Spokane forecast discussion

Synopsis

Friday will remain dry with mild temperatures and light winds. On Saturday breezy to windy conditions will develop with the passage of a cold front. Dry conditions return early next week with light winds and temperatures in the 60s.

Discussion

Friday: A strong upper-level ridge responsible for the recent string of warm and dry weather will begin to slide east. As the ridge axis shifts into Western Montana, southwest winds will increase aloft drawing warmer air into the region. High temperatures on Friday will warm another 5 degrees topping out in the upper 60s to lower 70s under sunny skies. Winds will remain light with a general easterly direction in the morning and slowly shift to the south in the afternoon. Speeds will remain below 10 mph except on the Palouse where easterly winds will be near 15 mph Friday morning.

Saturday: A shortwave swings out of the Gulf of Alaska and across the Canadian border dragging a cold front through the Inland NW. Gusty westerly winds will develop across the region as pressure gradients tighten and afternoon mixing draws down 25-35kts of winds aloft. The track of this system to the north is not ideal for strong enough winds for wind highlights but there will undoubtedly be the potential for some impacts. Anglers should be prepared for choppy lakes. Following a string of warm and dry weather, fuels remain unseasonably dry and the threat for swift fire spread in dry grasses will remain elevated, especially in the late afternoon as humidity levels drop between 25-30%. There will also be a threat for patchy blowing dust near recently worked fields on the Waterville Plateau and areas of the western and central Columbia Basin. Typically this time of year, dust sources are centered near recently plowed potato fields and where winter wheat has been planted. Ag reports suggests 70% of the winter wheat has emerged which tends to lower the risk. Nonetheless, this is something that will need to be monitored closely.

Winds will increase Saturday morning, peak mid afternoon and come down in the evening. Sustained speeds of 15 to 25 mph will be accompanied by gusts of 25-35 mph. The higher range of the winds will be found across the foothills of the East Slopes, across the Waterville Plateau, and into the upper Columbia Basin. A second area of enhanced winds will channel along the Highway 12 corridor in the foothills of the Blue Mountains. There is a 65-75% chance for sustained winds of 20 mph or greater across the Waterville Plateau and Wilbur area and near 40% at Pomeroy. There is a 80% chance for gusts to reach at least 30 mph in these areas and 35% chance for gusts to reach 40 mph. For much of North Idaho, Spokane Area, Moses Lake, and Omak gusts will be more on the order of 25-30 mph with sustained speeds around 15 mph. Wind direction will start off from the west/southwest and shift toward the west/northwest into the afternoon into the evening.

Little to no precipitation is expected with the incoming front east of the Cascade Crest. The Cascade crest will have a 90% chance for showers, some enhanced by the Puget Sound Convergence zone but as precipitable water value tank late in the day, I expect these showers to wane by the evening. Snow levels on the Cascade Crest will be near 8000 feet, briefly dipping near 5000 feet before showers taper off.

Sunday-Wednesday: In the wake of Saturday's cold front, a shortwave ridge of high pressure will build over the region promoting lighter winds, sunny skies, and afternoon temperatures in the lower 60s. Another trough will approach the WA Coast Monday but a bulk of its energy will dig southward into California as a strong northerly jet develops on its backside. This will leave the Inland NW in the decaying northerly branch of a elongated trough. A trickle of moisture working its way into the region will introduce a 10-15% chance for showers but little in the way of rainfall. Temperatures will not change much from Sunday through Tuesday cooling a degree or two and winds will shift around at light speeds from the east to south to north over the three day period. Overall, weather impacts are expected to be minimal.

Thursday-Friday: There is strong support from the ensemble models for another trough to swing across the northern Pacific and through the PacNW. This will bring another bout of windy conditions and shot of cooler air in the region bringing the first potential for seasonal temperatures for the entire week (normal highs are in the 50s to low 60s). The incoming system will phase with the cutoff low over Northern California and has some potential to bring more shower activity into the region. Though, I am not convinced this will bring wetting rains (>0.10 inches) as models seem to be trending drier and drier each consecutive run and only carry a 10-20% chance for a hundredth on the latest run. We'll have to see how this period evolves in the coming days. /sb

Aviation

06Z TAFS: High pressure over the region will promote VFR conditions. Strengthening high pressure in the lee of the Rockies in NW Montana will lead to predominately easterly flow with the strongest winds at KPUW 13-19z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions.

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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        37  71  44  64  36  60 /   0   0   0   0   0   0 
Coeur d'Alene  38  69  42  64  37  60 /   0   0   0   0   0   0 
Pullman        40  70  44  65  36  61 /   0   0   0   0   0   0 
Lewiston       39  73  43  72  41  64 /   0   0   0   0   0   0 
Colville       33  69  36  67  30  62 /   0   0   0   0   0   0 
Sandpoint      36  66  39  62  35  59 /   0   0   0   0   0   0 
Kellogg        38  69  42  63  35  60 /   0   0   0   0   0   0 
Moses Lake     38  70  39  68  32  63 /   0   0   0   0   0   0 
Wenatchee      45  69  49  67  40  62 /   0   0   0   0   0   0 
Omak           41  68  43  68  38  62 /   0   0   0   0   0   0 

Otx Watches/Warnings/Advisories

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