Benton City, WA Weather

Key Messages

- Persistent chances of mountain rain and high elevation snow through Thursday

- Breezy winds Tuesday and Wednesday in the lower elevations

- Near to below normal temperatures through the week

Discussion

Nighttime and water vapor satellite imagery tonight shows an upper closed low spinning off the coast of the PacNW. A band of mid to high level cloud cover is currently pushing across eastern WA/OR, while mid layer cloud cover with embedded light rain showers have developed along the Cascade east slopes, with more showers west of the crest.

Today through Friday: A prolonged broad troughing/low pressure pattern is in store for the PacNW through this work week (confidence 80-90%). This will start with the upper low currently offshore the PacNW swinging inland later today, producing light rain showers with high mountain snow showers (above 5-6kft). While the upper low transitions into an open wave trough this evening, a reinforcing shortwave trough will dive along the PacNW coast then swing inland Tuesday morning and afternoon. While persistent mountain rain/snow showers continue in the northern Blues and Cascades, the shortwave passage will result in increased shower chances across the eastern mountains through early Tuesday.

Tuesday evening, a second upper closed low will develop along coastal BC, then remain parked just offshore WA Wednesday through Friday. Light to moderate mountain rain showers with snow showers mainly above 4kft will result in the heaviest accumulations of around 1-3 inches with higher amounts above 5kft Tuesday night into Wednesday morning (confidence 60-80%). Snow levels across the forecast area will lower gradually through the latter half of the work week, however rain/snow showers will become light through Friday as the low remains offshore. Snow levels will lower enough for a light dusting to attempt to accumulate at pass level (Snoqualmie, White, Santiam) with light snow or rain/snow mix above 4.5kft in the northern Blues. There's moderate confidence (55-65%) in additional mountain snow accumulations totaling around 2 inches through Friday.

Otherwise, the parade of upper low pressure systems through the region will result in afternoon temperatures lowering into the 50s Monday through Wednesday, then lower further into the mid 40s to low 50s Thursday/Friday (confidence 60-85%). Breezy winds (15-25mph with gusts to around 35mph) will develop through the Cascade Gaps and lower elevations Tuesday with the shortwave passage, then mainly across central OR to the Columbia Basin Wednesday with the approach of the second closed low (confidence 55-70%).

Saturday and Sunday: Ensemble guidance is in agreement of the upper closed sliding inland starting Friday night into Saturday, with continued chances of light rain/snow in the mountains. However, guidance splits on whether the upper closed low becomes an open wave trough and digs south or remains a broad closed low that continues to move across the PacNW. The upper trough solution would result in mountain showers dissipating across the forecast area by Saturday afternoon, then dry conditions persisting through Sunday. The upper low solutions result in continued light mountain rain/snow chances through the remainder of the weekend. With a close to 40/60 split amongst ensemble members, confidence in the precipitation forecast over the weekend is low (15-20%). Otherwise, both solutions will result in cooler conditions prevailing through the weekend, with afternoon high temps in the mid 40s to low 50s (confidence 45-55%). Lawhorn/82

Aviation

VFR conditions expected to prevail through the period. A low pressure system impacting the region today will continue to bring rain impacts, or chances of rain impacts, to all sites through around 00Z, except through 05Z at site DLS. CIGs will mainly be above 4kft AGL through the period, however bkn-ovc CIGS will lower to around 3.5kft at site DLS after 05Z. Winds will be around 12kts or less through the period. Lawhorn/82

Pdt Watches

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