Marine Weather and Tide Forecast for Ponderay, ID

SYNOPSIS
A cool and showery weather pattern will continue through at least early next week. In addition, breezy winds are expected at times.

DISCUSSION
Morning update: A quick update has been sent to increase POP's for this morning into the early afternoon based on observations and radar trends. A band of widespread light rain this morning from the Okanogan Valley and Highlands extending southeast into the Spokane Area, Palouse, and LC Valley will continue to slowly move east into the remainder of NE WA/N Idaho Panhandle through the early afternoon. Given the stratiform nature, have increased the chances of precipitation for areas under or soon to be under the band of stratiform rain. JW

Previous Discussion:

Today and tonight: Shower chances and cool weather marks the weather. A mid-level shortwave will moves across the region this morning and shift east this evening into tonight. This relatively weak feature will bring cloudy skies to much of the area and track light showers across eastern WA and north ID this morning. The steadier shower threat start to shift toward the Idaho Panhandle this afternoon, leaving more hit-and-miss shower chances over the eastern third of WA and some decrease in the clouds. The shower risk wanes this evening away from the mountains. The next system will start to move in and the precipitation chances will increase again overnight into Saturday morning over the Cascades and western basin. The best chance of wetting rain will be over the northern mountains and ID Panhandle, though the Spokane/Coeur d'Alene area could come close. High temperature will largely be in the 50s, with 60s over the lee of the Cascades through upper Columbia Basin and L-C Valley and low 70s over the deeper basin. Patchy fog is also in the forecast for tonight into Saturday morning over the eastern valleys and higher Palouse and near bodies of water, given the rain moistening up the boundary layer and declining winds tonight.

Saturday and Sunday: A deeper low pressure system impacts the area with some rain, a risk for t-storms, and developing breezy conditions. A mid-level shortwave tracks into the Oregon and south of the area early Saturday, then a more robust upper low tracks into the WA Cascades and slides east-southeast through the day, before dropping toward southern ID and the Great Basin heading into Sunday. For being only about 48 hours out, there is an uncommon amount of disagreement between the track and timing of this low. The current GFS and Canadian hold it near the Cascades and track in more quickly south into the Great Basin by later Sunday; the ECMWF and NAM track it slower and further east into central WA, before tracking toward southern Idaho by late Sunday. This has implications on how where the higher precipitation amounts lay, especially Saturday.

However the potential for precipitation still remains high. The system carries modest lift the NE quadrant of the upper trough, with strong DIV-Q and 700-500mb omega and PWATs are about 120-150% of normal, with deformation axis over the southeast to eastern CWA Rain chances increase over the Cascades and central WA Saturday morning, expanding eastward and increasing over east WA and ID in the afternoon into evening. The highest PoPs will be over the eastern third of the CWA Saturday night and Sunday, where the moisture will focus along the deformation axis, before the overall risk starts to wane Sunday night.
Instability increase in the afternoon Saturday, bringing with the chance for some embedded t-storms.

Rain amounts over the eastern third of WA and ID over the weekend are currently forecast to between 0.25 to 0.50, with local amounts near 0.75 to 1 inch over the mountains zones. We will have to watch for ponding of water on roads, rock and/or debris flow. An eye will have to be kept on some of the burn scars in the southeastern CWA too. Some cooler air with the system will also mean some higher mountains. There could even be a bit of snow around the passes; non-impactful snow at less than a half inch and even then it is hard for any snow to accumulate effectively on road surfaces this time of year.

Winds increase Saturday night into Sunday. The winds first increase more notably near the downwind of the Cascades and the Blue Mountains Saturday night, then expand throughout much of the basin and Palouse even into the Spokane areas Sunday afternoon. Speeds of 15-25 mph are forecast, with gusts of 20-30 mph and locally up to 40 mph near the Waterville Plateau and near the Blue Mountains.

High temperatures will be mostly in the 60s Saturday, with some upper 650s near the higher Cascade valleys and some low 70s in the deeper basin. Sunday will largely see highs in the 50s, with 60s in the lee of the Cascades/deeper basin and L-C Valley.
Overnight lows will be in the upper 30s and 40s, with some lower to mid-30s over the northern valleys with possible frost heading into Sunday night/Monday AM. So anyone with sensitive plants will have to think about protection. In addition to the cooler temperatures and possible frost, there is fog in the forecast. This will largely be in the sheltered valleys and near bodies of water. /Solveig

Monday through Friday: The region will be under a zonal flow pattern a weak trough in the Gulf of Alaska and a flat ridge over Southwest Conus. It is expected to push several weak shortwaves through the Pacific Northwest and bring off and on showers for the period. The ensembles are in decent agreement for the period. As for amounts, the zonal movement of the waves will keep moisture content fairly low. Precipitable water is less than 100% of normal for the period. The West to East movement of the waves will limit precip amounts for the Central Basin. The rest of the region is only expected to receive a few hundredths with each wave. Winds will be breezy through the period. The winds will peak during the day with sustained in the teens and gusts into the 20-30 mph range. Winds will calm overnight. Temperatures will trend higher. Highs will climb from the 50s and low 60s on Sunday to the upper 60s and 70s by Wednesday. Overnight lows will be in the upper 30s and 40s. /JDC

AVIATION
18Z TAFS: Band of stratiform light rain over Eastern WA/N Idaho will continue to slowly move east into the afternoon. MVFR and local IFR CIGS this morning will gradually rise into the afternoon and evening as the rain moves out, becoming VFR at KGEG/KSFF/KPUW near 22-23z this afternoon, and then at KCOE near 03z this evening. Overnight there is a risky of patchy fog over the valleys of NE WA/N Idaho due to a moist boundary layer, but confidence isn't high enough to include for the KGEG/KSFF/KCOE TAF sites. The next system will bringing in increase chance for rain showers in North Central WA Saturday morning, along with lowering CIGS possibly reaching MVFR at KEAT.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in continued MVFR conditions this morning through the early to mid afternoon over GEG/SFF/COE/PUW. Moderate confidence in timing of shift to VFR for these sites. Low confidence in fog with MVFR/IFR conditions at GEG/SFF/COE TAF sites overnight/early Saturday. 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 57 43 64 43 58 40 / 100 20 50 60 50 20 Coeur d'Alene 53 41 64 43 55 40 / 100 20 40 70 60 30 Pullman 55 40 62 40 54 38 / 100 10 50 80 50 20 Lewiston 62 47 68 48 61 44 / 100 0 50 80 40 20 Colville 57 37 63 40 58 35 / 70 20 70 70 50 20 Sandpoint 54 42 64 44 53 41 / 100 30 50 60 70 40 Kellogg 51 43 63 43 51 41 / 100 20 40 70 80 30 Moses Lake 69 48 68 44 68 39 / 10 30 60 30 10 0 Wenatchee 68 51 65 46 64 41 / 10 30 60 20 10 0 Omak 65 46 64 43 66 39 / 60 20 70 50 20 10

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