Marine Weather and Tide Forecast for Herron Island, WA

SYNOPSIS
Front over Cascades late this afternoon will continue to move east. High pressure, both at the surface and aloft, building offshore Thursday and remaining in place into next week.
Upper level ridge strengthening Tuesday and Wednesday with thermally induced surface trough moving up the coast. The resulting low level offshore flow could push highs into the 90s over the southern portion of the interior Wednesday.

SHORT TERM /TONIGHT THROUGH SATURDAY/
Satellite imagery shows cloudy skies over most of the area this afternoon. A little downslope off the Olympics has created clearing on the east slopes of the Olympics. Doppler radar has showers mostly confined to the Northwest Interior and Central and Northern Cascades.
Temperatures at 3 pm/22z were in the 60s and lower 70s.

Cold front over the Cascades this afternoon will continue to move east. Onshore gradients increasing with convergence zone developing over Snohomish and extreme Northern King County by late this afternoon. The convergence zone will remain in place through the evening hours before dissipating. Up to another tenth of an inch of rain in the zone with the highest amounts in the Cascades and Cascade foothills. For the remainder of the area some clearing over the South Puget Sound in response to the convergence zone otherwise mostly cloudy skies. Lows tonight in the 50s.

High pressure, both and the surface and aloft, building offshore Thursday. Marine layer over the area in the morning will dissipate in the afternoon with weakening onshore flow and the strong mid July sun. The cloudy morning will keep high temperatures below normal, in the mid 60s to mid 70s.

Not much change to the pattern Thursday night through Saturday.
Upper level ridge remaining centered offshore with light low level onshore flow. With the weak onshore flow, marine layer along the coast will have a hard time moving inland in the overnight hours.
Temperatures aloft with the ridge axis offshore will be fairly steady through the period. Model 850 mb temperatures bouncing between plus 14C and plus 17C. This combined with light onshore flow will keep temperatures from getting too warm Friday and Saturday. Highs over the interior in the mid 70s to mid 80s.
Afternoon seabreezes will keep highs on the coast near 70.

LONG TERM /SUNDAY THROUGH WEDNESDAY/
Extended models in good agreement with the Friday and Saturday weather pattern remaining intact for Sunday and Monday.

Changes start to occur Tuesday with the ridge offshore gaining amplitude and a thermally induced thermal surface trough moving up the Pacific Northwest coastline. By Wednesday the thermal trough will be along the Washington coast. Temperatures aloft warming Tuesday with model 850 mb temperatures in the plus 18C to plus 21C. More warming Wednesday as the ridge continues to amplify with 850 mb temperatures in the plus 21C to 24C range. Warmer temperatures aloft combined with increasing low level offshore flow will give the area a short heat wave. Highs Tuesday in the interior upper 70s to near 90 with mid and upper 70s along the coast. About 5 degrees warmer Wednesday with 80s to mid 90s interior and 80s along the coast. While not a record, the current forecast high of 90 degrees for Seattle next Wednesday would be only the 5th time in 81 years with a high 90 degrees plus on July 16th. HeatRisk solidly in the moderate category both days for the interior. The hot and dry weather could also produce some fire weather headlines. Felton



AVIATION
Northwesterly flow aloft as an upper level trough continues to exit W WA this evening. South to southwesterly winds at the surface generally running 5-10 kts will gradually ease further overnight to 3-8 kts. CLM and HQM are more westerly with HQM running speeds similar while CLM seeing speeds more in line with 8-12 kts with occasional gusts. PAE seeing more northerly winds, also resulting from the push down the Strait.

Majority of cigs very borderline VFR/MVFR, some on the lower side, some on the upper. PAE is the only reporting IFR as of 7 PM PDT.
With plenty of moisture at the lower levels, cigs expected to degrade tonight with widespread MVFR to IFR conditions. Conditions improving by early Thursday afternoon with widespread VFR expected at the majority of terminals, with the exception of along the coast.

KSEA...Cigs bouncing back and forth between MVFR and VFR this evening and that may continue through around 07-09Z before conditions finally degrade to solidly MVFR. Further lowering will gradually occur with cigs expected to bottom out between 1500-2000 ft just slightly after 12Z and remain there into the late morning/early afternoon. Some light drizzle may be possible, but confidence remains low enough to not include in TAF. VFR conditions will return Thursday afternoon.
Thursday morning after 14z-15z.

Southwesterly surface winds 5-10 kt this evening, easing a little bit more overnight as discussed above. Guidance hints at northerly winds returning after 23z Thursday.

29/18

MARINE
A weak front continues to exit the inland waters this evening. Another push of westerlies down the Strait of Juan de Fuca allows the inherited Small Craft Advisory to remain in effect.
Westerly pushes will continue to occur across the Strait each evening, but at this time look to remain below small craft criteria.
Another weak system will move across the waters Thursday morning.
Following this system, strong high pressure will build over the waters, and will remain the dominant surface feature into early next week, establishing northwesterly flow over the coastal waters. High pressure will weaken slightly on Saturday into early next week.
Guidance hints at steep seas Sunday into early next week, with seas building to 7-9 ft at 8-9 seconds.

29/18


FIRE WEATHER
Cooler and more moist conditions will begin to cease on Thursday as skies clear and conditions being to warm up with a weak upper level ridge building over the area. Friday will be the warmest/driest day this week with RH values dropping back into the 25 to 35% range over the mountains and across the interior lowlands south of Puget Sound. More robust onshore flow will help usher in more moisture this weekend despite high temperatures remaining in the 80s.

While there is some model discrepancy, there is consensus that a more robust upper level ridge will being to build and move into the area by the middle of next week. Models are beginning show the development of a thermal trough along the coast, which would allow for winds to shift to offshore, promoting much drier and warmer conditions as well as some potential breezy winds through the Cascade gaps. This pattern will continue to be closely monitored as we approach next week.

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SEW WATCHES/WARNINGS/ADVISORIES
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Thursday for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.