Area Forecast Discussion

SYNOPSIS

Weakening upper level low off the north coast will elongate and continue to weaken through Saturday. What is left of the low will move inland Saturday night. Upper level ridge building over the area Sunday. The ridge will move east Monday allowing a warm front to nick the north coast. Another ridge will build Tuesday into Wednesday. The ridge will move to the east Thursday with a splitting front moving into Western Washington.

SHORT TERM /TODAY THROUGH SUNDAY/

Satellite imagery shows upper level low now west of KUIL. Showers rotating around the low from the Puget Sound area westward. Temperatures at 3 AM/10Z were in the 40s.

Upper level low drifting southwest today. Flow aloft over Western Washington already southerly this morning. As the low moves southwest difluent flow aloft developing this afternoon. This combined with a little daytime heating to increase the instability over the area will produce more widespread shower activity this afternoon especially over the interior. Increasing shower activity in the afternoon will knock a couple of degrees off the high temperatures with lower 50s common across the area. The forecast high of 51 degrees for Seattle would be the coldest day since another 51 degree day back on May 15th.

Upper level low elongating and weakening tonight and Saturday but will still be off the coast by late Saturday afternoon. Jet stream moving inland over Northern California. Shower activity drying up quickly this evening. Shower chances becoming confined to the coast after midnight and to the coastal waters Saturday morning. Varying amounts of middle and high level clouds moving through the area. Lows in the 30s and lower 40s. If there is enough clearing chance for lows in the upper 20s in the Lower Chehalis Valley and Southwest Interior. A freeze watch for these areas will remain in effect. Highs Saturday in the lower to mid 50s.

Upper level low weakening to an upper level trough and moving inland Saturday night. Nothing left with this feature by this point. Light surface gradients early Sunday morning with patchy fog developing in the fog prone locations like the Southwest Interior. Lows in the 30s and lower 40s.

Light onshore gradients Sunday morning for areas of morning low clouds and fog. Upper level ridge building into the area during the day making for a sunny afternoon. Highs in the lower to mid 50s. Felton

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Extended models in pretty good agreement with the upper level ridge over the area Sunday night moving east Monday. This will allow a warm front to nick the north coast later Monday into Monday night. Another upper level ridge building Tuesday remaining over Western Washington Wednesday but the ridge axis will be east of the area. Splitting front reaching Western Washington Thursday for a chance of rain. Highs in the mid 50s with some upper 50s Wednesday. Lows in the 30s and lower 40s. Felton

AVIATION

An upper level trough will remain over the coastal and offshore waters today and Saturday producing south to southwest flow aloft over Western Washington. Surface winds at many terminals generally light and variable while those reporting winds are mainly seeing northeasterly to easterly with speeds ranging 4-8 kts. As the day progresses, a slight shift to easterly to southeasterly winds is expected, although winds likely will not get beyond the previously mentioned 4-8 kts range.

Shower activity over W WA has eased considerably, two bands still remain, one moving over the Puget Sound while the other remains just off the coast over the nearshore waters. Impacts to terminals have been minimal as widespread VFR conditions persist, although locations more prone to lower cigs such as OLM and HQM have seen conditions erode to MVFR or IFR. As another round of showers is expected to pick up this afternoon, widespread MVFR conditions are expected to emerge. Activity is expected to taper off in the early evening with widespread VFR conditions returning, although some isolated examples of MVFR could linger.

KSEA...Ceilings are expected to remain at or above 4000 to 5000 feet for much of the remainder of the morning. A general deterioration to MVFR ceilings is expected between 16Z and 21Z as showers increase once again. Wind discussion above applies.

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MARINE

Weak surface low pressure over the coastal waters will remain in place into Saturday before dissipating as high pressure builds across the interior of Western Washington early in the coming week. East or southeast winds across the coastal waters and near the west entrance to the strait will occasionally reach 15 to 20 knots over the next couple of days until the offshore low finally dissipates. Otherwise, winds into early next week look to remain rather light across area waters.

Coastal seas generally 4 to 6 feet today and into the weekend. They are expected to build back to around 10 feet Monday as another larger swell train reaches the waters.

27/18

SEW WATCHES / WARNINGS / ADVISORIES

WA...Freeze Watch from late tonight through Saturday morning for Lowlands of Lewis and Southern Thurston Counties-Middle Chehalis River Valley.

PZ...None.