Thursday started out mild, with temperatures in the mid-30s and lower 40s Fahrenheit at most NWAC weather stations at approximately 5000 ft. However, thanks to light ridgeline winds, very light low-level E flow, and mostly clear skies, some lower-elevation valleys and mountain gaps are chillier. Most notably, the Washington Pass lower station experiences 22F while the Upper Station hovers around the freezing mark. The inversions are less pronounced in the central Cascade Passes, but Snoqualmie and Stevens Pass both have temperatures near or slightly below freezing. These inversions should mix out by 9 or 10 AM across the region.
Thursday will bring plenty of sunshine as our region sits between the northern branch of the jet stream (well to our north in Canada) and a closed low off the northern California Coast. Thursday features light, generally SE ridgeline winds, which continue overnight. Some mid and high-level moisture associated with the closed low begins to work northward Thursday night through Friday. These clouds will be experienced more in the southern portions of the forecast region. Clouds are likely to thicken in the Mt Hood area Friday afternoon with a chance of rain showers (and possibly a weak thunderstorm). This precipitation may or may not arrive before the end of the day on Friday.
Expect freezing levels to rise to 7500-9500 ft by Thursday afternoon and remain in this range through Friday. 5000 ft temperatures are likely to be warmer in the central and southern Cascades on Thursday afternoon, then cool slightly on Friday with more influence from the closed low. The northern Cascades should continue to warm through Friday.
Weather Forecast
Olympics
West North
West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
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Thursday
Mostly sunny.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny. Light ridgeline and E wind at the Pass.
Thursday
Night
Mostly clear with increasing high clouds overnight. Light ridgeline and E wind at the Pass.
Thursday
Mostly sunny. Light ridgeline and E wind at the Pass.
Thursday
Night
Mostly clear with increasing high clouds overnight. Light ridgeline and E wind at the Pass.
Thursday
Mostly sunny. Temperature inversions gradually weaken through mid-morning.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny. Temperature inversions gradually weaken through mid-morning.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny. Temperature inversions gradually weaken through mid-morning.
Thursday
Night
Mostly clear with increasing high clouds overnight.
Thursday
Mostly sunny.
Thursday
Night
Mostly clear with increasing high clouds overnight.
The NWAC program is administered by the USDA-Forest Service and operates from the National Weather Service Forecast Office in Seattle. NWAC services are made possible by important collaboration and support from a wide variety of federal, state and private cooperators.
The 5000’ temperature forecast does not imply a trend over the 12 hr period and only represents the max and min temperatures within a 12 hr period in the zone. The 6-hr snow level forecast, the forecast discussion, and weather forecast sections may add detail regarding temperature trends.
The snow level forecast represents the general snow level over a 6 hr time period. Freezing levels are forecast when precipitation is not expected.
*Easterly or offshore flow is highlighted with an asterisk when we expect relatively cool east winds in the major Cascade Passes. Easterly flow will often lead to temperature inversions and is a key variable for forecasting precipitation type in the Cascade Passes. Strong easterly flow events can affect terrain on a more regional scale.
Ridgeline winds are the average wind speed and direction over a 6 hr time period.
The wind forecast represents an elevation range instead of a single elevation slice. The elevation range overlaps with the near and above treeline elevation bands in the avalanche forecast and differs per zone.
Wind direction indicates the direction the wind originates or comes from on the 16-point compass rose.
Water Equivalent (WE) is the liquid water equivalent of all precipitation types; rain, snow, ice pellets, etc., forecast to the hundredth of an inch at specific locations. To use WE as a proxy for snowfall amounts, start with a snow to water ratio of 10:1 (10 inches of snow = 1 inch WE). Temperatures at or near freezing will generally have a lower ratio (heavy wet snow) and very cold temperatures can have a much higher ratio (dry fluffy snow).