Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
201 FXUS66 KSEW 290359 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 859 PM PDT Tue May 28 2024 .UPDATE...Radar and satellite imagery show the well defined convergence zone over Island and Snohomish County which will continue through the overnight hours tonight. Elsewhere, a few light scattered showers will pass across the region. Shower activity will increase tomorrow as the upper-level trough axis passes through western Washington. Lapse rates tomorrow continue to show support for the potential of a few lightning strikes this afternoon, with the best chances along the Pacific Coast tomorrow morning and with the convergence zone that develops tomorrow afternoon and evening, which looks sink southward toward King County. LH && .SYNOPSIS...A convergence zone east of the Puget Sound will continue this evening with scattered showers and perhaps a few lightning strikes elsewhere across the region tonight into Wednesday. A shortwave ridge and surface high to the south will bring warmer and drier conditions for the rest of the week. A series of systems will cross the Pacific Northwest over the weekend and into early next week, bringing more rounds of wet weather. && .SHORT TERM /TONIGHT THROUGH SATURDAY/...Stratiform rain spreading inland will continue to destabilize this afternoon and transition to showers. Skies will stay mostly cloudy today, limiting high temperatures to the 50s for most areas. While mean model instability is fairly limited at 100 J/kg or less, a lightning strike cannot be ruled out this afternoon. Confidence is high that convergence zone activity will form this evening over the Puget Sound which will slowly propagate eastward, lingering through the early morning hours on Wednesday. Short range ensembles keep most of the PSCZ shower activity north of Stevens Pass before dissipating. More post-frontal showers will spread inland on Wednesday as an upper level trough axis passes overhead, and models continue to show another round of PSCZ showers developing in the evening. A few lightning strikes are possible once again on Wednesday afternoon in any stronger showers that develop, with slightly more instability available. Temperatures will peak a couple degrees higher on Wednesday, closer to 60 degrees for most areas. High pressure will build inland on Thursday and Friday, allowing conditions to dry out. Any lingering showers will be limited to the northern Olympic Peninsula and North Cascades. Temperatures will warm towards the end of the week, reaching a degree or two below normal by Friday in the mid to upper 60s for most lowland locations. .LONG TERM /SUNDAY THROUGH WEDNESDAY/...Ensembles show good agreement that cooler and wetter conditions will return throughout the long term. A weak shortwave trough is on track to move across the region on Saturday, cooling temperatures off a few degrees and bringing in scattered showers. The region will have little time to dry out with a series of deeper storm systems following close behind. Long range ensembles continue to show much wetter conditions entering the region Sunday through Tuesday, especially over the western Olympic Peninsula and Cascades, where up to 4 inches of rainfall is currently forecast to fall over the span of three days. However, models continue to show a wide range of possible solutions with GFS precipitation amounts nearly double that of the ECWMF. Uncertainty remains in terms of rainfall totals and the placement of heaviest rainfall through the period. Temperatures will return to near- normal with highs in the low to mid 60s through the weekend and into early next week. Lindeman && .AVIATION...Upper level trough axis moving east of the are tonight. Southwesterly flow aloft becoming northwesterly behind trough axis. Northwesterly flow aloft continuing through Wednesday. Onshore flow in the lower levels easing Wednesday. Air mass moist and somewhat unstable Wednesday afternoon. Convergence zone over Snohomish county continuing until around 09z with IFR ceilings. For the remainder of the area VFR ceilings. All areas ceilings lowering to MVFR 12z-15z with an slow improvement trend midday lifting the ceilings back up to the low end of VFR. Air mass somewhat unstable Wednesday afternoon with isolated thunderstorms. KSEA...VFR ceilings lowering to MVFR 12z-15z. Ceilings lifting back up to VFR 19z-22z. Thunderstorm chance not high enough to put in terminal forecast. Light and variable winds becoming southerly 4 to 8 knots by 08z. Southerly winds becoming southwesterly and increasing to 10 to 15 knots around 19z. Felton && .MARINE...Onshore flow tonight easing a little Wednesday. Small craft advisory westerlies in the Central and Eastern Strait will ease after midnight. A similar westerly push in the Strait is expected Wednesday night into Thursday morning. Onshore flow continuing into the weekend. Waves 4 to 6 ft through the period. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$