textproduct: Seattle/Tacoma

SYNOPSIS

Zonal flow aloft and increasing onshore flow will lead to daytime high temperatures near seasonal normals. This pattern will persist through the first half of this week. A high degree of uncertainty continues for the second half of the week, although conditions are expected to remain generally dry.

SHORT TERM /TODAY THROUGH TUESDAY/

Latest satellite imagery is more akin to this time Friday morning than 24 hours ago, with marine stratus pushing inland along both the north and south coast. The extent of the northern portion is still fairly limited...although there is a little seepage down the Strait. The southern portion however is very similar to yesterday morning, already reaching into Shelton. Eastward progress seems to have stalled, but will continue to monitor. Variations on this theme are expected again during the overnight period tonight/early Monday morning and Monday night/early Tuesday morning.

When it comes to the forecast, the song remains the same as the combination of zonal flow aloft and low-level onshore flow will allow for another degree or two of cooling when compared to high temps yesterday. At this point, daytime highs will level out, with similar temps expected for Monday and Tuesday. This pattern will keep HeatRisk limited to Minor/Yellow.

18

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Models are trying to come to a consensus with regards to the second half of the week, but as this is seemingly the first time this solution has arisen, one would be wise to take it with a grain of salt until this solution becomes consistent over future runs. That being said, an upper level trough dipping down through BC is expected to start impacting W WA as early as Tuesday night or holding off until Wednesday morning. Largely, this feature will be dry for much of the CWA with any potential precip being confined to right along the international border on the generous side of the solutions or just to the far NE corner of the North Cascades on the stingier side. There are hints that isolated thunderstorms may be possible with this feature, again, confined to the locations where chance for precip exist, mainly late Wednesday afternoon into Wednesday evening. This troughy pattern continues for the remainder of the week and into the weekend, with some slight hints at the possibility of a more active pattern for the upcoming weekend.

In spite of this potentially troughy pattern, extended guidance continues to suggest a warming trend Thursday through Saturday. High temps Thursday are expected to climb back into the upper 70s to lower 80s. Daytime highs reach their peak Friday with mid 80s to near 90 forecast for the interior lowlands before slipping a little bit for Saturday, ranging in the lower to mid 80s.

18

AVIATION

Zonal flow persists today and again Monday as low level flow remains onshore. This pattern will allow for some terminals to have winds go light and variable during the overnight and early morning hours with direction being variations on a westerly theme, though there seems to be a general consensus that most terminals will favor southwesterly winds this afternoon, becoming more northwesterly this evening and tonight. Speeds during this time frame will typically range 4-8 kts although CLM and HQM may see slightly higher speeds ranging 8-12 kts with occasional gusts.

Cigs depend greatly on how far eastward marine stratus has pushed inland. Coastal sites remain MVFR to IFR and IFR conditions stretch as far inland as SHN...although not quite getting to CLM at the time of this writing. Models seem content to leave these cigs confined with little additional eastward progress expected, but will continue to monitor. Remainder of terminals VFR and expected to remain that way for the bulk of the day.

KSEA...VFR conditions expected to persist for the TAF period. As mentioned above, marine stratus having a tough time getting east of SHN but some SCT at or around 1000 ft seems like a good possibility. Light NW winds in the early morning expected to switch to SW by 18Z for sure, but could do so earlier. Returning to NW is expected late this afternoon/early this evening before becoming light and variable overnight. Speeds generally 4-8 kts.

18

MARINE

Broad surface high pressure will remain centered over the offshore waters with lower pressure east of the Cascades into next week. This will maintain onshore flow over the next several days and bring diurnally driven small craft advisory strength westerlies to the central and east Strait of Juan de Fuca daily. A series of weak systems passing to the north of the area this upcoming week may strengthen onshore flow at times for additional risks of gales along the central and eastern Strait.

Seas across the coastal waters will primarily persist at 4-6 ft into early next week and may become steep at times this weekend under locally driven winds. Seas will then subside to 2-4 ft by Tuesday, before increasing back to 4-6 ft by midweek.

27/18

FIRE WEATHER

Onshore flow remains in place so although conditions remain dry, more seasonable temperatures and persistent good to excellent overnight RH recoveries will prevent any widespread fire weather concerns at least until Wednesday. Models are starting to gel around a consensus showing an upper level low tracking just north of the area late Tuesday/early Wednesday. Any impacts to W WA will be minimal, however there is a suggestion for possible thunderstorms Wednesday afternoon and evening for the far northern Cascades. The extend of this possibility is extremely limited in model solutions right now, but it will be something to keep an eye on. Warming temperatures over the second half of the week could result in increased potential for elevated fire weather concerns, but too early to speculate on that just yet as a high degree of uncertainty continues to surround the long term forecast.

18

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Gale Warning until 3 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 3 PM this afternoon to 5 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.