textproduct: Pendleton

KEY MESSAGES

- Above-normal temperatures likely (80-100 percent confidence) into the middle of next week

- Very low to slight chance (5-20 percent) of mountain showers and thunderstorms late Friday through early next week

DISCUSSION

Day Cloud Phase RGB imagery reveals few to scattered fair weather cumulus over the east slopes of the Washington Cascades and adjacent ridges that extend eastward through Kittitas, Yakima, and Klickitat counties. Farther east, few to scattered cumulus are also present over the Blue Mountains. Chances of showers are very low (5 percent or less) this afternoon.

Zooming out to examine the broader picture, a Rex block look- alike pattern has set up across the region. An amplified upper- level ridge in the northeast Pacific extends across the Pacific Northwest pole-ward through the Canadian Rockies and into the prairies. Meanwhile, a closed low is visible over Baja California (ensemble guidance takes it inland across the Southwest this evening through Friday, so will argue this is not a true blocking pattern). A couple shortwaves are evident upstream of the ridge, the latter of which will be the main feature of interest Friday through early next week.

By Friday afternoon through Saturday morning, the second shortwave will approach the Pacific Northwest, deepening into a closed low. Ensemble and deterministic guidance show some slight spread with regard to its location, which will modulate convective potential across the Cascade crest and western half of our forecast area. Solutions that are closer to the coast present a better chance of convection. Currently, have a very low chance (5-15 percent) of showers and thunderstorms for the Washington Cascade crest and areas east of the Cascade crest, while the Cascade crest of Oregon has a 15-25 percent chance of showers and 10-15 percent chance of thunderstorms.

All clusters of ensemble solutions take the upper-level closed low south along the coast of Oregon and California over the weekend. As a result, a slight chance to chance (10-25 percent) of showers and slight chance (5-20 percent) of thunderstorms remains in the forecast for portions of the Cascades and Blues each day.

By Sunday, the upper-level pattern resembles more of a true Rex block with the closed low along the coast of California and an amplifying ridge pole-ward in the northeast Pacific, Pacific Northwest, and Canadian Rockies. This will lead to continued above-normal temperatures across the forecast area, especially north of central Oregon and the southern Blue Mountains.

Monday and Tuesday, have seen a continued southward trend in the location and track of the closed low in ensemble guidance over the last couple runs, resulting in lower chances (5-20 percent) of precipitation for our forecast area than previously forecast yesterday. A note on uncertainty, all clusters take the closed low inland across California, the Great Basin, and the Southwest sometime between Monday and Tuesday, but details in timing vary.

To touch on forecast temperatures, while there is still some uncertainty in how hot conditions will be under the ridge Friday into early next week (partly due to the aforementioned uncertainty in shower and thunderstorm chances and resultant cloud cover), chances of afternoon highs exceeding 80 degrees across all major population centers are medium to very high (50-99 percent) each day per latest NBM calibrated probabilities. Sunday through Wednesday, chances of reaching 90 degrees are low-medium (20-65 percent) for the Yakima Valley and lower Columbia Basin as well as heat-prone portions of the eastern Columbia River Gorge as well as central and north- central Oregon. Moreover, Sunday through Wednesday, there is a low-medium (20-60 percent) chance of HeatRisk reaching Moderate (level 2 of 4) in the Yakima Valley, lower Columbia Basin, and heat-prone portions of the eastern Columbia River Gorge as well as central to north-central Oregon. For context, this level of heat affects those who are sensitive to heat, especially those without cooling/hydration. 86

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

VFR conditions to prevail through the period. Winds will be light and diurnally driven. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 46 80 51 81 / 0 0 0 0 ALW 50 80 55 82 / 0 0 0 0 PSC 45 84 51 87 / 0 0 0 0 YKM 47 81 54 83 / 0 0 0 0 HRI 45 83 50 84 / 0 0 0 0 ELN 44 76 50 79 / 0 0 0 10 RDM 37 79 44 77 / 0 0 10 10 LGD 41 74 47 77 / 0 0 0 0 GCD 41 76 48 77 / 0 0 0 10 DLS 50 81 56 84 / 0 0 10 0

PDT WATCHES/WARNINGS/ADVISORIES

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