textproduct: Seattle/Tacoma

SYNOPSIS

Weak system dissipating along the Canadian border this evening. Upper level ridge building over the area Saturday with the low level flow turning offshore. Upper level ridge remaining over Western Washington through the middle of next week although the ridge will weaken beginning Monday. Low level flow turning back onshore later Sunday and will remain onshore through the week. Upper level ridge moving east Thursday with the next system possibly arriving Friday.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

Satellite imagery shows mostly cloudy skies over Western Washington this afternoon. Doppler radar has a few light showers near the Canadian border in the North Cascades. Temperatures were mostly in the 60s with lower 70s over the Southwest Interior.

System along the Canadian border dissipating this evening. Slightly unstable air mass stabilizing overnight. This combined with light flow in the lower levels will produce low clouds with patchy fog by sunrise. Lows in the mid 40s to mid 50s.

Morning low clouds with patchy fog to start the day for the lowlands Saturday. Shallow marine layer plus the low level flow turning offshore will help dissipate the marine layer by afternoon. Upper level ridge building with 500 mb heights in the lower to mid 580 dms by 00z Sunday. Highs mostly in the mid 60s to lower 70s with the Cascade foothills in the mid 70s.

Light low level offshore flow Saturday night will limit the low clouds and fog over the area Sunday morning. With the clear skies low dropping into the lower 40s to lower 50s.

Sunday the warmest day for the interior with a weak thermally induced surface trough over the area. The transition to light onshore flow along the coast will drop highs a couple of degrees back down to near 70. For the interior highs mid 60s to mid 70s. Seattle record 76 degrees set in 1966. Looks like we will be a couple of degrees short of the record.

Thermally induced surface trough moving east Sunday night with light low level onshore flow developing. Marine layer pushing inland overnight reaching the Puget Sound by sunrise. Lows in the mid 40s to lower 50s. Felton

LONG TERM /MONDAY THROUGH FRIDAY/

Models in good agreement with a flat upper level ridge over the area through Wednesday. Low level flow remaining light onshore with morning clouds giving way to afternoon sunshine through Wednesday. Highs in the mid 60s to lower 70s. Lows in the mid 40s to lower 50s.

Upper level ridge weakening Thursday as the next weather system moves down the british Columbia coast. Model consistency falls apart Thursday night into Friday with the GFS breaking the system up before it reaches Western Washington while the ECMWF keeps the system intact with rain over the entire area. Ensembles leaning towards the drier solutions. For now will just have some chance or slight chances pops in the forecast for Friday. Highs mid 60s to lower 70s Thursday and lower to mid 60s Friday. Lows in the mid 40s to lower 50s.

How often is the first week of October dry in Seattle? In the 81 years of records at Seattle-Tacoma airport the first week of October has been dry 14 years ( 17 percent ). It has occurred twice in the last six years, 2022 and 2020. Felton

AVIATION

High pressure building inland tonight and Saturday for drier weather. The flow aloft is westerly. Low level clouds likely early Saturday morning for MVFR to IFR conditions (and pockets of LIFR). Stratus clouds will burn back 18-21z with offshore flow for VFR in the interior. 33

KSEA...N wind shift expected 00-02z and will remain northerly through the period. Low clouds will form early Sat morning for IFR to LIFR conditions. Expect a return to VFR 18-21z Sat. 33

MARINE

The flow will turn offshore this weekend as a thermal through forms along the coast. Winds will turn onshore again early next week as low pressure shifts inland. Onshore winds will be strongest through the Strait of Juan de Fuca with Small Craft Advisory winds likely. 33

FIRE WEATHER

Fire weather concerns remain minimal through the next few days. Light offshore flow and warm temperatures this weekend could result in locations in the Cascades and adjacent valleys seeing minimum RH values approach 30 percent Sunday. This will be short lived with onshore flow returning Sunday night into Monday. This will boost minimum humidity values in addition to slightly cooler high temperatures. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.