####018002674#### FXUS66 KSEW 152155 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 255 PM PDT Thu May 15 2025 .SYNOPSIS...Cool, cloudy and a chance of rain through Friday as a frontal system moves in. An unsettled weather pattern will remain in place across the Pacific Northwest this weekend through early next week, maintaining widespread clouds and rain showers. && .SHORT TERM /TONIGHT THROUGH SUNDAY/...Precipitation is spreading inland this afternoon with light rainfall accumulations expected (less than 0.10"). Moist, westerly onshore flow continues on Friday for cloudy and cooler conditions. Forecast highs are only in the 50s or similar to today. Rainfall is mostly along the coast with isolated/scattered coverage inland. The weekend weather is wet and unsettled as a trough and trailing upper low slide through. The air mass is slightly unstable on Saturday with a chance of afternoon/evening thunderstorms (mainly near the Cascades). Snow levels are low on Sunday, around 3500-4000 ft, and may see light snow in the mountains (inch or less). 33 .LONG TERM /MONDAY THROUGH THURSDAY/...A ridge moves inland late Sunday and early Monday for a brief break in the weather. Temperatures rebound slightly with highs in the lower 60s. A quick-moving front clips through western WA later Monday for more showers and windy conditions, especially along the coast. Onshore flow prevails moving forward, leading to cloudy conditions and near to slightly cooler than normal temperatures. 33 && .AVIATION...West to northwest flow aloft will continue as a weak upper trough and associated frontal system approaches Western Washington. Ceilings will lower to MVFR in light rain at times this afternoon then persist across the region overnight into much of Friday as the system moves onshore. KSEA...VFR ceilings will lower to primarily MVFR in scattered showers 22Z-00Z. These conditions will then persist overnight and continue through much of Friday. Surface winds S/SW 7 to 10 knots. 27 && .MARINE...A weak frontal system will approach the area then dissipate as it moves onshore on Friday. Surface ridging will rebuild offshore on Saturday then shift into the coastal waters early next week. This will lead to increasing onshore flow and likely headlines for the coastal waters and strait. Another frontal system looks to move through the area on Monday. Seas will generally remain under 10 feet through the forecast period. 27 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ ####018005382#### FXUS66 KPDT 152156 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 256 PM PDT Thu May 15 2025 .SHORT TERM...This afternoon through Saturday night...A weak shortwave will arrive from the Pacific late this afternoon, traversing the region through Friday morning. The system will facilitate low chances (10-30%) of wetting rains for the mountains, highest for the northern Blues, and locally breezy westerly to northwesterly winds. Confidence in winds reaching advisory levels is low (<30%), highest for the Kittitas Valley. A brief break in active weather is forecast Friday as the region is between weather systems. Late Friday, the first of back-to-back waves is expected to arrive (>90% confidence). Shower chances will increase by Friday night, with some weak elevated instability perhaps facilitating isolated embedded thunderstorms for portions of the eastern mountains (highest chance of 10-15% in Grant County Friday night). The best area-wide shower chances will be Saturday as the second wave digs southeast into the PacNW and the first wave tracks east over the Great Basin. Delving into clusters of ensemble solutions does reveal some uncertainty in the evolution of the system as the two waves interact; ensemble members are split on whether the system will morph into a closed low overhead late Saturday through Saturday night or if it will remain a weaker open wave trough. Regardless, have included an area-wide slight chance (15-24% probability) to chance (25-35% probability) mention of thunder in the forecast through the day Saturday as the low/trough moves overhead. Best chances of thunderstorms will be over the Blue Mountains during the afternoon (25-35% probability). Westerly winds will increase in magnitude Saturday through the Cascade gaps as cross-Cascade pressure differences ramp up. NBM probabilities of exceeding advisory-level gusts (45 mph) through the eastern Columbia River Gorge, Kittitas Valley, and wind-prone portions of the Columbia Basin/Blue Mountain foothills are roughly 20-50%. Plunkett/86 && .LONG TERM...Sunday through Thursday...The upper