textproduct: Spokane

KEY MESSAGES

- Hydrology concerns: Rain-on-snow in the Idaho Panhandle will bring rises on smaller creeks and streams through Saturday.

- Next system: Unsettled weather returns Tuesday and Wednesday, bringing mountain snow and potential wind impacts and travel impacts over mountain passes.

UPDATE

High temperatures were increased today over Central Washington based on some of the latest MOS temperature guidance. While 850mb temperatures will be cooling today behind the cold front, full sunshine and strong mixing will allow high temperatures to top out in the mid 50s to upper 50s for the East Slopes of the Cascade valleys, and low to mid 60s from the Okanogan Valley down to the Moses Lake area. JW

SYNOPSIS

Saturday will mark the start of a cooling and drying trend as a cold front pushes the current plume of moisture southeastward out of the region. This will bring a dry and seasonably cool weekend. Unsettled weather is forecast to return Tuesday and Wednesday as the next low pressure system brings mountain snow, lowland rain, and breezy winds.

DISCUSSION

Saturday through Monday: A cold front will slowly move southeast through the Inland Northwest Saturday morning. As of 12AM, the front is near-stationary with north-central Washington, the Columbia Basin, and northeast Washington in a post frontal environment with dew points in the low 20s to 30s. North Idaho down into the Spokane area and southeast Washington remain in the pre-frontal environment with dew points still in the 40s.

A shortwave will move onshore early Saturday morning and provide the necessary forcing to accelerate the front southeastward. This will force a band of rain from the central Idaho Panhandle into southeastern Washington. Precipitation totals will range between 0.10 to 0.20 inches across southeast Washington, the southern Panhandle, and the central Panhandle lowlands. The heaviest totals will be across the Shoshone county mountains with totals between 0.50 to 1 inches. The additional rainfall on a primed snowpack will bring rises on rivers, but flooding is currently not expected.

Much drier air will advect into the region behind the front, with PWAT values across southeast Washington and the central Idaho Panhandle dropping from over 0.70 inches early Saturday morning to under 0.30 inches by the afternoon. Not only will this bring an end to the persistent precipitation that has occurred over the Cascades and the Idaho Panhandle this past week, but it will also bring much cooler temperatures to the region this weekend. A period of dry and cooler weather through Monday will reduce mountain snowmelt rates, allowing local rivers to begin receding.

Tuesday through Friday: Active weather returns mid-week as a surface low moves up the southern edge of broader troughing in the Gulf of Alaska on Tuesday. Models are in generally good agreement with a warm front lifting north across the Inland Northwest Tuesday, bringing a return in precipitation, and then the associated cold front moving into the Inland Northwest through Tuesday night into Wednesday. There remains uncertainty in the strength and progression of the surface low Tuesday night and then another shortwave moving in on Wednesday. A weaker, more northerly track across British Columbia would favor subtle upper-level ridging and a tighter surface pressure gradient, promoting a stronger wind threat Tuesday night into Wednesday. Conversely, a stronger and more southerly primary low would diminish the ridge influence and surface pressure gradient while accelerating the arrival of the subsequent system. This lessens the wind threat for Tuesday night into Wednesday, but increases it for Wednesday evening. Currently, the NBM gives the Inland Northwest a 50-80% chance of wind gusts greater than 40 mph on Wednesday and a 20-40% chance for gusts greater than 45 mph. Snow levels would be low enough to support snow the passes with a 50% chance for 6 inches at Stevens Pass between Tuesday night through Thursday night. This period will continue to be monitored. /vmt

AVIATION

18Z TAFS: Drier air will continue to move in today behind a cold front. As of 17z skies had cleared over most of Central and Northeast Washington and the North Idaho Panhandle except for flat cumulus developing mainly over the mountains. The drier air will push into SE Washington and the south ID Panhandle through the early afternoon. VFR conditions are forecast for all TAF sites through 18z Sunday. Winds will be breezy this afternoon regionwide out of the west and southwest with gusts of 15-25 kts.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in VFR conditions for all TAF sites through 18z Sunday. Although there is a 20% chance of MVFR CIGS at KPUW/KCOE through 20z as daytime heating and residual boundary layer moisture produced a lower stratocumulus deck before cloud heights rise. 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 55 29 50 32 55 40 / 30 0 0 0 0 20 Coeur d'Alene 55 29 51 30 55 38 / 50 0 0 0 0 20 Pullman 52 30 50 34 54 41 / 90 0 0 0 0 20 Lewiston 59 34 56 36 58 45 / 80 0 0 0 0 10 Colville 58 28 52 30 56 36 / 20 0 0 0 0 10 Sandpoint 53 30 48 30 52 36 / 50 0 0 0 0 20 Kellogg 50 31 48 33 54 39 / 90 0 0 0 0 30 Moses Lake 62 30 56 33 58 42 / 10 0 0 0 0 10 Wenatchee 59 32 53 35 56 41 / 0 0 0 0 0 10 Omak 64 31 55 32 57 40 / 0 0 0 0 0 10

OTX WATCHES/WARNINGS/ADVISORIES

WA...None. ID...None.