textproduct: Pendleton

KEY MESSAGES

1. Dry and warmer conditions through Tuesday

2. A front Tuesday will bring high mountain snow and low elevation rain Tuesday and Wednesday

3. Warming and drying conditions beginning Thursday

DISCUSSION

Current satellite shows upper level clouds moving into the area this morning. Overnight temperatures will occur with some areas seeing near freezing conditions with areas of frost. Especially through the Kittitas Valley and portions of the Basin.

The westerly flow aloft has brought in dry and cooler air last night and overnight. Dry and cool conditions will keep temperatures at or just above seasonal normal with NBM raw ensembles showing highs to be in the low to mid 60s across much of the region with 70-80% confidence. By Monday temperatures will slowly increase, with temperatures returning to 5 to 10 degrees above seasonal average with the region seeing the mid 60s with 60-80% confidence through Tuesday.

Models are in firm agreement that an upper level low will track to the north of the region bringing a frontal system across the Cascades ahead of it early Tuesday. Increased chances of precipitation will occur with NBM raw ensembles showing 0.50-1 inch of precipitable water along the Cascades with 65-85% confidence. With the snow levels above 4000 feet Tuesday, much of the precipitation will fall as rain. The lowlands will see 0.02-0.04 inches of rain Tuesday with 50-70% of the NBM raw ensembles in agreement. As we move into Wednesday and early Thursday and the front passes the region, gridded models show the snow levels to drop to below 2000 feet and models show a continued plume of moisture pushing into the region. This will bring snow accumulations of 2.5-5 inches along the I-90 corridor Wednesday with 70-80% confidence. The Blues will see only 0.01-0.05 inches above 4000 feet with 60% confidence, and the lower elevations will remain dry. Not only will this front bring precipitation, it will also bring breezy conditions back to the area. NBM raw ensembles show 70-80% probabilities of the region seeing gusty winds of 25-30 mph both Tuesday and Wednesday as the front passes over.

By Thursday models are in firm agreement that the leading edge of an upper level ridge will begin to push across the Cascades. Temperatures Thursday will remain at or below seasonal average with highs in the low to mid 50s with 60-80% of the NBM raw ensembles in agreement through the Basin, adjacent Valleys, the Gorge and central OR. By Friday, models show the ridge to be overhead and temperatures to begin to increase with in house comparisons showing temperatures to be 5-10 degrees above normal for the southern portion of the region and at or near normal for the northern portion. By Saturday, temperatures are expected to be 5-10 degrees above seasonal normal with some isolated areas seeing as high as 15-20 degrees above seasonal normal. Temperatures Saturday and over the remainder of the weekend will be in the mid to upper 60s along central OR and the eastern mountains to include the John-Day Basin with 60-80% confidence, while the Basin and surrounding areas will see low to mid 60s with 40-60% confidence.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

VFR conditions persist through the forecast period. CIGs will start as SKC before increased clouds move in after 20Z at 25kft. Winds will be below 6 kts through the period an mostly variable.

HYDROLOGY

Minor river flooding from snowmelt and previous rainfall is ongoing for the Yakima and Naches rivers in south-central Washington. These rivers have crested for most locations in the Yakima and Kittitas valleys. However, downstream locations towards the lower Columbia Basin have yet to crest, and the Yakima River at Kiona is forecast to crest Monday morning.

Looking ahead, several forecast points along the Yakima and Naches rivers, including those at Easton, Cliffdell, Naches, and perhaps Umtanum, are anticipated to remain above action stage through the week according to the latest forecasts from the Northwest River Forecast Center in Portland.

Preliminary Point Temps/PoPs

PDT 60 44 65 43 / 0 10 50 50 ALW 59 47 63 45 / 0 10 80 80 PSC 63 47 64 46 / 0 10 50 40 YKM 61 42 62 36 / 0 10 70 30 HRI 62 45 64 43 / 0 10 40 40 ELN 56 38 54 34 / 0 10 80 40 RDM 64 41 65 38 / 0 10 20 30 LGD 64 44 64 43 / 0 20 60 70 GCD 65 43 67 47 / 0 20 40 40 DLS 62 45 61 43 / 0 10 80 70

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.