trough with the associated system will gradually move eastward, leaving behind mountain showers with light snow, isolated thunderstorms and gusty winds for Sunday. QPF amounts may range between 0.05-0.15 inches over the Blues, eastern mountains and WA/OR Cascades (30-60% chance). The lowlands will be left dry.Given the frontal lift, isolated thunderstorms may develop late Sunday morning through evening over portions of the Blues and across the eastern mountains. However, chances are low due to inhibition from low moisture level and lack of instability. Winds over the Cascade gaps will become gusty at 30-40 mph along with breezy winds across the lowlands from the cross-Cascade surface pressure difference. Wind conditions should return light around later Sunday evening into night when the system begins to tamper off. Another frontal system will arrive Monday with light showers at first the Cascades before spreading to the Blues and eastern mountains (20-40% chance). And with increased westerly flow, winds could become gusty over the Cascade gaps Monday afternoon into the evening before steadily decreasing to breezy. Models are aligned with system's arrival but differs on the timing a bit where the Canadian model has it sooner than the others. This might make forecasting the timing of showers development slightly tricky for Monday. The PacNW will be mostly over a zonal pattern Tuesday onwards with a brief shortwave Wednesday. the forecast area will be relatively dry, but may have some lingering mountain showers over the Cascades and eastern mountains (<30% chance). The westerly flow will dominate the remaining long term thus inducing slightly gusts at 25-35 mph at the Cascade gaps Tuesday morning through the evening. Winds Wednesday through Thursday may be locally breezy across the Cascade gaps but light everywhere else. Feaster/97 && .AVIATION...18Z TAFs...All sites will be VFR through today. However, KRDM/KBDN may drop to MVFR due to showers from the frontal system this evening (30-40% confidence). KDLS/KPDT/KALW could drop to MVFR as well for tomorrow due to mainly low clouds as the system passes (<30% confidence). KDLS/KALW are currently gusting at 20-30 kts with sustained winds of 12-20 kts, though with KALW ending this afternoon and KDLS continuing through tomorrow morning. KPDT/KRDM/KBDN will be mainly breezy at 20-25 kts with sustained winds of 12-15kts until this evening. Feaster/97 && .PRELIMINARY POINT TEMPS/POPS... PDT 46 67 47 66 / 70 30 10 80 ALW 47 65 49 66 / 60 60 10 80 PSC 46 72 47 71 / 50 20 10 60 YKM 44 70 49 68 / 30 10 10 50 HRI 46 72 49 71 / 60 20 10 70 ELN 42 67 46 66 / 30 10 20 60 RDM 37 67 42 63 / 50 0 10 80 LGD 42 59 42 58 / 70 50 10 90 GCD 40 62 43 57 / 80 20 30 100 DLS 46 69 49 68 / 40 0 20 60 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....97 AVIATION...97 ####018003438#### FXUS65 KBOU 152156 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 356 PM MDT Thu May 15 2025 .KEY MESSAGES... - Breezy to windy conditions through Friday with fewer showers, mainly over the mountains in the afternoons. A small increase in the showers Saturday. - Windy again with increased shower and thunderstorm activity expected starting Sunday. && .DISCUSSION /Through Thursday/... Issued at 338 PM MDT Thu May 15 2025 We bumped up PoPs through early evening as there's a pretty good crop of light showers over northwestern Colorado heading east. They'll be fighting the downslope, so we only made minor changes for the I-25 corridor, but there's a pretty good chance of off and on showers in the mountains through early evening. The snow level is still around 8,000 feet, but it's warm enough that accumulations should be limited to areas above 10,000 feet with just light amounts above that. Winds are gradually decreasing overall. There may be a little pop of stronger winds in the foothills west of Denver and Boulder later tonight as a weak shortwave trough passes. This should be fading again in the morning. Friday will be drier, but still some low PoPs. There will also still be some wind, but it will be less than this afternoon. There's fair agreement now on some increase in moisture over northern areas on Saturday, so we'll have a modest increase in PoPs for the afternoon and evening. Sunday through Tuesday remains a question mark. The models have trended back towards each other and the idea of two shortwaves rotating around the mean trough. One would pass Sunday and another late Monday or early Tuesday. There's still some wobble in the latitude of the low on Sunday, which would decide whether it's a stormy day