textproduct: Pendleton

KEY MESSAGES

1. Dry and cool conditions through early in the week

2. At or near seasonal average temperatures

3. A pattern change will bring back chances of lowland rain, mountain snow and breezy conditions

DISCUSSION

Current satellite shows mostly clear skies over the region with some mid-level clouds moving into central OR. Models show west flow aloft ushering in the dry air mass over the region. With the lack of cloud cover and the cold air mass coming in, temperatures could drop to freezing across portions of central OR and the foothills of the Blues as well as the Simcoe Highlands and adjacent valleys. Models are in firm agreement this pattern will persist through Monday.

The westerly flow aloft has brought in dry and cooler air last night and overnight. Dry and cool conditions will bring temperatures back to near seasonal normal with NBM raw ensembles showing highs to be in the low to mid 50s across much of the region with low 60s in central OR and isolated spots in the Basin (60-70% confidence). By Sunday temperatures will slowly increase, however, still remaining near seasonal averages with temperatures across much of the region seeing the low 60s (60-80% confidence) through midweek.

Models are in firm agreement that by Tuesday/Tuesday night an upper level low will track to the north of the region bringing a frontal system across the region. Increased chances of precipitation will occur with NBM raw ensembles showing 0.50-1 inch of precipitable water along the Cascades. With the snow levels above 4000 feet Tuesday, much of the precipitation will fall as rain. The lowlands will see 0.02-0.05 inches of rain Tuesday with 60-70% 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 (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 60-80% probabilities of the region seeing gusty winds of 25-30 mph both Tuesday and Wednesday as the front passes over.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

VFR conditions persist through the forecast period. Winds will remain light and variable under 10kts.

HYDROLOGY

River flooding from snowmelt and previous rainfall is ongoing for the Yakima and Naches rivers in south-central Washington. These rivers have crested, or will crest this afternoon, for most locations in the Yakima and Kittitas valleys. Locations downstream towards the eastern end of the Yakima Valley and the lower Columbia Basin have yet to crest, and the Yakima at Kiona is forecast to crest between late Sunday afternoon and early Monday morning.

Looking ahead, several forecast points along the Yakima and Naches rivers, including those at Easton, Cliffdell, Naches, and perhaps Umtanum, are then 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 57 34 60 44 / 0 0 0 10 ALW 57 37 60 47 / 0 0 0 10 PSC 60 35 63 45 / 0 0 0 10 YKM 56 34 60 42 / 0 0 0 10 HRI 60 34 63 45 / 0 0 0 10 ELN 53 31 55 38 / 0 0 0 10 RDM 60 31 64 42 / 0 0 0 10 LGD 58 35 64 45 / 0 0 0 10 GCD 61 37 65 45 / 0 0 0 10 DLS 61 38 62 45 / 0 0 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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