textproduct: Seattle/Tacoma

SYNOPSIS

High pressure will resume today for warmer temperatures and sunnier skies today. A weak, dry front will progress through the region late Thursday into Friday for another round of cloud cover and reduced temperatures, but high pressure amplifies over the weekend and into early next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Overall forecast remains on track with temperatures as of 8 AM in the 40s across the area with decreasing clouds as dry air filters in. Expect a much sunnier day with temperatures climbing into the upper 60s as high pressure returns to the region. Winds will be light and generally out of the north. A break in the high pressure pattern is in store for late Thursday into Friday as a weak front moves through the region. This will bring an increase in cloud cover and a few degrees cooler on Friday. Temperatures on Thursday will be in the low 70s, approaching the upper 70s in the Chehalis Valley. This corresponds to minor HeatRisk through Friday.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Clouds will stick around through Friday night, though the temperatures will still be pleasant in the upper 60s and low 70s. High pressure developing along the west coast will continue to amplify late in the week and into the weekend. Clearing skies and thermal trough developing along the coast are increasing confidence in temperatures climbing to the 80s by Sunday. The locations with the highest likelihood of seeing the upper 80s will be the Chehalis Valley and some of the Cascade valleys. This is also suggesting a 30-40% chance of moderate HeatRisk in areas generally south of the Seattle Metro area, and above 50% in the aforementioned warmer locations. In addition to the temperatures climbing, afternoon relative humidity values will be decreasing. Right now, the forecast calls for minimums on Sunday afternoon of 28-38%. While not in the peak of our dry season, it's never too early to start taking extra precautions around sources of ignition and mitigating those.

Temperatures will remain warmer through Monday before decreasing a few degrees on Tuesday as onshore flow returns and the ridge begins to flatten.

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AVIATION

Northerly flow aloft as an upper level ridge moves inland today. Clouds are continue to clear out early this morning with increasing subsidence and drier air filtering in this morning. A few terminals in the southwest remain MVFR, elsewhere VFR conditions prevail and will continue to through the rest of the day and much of tonight. Guidance is hinting at the potential for IFR conditions along the coast early Thursday morning associated with a marine layer developing and moving inland. There is a 35-45% chance of IFR cigs at HQM btwn 09Z-18Z Thur. Elsewhere, skies remain mostly clear. There will also be a slight chance for some localized fog development at the typical locations with calm winds (OLM, PWT, etc.) but confidence remains low (15-20% prob.)

KSEA...VFR conditions this morning will prevail through the TAF period. NE winds 8 to 10 kt becoming more NW after 18Z, increasing to 10 to 13 kt. Winds return to NE tonight, after 06Z Thur.

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MARINE

High pressure is offshore with lower pressure inland, maintaining onshore flow across western WA. A stronger push down the strait is expected Thursday afternoon and evening with a weak front. The flow turns more N to NE (and offshore) over the weekend with low pressure to our south. 33

HYDROLOGY

No river flooding is expected in the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

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