####018008695####
FXUS66 KPQR 032134

AFDPQR



Area Forecast Discussion

National Weather Service Portland OR

234 PM PDT Fri May 3 2024



.SYNOPSIS...

Cool and wet this weekend as an upper low moves into

western OR and northern CA, bringing a prolonged period of light to

occasionally moderate stratiform rain late Friday through Saturday.

Remaining cool Sunday through Tuesday with showers at times. Upper

level ridging will then bring a quick warmup mid to late week, with

high temperatures likely rising above 80 degrees across the interior

lowlands by Friday.



&&



.SHORT TERM...Friday through Sunday night...Surface weather 

analysis from 1pm Friday revealed a warm front/cold front pair 

over the coastal waters moving east towards the coast. This 

frontal system was associated with a broad area of low pressure 

centered around 400-500 miles west of Vancouver Island. A wave 

of moisture ahead of the aforementioned warm front has already 

resulted in light rain at the coast. This moisture will continue

spreading inland Friday afternoon as the system's warm front 

lifts over the area. Once rain begins, expect a prolonged period

of light to occasionally moderate stratiform rain across all of

northwest OR and southwest WA through the day on Saturday as 

the trailing cold front pushes through. Precip will transition 

to showers on Sunday within the post-frontal environment. This 

system will have an abundant amount of moisture as IVT values 

max out around 300-400 kg/ms this evening. Models still show 

precipitable water values around 1 inch, which is about two 

standard deviations above normal for this time of year. 



There have been minimal changes the total QPF forecast with 

this system. Still expect around 1-1.5 inches for the interior 

lowlands, and 1.5-2 inches for the coast and mountains from late

morning today to tomorrow (Saturday) afternoon. No impactful 

winter weather is expected for the Cascade passes today as snow 

levels will rise above 6500 to 7000 feet. Despite the impressive

rain amounts for early May, no flooding concerns are expected as

hourly rain rates look to generally be under 0.2 inches/hr, except

under heavier showers on Sunday. HEFS probabilistic guidance

continues to show a less than 5% chance of reaching action stage for

the majority of rivers. Two rivers with the highest chances of

reaching action stage are Marys River at Philomath (5-10% chance) and

Tualatin River near Dilley (15% chance).



As the low pressure system progresses southward toward California

Saturday, cold air aloft will return and snow levels will fall 

back down to around 3500 to 4000 feet. Given the precip expected this

weekend, another round of winter weather will impact the Cascades. A

Winter Weather Advisory has been issued above 3500 feet for the North

Oregon Cascades to the Lane County Cascades from 5 AM Saturday to 11

AM Sunday morning. These locations are forecast to receive around 4

to 10 inches of snow, except up to 16 inches for the highest peaks

above 5000 feet. Those traveling through the passes this weekend

should prepare for winter weather conditions. Meanwhile, the lowlands

will continue to see rain showers through the weekend.	-TK/Alviz





.LONG TERM...Monday through Friday...The long term forecast is

highlighted by a rapid change in the weather pattern from cool and

showery conditions Monday through Tuesday to much warmer and drier

conditions late in the week. Models and their ensembles continue to

show a shortwave trough moving across Washington and Oregon Monday

into Tuesday, bringing a shift from westerly flow aloft to

northwesterly behind the trough axis. This trough will bring the

continuation of cool and showery weather with high temps mainly in

the 50s and snow levels around 4000 ft on Monday falling to 3000 ft

on Tuesday.



Beyond Tuesday, confidence is high for a rapid shift in the weather

pattern from cool and wet to warm and dry. This abrupt shift is the

result of an upper level ridge that is set to build over the region,

and all four clusters shown in WPC's cluster analysis depict this

ridge with varying amplitudes. The deterministic NBM currently

suggests highs in the 60s Wednesday, 70s Thursday (except 60s at the

coast), and 80s Friday (except low 70s at the coast). The coolest

model solutions are similar to the NBM 10th percentile, showing

inland high temps only peaking in the mid 70s on Friday. Meanwhile,

the warmest model solutions show highs near 90 degrees from Portland

to Eugene. Either way, temps will be running above normal for this

time of year. The probability for high temps at or above 80 degrees

on Friday is already at 70-80% across the interior lowlands, which is

quite high for a forecast that is seven days out. Overall, the

warmest temps of the year so far are likely to occur next weekend.

