Marine Weather and Tide Forecast for Leavenworth, WA

SYNOPSIS
Unsettled weather conditions continue throughout the next seven days with a series of systems bringing periods of rain, high mountain snow, and gusty winds.

DISCUSSION
Models continue to be in good agreement of a strong pacific zonal jet stream stretching across the entire Pacific Ocean through the upcoming week bringing a series of weather systems across the region. Models show three distinct weather systems to pass through during the week. As each weather system passes the jet stream over our region will take on a southwest-northeast orientation resulting in a mild weather pattern with above normal temperatures through the week. This flow pattern will also tap into subtropical moisture at times leading to periods of moderate rain in the Cascades.

Sunday: The first system arrives this morning with swift mid level westerly flow as a cold front crosses the Cascades producing a pronounced rain shadow across Central Washington.
Then as the front encounters the higher terrain across Eastern Washington and North Idaho precipitation will redevelop with the highest POP's over the ID Panhandle. Gusty winds will occur along and behind the cold front with gusts of 20-30 MPH across the region, and even stronger in the mountains with gusts of 35-55 MPH. As snow levels drop to 4500 feet Sunday morning in the Cascades rain will change to snow over Washington Pass with 2 to 3 inches forecast. Other mountain passes across the region will see little to no snow accumuation due to the high snow levels.

Monday through Tuesday: The next surge of precipitation arrives by Monday evening and this one the 850mb winds back to the south and southeast leading to less downslope flow off the Cascades with widespread light precipitation developing. Snow levels Monday night climb to 5000 feet near the Canadian border and 7000 feet over SE WA into the Central Panhandle Mountains. Then heading into Tuesday the lower level flow increases out of the southwest as another surge of precipitation enters, with the moisture plume aimed at the Cascades, and skirting northern Washington into the Idaho Panhandle. Snow level continue to climb reaching 7000-8000 feet regionwide as a warm front passes.

Wednesday and Thursday: A mild and dry period is in store following the Tuesday warm front as the cold front stalls off the coast. Areas of fog and stratus are expected but overall the mild air mass will mean well above normal temperatures especially in the mountains.

Friday: The third system of the week pushes in leading to another round of precipitation especially for the Cascades. Snow levels remain high, around 6000-7000 feet.

As far as impacts go in this pattern, we continue to monitor the burn scars in the Cascades. With the passage of each system the NBM is carrying a 30-50% chance of 24 hour rain amounts exceeding an inch near the Cascade crest. The good news is that there will be breaks in the precipitation which should help keep river levels in check. The one exception to monitor is the Stehekin River which has a 22 percent chance of reaching flood stage by Thursday. High elevation snow melt and periods of rain could result in localized debris flows or rockslides near burn scars. JW

AVIATION
06Z TAFS: A cold front will quickly track across Central and Eastern Washington into North Idaho tonight into Sunday morning.
Timing of front reaches the Cascades around 06-08z and the ID Panhandle between 15-18z. Strong westerly flow will result in the bulk of precipitation falling in the Cascades and ID Panhandle, with brief rain also possible at KEAT/KGEG/KSFF/KPUW/KLWS. Winds are expected to increase and shift out of the west and southwest along and behind the front, so this is reflected in the TAFs after 09-12Z. Rain will moisten the boundary layer Sunday morning, with REFS showing a 30-40 percent chance of MVFR conditions for KGEG/KSFF/KCOE/KPUW from 14z-17z.

FORECAST CONFIDENCE AND/OR ALTERNATE: High confidence in VFR conditions through the TAF period, except 14z-17z at KGEG/KSFF/KCOE/KPUW where REFS data shows a 30-40 percent chance of MVFR conditions. JW

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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 45 54 36 49 40 54 / 10 40 0 40 90 30 Coeur d'Alene 44 53 36 49 41 53 / 10 70 0 50 90 40 Pullman 43 51 37 50 40 55 / 0 50 0 20 90 20 Lewiston 44 55 43 54 45 60 / 0 30 0 20 70 10 Colville 35 55 27 48 33 51 / 50 10 0 20 70 40 Sandpoint 39 51 32 47 36 49 / 10 80 0 40 90 50 Kellogg 42 51 36 50 41 52 / 0 80 0 50 100 50 Moses Lake 38 57 32 52 34 54 / 0 0 0 20 70 20 Wenatchee 44 54 37 51 39 49 / 40 10 10 20 70 30 Omak 40 55 32 49 39 51 / 10 0 0 10 70 40

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