textproduct: Seattle/Tacoma

SYNOPSIS

The pattern remains very dry across western Washington for the next seven days. A weak ridge will pass overhead on Friday with slightly warmer temperatures. A weak trough will follow on Saturday, with slightly cooler temperatures. A larger ridge offshore will amplify over the weekend, and move over western Washington early next week. Highs in the 80s and 90s with moderate HeatRisk remains likely, with elevated fire weather concerns due to dry relative humidity values.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

It's a near crystal clear afternoon across western Washington on the satellite, with just a couple cirrus clouds. The synoptic picture remains relatively the same from the past few days, with a large jet streak/stream over the northern United States under an upper low in Manitoba/Ontario. Washington remains on the right entry region of the jet stream, so in turn the weather pattern remains dry with the sinking motion associated with this region of the jet. Highs for Thursday remain on track to climb into the 70s, with a few 80s in the south interior. Winds remain out of the north at around 5 to 10 mph with a few gusts up to 20 mph this afternoon in Puget Sound. Lows tonight will drop into the mid 50s.

A weak ridge will pass overhead on Friday, with a slight warmup from Thursday. Highs will still range in the 70s and 80s, with a few more 80s in Puget Sound/slopes of the Cascades. While HeatRisk will largely remain minor for the region, a few areas in metro Seattle away from the water (particularly from Bellevue to Tacoma and down to Olympia) will have a 60-80% risk of seeing isolated areas of moderate HeatRisk. A trough will pass to the north late Friday into Saturday. This trough will pass through dry, although cloud coverage will increase overnight Friday into Saturday, and also result in overnight temperatures in the mid 50s. The clouds Saturday morning will cool the high temperatures, with highs in the 60s and 70s. Expect winds to turn to the southwest with a few gusts up to 25 mph in the south interior during the overnight period. The Cascades Crest also has the potential for a few gusts from the west up to 20 mph.

LONG TERM /SUNDAY THROUGH THURSDAY/

Ensembles are locked in on a ridge amplifying offshore the Washington coastline Sunday, as it gets sandwiched in between two upper level lows in the Gulf of Alaska, and far northern Alberta. This ridge will shift inland on Monday, and move out of the area on Tuesday. A thermal trough is also expected to build along the coast Sunday, shifting inland Tuesday into Wednesday. This pattern is quite similar to the couple warm days previously seen the past Sunday and Monday across the state. As such, a brief warm spell is in the forecast in this period, with temperatures peaking on Monday and Tuesday. There remains somewhat of a temperature spread, but mean highs have temperatures peaking into the 80s and 90s, with the warmest temperatures in Puget Sound areas away from the water, through the Chehalis Valley and southwest interior. A couple instances of 100 can't be ruled out either for areas west of Olympia. Overnight temperatures again will be warmest in the Seattle metro, with temperatures only dropping into the low 60s (everywhere else will likely see mid and upper 50s). HeatRisk on Monday and Tuesday will likely be moderate for those in lowland or mountain valley areas, with Seattle southward through Tacoma/Olympia having a 20-30% chance of major HeatRisk. Due to dry relative humidity values with the light offshore pattern, low relative humidity values will produce elevated fire concerns (see fire discussion below).

There are some model discrepancies as to how quickly the region cools off as the ridge moves inland. The immediate Washington coast will see quick relief with the return of onshore flow, but the interior may take an extra day to cool off, as there is a descent spread in the high temperatures on Wednesday. If the high temperatures remain in the mid 80s in the interior, the Seattle metro may see another day of solid moderate HeatRisk. The temperatures continue to cool into Thursday, with HeatRisk reducing to minor, and most areas out of the 80s, and into the 70s.

HPR

AVIATION

Northwest flow aloft continues with a jet stream beginning to move out of the area. VFR conditions are expected to continue this afternoon for all terminals. Winds will remain out of the northwest during the day at 8 to 12 kt for most terminals, and a few gusts to 20 kt in the Puget Sound through late this evening. Winds turn to the northeast overnight at around 5 kt. IFR probabilities remain highest along the immediate Washington coastline and south Cascades Friday morning (40-60%) with probabilities for ceilings elsewhere remaining very low. The low ceilings will dissipate by around 18Z, for VFR regionwide Friday. Winds will turn northwest again Friday afternoon and evening at 6 to 12 kt, with a few potential gusts to 20 kt in the Puget Sound.

KSEA...VFR remains expected through the TAF period. Winds this afternoon/Friday afternoon out of the northwest 8-12 kt gusting to 20 kt. Winds turn northeast around 5 kt overnight.

HPR

MARINE

High pressure remains centered offshore over the Pacific. Strong northwest flow continues in the outer coastal waters, with a trough moving into southern B.C. Friday behind a weak ridge. Winds and seas in the inner coastal waters have dropped during the day (based on buoy observations). The latest small craft advisory update for the inner coastal waters cancels the inner coastal zone, with the segment for the outer coastal zones continuing through Friday night. Winds up to 20 to 30 kt, and seas of 9 to 12 ft remain likely in the outer coastal waters through Saturday, as the larger ridge offshore begins to amplify and move inland. A thermal trough will also build along the coastline, resulting in weak north to offshore flow going into early next week. Once the ridge and thermal trough move inland, onshore to northwest flow will return with stronger winds for the outer coastal waters, and the Strait of Juan de Fuca.

Seas will continue to drop from 8 to 11 ft today to 6 to 8 ft Saturday, and 4 to 6 ft Sunday through Tuesday before building to 6 to 8 ft briefly Tuesday.

HPR

FIRE WEATHER

Elevated fire weather concerns remain for Friday and again Monday and Tuesday with minimum relative humidity values dropping into the 30s. In some locations Monday and Tuesday, minimum RH values will be as low as the 20s and teens. Fuels will continue to dry and the atmosphere may become conditionally unstable with the surface thermal trough Monday and Tuesday. Even though the fuels have not reached critical levels, fine fuels like grass and brush will ignite quickly with it being so dry. Felton/HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT Saturday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.