textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low off the Northern California coast will slowly move inland tonight and weaken throughout Sunday. Moisture around the low will remain south of Western Washington. Puget Sound convergence zone Monday over Central Puget Sound drifting north during the afternoon and evening. The next system will bring additional rainfall Tuesday before the main front moves through Tuesday night, bringing breezy conditions plus possible heavy mountain snow. Upper level low over Western Washington Wednesday. Drying northerly flow aloft developing Thursday.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

Latest satellite imagery shows clouds remaining over much of W WA this evening while current radar shows most of the shower activity has tapered off. A narrow, dissipating band of showers is still present over portions of the Strait, the southern tip of Vancouver Island and along the Canadian border in far northern Whatcom county. All other remaining activity lingers south of the area in OR, where echoes appear to be having a hard time making any northward progress. This fits well with latest model data showing the upper low this activity is associated with moving into northern CA and any showers linked to it remaining well south of the area.

Inherited forecast remains on track with no evening update planned. For further forecast details, please refer to the Previous Discussion section below. 18

From Previous Discussion...Satellite imagery shows upper level low still spinning off the Northern California coast. Bands of moisture rotating around the low with the latest one just reaching the Central Puget Sound at 3 pm/22z. Previous moisture band bringing rain between Bellingham and Forks. Rest of the moisture spinning around low south of the area. With all the cloud cover temperatures were only in the upper 40s to mid 50s.

Upper level low slowly moving east tonight into Sunday. Current bands of moisture over Western Washington rotating out of the area tonight. As the low moves east the flow aloft will begin to cut off the moisture from getting as far north as Western Washington. Air mass will be slightly unstable with weak troughiness over the area keeping a chance or slight chance of showers in the forecast Sunday into Sunday night. With plenty of cloud cover lows tonight staying in the 40s. A little less cloud cover Sunday warming highs into the mid 50s to lower 60s.

Low weakening into an upper level trough Sunday night with the flow aloft over Western Washington turning northwesterly. Air mass still slightly unstable for a continuing chance of showers. Lows once again in the 40s.

West northwesterly flow aloft Monday with the low level flow going onshore. Puget Sound convergence zone developing in the morning over the Central Puget Sound with the convergence zone continuing into the afternoon hours. Outside of the convergence zone shower activity drying up. At least mostly cloudy skies with the onshore flow will keep highs in the mid 50s.

Convergence zone dissipating Monday night. Rain out ahead of the next frontal system still mostly to the west. Warm front could nick the north coast. Lows in the 40s. Felton

LONG TERM /TUESDAY THROUGH SATURDAY/

Extended models in good agreement with a strong for April front moving through Western Washington Tuesday night. Rain out ahead of the front spreading over the area during the day. Winds picking up in the afternoon with breezy/windy conditions Tuesday night. Not expecting record low maximum temperatures due to the short cold spell in 2022. Highs only near 50. Snow levels dropping to near 3000 feet with heavy snow in the mountains possible Tuesday night.

Cool upper level low dropping down over Western Washington Wednesday and Wednesday night. Air mass unstable enough to include a chance of thunderstorms along with the showers. Highs remaining near 50.

Upper level low kicking out of the area with drying northerly flow aloft developing Thursday. Weak upper level ridge trying to build over the area Thursday night into Saturday. Highs in the mid 50s Thursday warming to the mid 50s to lower 60s Saturday.

Wednesday and especially Thursday morning on the cool side with frost advisories for the colder locations like the Southwest Interior possible both mornings. Lows warming slightly Friday and Saturday morning.

AVIATION

Southerly winds aloft becoming variable to northerly late overnight into Sunday. All terminals are between MVFR and VFR this evening, with further reductions expected overnight into Sunday morning. Some fog development cannot be ruled out in the SW interior and along the coast. Otherwise, low stratus is likely to impact other terminals in the Puget Sound region through tomorrow morning and cause IFR and LIFR cigs. A return to VFR is in the cards on Sunday afternoon as ceilings lift and WSW flow resumes.

KSEA... MVFR conditions have continued this evening, with winds beginning to turn WNW. Speeds are light, generally 5 kts or less. This will continue through much of the valid TAF period. Low ceilings are favored to redevelop tonight generally after 09Z, as a the NBM suggests a 70% chance of MVFR cigs developing by 12z and a near 40% chance of LIFR conditions setting in around the same time. This will most likely be low stratus clouds and not fog. A return to VFR likely by 20z Sunday.

McMillian/21

MARINE

Surface low pressure will move south of the coastal waters this evening. Seas are to remain benign tonight but a SCA has been issued starting Sunday evening for the central/eastern strait as westerly wind forecasts have increased in the latest update. A stronger frontal system arriving Tuesday into Wednesday will likely yield more widespread headlines with enhanced winds and seas.

Coastal seas 4 to 6 feet throughout the weekend. Seas will then start to build upwards to 8 to 10 feet by Tuesday evening and remaining elevated through Thursday.

McMillian

HYDROLOGY

No river flooding the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 5 PM Sunday to 11 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.