textproduct: Seattle/Tacoma

SYNOPSIS

A dry and warm airmass associated with a strong upper level ridge will settle over western Washington this weekend through Monday. Temperatures peaking in the 80s and 90s will bring widespread Moderate HeatRisk to the region on Sunday and Monday. Offshore flow will bring lower relative humidities and elevated fire danger. The ridge will weaken on Tuesday, resulting in increased onshore flow and cooler temperatures through the rest of the week.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

The short term forecast is highlighted by hot and dry conditions with clear skies and widespread high temperatures in the 80s and 90s across the interior lowlands of western Washington on Sunday and Monday. The very warm and dry airmass in place is in response to a highly amplified upper level ridge over the coastal waters that will begin moving inland late Sunday. The LREF ensemble mean continues to show 500 mb heights peaking near 588-589 dam Sunday night into Monday, which is near the climatological 98-99th percentile for this time of year. As a result, several daily record high temperatures are likely with widespread Moderate HeatRisk. Please refer to the climate section below if interested in details regarding potential records that may be broken.

The forecast remains on track with Sunday and Monday still shaping up to be the hottest days of the week as a thermally induced surface trough settles over the region. In addition to warm daytime temperatures well into the 80s and 90s, poor overnight relief is expected as low temperatures will only decrease into the upper 50s to low 60s for a brief period of time shortly before sunrise. In fact, there is a 10-30% chance urban areas to the south and east of the Puget Sound will see overnight lows at or above 65 degrees Sunday night and Monday night, particularly from Olympia to Tacoma to Kent to Seattle. Poor overnight relief will increase the risk of heat-related illnesses for populations that are vulnerable to heat and do not have access to air conditioning. Populations who may be vulnerable to heat include newborns, children under age four, the elderly, those with chronic medical conditions, and pregnant people.

In addition the heat, breezy northerly winds are expected across the Puget Sound this afternoon/evening with gusts reaching 15-20 mph as the aforementioned thermal trough shifts in from the south, with periods of offshore flow expected across the foothills and Cascades. Offshore flow will increase late Saturday night/Sunday morning across the southern Cascades and foothills, with gusts 15-20 mph funneling through the gaps. Another round of breezy winds are expected Sunday afternoon across the Puget Sound. -23

LONG TERM /TUESDAY THROUGH SATURDAY/

The long term forecast is highlighted by a return to onshore flow with relatively cooler temperatures closer to seasonal normals. On Tuesday, WPC's cluster analysis continue to suggest the ridge over the region will flatten out, bringing near zonal flow to the area. Near zonal to northwesterly flow aloft is then favored to persist through next Saturday. This will maintain fairly consistent temperatures each day, with highs generally ranging from the mid 70s to lower 80s over the lowlands, except 60s at the coast. Chances for precipitation are less than 10% each day, suggesting confidence is high the ongoing dry weather pattern will continue. -23

AVIATION

Dry conditions and VFR ceilings prevail through the TAF forecast period due to high pressure centered offshore. Northerly winds increasing to around 10 kts during peak diurnal heating this afternoon and evening. Wind gusts to approximately 15 kts are possible this afternoon and early evening, especially in and around the Seattle metro area.

KSEA...Clear skies will continue through 00z Monday. Surface northerly winds of 6 to 8 knots this morning will rise to 8 to 12 knots early this afternoon with gusts up to 16 kts possible. -23

MARINE

Expansive surface high pressure centered offshore will persist through early next week. A thermal trough will build over western Oregon and shift into the interior of western Washington starting Sunday night. This will induce onshore flow for the interior coastal waters starting Sunday night into Monday. Onshore pushes likely occur for the Straight of Juan de Fuca Monday through Wednesday, with potential for gales on Monday and Tuesday. Chances for gale force wind gusts over 34 kt peak Tuesday afternoon/evening at 80-90% over the Straight of Juan de Fuca.

Coastal seas will remain well under 10 feet through the weekend before building to around 10 feet by late Tuesday. Higher swells to around 12 ft are possible Wednesday. -23

FIRE WEATHER

Abnormally warm and dry conditions over the next few days will bring elevated fire weather concerns through Monday. An upper level ridge over the area this weekend with low level flow turning offshore Saturday night. Widespread high temperatures in the 80s and 90s are expected Sunday and Monday, with low relative humidity values, especially over the southwest Interior where humidities may drop into the teens both Sunday and Monday afternoon. Even though fine fuels have not reached critical thresholds, this rapid drying will create elevated fire concerns especially for dry grassy/shrubby areas, as well as piles of dead fuels. Offshore flow Sunday into Monday will prevent good relative humidity recoveries overnight. Relative humidities will improve with the return of onshore flow Tuesday. Low level onshore flow and cooler temperatures throughout the week will ease fire weather concerns.

CLIMATE

SeaTac is forecast to reach 87-89 degrees on Sunday, June 14, which would break the current record of 86 degrees set back in 1988. NBM probabilities for highs of 90 degrees or warmer at SeaTac on Sunday are at 5%. SeaTac is forecast to reach 90-92 degrees on Monday, June 15, which would break the current record of 88 degrees set back in 1963. While it is not the most likely outcome, two consecutive days of 90 degrees or warmer cannot be completed ruled out. This is very rare at SeaTac during the first half of June; the last time that occurred is June 6-7, 2003.

Olympia is also likely to break record high temperatures on Sunday, June 14 and Monday, June 15. Forecast highs on both days are currently at 94 degrees. This would break two daily record highs, as the current record high for June 14 is 88 degrees set back in 1999, and the current record high for June 15 is 88 degrees set back in 1963.

Even Hoquiam is likely to break a record high temperature on Sunday, June 14. The current forecast suggests Hoquiam will peak near 86 degrees on Sunday, which would break the current record high of 79 degrees set back in 1988.

-23

SEW WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory from 11 AM Sunday to 5 AM PDT Tuesday for City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Eastern Strait of Juan de Fuca-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-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-Lake Crescent Area Including US 101-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King 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-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...None.