textproduct: Pendleton

KEY MESSAGES

- Shower chances across the WA Cascades with low chance (5-15%) of isolated thunderstorms across the WA Cascade east slopes and northern Blues through this afternoon

- Elevated fire weather conditions will continue through this evening due to breezy winds

- Drying and warming trend Sunday through early Tuesday before an upper low passage late Tuesday into Friday brings increasing shower chances, breezy westerly winds, and cooler conditions

DISCUSSION

Water vapor satellite imagery this afternoon shows an upper level low sliding across northern WA, with visible satellite and radar imagery showing isolated to scattered showers/thunderstorms mainly in the Upper Columbia Basin. Breezy winds have developed through the Cascade gaps and into the lower elevations as well, with strongest winds being reported through the Kittitas valley and along WA Cascade east slopes.

Rest of Today through Early Tuesday: Showers and any remaining convection across the forecast area will diminish before this evening as the upper low lifts northeast into Canada. The breezy westerly winds that developed with the low passage will continue into this evening as cold air advection behind the low will maintain tightened surface pressure gradients. While RHs will remain above critical criteria over the region, the breezy winds will continue to present elevated fire weather conditions across the lower elevations and along the Cascade east slopes.

The aforementioned cold air advection into the region will keep temperatures about 3 to 8 degrees below normal through Sunday afternoon, with some mountain valleys in the eastern mountains looking at near to below freezing temperatures tonight (confidence 65-80%). With winds expected to weaken and skies remaining mostly clear, confidence is high enough (65-80%) to warrant a freeze warning for tonight in the Wallowa valley.

Sunday through early Tuesday, upper level ridging will move over the region, resulting in a warming and drying trend through this period. At this time, given the increased high pressure over the region and expected warming, confidence is low (25-35%) in another round of near to below freezing temperatures developing across most of our mountain valley locations.

Tuesday through Friday: Confidence is mod-high (60-80%) that an active period of weather will develop through the remainder of the work week. Ensemble cluster and deterministic guidance are in agreement of a weakening upper low offshore becoming an open wave and lifting northeast. The upper shortwave trough passage over the PacNW will bring scattered shower chances across mountain areas as well as in central OR with slight chance (15-205% of isolated thunderstorms in central OR, WA Cascades, and portions of the eastern mountains. Breezy westerly winds will develop across the Lower Columbia Basin, central OR, and portions of the eastern mountains Tuesday afternoon. RHs along the periphery of the southern Blues will remain low into Tuesday afternoon, resulting in elevated fire weather conditions as the winds begin to increase.

Early Wednesday, ensemble cluster guidance is in good agreement that an upper low will drop down the BC coastline and setup just offshore the PacNW, increasing shower chances along the Cascade crest. Late Wednesday into Friday, however, ensemble cluster solutions are split between two solutions. The first solution being the upper low sitting offshore through Thursday into early Friday, then moving inland. The second solution is for the upper low to push inland on Thursday and slowly move across the region through Friday. The first solution would result in rain shower chances developing across the eastern mountains late Thursday into Friday; the second solution would result in shower chances as early as Wednesday night, with widespread mountain chances and isolated lower elevation chances through Friday. Current confidence is moderate (50-60%) in shower chances developing area-wide sometime late in the workweek, but confidence is low (20-30%) in timing and precipitation amounts. Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

VFR conditions continue with mid to high clouds around the general area. Not expecting low ceilings, but could see some overnight smoke makes it way down to the surface, temporarily bringing MVFR conditions (5 to 15 percent chance for all TAF sites). Otherwise, general breezy conditions across all sites, with winds weakening as we head into the evening and overnight hours.

Preliminary Point Temps/PoPs

PDT 43 77 44 86 / 0 0 0 0 ALW 49 77 50 89 / 0 0 0 0 PSC 47 80 48 88 / 0 0 0 0 YKM 49 81 53 86 / 0 0 0 0 HRI 48 81 48 88 / 0 0 0 0 ELN 43 76 46 81 / 0 0 0 0 RDM 35 79 40 87 / 0 0 0 0 LGD 40 79 43 89 / 0 0 0 0 GCD 41 80 46 92 / 0 0 0 0 DLS 52 81 55 88 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until noon PDT Monday for ORZ041-505-506- 509>511. Freeze Warning from 1 AM to 9 AM PDT Sunday for ORZ050.