textproduct: Seattle/Tacoma

SYNOPSIS

Upper level high pressure will continue to gradually build across the Pacific Northwest, resulting in gradually warming temperatures through the early part of this week. Temperatures will peak on Tuesday, resulting in Minor to Moderate HeatRisk. Onshore flow will increase Wednesday as the upper ridge weakens, followed by the next disturbance approaching Western Washington late this week.

SHORT TERM /TODAY THROUGH TUESDAY/

Clear skies and mostly light winds across much of western Washington will allow for a relatively cool start to the morning today, with lows in the low to mid 40s. Some more outlying areas along the coast and the southwest interior may dip down to the upper 30s, briefly. Clear skies from a building upper level trough offshore will allow temperatures to rise up to the mid 60s to low 70s today.

Temperatures will warm successively each day, being enhanced by light offshore flow developing from a weak surface thermal trough. Highs on Monday will rise into the 70s to near 80 on Monday. Tuesday will be the warmest day as the upper level ridge axis moves overhead over the region and the surface thermal trough moves inland. With high temperatures in the upper 70s to near 90, as well as lows in the mid to upper 50, this corresponds to Minor (Yellow) HeatRisk for the coastal areas and northern interior locations, as well as 50-60% chance of reaching Moderate (Orange) HeatRisk through the Chehalis Valley, South Sound, interior portions of southwest Washington, and areas of the Seattle Metro away from the water.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Ensemble guidance continues to remain consistent for the midweek period with a flattening upper ridge and the thermal low pressure sliding eastward. This will bring a return of onshore flow at the lower levels Wednesday and Thursday, with temperatures returning closer to seasonal normals and relative humidities increase. The next disturbance then is likely to move into the region late the week, bringing a return of increasing clouds and a return of precipitation toward next weekend.

AVIATION

West to northwesterly flow continues aloft as an upper level ridge builds offshore today. VFR conditions prevail through the TAF period with mostly clear skies. Some scattered mid-level clouds will hang around this morning but remain above 050-070 kft. Light north/northwest winds will increase during the day to 8-15 kt, decreasing to around 5 to 10 kt tonight and becoming more northeast/easterly.

KSEA...VFR conditions prevail through the TAF period. NE winds 8-12 kt early this morning becoming NW 10-15 kt during the day, transitioning back to NE tonight.

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MARINE

Northwesterly flow continues to prevail over the coastal waters as high pressure remains offshore with low pressure over land. Westerly winds of up to 20-30 kt continues through the Strait of Juan de Fuca and into Admiralty Inlet, but remains on track to ease early this morning.

High pressure will briefly build this evening, allowing winds over the coastal waters to bump up to 15-20 kt with gusts up to 25 kt. This will allow seas to build up to around 6-8 ft, and they will be steep with a dominant period of around 6 to 7 seconds. This will ease early Monday morning as winds also ease accordingly.

Conditions become more tranquil Monday into Tuesday as high pressure weakens and is replaced by weak thermal troughing along the coast, which may briefly turn winds more offshore early Monday, and then again Monday night into early Tuesday. Onshore flow will resume during the day on Tuesday as the thermal trough is forced eastward. Onshore flow will become stronger Wednesday and through the rest of the week as weak disturbances move across the coastal waters. An extended period of SCA conditions is expected through the strait, with the best chance of gale force winds being Thursday afternoon and evening.

Seas 5 to 6 ft today will increase to 6 to 8 ft with a dominant period of around 6 or 7 seconds tonight into early Monday. Seas fall Monday back to around 4 to 6 ft and remain around there through the week.

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FIRE WEATHER

An upper level ridge will setup a drier pattern on Monday and Tuesday, with maximum temperatures reaching into the 80s (with a few spots touching 90). Expect a weak thermal trough to build north over the region, with some light offshore flow developing as a result. Winds appear to remain rather light, but a few gusts to 15 mph near the Cascades remain possible. This will help to bring drier conditions in to the area with daytime RHs down approaching critical thresholds. This stretch appears short-lived, with a resumption of onshore flow bringing higher humidities for the second half of the week.

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 7 AM PDT this morning for Admiralty Inlet-Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 2 PM this afternoon to 2 AM PDT Monday 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.