textproduct: Seattle/Tacoma

Update

Aviation discussion updated. Otherwise, no changes to the main forecast.

SYNOPSIS

Upper level ridge offshore moving over the area tonight into Tuesday. The ridge will shift east Wednesday. Thermally induced surface trough developing along the coast today moving inland Tuesday night and east of the Cascades Wednesday morning. Very warm temperatures over the interior the next three days. Much cooler Thursday with low level onshore flow. First weather system in two weeks moving through Friday. Upper level low moving over Western Washington Saturday will move east Sunday.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Satellite imagery shows low stratus along the coast, moving down the Strait of Juan de Fuca to near Whidbey Island and over the Lower Chehalis Valley at 3 am/10z. Just some high clouds over the remainder of the area. Temperatures were in the upper 40s to near 60.

Stratus will not move much further inland and dissipate later this morning. Upper level ridge centered offshore moving east today while a thermally induced surface trough develops along the coast. Low level flow turning offshore warming high temperatures up to mostly the 80s. A few places near the water will stay in the upper 70s.

Upper level ridge moving overhead tonight and Tuesday while the thermally induced surface trough remains over Western Washington. Low level offshore flow continuing producing a mild morning, lows in the 50s and lower 60s, and a very warm day with highs in the 80s and lower 90s. Most locations falling just a couple of degrees short of a record high. The best chance for a record breaking high will be at Bellingham (record 82 set in 1992).

Upper level ridge weakening Tuesday night with the ridge axis moving east Wednesday. Thermally induced surface trough moving inland Tuesday night and east of the Cascades Wednesday. 850 mb temperatures cooling to plus 14C to plus 16C by Wednesday afternoon with the winds from 850 mb down to the surface turning westerly Wednesday morning. All these variables add up to a weak marine push for the interior with high temperatures dropping 5 to 10 degrees versus Tuesday readings, into the mid 70s to mid 80s. More cooling along the coast with highs in the mid 60s. It will be another mild morning with light flow in the lower levels. Lows Wednesday morning in the mid 50s to lower 60s.

Moderate HeatRisk over all but the coastal beaches today and Tuesday. There is a small chance, 10 to 20 percent, of major HeatRisk Tuesday between Seattle and just south of Olympia. Moderate HeatRisk confined to the Central and Southern Puget Sound and Cascade foothills Wednesday. A heat advisory will go into effect today at 11 am/18z until 11 pm/06z Tuesday evening for all lowland locations except the coastal beaches. The area under the heat advisory will decrease Wednesday with Northwest Washington getting dropped from the advisory. The heat advisory for all areas will come to an end at 11 pm/06z Wednesday evening. Felton

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Models remaining consistent with much cooler temperatures Thursday due to low level onshore flow and an approaching frontal system. Front moving through Western Washington Friday morning through midday. Rain starting on the coast as early as Thursday afternoon spreading inland Thursday night. Rain changing to showers behind the front Friday afternoon. Post frontal convergence zone possible over Snohomish and Skagit county Friday afternoon into Friday evening which could leave the Seattle metro dry. Upper level low moving down from the northwest over the top of the area Saturday keeping showers in the forecast. Low kicking out to the east Saturday night making for a dry but mostly cloudy and cool Sunday.

There is a good chance that even though Thursday and Friday will be only the 4th and 5th day that it has rained this month in Seattle, the rainfall from this system will put Seattle above normal for rain in June. The monthly normal is 1.45 inches. Current rain total for the month is 1.24 inches.

Highs Thursday in the 60s and lower 70s, Friday in the mid 50s to lower 60s, Saturday in the lower to mid 60s and Sunday in the 60s. After getting close to record highs Tuesday, it is possible we could set some record low maximums Friday. The record low maximum for Seattle Friday is 62 degrees set in 1999. Felton

AVIATION

VFR across the majority of the terminals, with the exception of the coast and Strait of Juan de Fuca, where stratus is bringing LIFR cigs. Stratus layer has started to retreat back into the Pacific, leading to improvement of conditions through the rest of the morning. Widespread VFR conditions expected in the early afternoon. Another round of low ceilings expected along the coast after 03z, with moderate chances (40-55%) for MVFR/IFR cigs and 30-40% chance for LIFR cigs. Breezy northerly winds will develop this afternoon along Puget Sound terminals with moderate chances (30-50%) for gusts up to 15-20 kt.

KSEA...VFR conditions today. Breezy NW winds will develop this afternoon after 18z, turning NE in the evening with sustained speeds of 10-12 kt and gusts to 15-18 kt. NE winds will subside late this evening to 4-6 kt.

MARINE

High pressure will remain over the waters for the majority of the week. It will start weakening on Thursday in the wake of an approaching cold front. The front is expected to move over the waters on Friday and an additional front on Saturday. High pressure will rebuild again over the waters on Sunday.

Breezy conditions will develop over Puget Sound this evening through Thursday morning. However, winds are expected to remain below small craft thresholds. Strong northwesterly winds over the Strait of Georgia will also bring breezy conditions to the northern interior waters Tuesday morning and may see an occasional gust to 21 kt. Winds will also increase over the outer coastal waters on Tuesday with a 40-70% chance of small craft winds. Westerly pushes through the Strait of Juan de Fuca will continue throughout the week. Guidance has been consistent with Wednesday being the strongest push, with a 75-95% chance of small craft winds and 25-35% for gales. A weaker push will follow on Thursday, with latest probabilities around 35-55% of small craft winds. The chances for gales on Thursday has trended downwards and latest guidance suggesting a 5% chance or less. The frontal systems on Friday and Saturday will also bring additional chances (50-80%) for small craft winds for the coastal waters and Strait of Juan de Fuca.

Seas will remain below 10 ft through Tuesday, before building to 7- 10 ft on Wednesday. Seas will then decrease below 10 ft on Thursday and will build to 10 ft Friday with the incoming frontal system. In addition, seas may get steep at times this week over the coastal waters.

29

FIRE WEATHER

High pressure aloft combined with a thermally induced surface trough over the area will create elevated fire conditions through Tuesday. In addition to the warm, dry, and conditionally unstable air mass, low level offshore flow will drop minimum relative humidity values into the twenties, and even the teens this afternoon and Tuesday afternoon. The upper level ridge and thermally induced trough moving east Wednesday but elevated fire weather concerns could linger. Fuels are approaching critical levels, but the main concern remains dry grasses or shrubs, or dead piles of fuels where brush fires may be able to start (as seen the last few days). Onshore flow will return with improved low level moisture Wednesday night and Thursday. Weather system moving into the area will bring a chance of wetting rains for the first time in a couple of weeks Thursday night and Friday. Cool weather will continue through the weekend. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory until 11 PM PDT Tuesday for Eastern Strait of Juan de Fuca-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Island County-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Middle Chehalis River Valley- Northern Hood Canal-Olympia and Southern Puget Sound-Port Townsend Area-San Juan County-Southern Hood Canal-Willapa and Black Hills.

Heat Advisory until 11 PM PDT Wednesday for City of Seattle- Downtown Everett / Marysville Area-Eastern Kitsap County- Eastside-Foothills and Valleys of Central King County- Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Snohomish and Northern King Counties-Lowlands of Pierce and Southern King Counties-Shoreline / Lynnwood / South Everett Area.

PZ...None.