Area Forecast Discussion

KEY MESSAGES

- Increasing westerly winds, showers, and thunderstorms forecast with incoming system Tuesday evening into early Wednesday morning.

- Widespread moderate rain Wednesday will bring potential for small stream and urban flooding in Southeast WA.

- Strong wind gusts continue through Wednesday into Wednesday evening.

SYNOPSIS

Unsettled weather returns Tuesday evening into Wednesday with potential for moderate rain, thunderstorms, and gusty winds. Main risks with thunderstorms will be gusty outflow winds, small hail, and infrequent lightning. Moderate rainfall on Wednesday could result in small stream flooding over the Palouse. Gusty winds will continue through Wednesday. Conditions trend drier heading into the weekend.

DISCUSSION

Tonight through Wednesday: This evening marks the start of a busy weather period as a deformation axis sets up over the Inland Northwest, bringing increasing chances for showers and thunderstorms along with gusty westerly winds. Thunderstorms will be the primary concern for tonight with a 15 to 30 percent chance of storms across much of the region. Thunderstorm chances last into early tomorrow morning before tapering off. Storms will be capable of gusty winds, pea- sized hail, and isolated lightning strikes.

Moving into Wednesday precip will become more stratiform with moderate to heavy precip focused over Southeast WA and the Central ID Panhandle along the deformation band. The Palouse will be the area to watch for flooding given the saturated soils in that area limiting the amount of additional rain that can be absorbed into the ground. Given how saturated the soils are and the potential for over an inch of rainfall in that area (depending on where exactly the deformation band sets up), a Flood Watch has been issued for the WA and ID Palouse.

The other concern on Wednesday will be westerly winds continuing to ramp up. Strongest winds will be over Southeast WA in the Pomeroy area and through the Cascade gaps impacting the Wenatchee area, Waterville Plateau, and lower Columbia Basin. Sustained speeds of 20 to 35 mph and gusts of 45 to 55 mph will be possible overnight tonight through Wednesday evening. Wind Advisories have been issued for the aforementioned areas.

Precip chances linger over the ID Panhandle Thursday and Friday before moving east. Limited precip chances show up over the Cascade crest heading into the weekend but otherwise, conditions are looking dry. /Fewkes

AVIATION

18Z TAFS: Mid and high level clouds will increase through the morning and afternoon as a system moves inland. Showers and thunderstorms develop between 00Z and 06Z over southeastern Washington, and after 06Z across northeastern Washington and far north Idaho. Main concerns with these thunderstorms will be gusty outflow winds, small hail, and isolated lightning. Models show a steadier band of rain moving into the Inland Northwest after 10Z with a 30-50% chance for MVFR conditions through 18Z tomorrow. Stronger northwest winds will develop through the Cascade gaps and over the Palouse this evening with sustained winds 15-20 knots and gusts up to 30 knots.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions through this evening. Moderate confidence for MVFR conditions after 10Z across much of the Inland Northwest with a steadier band of precipitation. Low to moderate confidence in showers and thunderstorm chances from 00-06Z Wednesday for PUW, LWS, MWH, and EAT. Low confidence in timing of showers for GEG, SFF, and COE with differences among high resolution models.

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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 47 52 39 55 35 54 / 60 90 30 40 20 20 Coeur d'Alene 46 51 37 52 34 52 / 60 90 60 60 30 30 Pullman 42 47 36 49 32 51 / 70 100 70 50 40 30 Lewiston 48 52 41 55 38 56 / 70 100 80 50 30 30 Colville 47 63 39 59 34 58 / 60 80 20 30 20 20 Sandpoint 48 50 37 48 31 50 / 50 90 70 70 40 40 Kellogg 45 49 38 47 32 48 / 50 100 90 80 50 50 Moses Lake 49 66 44 65 39 62 / 70 80 10 20 0 10 Wenatchee 52 63 46 63 42 62 / 60 70 10 10 0 10 Omak 52 67 41 59 37 62 / 40 50 10 10 0 10

OTX WATCHES / WARNINGS / ADVISORIES

WA...Flood Watch from late tonight through Wednesday evening for Washington Palouse. Wind Advisory from 8 AM Wednesday to 5 AM PDT Thursday for Lower Garfield and Asotin Counties. Wind Advisory from 8 PM this evening to 11 PM PDT Wednesday for Moses Lake Area-Waterville Plateau-Wenatchee Area. ID...Flood Watch from late tonight through Wednesday evening for Central Panhandle Mountains-Idaho Palouse.