or a warm/dry/windy day. Current NBM solution has this gradient over our area, which seems reasonable. It's not the best setup for severe weather across most of our area, but there could be some dryline action out near the eastern border if it all sets up right. While the upper level features are uncertain, we should get a surge of cooler and moister low level air. That will be reinforced Tuesday behind the second part of the trough. Right now it looks like just a little cooling with increased moisture, which could create an increased severe threat, though the cooler temperatures and position north of the jet should reduce the ingredients. We'll be warmer and drier again for Wednesday and Thursday, either under a weak ridge, or possibly with a shortwave passing north of us or approaching by Thursday. NBM PoPs through all of this are looking better today, although they may still be too high Sunday, and too low Tuesday. && .AVIATION /18Z TAFS through 18Z Friday/... Issued at 1141 AM MDT Thu May 15 2025 VFR conditions expected through the TAF period. Strong WNW winds will continue through tonight gusting up to 35 kts before decreasing by 03-05Z. There could be VCSH by 21Z, which would cause gusty westerly outflow winds up to 30 kts. Winds will return to drainage around 07Z. Friday morning will see winds pick up again from the west, with gusts up to 20 kts expected. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Gimmestad AVIATION...Ideker ####018008251#### FXUS63 KIND 152157 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 557 PM EDT Thu May 15 2025 .KEY MESSAGES... - Isolated to scattered thunderstorms this evening with the potential for severe weather - Higher-end threat for severe weather tomorrow evening, especially across southern Indiana - High temperatures in the upper 80s again tomorrow - Cooler and quiet for the weekend, additional precipitation again next week && .MESOSCALE UPDATE... Issued at 556 PM EDT Thu May 15 2025 RECENT SURFACE ANALYSIS SHOWS THE MAXIMUM TEMP AXIS OVER ILLINOIS WITH TEMPS IN THE LOW 90S. THE MOISTURE AXIS IS MORE BROAD WITH LOWER 70S DEWPTS EXTENDING FROM CETNRL/SW INDIANA INTO CENTRAL IL/SE MO. INSTABILITY REMAINS EXTREMELY HIGH OVER MOST OF THE FORECAST AREA WITH MLCAPE VALUES FROM 3500-4000 J/KG, WITH OVER 4500 J/KG OVER CENTRAL IL. A SUBTLE OUTFLOW BOUNDARY GENERATED BY CONVECTION OVER THE MO BOOTHEEL EXTENDS INTO SE MO AND FAR S IL. A DRYLINE EXTENDS ACROSS THE MS RIVER FROM NEAR THE QUAD CITIES DOWN TO JUST WEST OF ST.LOUIS AND IS MOVING EAST AROUND 20 KTS. SATELLITE IMAGERY SHOWS THE 850-700 MB FRONT NICELY OVER WEST/CNTRL MO WITH BANDS OF AGITATED ALTOCUMULUS ALSO CAUSING TURBULENCE FOR AICRAFT. ACARS (AIRCRAFT REPORTED) SOUNDINGS OUT OF ST. LOUIS SHOW A VERY STRONG INHIBITION LAYER CENTERED NEAR THE 850 MB LAYER (TEMPS NEAR 22C) WITH SOUNDINGS FROM KANSAS CITY SHOWING SUBSTANTIAL COOLING (850 TEMPS NEAR 12C). THERE REMAINS TWO SCENARIOS FOR CONVECTIVE DEVELOPMENT IN CENTRAL IN LATER THIS EVENING (AFTER 02Z/10PM EDT). THERE IS AN OUTSIDE CHANCE THAT THE ELEVATED SHOWERS/ACCAS CLOUD FIELD OVER SE MO/FAR S IL WILL MOVE INTO FAR SOUTH PARTS OF CENTRAL IND (NEAR THE US 50 CORRIDOR) AND ERODE THE CAP FROM ABOVE TO INITIATE SURFACE BASED STORMS. THE MORE LIKELY AND SECOND SCENARIO IS THAT CONVECTIVE LINE DEVELOP ALONG THE MS RIVER NEAR THE QUAD CITIES WILL CONTINUE TO BUILD FURTHER SOUTH AIDED BY INCREASING MID-UPPER LEVEL DYNAMICS AND LOW LEVEL FORCING/CAA. CONVECTION IS EXPECTED TO DEVELOP DOWN TO CENTRAL IL BY 8 PM EDT EVENTUALLY MOVING INTO WESTERN PARTS OF CENTRAL IND AFTER 10 PM EDT. && .SHORT TERM (This evening through Tonight)... Issued at 204 PM EDT Thu May 15 2025 Rest of Today and Tonight. Diurnally driven cu continues to expand in coverage across central Indiana with temperatures in the low 80s across the state. Dew points continue to rise with little mixing so far. Expectations going through the rest of the afternoon remain the same with a continual expansion of cu while dew points begin to fall towards the middle of the afternoon once the wind gusts become more frequent and the boundary layer steepens to around 4kft. The threat for 90 degree temperatures continue to look low for all but the far western counties where rain didn't fall as widespread yesterday. Latest ACARs soundings show the cap is well in place but a bit higher up than models have forecast with the strongest portions of the cap from 800mb to 700mb. A plume of even warmer aloft is moving in from the southwest which will further strengthen the cap through 23Z with models showing convective initiation