textproduct: Seattle/Tacoma

SYNOPSIS

Weak system moving through later this afternoon into the early evening hours. High pressure building behind system tonight remaining over the area into Tuesday. Stronger system moving down from the northwest arriving Wednesday with cool upper level low trailing the system Thursday. Weak upper level ridge trying to build Friday.

SHORT TERM /TODAY THROUGH TUESDAY/

Satellite imagery shows high clouds streaming over Western Washington this morning. A few breaks in the clouds has allowed some locations to drop into the 30s at 2 am/09z. Most locations in the lower to mid 40s.

Weak system just east of 130W early this morning will reach Western Washington later this afternoon. Rain out ahead of the system arriving on the coast this morning with the rain spreading inland this afternoon. Snow levels near 2500 feet for snow in all of the passes. With the late start to the precipitation new snow amounts just a couple inches with up to 5 inches in the North Cascades. Highs only in the mid to upper 40s, up to 10 degrees below normal.

System moving east of the Cascades this evening. Not much in the way of post frontal shower activity except for a convergence zone over King and Pierce county. This feature will dissipate by early Monday morning. Clearing skies will result in some chilly morning lows Monday with numerous places below freezing and the locations that don't get to freezing in the mid 30s.

Dry northwesterly flow aloft and low level offshore flow producing a sunny day Monday. The air mass will still be cool so even with plenty of sunshine highs only near 50.

Mostly clear skies continuing into Monday night. Surface gradients going light creating another very chilly for this time of year morning Tuesday. Lows in the mid 20s to mid 30s.

Seattle will make a run at freezing both Monday and Tuesday morning. Just how rare is a low at or below freezing this time of year in Seattle? Since records started in 1945 there have been 48 days with a low 32 degrees or less between March 30th and the latest day of the year with a low freezing or below in Seattle, May 1st. Out of those 48 days only 4 have occurred in the last 50 years ( 32 degrees on April 13, 2022, April 1, 2008 April 2, 1997 and April 21, 1985 ). The record low Monday is 27 degrees from 1954 and the record low Tuesday is 30 degrees from 1949. The last time Seattle set a record low in March was March 3, 1989. Record lows were tied on March 9, 2010 and March 21, 2009.

System dropping out of the Gulf of Alaska Tuesday still well to the west by Tuesday afternoon giving the area another dry day. High clouds out ahead of the system moving over Western Washington during the day. Highs in the lower to mid 50s. Felton

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Extended models showing good run to run consistency with the next system arriving Wednesday. Snow levels near 3000 feet for snow in all the passes except possibly Snoqualmie. Cold upper level low behind the front moving south offshore will slow the front's eastward movement keeping the system in the area into Wednesday night. Over six inches of new snow likely in the mountains along with locally windy conditions in the lowlands.

Cool upper level low moving over Western Washington Thursday. Showers in the forecast with relatively low snow levels.

Low kicks out to the east Thursday night. Weak upper level ridge trying to build offshore Friday into the weekend.

Highs near 50 Wednesday, in the lower to mid 50s Thursday and Friday and mid 50s to lower 60s Saturday. Lows in the mid 30s to lower 40s.

AVIATION

West to southwest flow aloft prevails today as a shortwave trough approaches and moves across western Washington tonight. Mid level clouds are beginning to form over portions of the interior of western Washington, and this will likely continue to expand through the morning. A weak system will move across the area today, which will bring lower ceilings as well as scattered showers. MVFR cigs will begin along the coast around 12Z this morning, but not reach much of the interior until around 17-20Z. Ceilings will likely scatter and raise to VFR for much of the area from west to east from 21Z along the coast to after 00Z Mon through the interior. A convergence zone will, however, keep lower cigs in the equation through much of this evening across the King County terminals. Skies will continue to clear out overnight tonight into early Monday morning. Fog potential will need to be monitored for locations that clear out for much of the night. Winds mostly light to calm will increase to southwesterly 8-12 kt after 18Z, becoming more northwesterly this evening. North winds will surge down through the Puget Sound from 22 Sun-02Z Mon. Winds become mostly light after 06-09Z Mon.

KSEA...VFR early this morning with mid-level clouds beginning to develop to the north of the area. Ceilings will continue to fill in and lower this morning ahead of a weak system today. MVFR cigs and showers will reach the terminal after 18Z. Then the convergence zone will develop likely near/over the terminal by around 00-02Z Mon and slowly drift south this evening, keeping showers and MVFR cigs in the equation through around 06Z Mon, after which clouds will scatter and VFR conditions return. Winds light northeasterly will swing around to southwesterly around 15-18Z this morning and increase to around 10-12 kt. Winds switch to north around 23-01Z. Winds then ease below 5 kt back to southerly at 06Z and remain there until Monday morning.

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MARINE

A brief break in the calmer weather will come today as disorganized low pressure system will move across the area waters today. Relatively strong high pressure will quickly fill in behind the system this evening which will increase northwesterly winds across the area. Small Craft Advisories will be in effect for the coastal waters, the West Strait of Juan de Fuca, and the Northern Inland Waters (primarily around the San Juans north to the international border) through early Sunday morning. Winds will then ease Monday and Tuesday as the high traverses the area. A more substantial low pressure will then enter the area early Wednesday. The cold front will traverse the area waters Wednesday morning, with the actual low center following behind Wednesday evening into early Thursday. Winds will start to increase early on Wednesday and peak as the front moves through. Winds have gone down a little bit in the guidance with this update, but there remains a 30-40% chance of gale force winds across the coastal waters and Eastern Strait. Winds will ease Thursday as the system moves through, with calmer conditions expected late week as high pressure once again redevelops.

Seas around 4-5 ft today will increase Sunday evening up to around 8- 10 ft. Seas then ease Monday into Tuesday before rising up to 10-12 ft Wednesday and Thursday. Seas ease once again late week.

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HYDROLOGY

No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 3 PM this afternoon to 5 AM PDT Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm- Northern Inland Waters Including The San Juan Islands.