Marine Weather and Tide Forecast for Heron, MT

SYNOPSIS
The Inland Northwest will be under an upper level ridge through Friday with dry weather. A cold front will bring rain and mountain snow this weekend into early next week.

DISCUSSION
Today and Tonight: The strong upper ridge that was over the region Thursday will be pushing east of the region today as an upper trough off the coast begins to push east. This will result in a southwesterly flow, with still plenty of warm air over the region. However most of this will stay up in the mountains today as fog and stratus continue to expand across the lower elevations. All elevations below 3500 feet are expected to be stuck under a low cloud deck as the stratus layer deepens over the region as the boundary layer flow turns light out of the southwest (upslope direction for NE Washington into the ID Panhandle). The few exceptions are the Methow Valley, and locally the Central Panhandle Mountains and Kamiah area. There have been several reports of visibility near a quarter mile or less this morning around the Upper Columbia Basin, Spokane area, Palouse, and Alpowa Summit area where a Dense Fog Advisory is in place through noon. There have been local reports of dense fog in other areas as well, and will continue to be monitored through the night. The low stratus will limit temperatures rises today, with most valleys topping out in the upper 30s to low 40s. The stratus and areas of fog will continue into Friday Night as well.

Saturday through Monday: Changes arrive as a moist precipitable water plume takes aim at the region from southwest to northeast this weekend. This will bring rain and mountain snow, with snow levels initially starting off high; ranging from 4500 to 6000 feet through Saturday Night. Snow levels then fall to around 4000 feet in the Cascades on Sunday, and then as low as 2500-3000 feet by Monday morning. Some of the latest deterministic model runs are showing a surface low strengthening as another wave moves in Sunday Night, tracking from Central Oregon into the Palouse with a deformation band of steady precipitation north of the low track around the Palouse/Spokane area into the Central Panhandle Mountains. If this pans out higher snow totals than forecast would occur with as much as 5-10 inches in the Central Panhandle mountains, and possibly wet snow mixing in down to the valley floors as well. Currently the NBM shows a 75% chance of 2" or more of snow at Lookout Pass, with a 20% chance of 6" or more. Similar probabilities are shown for Stevens Pass. Breezy winds are also expected with this passing system on the Palouse.

Tuesday through Thursday: A short wave ridge moves over the area Tuesday and Wednesday for drier conditions and temperatures slightly above normal. On Thursday the next system approaches but the NBM is only carrying a 20-30% chance of precipitation in the form of mainly valley rain and mountain snow. JW

AVIATION
18Z TAFS: Light winds and IFR-LIFR fog and stratus will largely continue through the next 24 hours. Models continue to be overly optimistic of improving conditions. There may be slight improvements in visibility into the afternoon and evening hours Friday but confidence is low.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Low confidence for improvements in the next 24 hours.

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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 38 33 45 41 47 34 / 0 0 20 70 70 70 Coeur d'Alene 41 33 46 41 46 35 / 0 0 20 80 70 80 Pullman 39 35 53 43 47 36 / 0 0 10 70 80 80 Lewiston 48 37 56 45 52 39 / 0 0 0 50 70 80 Colville 40 31 41 37 45 32 / 0 0 40 70 60 60 Sandpoint 40 33 41 39 44 35 / 0 0 30 90 80 80 Kellogg 50 36 49 43 45 36 / 0 0 10 80 90 90 Moses Lake 43 34 44 38 47 33 / 0 0 30 40 60 40 Wenatchee 42 36 42 38 46 34 / 0 0 40 50 60 40 Omak 41 35 40 37 45 34 / 0 0 30 30 40 40

OTX WATCHES/WARNINGS/ADVISORIES
WA...Dense Fog Advisory until noon PST today for Lower Garfield and Asotin Counties-Spokane Area-Upper Columbia Basin- Washington Palouse.
ID...Dense Fog Advisory until noon PST today for Idaho Palouse.