textproduct: Pendleton

KEY MESSAGES

- Scattered showers and isolated thunderstorms over Wallowa County today

- Breezy to locally windy westerly winds through the Cascade gaps today and Tuesday

- Warming and mostly dry Tuesday through the week

DISCUSSION

Daytime heating has led to modest instability (surface-based CAPE of a couple hundred J/kg or less per SPC's RAP-based mesoanalysis and forecast soundings from the 12Z HREF/REFS) this afternoon across the Blues and Washington Cascades. While activity has been isolated elsewhere, scattered rain showers have developed across Wallowa County. Through evening, there is a slight chance (15 percent) of thunder across Wallowa County, with lower (5-10 percent) chances of rain showers and thunder for other parts of the Blues as well as the Washington Cascades.

Tuesday through Saturday, warming temperatures and mostly dry conditions are forecast region-wide as an upper-level ridge of high pressure will likely (90-95 percent chance) build into the region from the Pacific and dominate the weather. A couple weak shortwaves passing through northwesterly flow aloft coupled with modest diurnally induced instability (surface-based CAPE of a up to a couple hundred J/kg from forecast soundings) may facilitate some isolated showers for the mountains through Thursday, but PoPs are low (10 percent or less).

Breezy to locally windy westerly winds are forecast through the Cascade gaps today and Tuesday, but not anticipating a need for any wind headlines. In yesterday's discussion, mentioned the potential for westerly winds to meet advisory criteria on Thursday. Ensemble guidance has since trended towards a solution that would lead to a wind reversal to mostly light northeasterly (offshore) winds late Wednesday and Thursday as a shortwave digs south across the northern Plains and Rockies, just clipping the edge of our forecast area. Considering there is still some ensemble spread, will place confidence in this solution at medium (60 percent).

Considerable uncertainty in the 500-hPa pattern is present in ensemble solutions by the weekend, with roughly 45-50 percent of the variance in solutions explained by timing differences among solutions regarding the arrival of a trough or closed low from the Pacific.

The NBM has westerly winds returning to the region by late Friday, persisting through the weekend. Highest chances (10-40 percent) of reaching advisory-level winds have now been pushed back to Saturday and Sunday through wind-prone areas of the lower elevations, primarily the eastern Columbia River Gorge, north-central Oregon, the foothills of the Blue Mountains, and the Kittitas Valley. Of course, the magnitude of winds will be tied to the synoptic pattern, and given the uncertainty (see paragraph above), can't really talk about much confidence in forecast details yet.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

VFR conditions are forecast for the next 24 hours at all sites. Winds will be diurnally and terrain-driven, breezy from late morning through evening. There is a very low (10 percent) chance of rain showers this afternoon at YKM with even lower chances (5 percent or less) elsewhere.

Preliminary Point Temps/PoPs

PDT 42 72 46 73 / 0 0 0 0 ALW 46 72 49 73 / 0 0 0 0 PSC 44 77 48 79 / 0 0 0 0 YKM 44 76 47 79 / 0 0 0 0 HRI 44 75 48 77 / 0 0 0 0 ELN 41 68 43 73 / 0 0 0 0 RDM 30 72 37 74 / 0 0 0 0 LGD 36 68 40 70 / 0 0 0 0 GCD 34 71 38 74 / 0 0 0 0 DLS 45 74 49 78 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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