Marine Weather and Tide Forecast for Troy, MT

SYNOPSIS
Today will be the last warm and dry day of the week before a weather system moves in tonight and into this weekend. Chances for showers increase tonight into Saturday along with isolated afternoon thunderstorms, breezy winds, and slightly cooler temperatures. Showers continue over the Idaho Panhandle on Monday before a break between systems Monday night into Tuesday.
A cold front passage Tuesday afternoon into Wednesday will bring additional rain in the lowlands (with the exception of the Columbia Basin which will stay mostly dry), mountain snow, and breezy to windy conditions.

DISCUSSION
Tonight through Monday: A couple areas of low pressure will influence our weather conditions through the weekend. One low is currently digging south from the Gulf of Alaska, and another low is sitting off the OR/CA coast. As we head into tonight and this weekend, the OR/CA low weakens and migrates east- northeast toward the northern Rockies, while the Gulf of AK low continues moving south toward the CA coast and follows the first low inland by Monday morning.

Increasing mid level clouds will be seen moving into the Inland Northwest this afternoon and evening as these low pressure systems shift around. A deformation axis lifts northward into the region between tonight and Saturday, lingering into Sunday.
Combined with the areas of low pressure directing increased moisture into the region, this points toward increasing precipitation chances through the weekend. Precip will continue across the region through Sunday and over the ID Panhandle into Monday before tapering off Monday evening.

Snow levels will remain above 5000 feet through Monday, so precip will be mostly rain and high mountain snow. Between 0.40 to 0.80 inches of rainfall are forecast between Saturday and Monday over southeast WA and the central and southern Panhandle with locally higher amounts possible, especially in mountain areas. Toward the northern mountains, north ID, and Spokane/CdA area, between 0.25 to 0.50 inches are in the forecast. Similar amounts are possible toward the Cascades, while the central WA/deeper basin could see trace to 0.15 inches of rain. If any snow does fall in the mountains it is looking minor with little to no impacts.

In addition to rain showers, there is a 10-30 percent chance for thunderstorms each afternoon between Saturday and Monday.
The highest risk is on Saturday, with most of the region seeing at least some risk. Sunday the risk become more localized to the eastern third of WA and ID, and by Monday mainly over the far northeast WA and north ID counties. Brief downpours, gusty winds, lightning, and small hail will be the main risks with any thunderstorms that develop.

Winds will be breezy out of the west-southwest Saturday afternoon across the Columbia Basin and Blue Mountains with gusts up to 25 mph. Winds will subside Saturday night through most of Sunday, then heading into Sunday night, winds will ramp up again as the system starts to move out and drier westerly flow develops. Gusts of 25-35 mph are forecast by Monday afternoon for the Cascades and across much of eastern WA with the highest gusts through the Cascade gaps and on the Waterville Plateau.

Highs will be largely in the 60s to low 70s this weekend, then the upper 50s to 60s Monday. Lows will be in the 40s for most areas.

Tuesday through Thursday: The region starts off in the westerly flow, but another strong low pressure drops in from the Gulf of Alaska Tuesday night into Wednesday before moving east of the region Thursday. This more direct track into the region will mean more precipitation chances and lower snow levels, potential for moderate snows around the mountain passes, gusty winds, and cooler than normal temperatures. Limited precipitation chances from the weekend system will linger around the mountains Tuesday, then start to expand back out Tuesday night and Wednesday. The highest potential for precip (70 to 90 percent chance) will be around the mountain zones. This will be largely mountain snow and lowland rain, but a rain/snow mix will be possible for some lowland areas Tuesday night and Wednesday.

Current snow amounts forecast for Tuesday and Wednesday over mountain passes are as follows:

- 10 to 13 inches for Stevens Pass - 4 to 7 inches for Lookout Pass - 5 to 8 inches for Snoqualmie Pass - 4 to 7 inches for Sherman Pass

It appears wintry weather is not over with after all. In addition to mountain snow and lowland rain or a rain/snow mix, winds will be gusty Tuesday and Wednesday with gusts between 25 and 40 mph. Winds decline some for Thursday with gusts right now forecast between 15 and 25 mph. Afternoon highs Tuesday through Thursday will be in the upper 40s and 50s. Lows will be mainly in the 30s Tuesday and Wednesday morning, then Thursday morning will be colder in the mid 20s to low 30s. /Fewkes

AVIATION
00Z TAFS: Impulses drifting south to north will result in increasing mid and high clouds along with an increasing risk for rain showers. There are several waves lined up over Oregon. The first will result in little to no rainfall. The second arriving 9-15z will increase probabilities for rain at the terminals and develop in to steady showers while tracking into northern WA and north ID 10-18z. Clearing behind this wave Saturday afternoon will help destabilize the air mass with isolated convection for most areas south of Hwy 20. Coverage will be scattered across southeastern WA and the lower Idaho in vcnty of KLWS and just south of KPUW. Would not rule out isolated lightning KCOE-KSFF-KGEG-KMWH but confidence is not high enough to include in the TAF at this time. Main hazards with showers overnight will be brief, erratic wind gusts around 25 mph. On Saturday afternoon, convection will be capable of localized MVFR vis from heavier downpours. Wind gusts around 25 mph will remain possible near any cells as well.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in VFR conditions for majority of the TAF period. Low confidence is timing of showers at individual sites.
Moderate confidence for lightning in vcnty of KLWS and low for other terminals. /sb

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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 59 41 64 43 59 / 10 70 30 30 40 40 Coeur d'Alene 44 58 43 63 43 56 / 10 80 50 40 60 60 Pullman 45 59 41 61 42 53 / 30 80 30 60 70 70 Lewiston 50 64 44 64 47 58 / 30 80 30 60 70 60 Colville 43 65 42 67 41 64 / 10 70 60 50 40 40 Sandpoint 43 57 43 61 43 54 / 10 80 60 60 60 80 Kellogg 45 57 43 62 43 51 / 10 90 40 60 70 90 Moses Lake 49 67 40 69 43 67 / 30 40 10 10 20 10 Wenatchee 51 63 43 67 46 63 / 30 50 10 10 10 0 Omak 49 66 45 68 43 68 / 20 50 30 20 10 10

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