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.
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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 destabilizes 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
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
Radar loop indicates a few showers along the coast ad north interior, with an overall decrease in coverage continuing. Most interior lowlands will stay dry the rest of today, although a stray shower cannot be ruled out. Light showers will probably linger into the afternoon toward the coast and over the mountains until this evening with the loss of diurnal instability. Highs today should reach the upper 50s, but given the sunshine expected this afternoon, some locations from seattle south have a shot at the low 60s.
The period of mostly dry weather will persist through wednesday morning. Another band of rain is expected to lift north into western washington starting wednesday afternoon and evening. Some sunshine is expected ahead of any rainfall and highs could still manage to reach close to 60. Precipitation with this next system looks very light, with rain amounts generally under a tenth of an inch. No changes to the forecast planned this morning.
River flooding is not expected for the next 7 days.
Southerly flow will gradually become offshore this evening into wednesday with a low pressure system well to the southwest. offshore flow will strengthen wednesday morning, potentially reaching sca criteria along the coast through wednesday. Generally quiet weather pattern expected following wednesday with systems well to the south of the area. Jd
Wa...none. Pz...none.
/issued 458 am pdt tue mar 26 2019/
Southwesterly flow aloft into tonight with an upper level low located well to the southwest. Post frontal spotty showers generally north of seattle and along the coast through the morning. vfr ceilings for most locations with mvfr mainly associated with showers and along the coast this morning. Improving ceilings by early afternoon to vfr with some mid and high level clouds around. dry weather through tonight with vfr continuing. Winds light mainly under 8 kts becoming offshore late this afternoon.
Ksea...improvement to ceilings into the afternoon as vfr continues. mostly clear skies tonight with a few high clouds. Southerly winds generally 4 to 8 knots becoming northerly 00z-03z. Jd