on the western edge of the warmer air across Illinois towards 23Z. Forecast remains on track for the convective threat late today into tonight with better model agreement in scenario #2 of the previous forecast discussions where convection initiates across Illinois towards 23Z to 01Z and moves into central Indiana but doesn't strongly organize. There is a potential that the convection remains elevated above the gradually eroding cap with hail being the primary threat. The primary timeframe of concern for central Indiana will be from 00Z to 04Z with confidence highest across the far western and northern portions of the forecast area. Confidence is lower towards the Indianapolis area as there is a fairly low potential that storms will have enough time with high instability to develop a mature cold pool which would help them propagate into an increasingly less favorable thermodynamic atmosphere. There could be a few lingering storms across the southern portions of the area during the second half of the overnight, but chances look minimal. The residual humid airmass will keep temperatures very mild through the night with overnight lows only falling into the mid to upper 60s with the potential for some sites to see lows near 70. Skies will gradually begin to clear after midnight with gusts falling off after 03Z. && .LONG TERM (Friday through Thursday)... Issued at 204 PM EDT Thu May 15 2025 Friday and Friday Night. Another round of severe weather is expected for late Friday into the early overnight hours with much higher confidence in weather impacts for central Indiana. Another surface low will be tracking across the Midwest with strong moisture advection ahead of the low as the LLJ ramps up. 40-50kts of effective bulk shear will combine with nearly 4000 J/kg of ML CAPE with a much weaker cap to create a favorable environment for the development of severe storms. All severe weather types will be on the table with damaging winds the most likely threat as models continue to trend more towards an organized complex of storms vs discrete supercells. Highest confidence in timing will be from 6PM to 10 PM with the greatest threat for severe weather across the southern counties where most models show the progression of a storm complex. If storms remain discrete, which is not the most likely outcome, there will be a threat for higher-end tornadoes with STP values maxing out between 8 and 12 at times. Saturday Through Monday. Broad ridging across the Central US states will then dominate the weather pattern for the first half of the weekend with some residual near surface pressure gradients creating an environment favorable for wind gusts to around 25 mph during the afternoon hours on Saturday. With the surface flow now westerly, dew points will be much more comfortable with highs in the low to mid 70s. A weak upper level wave will move through the Tennessee Valley late Sunday into Monday but other than some increased clouds, no impacts expected for the forecast area. Tuesday Through Thursday. The pattern then looks to become much more active during the middle to latter portions of the week as a warm front associated with the late weekend system begins to move northward and interacts with forcing from another low pressure system. Models are struggling to resolve the details and strength of this upper level low, but there is fairly high confidence in a multi-day heavy rain threat for the Ohio Valley as early as Tuesday but more likely Wednesday into Thursday. Models are all over the place with QPF, but there is a decent threat for at least 1-2 inches over the course of the event. Rain chances then look low for the holiday weekend with broad northwesterly flow and mild temperatures in the 70s. && .AVIATION (18Z TAF Issuance)... Issued at 1242 PM EDT Thu May 15 2025 Impacts: - Southerly wind gusts to 22kts through 02Z. - Isolated TSRA 23Z to 04Z, again tomorrow after 21Z Discussion: VFR conditions expected outside of convection with two rounds of storms. The first round is conditional with only small chances at BMG and IND with a higher potential at LAF and HUF. Diurnal cu will continue to become more prevalent through the afternoon. Skies will partially clear tonight after the convection threat ends with a return in diurnal cu tomorrow. Higher confidence in storms arrives late tomorrow afternoon and evening. Winds will remain southerly through the TAF period with gusts to 22kts this afternoon and evening. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ MESOSCALE...Crosbie SHORT TERM...White LONG TERM...White AVIATION...White