This may draw some people to area rivers and/or lakes, but keep in

mind water temps are still very cold and river currents will be swift

with mountain snowmelt. We plan on actively messaging cold water

safety tips late next week in preparation for the warm weather ahead,

as cold water shock and hypothermia will be a very real risk for

anyone who decides to take a swim.  -TK



&&



.AVIATION...Satellite and radar observations this afternoon show

rainfall quickly spreading across western Oregon as our next

weather disturbances races into the Pacific Northwest. Confidence

is high after precipitation initially begins 21-23z cigs drop to

MVFR with model guidance indicating a 70-95% chance for less than

3kft CIGS after 03-06z for all sites. KONP likely continues to

fluctuate between MVFR and IFR conditions the rest of the

afternoon before trending solely to IFR overnight and through

Saturday. We’ll also have to watch for a period of IFR CIGS at

inland sites Saturday morning between roughly 10-16z, although

confidence in the timing of any such category change is low to

moderate currently. Given the deep moisture, expect mountains to

become obscured. Wet weather persists through the rest of Saturday

accompanied by a mix of MVFR to temporarily IFR conditions through

at least 00z. 



Winds remain fairly variable and light (<10 kt), but once the 

front nears, winds will take on a stronger southerly character. 

Winds at coastal terminals will begin to gust to around 20-25 kt

from the south around ~22z Fri to 03z Saturday, then gradually 

veer more southwesterly and weaken through Saturday morning 

before increasing again to the 15-20 knot range Saturday 

afternoon. 



PDX AND APPROACHES...VFR conditions under increasing high clouds

will soon transition to rain(~2130-2200z) with gradually lowering

CIGS the rest of the afternoon into the early evening hours.

Chances for CIGS less than 3kft increase to around 80-90% by 06Z 

Sat. Winds generally east through about 00Z Sat then more south to

southeasterly. Expect periods of rain and low-end(<2kft) MVFR 

conditions to continue early Saturday morning through the rest of

the forecast period. -Schuldt



&&



.MARINE...A cold front associated with a low dropping out of the 

Gulf of Alaska continues to spread rainfall across the region this

afternoon. Winds associated with this feature have been gusting

around 20-35 knots based on the very limited bouy observations

available but at least this lines up well with the latest high-

resolution guidance. The current Small Craft Advisory was 

expanded to include the inner waters south of Cape Falcon where 

gusts up to 25 knots are expected to occur with more regularity 

into the evening - although that's not to say isolated gusts of 

this magnitude won't be found further north. Winds ease this 

evening into Saturday morning, but expect to see a period of 

marginally steep seas (6 to 8 ft at 8 to 9 seconds) Saturday 

afternoon and evening over both the inner and outer waters. 

Otherwise, anticipate another burst of SW wind gusts near 20-30 

knots Sunday into Monday morning before we begin a transition to a

calmer weather pattern and eventual shift to N-NW winds Tuesday 

and Wednesday. -Schuldt



&&



.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory from 5 AM Saturday to 11 AM PDT Sunday 

     for ORZ126>128.

WA...None.

PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ252-

     253-271>273.

&&



$$



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####018005717####
FXUS66 KSEW 032138

AFDSEW



Area Forecast Discussion

National Weather Service Seattle WA

238 PM PDT Fri May 3 2024



.SYNOPSIS...A shift back to cool, wet unsettled conditions will 

prevail across Western Washington through early next week. A

significant change in the weather pattern is expected for the

second half of next week as high pressure aloft leads to warmer

and drier conditions.



&&



.SHORT TERM /TONIGHT THROUGH MONDAY/...Rain had yet to reach

coastal areas as of 130 PDT (2030Z) as an occluded front ahead of

a broad upper trough offshore gradually advances toward the

region. Rain will spread across the Olympic Peninsula by early

evening, but will be slow to get into Puget Sound eastward

initially. As the upper trough axis shifts into the Oregon 

coastal waters early Saturday, a weakening frontal boundary will 

slowly lift northeastward across Western Washington. Low level

easterly flow will shift onshore and increase behind it. This 

will allow the air mass to moisten up for increasing precip 

coverage by Saturday afternoon. Overall QPF will be heavily 

focused on the southwest half of the CWA. 



