textproduct: Seattle/Tacoma

UPDATE

Mostly clear skies in place over western Washington although some high clouds possible over the northern third of the CWA. Already starting to see some low stratus and fog development over portions of the south Sound and Chehalis River Valley and will expect fog to spread into portions of the east Sound, the islands and as far north as Bellingham overnight. Inherited forecast is on track with no need for updates. An updated Aviation Discussion is below.

SYNOPSIS

Strong high pressure continues to remain over the region this week, maintaining unseasonably warm and dry conditions across western Washington. Areas of fog and low clouds may develop the next few mornings. Expect a return to cooler and wet conditions this weekend, with snow levels falling to around 4000 ft for the start of next week.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

High pressure remains solidly in place over western Washington for the next several days. Temperatures are already well into the upper 50s to around 60. With high cloud cover continuing to lift north, this should lead to some clearing into the overnight hours allowing temperatures to dip a little cooler than this morning's warm overnight lows. Little change the next few days with some areas of morning fog giving way to a dry and mild afternoon through Friday. Ensemble guidance suggests rain with the next system likely (>70%) holds off until late Friday afternoon for the coastal areas, before pushing inland late Friday night. This will usher a return to much cooler temperatures and renewed precipitation.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Ensemble guidance remains in good agreement for a more active period as the next upper trough moves into the region for the weekend and continued disturbances cross through the start of next week. This will return temperatures much closer to seasonal normals and maintain rounds of precipitation across the region. Snow levels initially remain higher (5000 ft or higher), but lower to 4000 ft by the end of the weekend. This brings most likely amounts of 4-6 inches to Stevens Pass Sunday and Monday and perhaps even a few inches at Snoqualmie into Monday. With cooler air spreading in next week, the snow level likely remains around 3000 ft or so through mid week. However, limited moisture remains as colder air enters the region, which will preclude higher chances of significant snowfall amounts. Spread in the ensemble members increases more significantly midweek and beyond with differences in how the pattern evolves yielding a wider range of potential outcomes. That said, about 70% percent of global ensemble members suggest the return of zonal flow over the region, which leaves the region open to showers passing at times and temperatures remaining near normal values for the time of year.

AVIATION

An upper ridge centered over the Great Basin and broad troughing offshore will produce southwest flow aloft becoming southerly on Thursday. Low level offshore flow continues. High level moisture filtering through the ridge is expected to thin today with continuing VFR conditions. Greater coverage/probability of LIFR fog and low clouds is expected late tonight into Thursday morning for interior areas (from central Puget Sound southward into the Chehalis Valley, as well as the Strait of Juan de Fuca areas). Most areas are expected to clear Thursday afternoon, though low clouds may linger much of the day across the Southwest Interior. Winds through the forecast will remain light and variable between the NE/SE less than 5 kt, increasing to 4-8 kt during the day Thursday.

KSEA...VFR through the first part of tonight. LIFR conditions with fog and/or low clouds and periods of surface visibility below 1SM are expected between 11Z and 18Z. VFR is expected again Thursday afternoon. Surface winds light and variable today becoming N/NE 7 to 10 knots on Thursday morning.

27/HPR

MARINE

Surface high pressure will remain centered over the interior with a broad trough of low pressure offshore producing offshore flow across area waters on Thursday. Active conditions well offshore will continue to produce hazardous seas over the coastal waters this week. A series of frontal systems will begin to reach the waters this weekend into early next week.

Dense fog will be a possibility over the inland waters through the next couple of mornings.

27

HYDROLOGY

The return to a wet and active pattern late in the week will bring another rise above action stage to the Skokomish River. With 2-day rainfall totals of 2.5 to 3 inches across the Olympics, flooding is not currently forecast and there remains less than a 30% chance of this occuring. However, with snow levels near 5000 ft for much of the precipitation this weekend before lowering to around 4,000 to 3,500 ft later Sunday and Monday, this potential will need to be monitored closely. Elsewhere, rainfall amounts and snow levels are expected to preclude river flooding elsewhere through the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 4 PM PST Thursday for Grays Harbor Bar.

Small Craft Advisory until 4 AM PST Thursday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.