textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridge over the area today with low level offshore flow. Today could be the warmest day of the year so far. The ridge will weaken tonight with the low level flow turning onshore. Upper level trough moving through Wednesday with unsettled weather continuing into the first part of next week. Cold upper level low moving into the area Saturday for a chance of thunderstorms.

SHORT TERM /TODAY THROUGH THURSDAY/

Satellite imagery shows band of high clouds from near the San Juan Islands down to around Goldendale. Mostly clear skies over the remainder of the area. Wide range of temperatures with mid 40s in the calm wind locations to lower 60s in locations with some east wind exposure.

Low level flow offshore this morning will weaken this afternoon. Temperatures aloft are warm but not near record levels. Model 850 mb temperatures this afternoon in the plus 14C-18C range. This combined with the low level offshore flow will give the area highs mostly in the 80s. Lower 90s possible in the warmer locations like the Cascade Foothills and the Southwest Interior. The Central Coast will be the first to see the transition to onshore flow this afternoon keeping highs mostly in the 70s along the beaches. Forecast high of 85 in Seattle would be the first 85 degree plus day of the year. This is a little ahead of schedule with the average first 85 degree plus day June 10th ( earliest April 18, 2016 (89), 1954 and 1957 did not have an 85 degree plus day ).

Low level flow turning onshore across the entire area this evening. Upper level trough approaching offshore will lower the surface pressure enough to prevent gales through the Strait. High clouds out ahead of the trough moving over Western Washington overnight keeping lows in the 50s.

Upper level trough moving through Wednesday plus low level onshore flow giving the area a 15-20 degree cool down with highs in the 60s and lower 70s under mostly cloudy to cloudy skies. Trough axis over the Cascades in the afternoon for a chance of showers and a slight chance of thunderstorms.

Increasing onshore behind the trough Wednesday night will continue into Thursday. Convergence zone forming over the Central Puget Sound late Wednesday night/early Thursday morning for a chance of light showers or drizzle through Thursday morning. Onshore flow keeping skies at least mostly cloudy with highs again in the 60s and lower 70s. Lows Thursday morning in the upper 40s to mid 50s. Felton

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

Upper level trofiness Thursday night through Friday night with low level onshore flow. Increasing shower chances Friday night. Cool upper level low moving over the area Saturday. Model 500 mb temperatures in the -25C to -29C range. Air mass unstable Saturday especially in the afternoon with lifted indexes in the 0 to -3 range and convective temperatures in the mid to upper 50s. There is even a little CAPE present, 300-500 J/KG. Have a chance of afternoon thunderstorms for portions of the area. Low kicks out Saturday night. Another upper level low behind it currently projected to move inland to the south Monday. Cool Friday and Saturday with highs in the mid 50s to lower 60s. Highs trending back towards normal Sunday and Monday, 60s and lower 70s.

AVIATION

An upper level ridge/thermal trough will shift eastward today - expect the flow aloft to transition to westerly. The flow will turn more onshore Tuesday into Wednesday as a trough moves inland. For Wednesday: VFR expected regionwide with a few high clouds overnight, with light north winds at around 4-8 kt. Tonight/Wednesday: Expect winds to shift to the south and west early Wednesday morning as the onshore gradient increases. Mid-level clouds will fill in regionwide, with a line of lower stratus developing along the coast (40% for MVFR conditions for coastal terminals, although stratus may lower offshore). A few showers possible on Wednesday.

KSEA...VFR - clear skies today, then mid clouds filling overnight/Wednesday. North winds 4-8 kt becoming southwest after 10Z Wednesday morning at the same speed.

HPR

MARINE

A thermal trough under a ridge will begin to shift inland this afternoon, with offshore flow returning to onshore. A trough/front will move through on Wednesday, with high pressure building in behind the trough resulting in stronger onshore gradients. Few showers will also be possible with this system over the waters. The winds will pick up Wednesday into Thursday for the eastern two thirds of the Strait of Juan de Fuca. A small craft advisory was issued for the first round of winds Wednesday for this area. The push on Thursday is expected to be the strongest, although recent ensemble guidance lowered the probability of gale gusts. The pushes through the remainder of the week are much weaker, and do not have enough likelihood of producing marine impacts.

Seas will vary from 4-6 to 6-8 ft at times of the week, but again likely to remain below any impactful levels for small craft.

HPR

FIRE WEATHER

Dry and warm today with light offshore flow into the afternoon hours. High temperatures in the 80s and a few spots touching 90. Winds will be light, but a few easterly gusts 10-15 mph near the Cascades and over the exposed ridgetops remain possible. Daytime RHs will bottom out near 20%. Even though this is a short warm up and fuels have not reached critical levels lets be careful out there. Onshore flow kicking in tonight bringing higher humidities Wednesday. Temperatures near to a little below normal Wednesday into the first part of next week. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 AM Wednesday to 5 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.