textproduct: Seattle/Tacoma

UPDATE

Marine stratus is well entrenched across western Washington this morning. With diurnal heating, stratus is slated to burn off this afternoon to mostly clear skies. A slight chance of thunderstorm is in the offing this afternoon as well, mainly for the North Cascades. Any lingering wildfire smoke aloft will push off and away into the evening. Highs today across the interior will top out around the mid 70s to lower 80s. Coastal sections are forecast to stay put in the 60s. The previous discussion is below along with an updated aviation and fire section.

SYNOPSIS

Upper level trough offshore today moving inland Thursday. Trough remaining over Western Washington through Saturday. Temporary upper level ridge moving through Sunday. Another upper level trough arriving the first part of next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite imagery shows stratus along the coast, down the Strait of Juan de Fuca to Whidbey Island and through the Lower Chehalis Valley into the Southwest Interior east of I-5 at 3 am/10z. Mostly clear skies over the remainder of the area. Temperatures were in the mid 50s to lower 60s.

Upper level trough offshore with the trough axis still west of 130W this morning. Low level onshore flow will allow the stratus to continue to fill in over the interior covering most of the lowlands by 15z. The layer is less than 2000 feet thick. This combined with the weakening onshore gradients will allow the stratus to dissipate over the interior midday/early afternoon. Stratus hanging tough all day along the coast. Much cooler today with the marine push overnight. Highs in the 70s inland and mid 60s coast.

Upper level trough moving east tonight reaching Western Washington Thursday. Chance of showers Thursday mainly coast and mountains with a slight chance of a thunderstorm near the Canadian border. Lows tonight in the 50s. Highs Thursday in the mid 60s to mid 70s.

Upper level troughiness remaining over Western Washington Thursday night into Friday with low level onshore flow. Chance of showers continuing over the northern portion of the area. Mostly cloudy and cool over the southern portion. Lows in the 50s. Highs Friday in the 60s and lower 70s. Felton

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Extended models in good agreement with upper level trough over the area Saturday shifting east Saturday night. Temporary upper level ridge moving through Sunday before another upper level trough moves into the area for the first part of next week.

Showers likely north Saturday. Dry all areas Sunday with shower chances returning Monday and Tuesday. Highs remaining cool, in the 60s and lower 70s. Lows in the 50s. Current forecast high for Seattle Tuesday is 69 degrees. This would end the consecutive 70 degree plus days streak at 46 days, 8th longest on record ( record 72 days June 29th to September 8th, 2017 ). The last day Seattle had a high temperature below 70 degrees, July 16th with 65 degrees.

Has it seemed like it hasn't rained much in Seattle this year? The yearly rain total is below normal but only by 9 percent ( 19.57 versus a normal of 21.55 inches ). What has happened this year is that we have not had a lot of days with rain. So far through the 25th, Seattle has recorded 71 days with measurable rain this year. The record for the least number of rain days between January and August is 72 days set in 1985 ( 1985 the second driest year on record in Seattle with 25.13 inches ). Number two on the list of the least amount of rain days between January and August is last year with 76 days. The normal number of rain days between January and August is 97 days. Felton

AVIATION

South to southwesterly flow aloft as upper level troughing approaches western Washington. Marine stratus has expanded across the lowlands, with an extensive mix of IFR/MVFR ceilings across most western Washington terminals this morning. In some lower prone areas, could see localized LIFR with the stratus. Stratus will slowly erode by the early afternoon, with most inland terminals seeing a rebound back to VFR by 19-20z. South to southwesterly winds will continue throughout the day, increasing to 5 to 10 knots throughout the afternoon.

KSEA...MVFR this morning in low stratus and light southwest winds. Conditions will remain MVFR through 18z-19z, as stratus will begin to erode with a return to VFR conditions by the early afternoon. Winds will remain from the S/SW, and increase to 5 to 10 knots this afternoon. Another round of low clouds will likely expand over the terminal early Thursday morning.

Mazurkiewicz/15

MARINE

A weak front will cross over the area waters today, with a slight uptick in southerly winds over the coastal waters this afternoon. Weak systems will continue to move over the coastal waters through the end of the week, which will continue to provide pushes down the Strait of Juan De Fuca, along with increasing southerlies over the coastal waters. At this time, winds look to remain under small craft advisory, although headlines may be needed late in the week. Chances for isolated thunderstorms over the waters increases on Thursday with the passage of a frontal system, which may locally produce gusty outflow winds and lightning.

Coastal seas will remain 4 to 6 feet through the weekend.

Mazurkiewicz

FIRE WEATHER

Updated: Overall, the low level onshore flow producing good overnight relative humidity recoveries and cooler daytime temperatures will help ease fire weather concerns for the next few days. However, models indicate increased thunderstorm probabilities for the afternoon/evening for today and Thursday. There is a slight chance ( 15-25 percent ) of isolated thunderstorms mainly in the north Cascades but it can't be ruled out around Mount Rainier. If there is a thunderstorm it will not be accompanied by much rain and it could produce erratic and gusty outflow winds impacting existing fires. In addition, the lightning strikes pose a hazard and could lead to new fire starts. JBB/Felton

SEW WATCHES/WARNINGS/ADVISORIES

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