Area Forecast Discussion

KEY MESSAGES

- Isolated to scattered showers over the northern mountains on Friday and a 10-25% chance for thunderstorms over the Northeast Mountains into North Idaho.

- Dry and breezy Friday Okanogan Valley with elevated fire weather conditions

- Warming well above normal over the weekend into early next week. Minor HeatRisk into the weekend and increasing threat for moderate HeatRisk Monday into Tuesday.

- Very warm and dry conditions and gusty westerly winds Tuesday into Wednesday with a dry cold front passage will bring the potential for critical fire weather conditions.

SYNOPSIS

Temperatures will warm above normal through the weekend into next week. The warm up will be muted on Friday with a low pressure system clipping the northeast portion of the region. The weather system will bring breezy northerly winds down the Okanogan Valley along with scattered showers and isolated thunderstorms primarily over the mountains of northeast Washington into North Idaho. Then a strong ridge of high pressure brings summer like temperatures to the region Monday into Tuesday with highs in the upper 80s and 90s. Fire weather will be a concern Tuesday into Wednesday with warm, dry conditions and gusty westerly winds with a cold front passage.

DISCUSSION

Tonight and Friday: Dry northwest flow continues tonight before a mid level over central British Columbia today drops southeast along the Continental Divide on Friday, clipping NE Washington and N Idaho during the afternoon and evening. Cooling aloft with this wave combined with afternoon heating will result in an unstable atmosphere. This will promote the development of scattered showers and isolated thunderstorms with uncapped surface base CAPE of 300-600 J/KG. The main concern with storms will be gusty outflow winds with gusts of 30 MPH. This wave will also bring a shift to north winds down the Okanogan Valley into the western Columbia Basin on Friday. Warm afternoon temperatures in the 70s to low 80s, relative humidity near 20 percent, and sustained winds of 15 to 25 mph with gusts of 25-40 mph will result in elevated fire weather conditions.

Saturday through Thursday: An upper ridge building off the coast will help turn the pressure gradient more north-northeast on Saturday. Winds will be locally breezy across the Columbia Basin, and the Purcell Trench of North Idaho. The ridge axis noses towards the WA coast on Monday, providing a continued warming trend for the Inland NW. On Tuesday the ridge flattens in response to a 140 kt upper jet punching into Central, or southern British Columbia. This will lead to increasing winds across the Inland NW as breezy to windy west winds develop with a dry cold front. These winds combined with warm temperatures and low relative humidity has the potential to produce critical fire weather conditions in dry grasses across the Columbia Basin, and East Slopes of the Cascades. Tuesday will be the warmest day of the 7 day forecast with highs in the mid 80s to mid 90s. Cooler air behind the front will drop highs down into mainly the upper 70s and 80s for Wednesday and Thursday. JW

AVIATION

00Z TAFs: VFR conditions will prevail. A shortwave trough dropping south from British Columbia will lead to cumulus buildups around 16-19z Friday for KGEG-KSFF-KCOE that may be capable of producing showers. The chances for showers are too low to include in the KGEG-KSFF TAF (10-20% chance). Those chances increase to 25% for KCOE so have included a PROB30 from 18z Fri-00z Saturday for -SHRA. Winds will be increasing from the north down the Okanogan Valley Friday morning, but elsewhere expect breezy westerly winds around 10 kt.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence in VFR conditions. Low confidence for shower impacts for KGEG-KSFF-KCOE.

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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 46 77 48 77 49 82 / 0 10 20 0 0 0 Coeur d'Alene 46 74 49 75 49 81 / 0 20 20 0 0 0 Pullman 44 73 45 75 46 80 / 0 10 10 0 0 0 Lewiston 50 80 52 82 52 86 / 0 0 0 0 0 0 Colville 41 77 44 79 45 85 / 0 20 10 0 0 0 Sandpoint 45 72 47 74 47 81 / 0 50 30 0 0 0 Kellogg 45 72 47 74 47 81 / 0 30 30 0 0 0 Moses Lake 49 83 53 85 53 89 / 0 0 0 0 0 0 Wenatchee 54 81 57 83 60 88 / 0 0 0 0 0 0 Omak 49 80 52 84 55 89 / 0 10 10 0 0 0

OTX WATCHES / WARNINGS / ADVISORIES

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