textproduct: Seattle/Tacoma

UPDATE

Satellite imagery shows upper level low moving into Northern California this evening. Deformation zone on the north side of the low producing rain as far north as Eugene at 8 pm/04z with just a few high clouds over the southern portion of Western Washington. Clear skies over the remainder of the area. Temperatures were in the upper 30s to mid 40s.

Upper level low weakening and moving east overnight. Flow aloft over Western Washington becoming northwesterly which will clear the remaining cloud cover. Temperature dew point spreads are already to 5 degrees or less in many locations. Still have some northerly surface gradients in place this evening but the gradients will go light overnight. Expect areas of fog to develop in the usual places like the Southwest Interior early Monday morning. Fog dissipating by afternoon. Upper level ridge moving through Monday and Monday night. Ridge axis well east Tuesday allowing a frontal system to reach the area. Warm front during the day Tuesday followed by the cold front later Tuesday night. Current forecast has the trends covered. No update this evening. Previous discussion follows with updated aviation and marine sections. Felton

SYNOPSIS

Dry conditions in place through Monday with high pressure over the region. The next frontal system arrives Tuesday, with a return of mountain snow and lowland rain. The pattern will remain active with additional rounds of precipitation through much of the week ahead and temperatures holding near or slightly above seasonal normals.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Not much in the way of cloud cover evident across Western Washington after the few patches of low stratus have cleared out and just a few high clouds across far southwestern portions of the state. Temperatures climbing into the 50s already this afternoon with the warmest spots into the mid to upper 50s with the light offshore flow in place bringing northerly winds through the I-5 corridor and easterly winds through the Strait of Juan de Fuca and through the coastal gaps.

With the clear skies and easing winds this evening and tonight, temperatures will again drop into the lower 30s but should trend a few degrees warmer than this morning. Nevertheless, a few patches of fog or freezing fog are still expected to develop south of Tacoma and in the more prone river valley locations. Otherwise another mild and mostly sunny day across the region tomorrow. We will have increasing clouds later in the day ahead of the next frontal system, but the precipitation shouldn't shouldn't reach the coast until tomorrow night.

A rather wet and cool day is then on tap for Tuesday with the next frontal system pushing east across the area. While the Puget Sound region might slip by with a mostly dry morning commute, expect the rain to arrive by mid morning and continue through the day. Some breezy winds are expected to develop, especially across Island County, with gusts to 30 mph in the afternoon. Precipitation then continues through the day and into Wednesday. Cullen

LONG TERM /WEDNESDAY THROUGH SUNDAY/

The active pattern continues on Wednesday with rain, mountain snow, and breezy winds continuing. Snow levels generally will stay around 4000 feet, with areas in the North Cascades receiving the bulk of the snowfall, especially at Mount Baker where advisory amounts are likely. Looking at the end of the week into the weekend, ensembles are keying in on several weak systems to keep lowland rain and mountain snow in the forecast, with the long term forecast remaining active.

Mazurkiewicz

AVIATION

Northwesterly flow aloft continues over western Washington keeping conditions dry and VFR for all area terminals this evening. Northerly surface winds for most terminals ranging 4 to 8 knots. HQM and CLM remain outliers in terms of direction as offshore flow, but speeds remain similar. VFR conditions likely to continue into Monday morning, with exceptions being PWT, OLM, and PAE...where there is a 20-30% chance of MVFR/IFR conditions at times through 17z, including the prospect of fog.

KSEA...VFR conditions at the terminal this evening continuing overnight and into Monday morning. Northerly surface winds 4 to 8 knots into tonight before becoming light and variable by early Monday. Winds then shift to southerly in the mid to late morning returning to around 4 to 8 kts. Conditions likely to stay VFR for the TAF period, although a 20-25% chance of brief MVFR conditions around 09z-15z is possible as some model solutions suggest patchy fog may attempt to develop near the terminal.

Mazurkiewicz/18

MARINE

High pressure remains in place over the area with northerly winds across much of the Salish Sea and a weakly offshore component maintaining easterly winds through the Strait of Juan de Fuca and out over the coastal waters through Grays Harbor. Seas are holding at 4 to 6 ft over the coastal waters.

Expect the next round of advisory conditions Tuesday as a front pushes across the waters, with southerly winds to 25-30 kt likely (>70% chance) and possible (40-50%) for the east entrance of the Strait. Gales remain very unlikely with this weaker system, with less than a 10 percent likelihood. Seas over the coastal waters will build to around 7 ft and steepen in conjunction with the stronger winds, becoming quite choppy. Additional advisories may be needed with the potential for west winds increasing through the Strait on Wednesday, and later in the week for the coastal waters as seas build further to around 11 ft late Wednesday through Thursday. Cullen/18

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.