Marine Weather and Tide Forecast for Winthrop, WA

SYNOPSIS
A strong cold front will bring gusty westerly winds on Sunday.
Persistent snow showers will bring several days of winter travel conditions over the mountains next week. We are monitoring Wednesday into Thursday for lowland snow across northern Washington and North Idaho. Elevated winds expected through the week.

DISCUSSION

WINDY CONDITIONS SUNDAY

WINTER TRAVEL OVER MOUNTAIN PASSES NEXT WEEK

Tonight-Saturday: Moisture spilling over the eastern flank of an upper-level ridge will bring increasing clouds through this evening. Precipitation chances will be on the rise overnight as the moisture is squeezed out along a weak frontal boundary.
Rainfall amounts will be extremely light in the lee of the Cascades and around a tenth in the lowlands of North Idaho and Eastern WA. The air mass will be mild with mainly rain or wet, non accumulating snow on the mountain passes.

There will be a noticeable increase in winds across the Inland NW.
We are already seeing gusts 25-35 mph along the Cascade East Slopes, Waterville Plateau, and foothills of the Blue Mountains this afternoon. Pressure gradients will be increasing further heading into Saturday as a 990mb low tracks through north- central BC-Saskatchewan. The track of this low is far enough to the north to keep concerns for stronger winds at a minimum, though widespread gusts 25-35 mph will be common. Local gusts of 35-45 mph will impact the higher peaks of the Cascades, Blue Mountains, and at times, mix to the benches around East Wenatchee, Entiat, and Waterville Plateau.

Sunday: The upper-level ridge will retrograde with a stronger and deeper shortwave spinning through south-central BC-Saskatchwen.
This will result in a deeper low pressure system tracking through western Canada and continue to ramp up pressure gradients and winds for the INW. Nearly all models support wind gusts of 30-40 mph (70-80% chance via the NBM) and 40-70% chance for wind gusts 40-50 mph. The greatest anomalies are showing up across the northern two-thirds of WA and far North Idaho. This is does equate to where the strongest winds will be but more indicative that these typically "less windy" areas will be experiencing gusts of at least 30 mph. Wind direction will be from the west/southwest in the morning and early afternoon with a subtle shift to the west/northwest in the late afternoon and evening. Impacts from the winds will be choppy lakes, challenging cross winds, and potential for isolated tree damage and power outages. Mountain showers will accompany the windy system. Snow levels will start off 5000-6000 feet and lower in the Cascades by Sunday evening to 2000 feet or lower with snow and winter travel conditions returning to the Cascade passes.

Monday-Friday: There is good agreement for a strong Polar Jet to reside over the PacNW with wavering north and south from southern BC/Alberta to WA/OR border. The placement of this jet suggest an active storm track for the Northwest. What we do know, there will be a prolonged period of snow showers bombarding the Cascade Crest with 3-4 day snow amounts measured in feet. Current NBM has a 60% chance 3 feet or more of snow over the 72 hour period ending Thursday night. The Cascades will intercept a bulk of the moisture but the strong west to northwest flow and orographics will allow for appreciable amounts over the multi-day period in the Central Panhandle Mountains and portions of the Selkirks of North Idaho and far NE WA. Lookout Pass has a 70% chance for at least 1 foot of snow and 25% chance for 2 feet.

For much of the period, the strong west to northwest flow will result in significant precipitation shadowing across much of Central and Eastern WA. The exception will be when shortwaves ripple through the jet and can result in cyclogenesis or development of surface lows. Models have been latching on to such an event for a few days during the March 11-12th or Wednesday-Thursday period. These systems have the potential to disrupt the strong shadowing and bring light to moderate precipitation to the lowlands and Kettle Mountains. This could be impactful bringing the potential for lowland snow. The details are far from certain this far out given several outcomes where the exact low will track and where the lowland rain/snow will set up out, but something we are closely monitoring.

The synoptic setup will undoubtedly result in multiple days of breezy to windy conditions given the placement of the jet over the region. Oscillations of the jet north and south will help determine which will be the windiest periods. It is common to for the windiest periods to come during times of cold advection.
When on the warmer side of the jet, we will closely monitoring for mountain waves and infrequent strong gusts. These are much more challenging to forecast in the lowlands. The aforementioned surface lows spinning up will also enhance winds for the lowlands and deliver wind shifts. All that being said, there is moderate uncertainty in precise day to day details but be prepared for elevated/impactful winds next week. /sb

AVIATION
18Z TAFS: A bank of MVFR stratus that developed with upslope flow between Pullman and Spokane will become scattered 18-20z and evolve into the strato-cumulus deck with cigs 4-5k ft AGL.
This comes with moderate confidence given model trends and recent satellite trends. Confidence is only moderate given HRRR probabilities of 20-30% for MVFR conditions to persist longer.
In Central WA around MWH-EAT, mainly increasing high clouds through 20z. A frontal boundary will pass through the region this afternoon and evening with continuing moistening and light rain developing. Rain chances in the lee of the Cascades will be near 30% or lower. Higher chances for the rising terrain of E WA and N ID. Steady south/southwest winds with the front will result in lowering cigs with 90% chance to lower MVFR and 30-40% chance for IFR conditions. Widespread mtn obscrns expected over the Cascades and Idaho Panhandle 05-18z Saturday.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Low probabilities (20-30%) for MVFR stratus to continue for GEG- SFF- COE through the afternoon. Main uncertainty is how fast bkn-ovc cigs will develop LWS-PUW-GEG-SFF-COE this afternoon.
Very low chances for light rain to develop ahead of the main frontal boundary but wouldn't rule out sprinkles. Moderate to high confidence for light precipitation and MVFR conditions at KGEG, KSFF, KCOE, KPUW, and KLWS after 04Z. Moderate to high confidence in IFR conditions developing after 08-09Z over KGEG/KPUW. Fog threat is low given steady winds in place and MOS showing vis above 5SM. /sb

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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 43 59 43 56 30 43 / 50 10 0 20 20 20 Coeur d'Alene 41 54 43 54 30 43 / 70 40 10 60 40 50 Pullman 41 55 42 54 31 41 / 60 30 10 50 50 60 Lewiston 45 63 44 62 37 48 / 50 20 0 20 40 30 Colville 39 57 40 57 28 44 / 50 10 0 20 10 20 Sandpoint 39 50 42 50 30 41 / 80 60 30 80 40 60 Kellogg 38 50 43 49 32 38 / 90 80 40 90 70 80 Moses Lake 44 65 44 62 31 49 / 40 10 0 0 0 0 Wenatchee 45 63 45 56 33 45 / 30 10 10 30 10 20 Omak 41 60 41 60 29 46 / 40 0 10 10 10 10

OTX WATCHES/WARNINGS/ADVISORIES
WA...None.
ID...None.