textproduct: Seattle/Tacoma

SYNOPSIS

Weak upper level low offshore through tonight with light flow in the lower levels. Low moves south Saturday and Saturday night. Upper level ridge building into coastal British Columbia over the weekend with the low level flow turning offshore Sunday. Record highs likely Sunday. Ridge moving over Western Washington next week. Above normal temperatures will continue but a switch to onshore flow in the lower levels will cool things down beginning Monday for the coast and Tuesday for the interior.

SHORT TERM /TODAY THROUGH SUNDAY/

No significant changes made to the forecast this morning. The previous discussion can be found below with updates to the aviation section:

Satellite imagery shows weak upper level low offshore. High clouds spinning out of the low moving over the area early this morning.

Upper level low remaining offshore today throwing mostly high clouds at Western Washington. Light flow in the lower levels so while more stratus will form before sunrise it will stay west of Puget Sound. The stratus will dissipate later this morning. Under partly sunny skies temperatures will be above normal, in the mid 60s to lower 70s except along the coast and near the Strait of Juan de Fuca where highs will be in the lower 60s.

Little change in the upper pattern tonight with the low remaining off the coast. High clouds spinning out of the low will continue to move through Western Washington. Increasing onshore flow in the lower levels with stratus forming along the coast spreading inland early Saturday morning. Lows in the 40s.

Upper level low moving south Saturday with high clouds decreasing over the area. Onshore gradients weakening with stratus dissipating by noon leaving mostly sunny skies for the afternoon. Highs over the interior remaining in the mid 60s to mid 70s. Decreasing onshore flow will allow the coast to warm into the mid 60s to lower 70s.

Low well to the south Saturday night and Sunday. Upper level ridge building into the British Columbia coastline. Temperatures aloft warming with 850 mb temps in the plus 14 to 16C range by Sunday afternoon. Low level flow turning offshore Saturday night and remaining offshore Sunday. Much warmer all locations with highs in the 70s to mid 80s. Good chance for record highs. Forecast high for Seattle of 81 degrees ( 16C at 850 mb is 61F then add 20F ) would break the current record of 77 degrees. Sunday will be the warmest day of the year so far.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Models in good agreement with the low level flow turning onshore Sunday night into Monday. This will cool the coast down on Monday with a little cooling as far east as Shelton. For the remainder of the interior light flow in the lower levels as the flow transitions to onshore. Temperatures aloft not cooling with 850 mb temperatures still in the plus 14 to 16C range. Marine air will have a tough time getting inland under these conditions making Monday highs similar to Sunday from the Puget Sound eastward.

Low level onshore flow combined with cooling temperatures aloft resulting in a weak marine push Tuesday with highs in the interior 5 to 10 degrees cooler than Monday.

Upper level ridge over the top of the area Tuesday through Thursday. Low level flow remaining onshore which will put a cap on how warm it can get. Temperatures still above normal over the interior, mid 60s to mid 70s. With a deeper marine layer highs on the coast in the lower 60s.

We have been getting calls in the office asking how dry was April. In Seattle the monthly rain total was 2.77 inches just 0.41 inches below the normal of 3.18 inches. Why it might have seemed like a dry April is because of the number of days it rained. In Seattle there was only 8 days with measurable rain. This ties for the third lowest number of April rain days in Seattle in the 82 years of records at Seattle-Tacoma airport. The two years with less rain days, 1956 with 5 and 1951 with 3. There have been 4 years with 8 rain days, 2026, 2021, 2020 and 1998. The normal number of rain days in Seattle in April is 15.

Since the start of the year there has been 55 days with measurable rain in Seattle. This is the lowest January through April rain day total since 50 days in 2005. The normal number of rain days for January through April is 67. Felton

AVIATION

A trough will dig offshore today for southwesterly flow today then northeasterly flow this evening. Marine stratus should slowly erode away this morning along the coast and the Strait of Juan de Fuca. Elsewhere, VFR conditions will prevail through the TAF period with high clouds streaming overhead. Another westerly push will bring stratus clouds slightly farther inland Saturday morning but should remain west of the Puget Sound terminals. Winds N/NW 5 to 10 kt today will become light NE overnight.

KSEA...VFR today with high clouds. Winds N/NE 5 to 10 kt becoming NW this afternoon. Light NE winds return overnight.

33/62

MARINE

Onshore flow continues with high pressure offshore and lower pressure inland. Outer Coastal Waters will see Small Craft Advisory conditions with both NW winds and choppy seas. Expect another push of westerlies down the strait tonight. The flow turns more N to NE on Saturday with gusty 10-20 kt winds over Puget Sound and Hood Canal. Offshore flow lingers into Sunday then a stronger onshore push Monday night. 33

HYDROLOGY

No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-East Entrance U.S. Waters Strait Of Juan De Fuca.