textproduct: Seattle/Tacoma

SYNOPSIS

An upper level trough over the area today will bring chances of thunderstorms across the mountains and critical fire weather conditions. Thunderstorm potential will continue along the Cascades on Saturday, but will wane throughout the weekend as an upper level ridge starts to builds into the area from the southeast. Another upper level trough will move into the region early next week. Uncertainty then increases in the forecast heading into midweek as guidance remains split between a warmer, drier pattern and a cooler, wetter one.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

The thunderstorm and fire threat have ended this evening as activity diminishes across both the Cascades and Olympics. Remainder of the short term section is on track for tonight/this weekend. Updates were also made to the fire and aviation sections this evening. -HPR

An upper level trough will weaken across the area tonight, allowing for a ridge to build into the area from the southeast over the weekend. Southwesterly flow will develop aloft and will help to push smoke out of the area this weekend. Low level flow will remain onshore, allowing for marine stratus to push inland during the overnight periods both Saturday and Sunday. While overall thunderstorm chances will primarily wane throughout the weekend, another round of thunderstorms will be possible across the Cascades on Saturday afternoon and evening as the air mass becomes unstable during the afternoon hours and some monsoonal moisture works its way up into the region. By Sunday, any thunderstorms that do develop will mostly be confined to the Cascade crest and areas east of the crest. Afternoon highs over the weekend will be in the upper 70s to low 80s across the interior and in the mid to upper 60s along the coast, while overnight lows will be in the 50s.

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LONG TERM /MONDAY THROUGH FRIDAY/

The first part of next week remains to follow a rather typical pattern of onshore low-level flow maintaining morning clouds, with some clearing in the afternoon. A passing trough around Tuesday could provide a reinforcing push of clouds and knock temperatures a few degrees cooler than normal. Otherwise, ensemble guidance begins to spread a bit larger toward the middle of next week with a fairly even split between a cooler trough pattern and a warmer (near normal) pattern under zonal flow or a weak ridge. In any event, there's not a significant signal for any precipitation of note.

AVIATION

VFR cigs at the majority of terminals this evening and MVFR along the coast. Another surge of stratus is likely later tonight through Saturday morning for most of the area, with IFR ceilings and visibility expected for most terminals. Improvement to VFR in the afternoon. The coast may see some brief improvement, but conditions will likely quickly deteriorate by the evening. Thunderstorm activity continues this evening and will remain confined to the mountains. Another round of thunderstorms possible for the Cascades tomorrow.

KSEA...VFR for the remainder of today. Some thunderstorms will develop well east of the terminal area and continue into the evening, but is not expected at KSEA itself. Winds predominantly from the southwest, becoming west/northwest (but 5 kt or less) this evening through 06z. A return to light southwest winds then follows overnight, along with the return of low stratus around 12z with IFR/LIFR conditions. Ceilings expected to improve in the afternoon to VFR.

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MARINE

High pressure remaining off the coast of California will keep winds over the coastal waters light through Saturday. High pressure will then rebuild offshore British Columbia and move southward on Sunday and remain situated off the Pacific Northwest into next week. This will bring the return of northwesterly winds to the coastal waters. Diurnally driven westerly winds down the Strait of Juan de Fuca will occur each afternoon and evening over the next several days, with winds approaching Small Craft Advisory strength at times.

Seas will primarily remain between 3 to 6 ft through the weekend and through much week.

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FIRE WEATHER

The red flag warning will be allowed to expire at 9 PM this evening for the west Cascades and Olympics. The thunderstorm threat in these areas has diminished this evening.

Elevated fire weather conditions will continue across the Cascades into Saturday with chances of thunderstorms possible again along the Cascade crest on Saturday afternoon and evening. Overall chances for convection will decrease through the weekend, however, as an upper level ridge starts to build into the area from the southeast. By Sunday, expect convection to mainly be confined to the Cascade crest and areas east of the crest. Another upper level trough will move into the area next week and could bring some additional elevated fire weather concerns to western Washington at times.

14/HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning until 9 PM PDT this evening for East Portion of the Olympic Mountains-West Portion of the Olympic Mountains-West Slopes of the Central Cascades Generally above 1500 Feet-West Slopes of the North Cascades Generally above 1500 Feet.

PZ...Small Craft Advisory until 5 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.