textproduct: Pendleton

KEY MESSAGES

- Light to moderate mountain showers across the WA Cascades and Northern Blues with breezy low elevation winds Tuesday

- Near to above normal temperatures throughout the week

- High uncertainty in return of light mountain showers Thursday or Friday, with better agreement of dry conditions and above normal temperatures over the weekend

DISCUSSION

Little to talk about on satellite tonight as much of the PacNW is under clear skies. At the surface, weak diurnally winds have developed, while areas of central OR and the Kittitas valley have seen temperatures drop into the 30s. If winds become calm, there is a potential for radiative cooling processes to drop temperatures to at or just below freezing tonight (confidence 30-60%).

Today through Wednesday: Dry and quiet conditions will prevail across the forecast area for much of today as zonal flow will develop over the PacNW while an upper trough drops through the Great Basin into the Desert Southwest. While winds will remain light across much of the area, winds will increase through the eastern Columbia Gorge ahead of an approaching cold front.

Monday night into Tuesday, flow aloft will remain zonal, however an upper shortwave trough passing through BC will clip the WA Cascades and northern Blue mountains. This will result in light to moderate rain showers developing across these areas, with a 35-45% chance of 0.1 inches in the Northern Blues and a 55-95% chance of 0.25 inches along portions of the WA Cascades and east slopes (highest chances in central WA Cascades, lowest south central WA Cascades). In the Columbia Basin and Gorge, a cold front passage will result in breezy west to southwest winds (15-25mph with gusts 25-40 mph) developing throughout the day, with light to locally breezy winds elsewhere.

Flat upper level ridging in the eastern Pacific will build into the western CONUS by Wednesday morning, resulting in a return to dry conditions and light winds.

Thursday through Sunday: High uncertainty amongst deterministic and ensemble guidance in the evolution of the synoptic pattern Thursday through Friday, however there is good consensus amongst the most recent ensemble members for low impacts during this period. Overall, disagreement surrounds the eventual passage of a shortwave trough that will bring light mountain showers. Ensemble members are in disagreement if the trough comes through sometime Thursday or sometime Friday, so confidence in precipitation timing/extent is very low (15-20%).

After Friday, agreement grows in upper level ridging building over the PacNW through the weekend, resulting in dry and quiet conditions with above normal temperatures. (confidence 45-60%). Lawhorn/82

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

VFR conditions prevail with dry and mostly clear conditions through the forecast period. Winds will be a bit elevated in the 7 to 12 knot range, with breezier conditions developing in the DLS by the afternoon. Otherwise, no CIG or VIS issues expected.

Preliminary Point Temps/PoPs

PDT 70 45 75 49 / 0 0 0 0 ALW 71 52 75 54 / 0 0 0 10 PSC 75 47 78 50 / 0 0 0 0 YKM 73 48 74 49 / 0 0 10 0 HRI 74 49 77 51 / 0 0 0 0 ELN 68 45 66 46 / 0 0 20 20 RDM 71 37 75 39 / 0 0 0 0 LGD 71 41 75 46 / 0 0 0 10 GCD 72 40 75 43 / 0 0 0 0 DLS 76 50 73 54 / 0 0 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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