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FXUS66 KOTX 032330 AFDOTX

Area Forecast Discussion National Weather Service Spokane WA 430 PM PDT Fri May 3 2024

SYNOPSIS
Temperatures on Saturday will be mild with highs in the 60s and low 70s. Bands of rain will spread into central Washington on Saturday. Widespread rain is expected on Sunday as a slow moving low moves through the Pacific Northwest. As the low pulls out of the region, look for cool, showery, and windy conditions Monday and Tuesday. Warmer and drier weather will likely arrive late next week.

DISCUSSION

Tonight and Saturday: Clouds will be on the increase tonight into Saturday as a slow moving low off the coast of Washington this afternoon pushes into Oregon and northern California on Saturday.
Rain will be slow to spread east of the Cascades. Chances for measurable rain will be less than 50 percent east of Omak, Waterville and Moses Lake until late Saturday evening. Even though Saturday will be mostly cloudy, temperatures will be mild. Morning lows will range from the 40s in north Idaho and northeast Washington to the low 50s in Moses Lake and Wenatchee. Highs are expected to be in the 60s Saturday for the majority of the Inland Northwest.

Sunday: There is decent model agreement that the most significant precipitation with this slow moving low will occur south of Washington and Idaho Saturday and Sunday with a foot or more of snow for the high elevations of the Oregon Cascades and mountains of northern California. However, this storm should deliver some much needed rainfall to eastern Washington and north Idaho. Models often struggle with wrap around precipitation, and we have seen some variability in the ensembles the last few days with the timing and location of the deformation band wrapping into the Inland Northwest. The latest National Blend of Models (NBM)
generates the most significant band of rain Sunday and Sunday night across the eastern third of Washington and over the north Idaho Panhandle. The NBM deterministic output (most likely scenario) has a swath of a quarter to half inch centered along the WA/ID state line Sunday and Sunday night. The NBM 75th percentile increases these amounts to localized amounts of two-thirds of an inch while the 25th percentile knocks amounts in the rain band down to a tenth to quarter of an inch. Rains across the Palouse and West Plains will be welcomely received by dryland farmers after a dry April. However, outdoor activities on Sunday will be dampened by the rain and much below average temperatures. Places that experience an all-day rain may struggle to get out of the 40s Sunday afternoon including Spokane, Pullman, and the Idaho Panhandle. Places like Omak and the Methow Valley may remain north of the main rain band and have a good chance of topping out in the 60s.

Monday and Tuesday: The beginning of the work week will be cooler than average, showery, and locally windy. As our deep weekend low migrates eastward, a tight westerly pressure gradient will set up across the Cascades on Monday. Then on Tuesday, a fast moving shortwave descending from the Gulf of Alaska will dig into the Pacific Northwest delivering another round of gusty west winds.
Guidance form the ECMWF ensembles suggest that wind gusts of 30 to 35 mph will be a good bet Monday with 70 percent of members generating gusts of 35 mph or higher across the open country of southeast and east central Washington on Monday and 50 percent of members on Tuesday. Showers will be more widespread Monday with a 60 to 80 percent chance of measurable precipitation over the Idaho Panhandle and the eastern third of Washington. Shower chances should decrease on Tuesday as drier air accompanies the Gulf of Alaska system, however snow levels will drop unseasonably low Tuesday...as low as 3000 feet in the morning and again overnight into Wednesday morning. If you haven't gotten your fill of graupel this spring, Tuesday will give you another shot at seeing our "corn snow", "snow pellets", or (insert your favorite graupel name).

Wednesday and Thursday: The medium range models are trending toward a more amplified ridge/trough pattern over North America by mid to late week. While there are some differences in where the ridge axis will set up by Thursday and Friday of next week, the majority of the ensemble members are forecasting above average temperatures and dry weather Thursday and Friday. The NBM advertises highs in the mid 60s to mid 70s Thursday and widespread 70s for Friday. /GKoch

AVIATION
00Z TAFS: A low pressure system will move slowly onshore off of the eastern Pacific tonight. This will spread mid to high level clouds across the region. Light rain is expected across the Cascades by the morning hours on Saturday with rain at KEAT by 14-16Z. Ceilings down to 3-4 kft with MVFR conditions possible.
South and easterly winds will pick up with the front approaching through the day today into Saturday as well. KPUW-KGEG-KCOE will see the potential for gusts up to 25 kts into Saturday morning with the easterly pressure gradient tightening up.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions through Saturday afternoon except for at KEAT where confidence is moderate. The HRRR/NBM model guidance for KEAT indicates a 50% chance ceilings lower down to between 2-3 kft agl. and visibility down to 4-6 miles with rain by 15Z. /SVH

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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 69 42 49 40 56 / 0 10 40 90 80 40 Coeur d'Alene 42 68 42 49 39 52 / 0 10 30 90 90 60 Pullman 46 65 39 45 38 52 / 0 10 80 100 80 60 Lewiston 47 73 46 54 44 59 / 0 10 90 100 80 60 Colville 40 68 42 57 38 60 / 10 20 20 90 80 70 Sandpoint 42 66 44 51 39 52 / 0 10 30 90 90 80 Kellogg 43 65 44 48 40 47 / 0 10 40 100 90 80 Moses Lake 53 71 44 58 42 63 / 10 40 60 80 30 10 Wenatchee 52 62 49 60 44 60 / 10 70 40 30 20 20 Omak 49 69 49 64 42 65 / 10 40 30 40 40 20

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

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