SHORT TERM /TONIGHT THROUGH SATURDAY/
Current radar trends show shower activity trending downward...although some sells can still be seen over portions of the Olympic Peninsula and over the southern half of the Cascades. Satellite shows lightning has not been a factor with this activity for at least the past hour to hour and a half...so would appear the thunderstorm threat has died.

Inherited forecast appears to be a little too generous with instability but over all not really worth the effort to get in there and noodle with it. Otherwise, the lingering chance PoPs over the Cascades looks fine as the combination of orographics and some lingering instability on the backside of the low will allow threat of scattered showers to persist there into Thursday.

All that said, no plans for any evening update. For additional forecast details, please refer to the Previous Discussion section below.

18

From Previous Discussion...A strong upper level low continues to progress inland over the Pacific Northwest this afternoon, with particularly strong meridional flow offshore. Down at the surface, an occluded front has slowed moving inland from the Pacific Ocean.
This front, along with a trailing surface trough, continue to provide enough lift to support showers all morning long.

This afternoon, the lull in activity has allowed for limited destabilization to take place. HRRR ensemble guidance shows 300-400 J/kg of CAPE in southwest Washington (this drops to 100 J/kg in the Cascades). Lapse rates are steady around 6 degrees C/km. Additionally, temperatures remain cool aloft with 500 mb temperatures hovering around -16 degrees C. Ingredients will come together for a few isolated thunderstorms to mix in with showers this afternoon. The best chance of seeing a thunderstorm this afternoon will exist around the Olympic Mountains, Chehalis Valley, and Olympia. There's a lesser chance in the Cascade Foothills of thunderstorms. The thunder threat will diminish after sunset. The storm mode will be pulse-mode, shortlived with a few lightning strikes and possible graupel/heavy downpours.

Going into Thursday/Friday, the upper level low from Wednesday will move inland. A transient ridge will break down over Canada rapidly on Thursday, with strong northwest flow aloft settling in.
Conditions will therefore be dry, but with mostly cloudy skies prevailing.

Saturday will see a return of active weather across western Washington. The next upper level low will an accompanying surface low with a notable cold front. Once this low arrives in B.C.
Canada, widespread stratiform precipitation will spread across the coverage area during the day. Ensembles show a strong likelihood of wetting rain, particularly across the north Cascades. There is medium confidence in isolated thunderstorms with this system Saturday (depending on how cold aloft it will end up being). Will continue to monitor the risk for possible hydro impacts over the weekend.

High temperatures remain constant through the short-term, with daytime highs in the mid and upper 60s, and lows in the mid 50s.
Winds will be light at or below 5 to 10 mph.

LONG TERM /SUNDAY THROUGH WEDNESDAY/
From Previous Discussion...The system from Saturday will continue to produce showers through Sunday across western Washington. Amounts for Sunday are expected to be light at this time. Dry weather will settle in again Monday and Tuesday, with northwest flow swapping to zonal.
Skies will remain mostly cloudy during this dry break. Ensembles are picking up on a strong upper level system passing through next Wednesday. This will be monitored for possible widespread precipitation chances.
Temperatures will continue to remain steady, with highs in the mid and upper 60s, and lows in the 50s.

HPR/Knauss

AVIATION
An upper level trough will shift inland tonight and allow for shortwave ridging to build into the region Thursday.
This will allow for southwesterly flow aloft to transition to more northerly by tonight. Radar showing showers diminishing across the CWA Cigs a mix of VFR to MVFR with isolated IFR along the coast.
However, light surface flow combined with ample low level moisture will bring the redevelopment of MVFR to IFR ceilings to the area terminals overnight into Thursday morning. Ceilings will lift towards VFR again by the afternoon hours.

KSEA...VFR conditions in place with remaining showers steering clear of the terminal. Expect MVFR to IFR ceilings to redevelop overnight with ample low level moisture and light flow in the low levels. W/NW winds 4-8 kt will transition back to S/SW tonight and become light.
S/SW winds will increase to 4-8 kt again by the afternoon. 14/18

MARINE
A weak surface low will continue to push inland tonight, allowing for surface ridging over the northeastern Pacific to build back into the coastal waters on Thursday. Another weak trough looks to slide southward from British Columbia late Friday into Saturday. Ridging will then build back into the coastal waters early next week. Onshore flow will persist over the next several days. Westerly winds along the Strait of Juan de Fuca may increase towards 10-20 kt Thursday night into Friday and may approach Small Craft criteria at times.

Seas are currently hovering between 3-5 ft over the coastal waters, but will build towards 5-8 ft over the outer coastal waters tonight. Seas will then gradually subside again towards 3-5 ft again by the weekend. 14

FIRE WEATHER
From Previous Discussion...A weak low pressure system will spread additional showers across much of the region evening. Some modest instability and cooler air aloft will bring the potential (15-20%) of an isolated thunderstorm, with the highest chances shifting into the Cascades. Expect any thunderstorms that develop to be short-lived and of the pulse variety, putting out only a strike or two before falling apart. Additionally, additional rainfall with these storms (60%+ chance of wetting rain in these areas) and abundant antecedent rainfall should preclude significantly elevated fire weather concern. Otherwise, fire weather concerns remain minimal with near to below normal temperatures and additional round of rainfall through the week ahead. Cullen

SEW WATCHES/WARNINGS/ADVISORIES
WA...None.
PZ...None.