 03Z Saturday drop even further with the loss of daytime heating. Chances for low clouds and some fog do remain possible, although model sounding shave outlined less moisture in the lower-levels that would promote fog formation. If any fog formation is to occur, best chances will be across SW PA at JST with lesser chances at AOO. Southeasterly winds will increase probability of fog in these locations as well, but with low confidence have opted to keep fog out of this TAF package. Light SHRA will continue on Saturday with restrictions expected at all airfields across central PA. Widespread MVFR conds are expected by 12Z Saturday with IFR cigs expected across Allegheny Front airfields (JST/AOO/UNV, lesser IPT) throughout the day on Saturday. Outlook... Sun...Widespread restrictions due to low cigs. SHRA likely with a chance of TSRA. Mon-Wed...AM fog/clouds poss. PM -SHRA possible areawide. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl/Bowen NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald/Bowen LONG TERM...Fitzgerald AVIATION...NPB ####018006863#### FXUS65 KBOU 040308 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 908 PM MDT Fri May 3 2024 .KEY MESSAGES... - A few showers and storms across the eastern plains this afternoon into tonight. - Warmer and windy on Sunday. - Active, cooler, and mainly windy pattern from late Sunday through most of next week. A few chances of accumulating snow across the mountains with isolated/scattered showers across the plains. && .UPDATE... Issued at 848 PM MDT Fri May 3 2024 We observed one severe thunderstorm in eastern Lincoln County this afternoon which generated strong outflow winds measuring at least 62 mph in and near Hugo. All of that action has now pushed east, with just some lingering light showers over the mountains where there's sufficient orographic lift to tap into a stream of mid- level moisture. These should dwindle in the next few hours as this corridor pushes east. Cloud cover appears less expansive than initially indicated, so have made pertinent adjustments and also lowered minimum temperatures for tonight by a couple degrees for most areas. Breezy conditions remain in the plains following the front, particularly in Lincoln County, but winds will gradually subside as the lower levels decouple. && .SHORT TERM /Through Saturday/... Issued at 303 PM MDT Fri May 3 2024 Current analysis shows a lee cyclone across the Palmer Divide area. From the north, a cold front is advancing southward with a push of gusty northerly winds behind it. Gusts 35-45 mph are being reported across the region from the front. Along this front, a line of thunderstorms moves across the northeastern plains. SPC mesoanalysis shows an axis of marginal instability across the far east plains (< 500 J/kg SBCAPE). This is overall supported by an shortwave trough moving eastward just north of the Colorado border. For the remainder of the afternoon and into the evening expect showers in the mountains with another round of showers moving across the northern border onto the plains. Areas such as Lincoln County remain unstable ahead of the advancing front, so can't rule out any shower or storm development in those areas in the next hour. Showers linger across the mountains this evening with remaining showers/storms exiting the eastern plains. Behind the front, temperatures cool sufficiently overnight with lows in the low to mid 30s across the plains. We are approaching Frost/Freeze headline territory for areas on the plains; however, given its current rating of mixed susceptibility for vegetation and closeness to average last freeze, we decided to hold off on headlines. For tomorrow, expect cooler temperatures with highs in the 60s across the plains, 50s for foothills/mountain valleys, and 40s for the mountains. Expect another round of showers and a few storms in the afternoon (marginal CAPE), mainly over the higher elevations and south of I-70. && .LONG TERM /Saturday night through Friday/... Issued at 303 PM MDT Fri May 3 2024 A strong upper low will be located near northern California on Sunday morning, with increasing south-southwesterly flow over our forecast area through the day. The result will be a warm, dry, and breezy end to the weekend as the dryline shifts towards the CO/KS/NE border. Temperatures should warm into the mid to upper 70s. Model soundings suggest boundary-layer average winds of 30-45kt, which would lead to wind gusts of 45-55 mph. Some guidance keeps just enough moisture out in the far eastern plains for an isolated shower or storm, though the models that keep some moisture here also maintain a strong cap through the day. The closed upper low is expected to transition to a sharp, negatively tilted trough axis by Monday morning... which then ejects into the northern Great Plains from Monday into Tuesday. A quick round of mountain snow is likely with the passage of the trough axis, though cross-sections show somewhat sparse moisture on this side of the trough. For the plains, a few showers will be possible, but the main story will be wind. A bora-like event appears likely as a colder westerly flow develops. Temperatures will hover in the upper 50s/low 60s. Gusty winds will continue, especially across the high country. Zonal flow is expected to persist Tuesday into Wednesday as the upper trough stalls over the far northern Great Plains. Guidance shows a bit of moisture lingering in this flow, which would lead to scattered snow showers across the high country while the plains remain generally dry. With fairly strong mid-level flow, gusty winds will be slow to subside in this period. As we get into the latter half of next week, there is increasing uncertainty in the overall synoptic pattern. Recent guidance attempts to stall out the trough or even retrograde it back to the south and west. Unsurprisingly, ensemble guidance lacks a clear, definitive signal, with a substantial amount of spread for T/QPF as we get into Thursday/Friday of next week. We'll likely have a ways to go until we see better agreement in this timeframe... but at the very least, it does appear that a cool and unsettled pattern will continue. && .AVIATION /00Z TAFS through 00Z Saturday/... Issued at 525 PM MDT Fri May 3 2024 Gusty NE winds will gradually weaken 01-04Z this evening, rotating to the southeast and likely persisting from that direction through the remainder of the night. On Saturday, expect strengthening SE flow by mid afternoon when gusts may exceed 20 kts. A period of lower CIGS with bases 040-060 looks favored for later this evening (starting ~02-03Z) through early Saturday morning, before transitioning back to VFR conditions for all terminals. && .FIRE WEATHER... Issued at 303 PM MDT Fri May 3 2024 Increasing fire danger is expected late this weekend into early next week behind the strong storm system. Gusty winds should develop on Sunday and continue daily through at least mid-week, with a gradual drying trend from Sunday through Tuesday. Near- critical to critical fire weather conditions appear likely across portions of the lower elevations at times, especially south of I-70. However, recent rainfall and ongoing green-up across the plains may limit overall fire danger. Still a couple of days out at this point, so no watches have been issued... but we'll be watching closely as we get into the weekend. