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FXUS66 KOTX 160927 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 227 AM PDT Tue Apr 16 2024

SYNOPSIS
Anticipate cool, brisk, and somewhat showery weather as a low pressure system aloft drops over the Inland NW and lingers through Thursday. It will be chilly early in the morning with lows dipping below freezing for many areas and the threat of frost.
The weather gradually warms and dries by Friday into the weekend and continues into early next week with above normal temperatures.



DISCUSSION
Today and Tonight: The arrival of a closed upper level low from the north will bring cool and unsettled weather to the region.
The band of high level clouds that spans across eastern WA early this morning is expected to slowly push southeast in advance of the closed circulation. Some sporadic wind gusts still seen over parts of Grant county in the Basin, although should gradually decrease this morning. The clearing will be short lived this morning as cumulus will bubble across the mountains and spread across the lowlands by afternoon. The best chances will be across the northern and Panhandle mountains by afternoon. Surface based instability increases with skinny wedges of cape to 120 J/kg over the northern tip of the ID Panhandle with a 5% of a thunderstorm.
Most convection will be snow or graupel showers based the cold -35C at 500mb with the area of low pressure.

Anticipate a return of the westerly gusty winds by afternoon but weaker than yesterday, spanning from the lee of the central Cascades across the Columbia Basin with gusts 25 mph. Winds shift from the north overnight and remain brisk across central WA, especially funneling down the Okanogan Valley, across the Waterville Plateau into the western Columbia Basin. Daytime temperatures will be noticeable cooler, by about 10 degrees compared to Monday. Meanwhile, lows tonight will dip into the 30s with many areas experiencing near freezing temperatures. After the mild temperatures lately, this may be concern for those who have done early planting. Areas of frost may be seen in many lowland areas where the winds decouple across extreme eastern WA.
Climatologically, the growing season has just started for the LC Valley, Moses Lake area, and Wenatchee area, and these areas are expected to see the least threat of frost.

Wednesday and Wednesday night: Cool conditions continue as the upper level circulation gradually weakens and shifts east, leaving a northerly flow aloft across the region. Chilly morning temperatures and areas of frost will be a concern early in the morning for parts of eastern WA. Brisk northerly winds will persist through the day in central WA with gusts of 25 to 30 mph.
Cumulus buildups return for the mountains with showers bubbling up by afternoon, especially for northeast WA and the ID Panhandle in the form of snow or graupel showers. Instability increases by afternoon but remains weak and spotty. Winds decrease gradually overnight while temperatures dip back into the 30s with the threat of frost and freezing temperatures especially in sheltered low lands. /rfox.

Thursday through Monday: Upper level longwave ridge is pinched up and rather narrow off the coast as an disturbances and frontal boundaries rotate counter clockwise along an upper level low moving slowly east along the US and Canadian border. The northerly flow on the east side of the ridge still still allows for some upper level instability and potential for weak disturbances and orographics to allow for minor pops for light rain and snow showers to linger mainly over North Idaho Thursday followed up with a dry Friday.
Ensembles still suggest a negatively tilted trof passage sometime over the weekend thus increasing clouds and a mention of showers as early as Saturday evening and possibly lingering on Sunday as the upper level ridging is rather flat and more zonal. Low amplitude shortwave ridging Monday confines any mention of showers to small portions of the Cascade Crest and very small portions of North Idaho. The below normal forecast temperatures continue a gradual warming trend through Monday with some areas of frost mentioned in spots on through the remainder of the workweek and first half of the weekend. /Pelatti

AVIATION
06Z TAFS: Westerly pressure gradients have begun to relax this evening following the passage of today's cold front. For the remainder of the night, winds will be less gusty at our TAF sites.
Breezy west or southwest winds will return by mid to late morning across the majority of central/eastern Washington and north Idaho with sustained 10 to 14kt winds with gusts up to 20kts. Between 19z-02z there will be a 20 to 40 percent chance of rain showers over the Idaho Panhandle and the eastern third of Washington including Sandpoint, Bonners Ferry, Coeur d'Alene, Spokane, Kellogg, and Pullman. With snow levels as low as 3000 feet, the high terrain near some of the north Idaho airports may be obscured by afternoon convective showers.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: The majority of the 0z HRRR members generate convection near the Spokane International Airport. The operational GFS and ECMWF push most of the shower activity east of GEG Tuesday afternoon. As the new National Blend ingests this data, we will get a better idea of the non-HRRR members support the introduction of PROB30 showers at KGEG. /GKoch

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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 52 31 54 32 54 32 / 0 10 10 0 10 0 Coeur d'Alene 50 31 52 31 52 30 / 20 20 10 10 10 0 Pullman 47 30 50 30 54 31 / 10 0 10 10 10 0 Lewiston 56 36 57 36 60 36 / 0 0 10 0 10 0 Colville 53 31 55 29 54 29 / 10 10 30 10 10 0 Sandpoint 50 33 50 32 49 29 / 40 30 20 20 20 0 Kellogg 45 33 48 32 50 30 / 30 20 30 10 20 0 Moses Lake 57 33 61 36 62 37 / 0 0 0 0 0 0 Wenatchee 54 36 58 39 59 38 / 0 0 0 0 0 0 Omak 56 36 60 34 60 34 / 30 20 10 0 0 0

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

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