Marine Weather and Tide Forecast for Winthrop, WA

SYNOPSIS
The Inland Northwest remains dry through early Friday. Patchy valley fog and freezing temperatures could result in slick roads each morning. A more active weather pattern returns this weekend, with mountain snow and a mix of rain and snow in the valleys. Falling snow levels will bring the potential for light lowland snow accumulations into early next week.

DISCUSSION
Tonight and Friday: The broad flat ridge in place across the Inland Northwest and to the east over the Northern Rockies continues to bring mid and high level clouds over the region.
Morning patchy fog and low stratus that developed has eroded away. Looking at the 18z OTX sounding comparing today versus yesterday, the strength of the upper level (above 500mb) winds are weaker and the depth of the inversion is deeper. The high- res ensemble guidance (HRRR, EC HRRR) is leaning to higher confidence and probability of seeing isolated patchy fog again Friday morning for some locations. Freezing fog on surfaces may again result in slick conditions for early morning travel.

Saturday through Tuesday: The upper level pattern will begin to change over the weekend bringing a return of precipitation to the Northwest. As temperatures slowly cool from aloft, the precip type and snow levels will play a role into the type of precipitation (rain or snow) that is observed at which elevation. Saturday will see a steady lowering of snow levels region-wide (which will continue into early next week), but more noticeable for the mountains and mountain passes. Precipitation in the form of rain for the lower elevations and valleys will begin as light intensities Saturday morning with snow in the mountains continuing through the weekend.
For the Cascades, Saturday only brings a 25-30% chance of seeing more than 2 inches of snow at the crest locations while the Idaho mountain passes have a 50-60% chance of stacking up more than 2 inches. At this point, storm total snowfall for the mountains and mountain passes through Sunday evening looks to bring 4-8 inches for those higher elevations.

The suite of ensembles begin to diverge on the solution as we move into early next week. This will bring additional uncertainty in timing of the weather system and amount of precipitation (rain or snow) for specific locations. The suite of models (cluster of models) showing a wetter and colder solution is in the minority with only 12% of all solutions while a larger set (29%) show an indication of additional low-land precipitation but do not support the colder temperatures. Thus, the uncertainty continues.

Wednesday and Thursday: The far extended forecast brings the continuing uncertainty of low-land snow amounts, however the timing and amounts continue to change. Something to be aware of as we near closer to midweek next week. /Dewey

AVIATION
00Z TAFS: Confidence in a recurring morning fog event with visibilities of 1/4 mile to 1 mile at area airfields is around 40% given the increase in coverage for probability of LIFR as shown by the EC HRRR. Have included a few hours of this LIFR vis from 13-16z for GEG-SFF-COE-MWH. Elsewhere, VFR or MVFR conditions should prevail with incoming increasing cloud cover ahead of the weekend precipitation which should begin impacting airfields on Saturday.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for primarily VFR conditions after 18z Friday.
Confidence is moderate to high to see a return of patchy fog and intermittent IFR/LIFR conditions for the terminals closer to water bodies with development of shallow fog, between 12-17z Friday morning. /Dewey

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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 30 42 35 44 33 41 / 0 10 60 40 50 30 Coeur d'Alene 30 43 35 43 33 41 / 0 20 70 70 50 50 Pullman 31 45 37 45 36 43 / 0 10 60 70 80 60 Lewiston 33 49 40 49 39 47 / 0 0 30 40 70 40 Colville 27 40 32 42 28 41 / 0 20 70 60 20 20 Sandpoint 30 40 34 40 31 39 / 0 30 90 90 50 50 Kellogg 32 43 37 41 35 40 / 0 20 80 90 80 70 Moses Lake 28 42 32 45 31 46 / 0 10 20 20 20 10 Wenatchee 32 41 34 44 32 43 / 0 10 30 20 20 10 Omak 31 41 34 44 28 43 / 0 10 30 20 10 10

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