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PZZ135 Puget Sound And Hood Canal- 251 Am Pst Sat Dec 9 2023
.small craft advisory in effect from 8 am pst this morning through this evening...
Today..S wind 15 to 25 kt. Wind waves 2 to 4 ft. A chance of rain in the morning then rain in the afternoon.
Tonight..S wind 15 to 25 kt easing to 10 to 20 kt after midnight. Wind waves 2 to 4 ft subsiding to 1 to 3 ft. Rain.
Sun..S wind 5 to 15 kt becoming to 10 kt in the afternoon. Wind waves 2 ft or less. Rain.
Sun night..SW wind to 10 kt becoming W after midnight. Wind waves 1 ft or less.
Mon..NW wind to 10 kt. Wind waves 1 ft or less.
Mon night..N wind to 10 kt. Wind waves 1 ft or less.
Tue..NE wind to 10 kt becoming light. Wind waves 1 ft or less.
Wed..S wind to 10 kt. Wind waves 1 ft or less.

PZZ100 251 Am Pst Sat Dec 9 2023
Synopsis for the northern and central washington coastal and inland waters..A sub 990 mb surface low will bring a front across the area waters today. Gales and small craft strength winds are expected for the majority of the area waters today. Winds will ease overnight into Sunday. The flow weakens and turns offshore early next week with high pressure moving back into the coastal waters. Another front looks to move across the waters on Wednesday.

FXUS66 KOTX 091430 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 450 AM PST Sat Dec 9 2023

SYNOPSIS
Widespread snow arrives today with potential for moderate snow amounts going into Sunday. Travel across the mountain passes could be challenging. Next week looks seasonal and drier than normal as a ridge of high pressure settles over the region.

DISCUSSION

...WIDESPREAD SNOW SATURDAY AFTERNOON THROUGH SUNDAY. HEAVY SNOW OVER THE CASCADE PASSES...

Today through Sunday night: In the next 24 hours, a plume of subtropical moisture associated with a weak atmospheric river will over top a dome of cold air currently enveloping the Inland Northwest. This will bring our next bout of winter weather and smiles to those who are tired of the rain and ready for some snow. Unfortunately, this bout of winter weather does not come with pure snow and a transition from snow to rain is a likely scenario at some point during the event. This is largely due to the subtropical origins of this moisture plume and the nature of the air mass to warm in efforts to carry the volume of water vapor that is set to arrive.
How quickly this transition occurs is the major challenge of this forecast, leads to wide range in snowfall amounts, and presents a decent bust potential for snow amounts at any given location.
Another element that is being considered and adding to uncertainty is the later timing for snow to start across the eastern third of WA and North Idaho. If surface temperatures warm above freezing which carries a 50-80% chance, snow will be falling initially with temperatures of 33-36F. The air mass is dry enough such that wetbulb temperatures support snow as the main p-type but until temps can wetbulb down to 32F, accumulations will be minimal. This also suggest that moisture will readily melt on roadways at the start of the event and then could become quite icy overnight as snow intensities pick up. Avoiding travel late Saturday night into early Sunday morning could be to your advantage. On the other end of the spectrum, it has gotten quite cold tonight with many locations in the twenties. If the high clouds are thick enough through the day, models may be overdoing the warming for today and the cold air could be more stubborn to scrub out. This could lead to snowfall totals on the higher end of the spectrum.

* Onset of snow/snow intensities: Snow will arrive in the Cascades and portions Central WA between 10AM-1PM. Snow will continue to expand eastward through the day reaching the eastern third of WA roughly 5-7PM and North Idaho 6-8PM. By about 1PM, snow intensities will ramp up over the Cascades with 80-100% chance for snowfall rates of 1"/hour and 30-40% chance for rates near 2"/hour. Look for these rates to continue into Saturday evening making travel across the passes very challenging. Snow fall rates for the lowlands in Central WA will pick up around 2-3PM and continue into the early evening. Snowfall rates will be closer to 0.5"/hour. Similar rates will expand into eastern WA with time reaching Spokane 6-8 PM and North Idaho 8-10PM. For the lowlands, expect these snowfall rates to last roughly 4 hours. Rates at Lookout Pass will also approach 1"/hr (70% chance) during this time and continue into early Sunday morning.

