textproduct: Seattle/Tacoma

SYNOPSIS

Thunderstorm potential will continue along the Cascades today, but will wane throughout the weekend as an upper level ridge starts to builds into the area from the southeast. Another upper level trough will move into the region early next week. Uncertainty then increases in the forecast heading into midweek as guidance remains split between a warmer, drier pattern and a cooler, wetter one.

SHORT TERM /TODAY THROUGH MONDAY/

Broad upper-troughing resides over the PAC coast this morning while upper-ridging is positioned across much of the nation. In the PNW, a weak upper-low will influence the weather today as the main highlight once again is showers and thunderstorms forecasted for the mountains. As a result, elevated fire weather conditions are expected for the Cascades.

Marine stratus has marched well inland this morning -stretching from the coast into Puget Sound. It'll remain in place before gradually burning off into the afternoon. However, aforementioned thunderstorms will potentially emerge this afternoon along the Cascade crest as a subtle shortwave within the mean flow tracks into the region and perturbs the environment. Latest HREF depicts 500-800 J/kg of Surface CAPE along the Cascades with 250-500 J/kg across the Olympics. Model derived 700-500 mb lapse rates are around 6 C/km, conditionally unstable for any saturated air parcels. The NBM has a 20-30% chance of thunderstorms this afternoon into the evening and less than 15% elsewhere across western Washington. The threat should end tonight barring a few stragglers. Highs today for the interior are forecast to range between the mid 70s to lower 80s. Coastal areas are favored to remain in the 60s. Overnight lows will be in the upper 40s to upper 50s.

Global guidance has ridging building into the region out of the southeast on Sunday. Southwest flow aloft will help push smoke eastward and away from the region. A slight chance (15-20%) of thunderstorms is forecast for the North Cascades with lesser probabilities southward along the range. Monday's forecast is quite similar in regards to convection but probabilities should remain capped at 15%, likely due to more large-scale subsidence provided by direct ridging overhead. Highs for Sunday and Monday in the mid 70s to mid 80s with overnight lows in the lower to upper 50s. Coastal areas highs are forecast in the 60s.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

The first part of next week remains to follow a rather typical pattern of onshore low-level flow maintaining morning clouds, with some clearing in the afternoon. A passing trough around Tuesday could provide a reinforcing push of clouds and knock temperatures a few degrees cooler than normal. Otherwise, ensemble guidance begins to spread a bit larger toward the middle of next week with a fairly even split between a cooler trough pattern and a warmer (near normal) pattern under zonal flow or a weak ridge. In any event, there's not a significant signal for any precipitation of note with temperatures leaning warmer than average.

AVIATION

A mix of conditions ranging from MVFR to LIFR this morning associated with marine stratus. VFR conditions are expected once the stratus dissipates, but models are hinting at a later clear- out timing, potentially as late as 19-21Z across the interior. The coast will likely not fully clear out in the afternoon before stratus rebuilds tonight into Sunday morning. Light WSW winds will increase in the afternoon. Winds look to switch NW across central Puget Sound terminals after 00-02Z. Winds will ease late tonight.

KSEA...Slow improvement this morning to MVFR. Models remain consistent with a later clear out time around 20Z. VFR conditions this afternoon will be followed by another round of stratus Sunday morning. Latest guidance suggests a 30% chance for MVFR cigs after 12Z Sunday. Winds predominantly from the SW at 4-7 kt, and may attempt to turn more W to NW between 02-06Z.

62/29

MARINE

High pressure will remain well off the coast of California today, keeping winds light over the coastal waters. Northwesterly winds will begin to resume Sunday as high pressure rebuilds of the coast of British Columbia. The high will strengthen as it shifts southward off the Pacific Northwest coast, maintaining NW winds into next week. Seas look to remain between 3-6 ft through next week.

Diurnally driven westerly winds will continue to occur each afternoon and evening in the Strait of Juan de Fuca through this weekend and into early next week with gusts reaching Small Craft Advisory criteria at times. The westerly pushes look to start to weaken by the middle of next week. 62

FIRE WEATHER

Elevated fire weather conditions will continue across the Cascades today with chances of thunderstorms possible again along the Cascade crest this afternoon and evening. Overall chances for convection will decrease throughout the weekend, however, as an upper level ridge starts to build into the area from the southeast. By Sunday, expect convection to mainly be confined to the Cascade crest and areas east of the crest. Another upper level trough will move into the area next week and could bring some additional elevated fire weather concerns to western Washington at times.

14/41

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.