Marine Weather and Tide Forecast for Heron, MT

SYNOPSIS
Unsettled weather conditions continue into the weekend and early next week with a series of systems bringing periods of rain, mountain snow, and gusty winds.

DISCUSSION
Saturday through Thursday: A parade of wet storm systems with ties to subtropical moisture will take aim at the Pac NW through the period. The Olympics, West Slopes of the North Cascades, and southwest British Columbia are favored to receive a brunt of the moderate to heavy precipitation as each axis of moisture comes in with a southwest to northeast orientation.
Periods of light to moderate precipitation will at times extend into the East Slopes of the Cascades and North Idaho with generally light activity over Central and Eastern WA. Between each round of precipitation, there will be a short-lived breaks allowing for some drying. Ensembles are in good agreement with the general, active weather pattern across the Eastern Pacific and into the Northwest with subtle differences coming with exactly how much of the moderate to heavy rain will extend over the immediate crest and potentially fall over the Cascade burn scars (Little Giant, Sisi, Pioneer) creating some concern for debris flows. The pattern is not particularly conducive for heavy rain directly over these scars but each slug of moisture will be capable of 0.20-0.50" every 24 hours. These soils are becoming saturated following the 0.25-0.50 inches of rain that fell over these scars over the last 12-15 hours. The main uncertainty comes with the intensity of these rains.

Saturday will bring the first short-lived break in the wet weather.
Satellite reveals a deeper trough digging into the Eastern Pacific which will allow heights to rise over the Inland NW and bend the next plume of subtropical moisture south to north off the WA Coast. Breezy south to southeasterly winds will develop over the Inland NW with the air mass warming 3 to 6 Celsius at 850 mb. Gusty winds are expected over the Blue Mountains, Palouse, Camas Prairie, and L-C Valley where there is a 50-70% chance for gusts 20-25 mph. The approaching cold front will move into the Cascades overnight and across the Inland NW Sunday morning. In addition to bands of moderate rain, gusty westerly winds will be likely. I expect a period of winds to surface with the cold front passage overnight and remain gusty into Sunday morning and early afternoon as the boundary layer becomes well mixed. There is 60-70% chance for wind gusts >30 mph and 10-30% chance for wind gusts >40 mph. Given the strong cold air advection (850mb temperatures cooling 6-7 Celsius), gusts of at least 30 mph seem like a sure bet but it may be harder to mix down the 40kt winds overnight from 2000 feet above ground layer.
I do have some concern that the models may be undergoing the mixing overnight for some of the higher benches on the Waterville Plateau and across the upper rim of the Columbia Basin and Palouse. Forecast wind gusts have been increased given these concerns. These stronger winds to subside closer to 30kts following the cold front passage leading to gusts closer to 30 mph through Sunday morning.

Travelers heading over the Cascade passes will mainly encounter rain for Saturday and Saturday evening. Following the cold front passage Saturday night, rain showers will change to snow showers for Stevens and Washington Pass. While Stevens Pass is not expected to receive impactful snow, will need to closely monitor where the Puget Sound Convergence Zone sets up which could lead to local accumulations of 1-2 inches. NBM is forecasting 3-4 inches for Washington Pass. Otherwise, precipitation with the front Saturday night into Sunday morning will deliver another 0.25-0.50" across the upper river valleys of the East Slopes and aforementioned burn scars and upwards of 0.70-1.00" to the immediate crest. Rainfall amounts in Idaho and eastern WA will vary from a few hundreths to quarter of an inch along the Montana border with little to no rainfall in the Cascade rain shadow. The highest intensity rain for the Cascades will come right along the cold front overnight.

Monday-Tuesday: The pattern is a bit messy with weaker waves coming through the region but with an usually moist air mass remaining overhead. This will continue to bring on and off preciptiation, generally light and lower impact on Monday but rain intensities will increase on Tuesday as more developed warm front develops. This will bring the next chance for another 0.10 to 0.50 to the Cascades and tenth to quarter of an inch over Eastern WA and North Idaho.

Wednesday-Saturday: There is moderate confidence for another ridge to blossom over the region Wednesday into Friday delivering the next period of dry conditions. Given several days if on and off rain, its almost a guarantee there will be areas of fog and low stratus. Uncertainty increases late Friday into Saturday whether the next front pushes inland or remains off the coast with high pressure in control. By this time, confidence is lower that the front will have ties to the richer moisture and is expected to weaken with lighter rainfall amounts. /sb

AVIATION
06Z TAFS: A weakening frontal boundary will stall across southeastern WA and North Idaho with light -shra btwn KPUW-KGEG.
Behind the front, winds have shifted to the south with MVFR stratus developing KGEG-KSFF-KCOE. South of the front, KPUW and KLWS will maintain southeast winds with low probabilities for conditions to deteriorate and remain VFR. The southeast winds will increase Saturday morning with gusts around 20kts for KPUW.
KMWH and KEAT will decouple with a mix of patchy fog or stratus.
Confidence remains low for KMWH to become IFR or lower due to a heavier presence of high clouds over the region. Confidence remains moderate for MVFR stratus to break up around KGEG-KCOE Saturday midday as the southeast winds increase and remain breezy for KPUW and at times, KLWS.

FORECAST CONFIDENCE AND/OR ALTERNATE: An alternate scenario is for KGEG to experience cigs as low as 800 feet with visibility 4-6SM. The decaying band of -shra may linger longer around KPUW than expected. If KMWH clears out aloft, would not rule out 1/2SM FG with temp-dewpoint spreads only 4F away and some clearing noted over Western WA tracking into Central WA overnight.

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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 52 40 60 44 54 34 / 10 30 0 10 10 0 Coeur d'Alene 50 40 60 43 52 34 / 10 20 0 20 40 0 Pullman 49 39 59 41 51 34 / 10 10 0 0 20 0 Lewiston 54 41 62 43 56 39 / 10 10 0 0 10 10 Colville 48 32 53 34 53 25 / 10 40 0 40 10 0 Sandpoint 48 38 55 38 50 31 / 10 30 0 30 50 0 Kellogg 50 39 61 42 50 34 / 0 10 0 10 80 0 Moses Lake 53 35 59 37 57 29 / 20 40 0 0 0 0 Wenatchee 50 40 54 43 54 34 / 30 40 0 40 0 0 Omak 49 36 53 39 54 30 / 30 40 0 10 10 0

OTX WATCHES/WARNINGS/ADVISORIES
WA...Dense Fog Advisory until 10 AM PST this morning for Spokane Area.
ID...Dense Fog Advisory until 10 AM PST this morning for Coeur d'Alene Area.