textproduct: Seattle/Tacoma

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 over and east of the terminals this morning, dragging a cold front along with it. Rain showers are progressing along the coast, with more widespread coverage north of Seattle up to the Canadian border. A few of the showers may drop visibilities down to MVFR as they pass over the terminals. The thunder threat with this activity remains at 15-20% through the morning. Otherwise ceilings have been dropping steadily overnight, with interior terminals reporting MVFR, and additional terminals keeping an elevated probability of seeing MVFR ceilings this morning. A few locations (between KPAE and KBLI), the Olympics and Cascades have 30-50% probabilities for IFR and LIFR ceilings this morning (as well as LIFR in the mountains). Most of the precipitation moves east of the Cascades this afternoon, and a few model members hint at a lingering convergence zone northeast of Seattle into the evening. Ceilings will remain generally broken or overcast today (with a few clear pockets late today). Timeframe for improvement to VFR is 18-21Z. Winds today remain southwest 6-12 kt. The convergence zone will cause winds to become variable out of the northeast in Puget Sound this afternoon/evening, but at around 5 kt. Expect a similar round of this morning's stratus Sunday morning.

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 northeast of the terminal this afternoon, although winds may briefly become variable in relation to the convergence zone this afternoon. Otherwise SW winds 5-10 kt.

HPR

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.