textproduct: Seattle/Tacoma

SYNOPSIS

An upper level trough over Western Washington today will shift eastward tonight. A weak upper ridge will produce a brief drying trend on Sunday before a series of systems produce cool and unsettled conditions for the first half of the coming week. A pattern shift toward dry and considerably warmer conditions is expected late next week as strong high pressure aloft builds into the region.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

Showers and thunderstorm threat winding down this evening as an upper low departs the region. Current trends look good and match the forecast. 33

Previous forecast...Daytime heating coupled with an upper trough axis over Western Washington will produce scattered showers, isolated thunderstorms and unseasonably cool temperatures into this evening. The higher terrain of the Cascades and Olympics above 4500 feet will see some light snowfall, but it is not expected to produce any travel impacts across the passes. The trough will shift eastward tonight and a weak shortwave ridge will slide onshore on Sunday allowing the area to briefly dry out though temperatures will remain below normal. The next in a series of troughs will spread additional clouds and showers into the region Sunday night into Monday. It's eastward progression will, however, be hindered as a weak surface low developing off the Oregon coast splits the system apart and takes the focus of the bulk of the precipitation into Oregon.

LONG TERM /TUESDAY THROUGH SATURDAY/

The cool and unsettled pattern continues into the middle of the coming week as another upper trough digging southward along the British Columbia coast keeps showers and cool temperatures in the forecast.

The narrative takes a decided turn from that point forward. Ensembles are virtually unanimous that we'll see a substantive change in the synoptic pattern heading into late next week and the days that follow. A building upper ridge will produce a warming trend that will result in temperatures climbing back to just above normal levels swiftly on Thursday. The climb upward continues as we round out the week and likely beyond. High temperatures by the beginning of next weekend could run 10 to 15 degrees above seasonal averages as anomalously strong upper ridging takes up residence just to our west.

Longer term guidance strongly suggests that the upward trend in temperatures will persist beyond the 7 day period. Probabilistic HeatRisk suggests a 90-100% chance of Minor HeatRisk across much of the lowlands by Friday and Saturday and a 40-70% probability of Moderate HeatRisk on Saturday for the interior lowlands of south Puget Sound and the Southwest Interior. Though it's early yet, current probabilistic data has a considerable portion of the CWA likely reaching Moderate HeatRisk as we enter the June 14th/15th period with potential daytime temperatures in the mid 80s to mid 90s for interior areas from Seattle southward. Stay tuned.

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AVIATION

An upper trough axis over the interior this afternoon will shift east of the Cascades tonight. Westerly flow aloft will become north to northwesterly tonight. Low level convergence will enhance some additional showers this evening across central Puget Sound, with most shower coverage diminishing tonight. MVFR ceilings can be expected around heavier showers. Remnant low level moisture and light surface winds will lead to greater coverage of MVFR ceilings across the region on Sunday morning. This will gradually lift to VFR Sunday afternoon.

KSEA...VFR conditions at the terminal this evening as most of the thunderstorm activity has diminished near the terminal. More predominant MVFR ceilings are expected Sunday AM as remnant low level moisture remains in the area. These will lift to VFR Sunday afternoon. Surface winds south to southwesterly 9 to 13 knots into the throughout the evening.

27/Mazurkiewicz

MARINE

A weak trough over the coastal waters will shift inland tonight as weak high pressure builds just offshore. Another trough and associated frontal system will approach the outer coastal waters Sunday evening then slow and dissipate in response to a weak surface low moving toward the Oregon coast. Onshore flow will increase Tuesday and Wednesday as broad high pressure gradually expands into the coastal and offshore waters. Onshore flow weakens late next week as thermally induced low pressure begins to expand northward across Western Oregon.

Coastal seas are expected to remain below 10 feet through the period.

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FIRE WEATHER

As upper level ridging builds into the area starting Thursday, conditions, including fuels, will need to be monitored as temperatures are expected to climb to above normal values entering into the week 2 time period.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.