The upper trough is expected to shift into the Great Basin by 

early Sunday with wrap-around precip continuing to fall across 

parts of Western Washington. Onshore flow will ramp up through the

day on Sunday as another upper trough moves toward the area. 

Increasing orographic lift will lead to a fairly wet Sunday 

afternoon and evening in the mountains, but much of the Puget 

Sound area looks to be rain shadowed. 



An upper trough axis will swing onshore on Monday. With colder 

air aloft, this will destabilize things enough to warrant the

mention of a slight chance of thunderstorms. Snow levels will dip

to some of the higher passes, but amounts look to be light. A

convergence zone looks likely to form on Monday as well.

Temperatures throughout the short term forecast period will be

several degrees below normal, but changes are afoot.





.LONG TERM /TUESDAY THROUGH FRIDAY/...Cool, showery conditions

will persist into Tuesday as the upper trough axis slowly shifts

east of the Cascades. For Wednesday and beyond, ensembles are

nearly unanimous that upper ridging will build over the northeast

Pacific as downstream a broad upper trough takes up residence 

over the eastern two thirds of the lower 48. There is still 

considerable uncertainty with regards to how warm it will get. 

Current forecasts reflect the NBM 50th percentile forecast...which

brings mid 70s to Seattle by next Friday. A noteworthy number of 

ensemble members (particularly the GFS) have temperatures teasing 

80 degrees by late next week for some areas. Rough winds do shake 

the darling buds of May, but we might compare thee to a summers 

day by next weekend. 27 



&&



.AVIATION...An upper level trough will move through western

Washington this evening with south to southwesterly flow aloft.

Mid to high level clouds have spread throughout most of the

interior ahead of an approaching frontal system. VFR conditions this

afternoon will likely continue throughout the majority of the

evening. Winds at the surface will remain south to southeasterly 

and be gusty at times as the frontal system moves through the 

area. Winds will turn more north/northeasterly into the overnight

period.



Rain will start along coastal terminals this afternoon around 

21-23z, with rain slowly making its way into the interior, likely 

around 03-07z. Ceilings will stay VFR into the evening before 

gradually falling to MVFR/IFR, starting with coastal locations 

around 05z, and interior terminals around 10-12z. A mixed bag of 

MVFR/IFR conditions will persist through Saturday morning as 

showers continue over the region.



KSEA...VFR this afternoon with high clouds already over the area

ahead of a front moving onshore. S/SE winds this afternoon around

8 to 12 knots will transition to more of a SW component this

evening as rain showers moves towards the terminal. Rain showers

will start to impact the terminal around 04z but VFR conditions

should continue. Winds will then turn N/NE around 08z and 

increase to around 10 to 12 kts by Saturday morning. Ceilings 

will gradually lower into Saturday morning, with MVFR conditions 

likely around after 12z 



Maz



&&



.MARINE...A frontal system will continue to move through the

coastal waters into afternoon with increased southerly winds over

the outer coastal waters. A small craft advisory for the outer 

waters will continue through the evening, with southerly winds 

will subside into the overnight hours. Heading into the weekend, 

guidance suggests several westerly pushes through the Strait of 

Juan De Fuca, likely yielding additional headlines. 



Another system looks to track into the area waters through the

first half of next week. 



Combined seas this afternoon around 3 to 5 feet will gradually

increase to around 6 to 8 feet by Sunday. Confidence is increasing

that seas look to hover around 9 to 11 feet Monday night into

tuesday, with the higher heights mostly in the outer water zones.



Maz



&&



.HYDROLOGY...No river flooding is expected over the next 7 days.





&&



.SEW WATCHES/WARNINGS/ADVISORIES...

WA...None.

PZ...Small Craft Advisory until 7 PM PDT this evening for Coastal 

     Waters From Cape Flattery To James Island 10 To 60 Nm-

     Coastal Waters From James Island To Point Grenville 10 To 

     60 Nm-Coastal Waters From Point Grenville To Cape 

     Shoalwater 10 To 60 Nm.



&&



$$