* Transition to rain: We continue to see a wide range in possibilities how and when this will play out. As mentioned in previous discussions, deterministic models are hedging toward a slower transition while the ensemble means are hours quicker.
The HRRR for example has the transition at Moses Lake around 6PM, Spokane around midnight, and Coeur D Alene and Sandpoint by 2AM. Deterministic models delay this nearly 3-8 hours.
Consequently, this difference is having huge ramifications on potential snow amounts for this event. Some of the deterministic models suggest snow will remain the dominant p-type throughout the event and only warming after the precip is ending. This is especially true for locations along and north of Hwy 2. GFS is one of these models. When comparing it to nearly 60 other ensemble member solutions, one could argue that this is an outlier but cannot be ruled out completely.

* Potential snowfall amounts: The forecast is still taking close to a middle of the road approach after the latest round of edits and tweaking. General amounts are between 2-4 inches for the Upper Columbia Basin between Grand Coulee and Spokane and into the northern mountain valleys. Thinking the Okanogan Valley will receive the least amount of QPF for this event and amounts on the low side of the advisory or closer to 1-2". For the Cascades, 1-2 feet along the crest and 6-10" for the upper ends of the river valleys. Amounts closer to the Hwy 97 corridor will be closer to the 2-5" range. Northeastern WA and North Idaho will remain snow for much of the event and have the potential for 3-6 inches with the exception of Bonners Ferry where local downsloping effects will reduce amounts. Heavier amounts are expected in the Central Panhandle Mountains and latest forecast continued to support 5-10 inches. Given the higher elevations of the Palouse (Eastern Whitman County into Idaho), snow should hold longer into the event with 4-7" and this goes for Cd'A Area as well. Also coming up with similar amounts along the US95 corridor across the Camas Prairie and Blue Mountains. For the lower Columbia Basin and L-C Valley, amounts range from a trace to 1.5".

* Freezing rain: There remains a moderate threat for a few hours of freezing rain in the lee of the Cascades around Wenatchee, Chelan, Waterville Plateau, and between Ephrata and Grand Coulee.
Potential ice amounts remain below a tenth of an inch and this should have low impacts falling on snow vs bare grounds.

* Confidence levels: By far, my lowest confidence extends from Chelan to Spokane to C'dA and points south. Snowfall amounts for locations like Wenatchee, Chelan, Grand Coulee, Spokane, Cd'A, and Pullman differ by as much as 5 inches when looking at individual ensemble members. Ranges within different suites of models vary from 1 to 6". Moving further north into Northeastern WA and North Idaho including Republic, Chewelah, Sandpoint, and Kellogg, there is higher confidence for at least 2-3" then additional amounts on top of that also range from 1-6" range. So locations like Kellogg and Sandpoint could end up with 7-8" if the stars align.

Precipitation and the plume of subtropical moisture will exit the region from west to east through the day Sunday with mainly lingering mountain showers continuing Sunday night and dry conditions for much of the Basin. /sb

Monday through Saturday: After a very busy period of active weather, the Inland Northwest will be mostly under the influence of an upper level ridge which will keep temperatures above normal and precipitation chances at a minimum.

The overall upper air pattern Monday afternoon includes a shortwave exiting the region toward the southeast as a ridge builds off the PacNW coast in its wake. That shortwave will continue to dig into an impressive trough over the 4-corners area in the southwest US. The deep trough results in an amplifying ridge along the western coastal areas. By midweek, the ridge axis will shift east centered over the Inland Northwest.

Given this upper pattern and abundant low level moisture, we anticipate that fog and stratus will develop under the ridge. This will lead to typical gloomy days Monday and Tuesday in many of the low elevations. The challenge with fog and stratus is always determining if and when areas break out and skies clear. For now, we have hedged toward a cloudy forecast with most regions experiencing some reduction in visibility due to fog.

That changes Wednesday as the ridge shifts inland, flattens, and a weak shortwave moves inland. This will shift the surface winds around from the east bringing drier air and eroding the fog and stratus. The break from the clouds will be short-lived as the shortwave spreads mid and high level clouds out ahead of it. The chance of rain/snow is low with this system outside of the terrain enhanced precipitation. The current forecast has a mix of rain and snow at the low elevations and only minor accumulations of snow at the higher elevations.

That system moves through Thursday night resulting in clearing skies under a building ridge. The ridge once again amplifies between two deep troughs, one over the southern plains and a second cutoff low well off the coast of California. This pattern looks to hold on through Friday and into the weekend with temperatures at or above normal for this time of year. Given the very low sun angle and limited day light, it is difficult to get temperatures to warm substantially without sufficient mixing.

In short, no hazardous weather or significant impacts are expected Monday through next weekend outside of areas of fog Monday and Tuesday followed by light mountain snow Thursday.
/AB



AVIATION
12Z TAFS: In the short term, pockets of freezing fog are developing within the valleys of North Idaho and Northeastern WA.
This has impacted KCOE and KSFF at times and steering flow suggest another bank of low clouds north of Pullman could drift toward Spokane 13-15Z. High clouds spilling into the region have made it nearly impossible to track this activity from satellite so relying on CAMS and surface observations.

