textproduct: Seattle/Tacoma

UPDATE

No changes made in this morning's update. The previous discussion remains below along with an updated aviation section:

SYNOPSIS

Upper level ridge over the area today with a weak system moving into Southern British Columbia. Ridge builds tonight before moving east Monday. Weak warm front moving into the area Tuesday night followed by a strong for September cold front Wednesday into Wednesday night. Upper level low associated with the front remaining in the vicinity Thursday and Friday. The low will move out of the area Saturday.

SHORT TERM /TODAY THROUGH TUESDAY/

Satellite imagery shows mostly cloudy skies over Western Washington early this morning with some breaks in the cloud cover over the South Puget Sound and along the Strait of Juan de Fuca. Temperatures at 3 am/10z were in the mid to upper 40s where there are breaks in the clouds and in the 50s elsewhere.

Flat upper ridge over the area today. Weak system moving into Southern British Columbia will give locations near the Canadian border a slight chance of showers this morning. Between the cloud cover this morning and increasing middle and high level clouds from the system moving by to the north mostly cloudy day in store. Highs in the 60s and lower 70s.

Upper level ridge building tonight in response to a digging trough offshore. Cloud cover decreasing overnight. Longer nights plus some low level moisture from Saturday leading to patchy to areas of fog in the fog prone locations after midnight. Cool morning with lows in the mid 40s to mid 50s.

Upper level ridge moving east Monday. Marine layer remaining west of Puget Sound in the morning retreating to the coastline in the afternoon. Under mostly sunny skies highs getting back to near normal, in the mid 60s to mid 70s.

Western Washington on the backside of the upper level ridge Monday night. Increasing middle and high clouds Tuesday as the warm front associated with a deep upper level low moving out of the Gulf of Alaska. Could see some sprinkles west of the Sound Tuesday afternoon. Highs in the mid 60s to lower 70s.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Weak warm front Tuesday night for a chance of rain over the area. Model solutions becoming inconsistent again with the current run. The models are having a hard time with the track of the upper level low. Current run has a more north south track off the coast which will slow down the arrival of the front into Western Washington with the cold frontal passage Wednesday night. A little slower than previous runs. Windy conditions developing along the coast and over the Northwest Interior. While the winds speeds might not get up to advisory category with plenty of foliage plus trees not in great shape after a dry summer there could be more impacts with this system versus a similar one a month or so later.

Model inconsistencies continue Thursday and Friday with the GFS taking the low far enough to the south to keep more precipitation out of the forecast. The ECMWF parks the low off the coast with a couple of impulses spinning out of the low moving through the area. Ensemble solutions favor the ECMWF solution Thursday and lean towards the GFS Friday. Confidence low at this point with a lack of consensus in multiple model runs. Will go chance to likely pops Thursday with chance to slight chance pops Friday.

Differences continue Saturday with the ECMWF kicking the low out to the northeast while the GFS sinks the low south. Saturday has the best chance of being a dry day in the extended. For now will keep some slight chance pops in the forecast.

Cool Wednesday and Thursday with highs in the lower to mid 60s. A little warmer Friday and Saturday with highs in the mid 60s to lower 70s. Lows in the upper 40s and 50s. Felton

AVIATION

West to northwest winds continue aloft as an upper level trough continues to depart east and brief ridging moves in. Ceilings are a mix of MVFR and VFR with scattered lower clouds and high clouds draped across the northwestern portions of the region. Expect low clouds to clear out between 18-21Z this morning becoming mostly clear, but mid-level clouds will remain in place over the northwest, including BLI. VFR conditions will then continue through this evening. Guidance is hinting at the potential for some localized fog development early Monday morning, but it may depend on the amount of clearing as high clouds will filter overhead. The locations most likely to see fog are HQM, OLM, and PAE. Winds generally light southwesterly to more north/northwesterly by this evening and continue overnight and into Monday.

KSEA...MVFR cigs continue early this morning, but are expected to lift up to VFR by around 18-19Z this morning and will continue to remain VFR overnight. High clouds will continue to stream overhead tonight. Fog development is uncertain (around 10% chc), but is more likely to remain outside of the terminal. SW winds around 5 kt will transition to N this evening and persist overnight into Monday. 62

MARINE

A trough will move out of the region and into the Rockies today, with additional systems bypassing the waters to the north Monday and Tuesday. Winds and waves across the waters will likely remain benign, although the light winds and combination of low level moisture from recent rains may lead to pockets of fog forming Monday morning across the coastal waters and west Strait of Juan de Fuca. Models remain persistent that a stronger low pressure system will move in Tuesday night, lasting into Thursday, bringing fall-like conditions across the waters. Probabilities for gusts up to gale force for portions of the southern coastal waters and east Strait of Juan de Fuca remain at 60-70%. Once the system moves out, winds will become light out of the north and west going into next weekend.

Seas at 3-6 ft through midweek, then increasing to 8-11 ft around Wednesday through Thursday, before dropping back to 4-6 ft next weekend.

HPR

FIRE WEATHER

Cooler weather with good relative humidity recoveries overnight through Tuesday easing fire weather concerns over the area. Strong for the first week of September system arriving Wednesday will bring abundant rainfall to the coast and Olympics. Two to three inches of rain are forecast in the Olympics, one to one and a half inches for the coast. For the interior and the Cascades a half inch to an inch is in the forecast through Thursday morning. This is good news for the fires still burning from the Cascade crest westward. Weather remaining cool through the end of the week with chances of additional precipitation keeping fire weather concerns in check. Felton

SEW WATCHES/WARNINGS/ADVISORIES

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