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Rodriguez SHORT TERM...Mensch LONG TERM...Hiris AVIATION...Rodriguez FIRE WEATHER...Hiris ####018006124#### FXUS66 KSEW 040309 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 809 PM PDT Fri May 3 2024 .SYNOPSIS...A shift back to cool, wet unsettled conditions will prevail across Western Washington through early next week. A significant change in the weather pattern is expected for the second half of next week as high pressure aloft leads to warmer and drier conditions. && .SHORT TERM /TONIGHT THROUGH MONDAY/...Light rain ahead of incoming front is making slow progress into the interior as expected. Rain chances around much of Puget Sound will increase on Saturday as weakening front pushes across the region, but the bulk of the precip with this initial system looks to fall south and west of Seattle. No changes anticipated this evening to existing forecast. Previous discussion follows with updates to marine and aviation portions. 27 Rain had yet to reach coastal areas as of 130 PDT (2030Z) as an occluded front ahead of a broad upper trough offshore gradually advances toward the region. Rain will spread across the Olympic Peninsula by early evening, but will be slow to get into Puget Sound eastward initially. As the upper trough axis shifts into the Oregon coastal waters early Saturday, a weakening frontal boundary will slowly lift northeastward across Western Washington. Low level easterly flow will shift onshore and increase behind it. This will allow the air mass to moisten up for increasing precip coverage by Saturday afternoon. Overall QPF will be heavily focused on the southwest half of the CWA. The upper trough is expected to shift into the Great Basin by early Sunday with wrap-around precip continuing to fall across parts of Western Washington. Onshore flow will ramp up through the day on Sunday as another upper trough moves toward the area. Increasing orographic lift will lead to a fairly wet Sunday afternoon and evening in the mountains, but much of the Puget Sound area looks to be rain shadowed. An upper trough axis will swing onshore on Monday. With colder air aloft, this will destabilize things enough to warrant the mention of a slight chance of thunderstorms. Snow levels will dip to some of the higher passes, but amounts look to be light. A convergence zone looks likely to form on Monday as well. Temperatures throughout the short term forecast period will be several degrees below normal, but changes are afoot. .LONG TERM /TUESDAY THROUGH FRIDAY/...Cool, showery conditions will persist into Tuesday as the upper trough axis slowly shifts east of the Cascades. For Wednesday and beyond, ensembles are nearly unanimous that upper ridging will build over the northeast Pacific as downstream a broad upper trough takes up residence over the eastern two thirds of the lower 48. There is still considerable uncertainty with regards to how warm it will get. Current forecasts reflect the NBM 50th percentile forecast...which brings mid 70s to Seattle by next Friday. A noteworthy number of ensemble members (particularly the GFS) have temperatures teasing 80 degrees by late next week for some areas. Rough winds do shake the darling buds of May, but we might compare thee to a summers day by next weekend. 27 && .AVIATION...An upper level trough will move through western Washington this evening with south to southwesterly flow aloft. A frontal system is beginning to approach the area, with light rain falling throughout the Pacific Coast and the Southwest Interior. Conditions remain VFR this evening with MVFR ceilings moving onshore as the front approaches. Rain will struggle to become widespread in the interior north of Seattle tomorrow. Scattered showers move in overnight becoming more widespread later tomorrow morning. VFR ceilings continue through tomorrow morning through the interior, falling to MVFR tomorrow afternoon. MVFR along the coast tonight and tomorrow and around OLM, with isolated IFR conditions possible. Winds at the surface will remain west to southwesterly through most of the TAF period. Winds may briefly turn light northerly overnight, but will turn back to southwesterly tomorrow. Winds may be gusty tomorrow with the frontal passage. KSEA...VFR this evening with ceilings gently lowering as a front moving onshore. Rain to the south and west of the terminal, likely not fully reaching the terminal until tomorrow. Ceilings lowering to low end VFR, with MVFR conditions possible as early as 15Z Saturday but not expected to be longer lasting until tomorrow evening. Winds WSW and decreasing overnight. Winds will likely turn northerly overnight before spinning back around to southwesterly tomorrow morning. LH && .MARINE...A frontal system is currently traversing the coastal waters and will continue to work its way onshore tonight into tomorrow. Winds will decrease tonight as the front moves through the area. As such, the Small Craft Advisory has been allowed to expire. Heading into the weekend, guidance suggests several westerly pushes through the Strait of Juan De Fuca, likely yielding additional headlines. Another system looks to track into the area waters through the first half of next week. Combined seas this afternoon around 3 to 5 feet will gradually increase to around 6 to 8 feet by Sunday. Confidence is increasing that seas look to hover around 9 to 11 feet Monday night into tuesday, with the higher heights mostly in the outer water zones. Maz/LH && .HYDROLOGY...No river flooding is expected over the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 7 PM PDT this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. && $$