textproduct: Seattle/Tacoma

UPDATE

KATX/KLGX analysis shows ongoing showers across western Washington so far this morning. The bulk of the action is over the interior with a few stragglers along the coast. Hi-res model reflectivity has the activity gradually diminishing into the afternoon as an upper-low exits and to be later on replaced by an incoming ridge. Highs today below average as temps top out in the 60s to lower 70s. The previous discussion remains below along with an updated aviation section:

SYNOPSIS

Small upper level low moving through the northern portion of the area today. Temporary upper level ridge building tonight moving east Monday. Strong for early September upper level low moving down the British Columbia coast Tuesday. Associated warm front brushing the area Tuesday night. Trailing cold front arriving Wednesday bringing rain and locally gusty winds. Upper level low remaining in the vicinity Thursday and Friday keeping conditions cool and unsettled.

SHORT TERM /TODAY THROUGH MONDAY/

Satellite imagery shows small upper level low over Southwest British Columbia. Doppler radar has showers spinning around the low along the coast and over the northern portion of the area. Temperatures at 3 am/10z were in the mid 50s to lower 60s.

Upper level low moving southeast today ending up in Eastern Washington by late afternoon. Showers over the entire area early this morning as the low moves overhead. Shower chances decreasing along the coast later this morning with shower chances confined to Puget Sound eastward by this afternoon. The exception to this will be over the northern portion of the Hood Canal eastward as a convergence zone forms later this morning. Quick shot of cooler air aloft associated with the low will destabilize the air mass enough for a slight chance of thunderstorms east of Puget Sound later this morning into the afternoon hours. Highs in the 60s and lower 70s. Seattle has a chance to break the consecutive day streak of highs 70 degrees plus today.

Upper level ridge building over Western Washington tonight will bring an end to the shower activity pretty quickly this evening. With the longer nights patchy fog forming in the fog prone places like the Southwest Interior and Cascade River Valleys before the stratus develops in the early morning hours. Temperatures aloft still cool in the wake of the low. Coldest morning in a couple months Sunday with lows in the mid 40s to lower 50s.

Cloudy start to the day Sunday. The upper level ridge will be weak and not provide much in the way of subsidence. Low level onshore flow weakening as the day wears on will help erode the marine layer but a system moving into British Columbia will spread middle and high level clouds over the area especially in the afternoon. End result is a mostly cloudy day even with the ridging. Highs again only in the 60s and lower 70s.

Upper level trough digging offshore Sunday night into Monday. Flow aloft becoming southwesterly pushing warmer air aloft into the area. Shallow marine layer late Sunday night into Monday morning. Stratus will have a hard time getting east of Puget Sound Monday morning. High clouds embedded in the flow aloft moving through at times. Highs warming into the mid 60s to mid 70s. Another cool morning, lows in the mid 40s to mid 50s. Felton

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Upper level trough remaining offshore Monday night as a strong for September system starts to make its way down the British Columbia coast. Under mostly cloudy skies lows in the 50s.

Upper level trough meshing with the warm front associated with the incoming system moving into the area Tuesday for a chance of rain. Highs in the mid 60s to mid 70s.

Models still in good agreement with the trailing cold front moving into Western Washington Wednesday bringing rain and locally gusty winds. Rain out ahead of the cold front reaching the coast Tuesday night. Rainfall amounts over an inch along the coast, 1.5 to 2.5 inches in the Olympics with a half inch to an inch inland and in the Cascades. It's possible Seattle gets more rain from this system in less than 24 hours than all of the last two and a half months. Highs in the lower to mid 60s. Seattle forecast high of 65 is the normal high for October 3rd through 5th.

Models having trouble Wednesday night into Friday with the associated upper level low location. The GFS drops the low far enough south for the shower activity to come to an end Friday. The ECMWF has the low further north keeping showers over the area into the end of the week. Ensemble solutions favoring the GFS solution but not enough to completely dry out the forecast Friday. At this point will go with showers Thursday and slight chance of showers Friday. Confidence not real high in this scenario. Snow levels getting as low as 7000 feet later Thursday into Friday. Highs remaining cool, in the 60s Thursday and Friday. Felton

AVIATION

An upper level low will track to the east of the area today, switching to northwesterly winds aloft. Ceilings are a bit of a mixed bag, through most locations showing MVFR to VFR ceilings as a weak disturbances makes its way across western Washington. The bulk of the precipitation has progressed east towards the Cascades, through a few isolated showers remain and showers may linger over the central Puget Sound area as a convergence zone develops. Ceilings are expected to scatter and most terminals should see VFR conditions by this afternoon. Stratus and potentially some areas of fog in the typical fog-prone locations is expected to develop late tonight into Sunday mering.

Winds today remain southwest 6-12 kt for most. Winds have been a bit erratic through the Puget Sound with winds going back and forth between N and S, but after 18Z should generally remain S/SW before beginning to turn back northerly after 00-03Z Sun. Winds look to return to S overnight into Sunday.

KSEA...MVFR ceilings present with the cold front passing through this morning, along with off and on showers in and around the terminal. Timeframe for improvement to VFR is 18-21Z. Convergence zone likely to keep showers mainly north and east of the terminal. VFR conditions look to continue until Sunday morning when low stratus bring a chance to return to MVFR cigs. Winds variable this morning but becoming more SW after 18Z. Winds may start to turn more N/NW between 00-06Z Sun.

MARINE

An upper level low is swinging a cold front through the interior waters this morning. Showers will continue to progress over the Strait of Juan de Fuca and interior waters this morning. The threat of thunder with this activity remains low at 15-20%. A stronger push of westerlies is likely in wake of the cold front this afternoon and evening in the central/east Strait of Juan de Fuca; thus have reissued a small craft advisory in these areas for tonight. Additional systems will pass north of the waters Sunday and Monday, with winds decreasing and remaining light out of the north. Models have a stronger low pressure system tracking over the coastal waters around midweek, which will bring an increased risk of upper-end small craft winds and gale-force gusts (especially in the east Strait of Juan de Fuca and far southern coastal waters).

Seas at 4-6 ft through Tuesday, peaking at 9-11 ft with the system passing through midweek next week.

HPR

FIRE WEATHER

Slight chance of thunderstorms today from the Puget Sound eastward will keep fire weather concerns elevated. Thunderstorm threat ending quickly this evening. Beginning Sunday a cooler and eventually wetter pattern developing over Western Washington easing fire weather concerns. System arriving Wednesday bringing wetting rains to most of the area. The Olympics could see as much as two and a half inches of rain. Cool and unsettled weather for the latter half of next week keeping fire weather concerns at a minimum. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 1 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.