The bigger story will be widespread snow developing in Central WA 18-20Z and into the eastern third of the state and North Idaho 00-03Z. Several hours of -SN expected for all terminals with periods of SN. Main challenge of this forecast is a surge of warmer air and when/if p-type transitions to rain. Timing carries very low confidence and could differ 3-5 hours. Brief -fzra possible during this transition within the Cascade valleys, Waterville Plateau, and between Omak and Grand Coulee. Ice accumulations are expected to be minimal and less than a tenth.
The for freezing rain is 40-60% in these areas and did include in KEAT taf. MVFR to IFR conditions expected across the aviation area given the winter weather coming through and warm overrunning precip event. All terminals except Lewiston expected to receive snow accum.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS: Low confidence in snow amounts for terminals along and south of Highway 2 across the Columbia Basin and just over the Idaho border. This is due to high uncertainty with warm surge and when p-type transitions from snow to rain. Otherwise, moderate to high confidence for extended periods of light to moderate precipitation and restrictions. /sb

------------------

Confidence descriptors: Low - Less than a 30 percent chance Moderate - 30 to 70 percent chance High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports, please refer to the Aviation Dashboard on our webpage: https:// www.weather.gov/otx/avndashboard

PRELIMINARY POINT TEMPS/POPS
Spokane 35 30 37 33 39 31 / 20 100 70 30 20 0 Coeur d'Alene 35 30 36 33 39 31 / 10 100 80 50 30 0 Pullman 35 31 38 34 38 32 / 10 100 90 60 50 10 Lewiston 40 37 44 39 44 36 / 0 100 90 50 40 0 Colville 32 28 33 26 38 23 / 50 100 40 20 20 0 Sandpoint 32 29 34 32 35 27 / 10 100 80 50 40 10 Kellogg 33 30 36 36 40 34 / 0 100 100 80 60 20 Moses Lake 37 31 39 31 40 29 / 50 100 30 10 10 0 Wenatchee 33 31 38 33 40 32 / 90 100 40 10 10 0 Omak 34 28 35 32 40 29 / 80 100 20 10 0 0

OTX WATCHES/WARNINGS/ADVISORIES
ID...Winter Weather Advisory from 5 PM this afternoon to 1 PM PST Sunday for Northern Panhandle.

Winter Weather Advisory from 5 PM this afternoon to 10 AM PST Sunday for Coeur d'Alene Area-Idaho Palouse-Lewis and Southern Nez Perce Counties.

Winter Storm Warning from 4 PM this afternoon to 4 AM PST Monday for Central Panhandle Mountains.

WA...Winter Weather Advisory from 5 PM this afternoon to 1 PM PST Sunday for Northeast Mountains.

Winter Weather Advisory from 5 PM this afternoon to 10 AM PST Sunday for Spokane Area-Washington Palouse.

Winter Weather Advisory from noon today to 8 PM PST this evening for Moses Lake Area.

Winter Weather Advisory from noon today to 10 AM PST Sunday for Okanogan Highlands-Okanogan Valley-Upper Columbia Basin- Waterville Plateau-Wenatchee Area-Western Okanogan County.

Winter Storm Warning from 10 AM this morning to 10 AM PST Sunday for Central Chelan County-Western Chelan County.

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Everett
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Sat -- 03:12 AM PST     9.22 feet High Tide
Sat -- 04:09 AM PST     Moonrise
Sat -- 07:46 AM PST     Sunrise
Sat -- 07:52 AM PST     6.58 feet Low Tide
Sat -- 01:22 PM PST     10.73 feet High Tide
Sat -- 02:07 PM PST     Moonset
Sat -- 04:15 PM PST     Sunset
Sat -- 08:41 PM PST     0.23 feet Low Tide
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Everett, Washington, Tide feet

Marysville
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Sat -- 03:21 AM PST     8.94 feet High Tide
Sat -- 04:09 AM PST     Moonrise
Sat -- 07:46 AM PST     Sunrise
Sat -- 08:22 AM PST     5.92 feet Low Tide
Sat -- 01:31 PM PST     10.40 feet High Tide
Sat -- 02:07 PM PST     Moonset
Sat -- 04:15 PM PST     Sunset
Sat -- 09:11 PM PST     0.20 feet Low Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Marysville, Quilceda Creek, Washington, Tide feet

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