textproduct: Pendleton

KEY MESSAGES

1. Dry and cool conditions through Sunday

2. Pattern shift at the beginning of the week will bring slightly below seasonal temperatures

3. Increased chances of precipitation at the start of the week

DISCUSSION

Current satellite is showing mid to high level clouds moving in over the WA Cascades with high level clouds moving in over the OR Cascades. Temperatures today will remain in the mid to upper 50s with some isolated 60s in central OR and the Colombia Basin/Gorge. Overnight temperatures will be sub-freezing along a few areas in central OR, the Columbia Basin and Yakima Valley as well as through the cold prone areas of Seneca and Wallowa Valley.

A weak upper level ridge is over the region through the day today and most of tomorrow. This will keep the region under dry conditions and cool conditions. In house calculations show the region to be at or slight below normal seasonal temperatures for today with the NBM showing temperatures in the mid to upper 50s across much of the region. A few isolated locations in central OR and the John Day Basin could see low 60s. Overnight temperatures will be sub-freezing along a few areas in central OR, the Columbia Basin and Yakima Valley as well as through the cold prone areas of Seneca and Wallowa Valley.

A change in the synoptic pattern will lead to below seasonal average temperatures continuing with the coolest day being Monday. Deterministic guidance models show an upper level low moving into the PacNW from the Gulf of Alaska by Sunday night. Models are in good agreement with the initial low making its way onshore by Monday afternoon. This will bring with it below seasonal average temperatures with in house calculations showing nearly 5-10 degrees below normal across central OR, eastern mountains and the foothills of the Blues while the Gorge Basin and adjacent valleys will see temperatures 1-5 degrees below seasonal normal. Monday NBM raw ensembles show 60-80% chances of these areas seeing mid to upper 50s. Temperatures will steadily trend downward through midweek.

Not only will this upper level low bring cooler temperatures, but models are also showing increased chances of precipitation. Looking at the mean 24 hour precipitation statistic, rain/snow will be along the Cascades as early as Sunday night. The rain will continue to spread across the region through Monday becoming widespread between 11 AM and 5 PM. Looking at the NBM raw ensembles for the 24 hour period, the ensembles show a 50-80% chance the eastern mountains, Blues, foothills and the eastern slopes of the Cascades will see near 0.05 inches of rain. The remaining locations will see 0.01-0.04 inches of rain. As the low continues to move to the east, clusters and deterministic models begin to diverge. NBM shows rain showers continuing on Wednesday while the variance between the models differ in timing and amounts.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Increasing clouds during this TAF period look mainly high to mid level, with extremely low confidence in any MVFR ceilings, or lower (5% chances or less for 3kft AGL or lower). Light winds under 10 knots and VFR is expected, but with developing gusts upwards of 20 knot late Sunday morning and through the afternoon at RDM.

Preliminary Point Temps/PoPs

PDT 32 61 32 55 / 0 0 10 30 ALW 38 62 38 55 / 0 0 0 40 PSC 29 58 36 58 / 0 0 10 30 YKM 32 57 37 58 / 0 10 20 20 HRI 30 59 34 58 / 0 0 20 20 ELN 25 53 31 54 / 0 10 30 50 RDM 28 64 30 50 / 0 0 40 60 LGD 34 61 37 54 / 0 0 0 80 GCD 30 64 34 53 / 0 0 0 70 DLS 36 59 40 59 / 0 10 30 50

PDT WATCHES/WARNINGS/ADVISORIES

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