Showers will decrease through the day behind a frontal system that moved northward across the region overnight. After mainly dry conditions tonight and early wednesday, another front will clip the southern part of the area wednesday afternoon then lift northward and dissipate over the area on thursday. Another front will approach the area from the southwest on sunday.
Wa...none. Pz...none.
Satellite along with portland and camano island radars show clouds and showers decreasing rapidly from the south early this morning. The today portion of the forecast was updated to account for these trends toward more rapid scattering of the clouds and lower shower chances. Albrecht
/issued 247 am pdt tue mar 26 2019/
Synopsis...showers will decrease through the day behind a frontal system that moved northward across the region overnight. After mainly dry conditions tonight and early wednesday, another front will clip the southern part of the area wednesday afternoon then lift northward and dissipate over the area on thursday. Another front will approach the area from the southwest on sunday.
Short term /today through thursday/...the front that gave some light rain to the area overnight has moved into southwestern british columbia. Satellite imagery shows a weak upper level low about 100 miles west of ocean shores moving slowly northward. Showers are rotating northward around this feature this morning and will decrease this afternoon with highest pops over the mountains this afternoon as the air mass destabilises somewhat and the upper low weakens and pushes northwesterly. Highs today will range from the mid 50s to around 60.
As has been the pattern of late, high pressure will develop over british columbia and eastern washington tonight into wednesday resulting in an increase in northeast to east flow at lower levels. This will result in good drying starting tonight and continuing into most of wednesday. There will be an increase in mid and high level clouds from the south during the afternoon on wednesday, but rain chances should remain mainly from about olympia and hoquiam southward during the afternoon hours. After cool morning lows in the 30s to lower 40s wednesday, highs will reach near 60 degrees.
Forecast models show the next frontal system moving in from the southwest stalling over the area on thursday and dissipating. The ecmwf is drier and holds precipitation farther south than the wetter and more showery gfs. Differences are due to the handling of features in split flow. At this time the forecast splits the difference between the two solutions with maybe some nudge toward the ecmwf. Clouds will hold lows from the mid 30s to mid 40s thursday morning and highs will remain mainly in the 50s. Albrecht
Long term /friday through monday/...split flow typical of el nino conditions will dominate during the extended period. Models typically have problems with the details in this pattern. But conditions should be a little warmer than normal and any southern stream systems affecting the region quite weak and dissipating as they move northeast into the area.
The gfs solution holds a weak upper level trough for a chance of mainly afternoon and evening convection over the mountains on friday. The ecmwf brings a northern stream upper level high southeastward through british columbia into eastern washington a little faster than the gfs, which results in dry conditions across the region. At this time, the forecast splits the difference between the two solutions. The upper level high/ridge results in dry conditions across the area over a majority of the weekend period. Highs over the weekend should be mainly in the upper 50s to mid 60s across the area.
Sunday night and monday become more uncertain as the ecmwf is consistent in showing another front coming in from the sw and the gfs keeps the front to the south of the area. With such uncertainty in the details, a model mean was used. Albrecht
Aviation...southwesterly flow aloft through tonight with upper level low well to the southwest. Post frontal showers over the area this morning will mostly be confined to north of seattle after 20z. ceilings in the 3500-5000 foot range lowering to 1500-2000 with showers this morning. Ceilings improving seattle south this afternoon with just mid and high level clouds. North of seattle ceilings near 5000 feet in the afternoon lifting late afternoon into the evening hours to aoa 10000 feet.
Ksea...ceilings near 3500 feet lowering at times to around 1500 feet in showers through 16z. Ceilings lifting to aoa 10000 feet in the afternoon with mostly clear skies tonight. Southerly wind 6 to 10 knots becoming northerly 00z-03z. Felton
Marine...southerly flow in the wake of a weak front will gradually diminish in strength through today, becoming offshore this evening into wednesday. Overall wind speed forecasts have decreased across the board and all marine hazards have been cancelled. Offshore flow will strengthen wednesday morning, potentially reaching sca criteria off the coast through the day wednesday. Relatively quiet conditions are expected for much of the week. -wolcott-
Hydrology...river flooding is not expected for the next 7 days.