textproduct: Pendleton

KEY MESSAGES

- Isolated to scattered thunderstorms over the Blue Mountains this afternoon and evening. Very low chance (5-14 percent) to slight chance (15-24 percent) elsewhere.

- Below-normal temperatures, breezy to windy westerly winds, and periods of showery weather are very likely (99 percent confidence) tonight through the weekend.

DISCUSSION

Water vapor imagery shows a broad area of low pressure stretching from the Gulf of Alaska to the western CONUS. There are currently a couple main low centers; one is located over Vancouver Island and one farther northwest in the Gulf of Alaska. Meanwhile, a strong shortwave is tracking inland over the western CONUS along the southern periphery of the low.

At the surface, cool conditions (lower 50s to lower 70s) are present from central Oregon through the Blue Mountains and their foothills. Somewhat warmer temperatures (upper 60s to very low 80s) are in place across the Columbia Basin and adjoining lowlands of south-central Washington and north-central Oregon.

Isolated thunderstorms have developed over the Blue Mountains this afternoon, and are expected (80 percent confidence) to expand in coverage through the afternoon hours before diminishing later this evening. There is still a slight chance (15-24 percent) of thunderstorms along the Blue Mountain foothills and portions of the lower Columbia Basin this afternoon as well.

Looking ahead, continued below-normal temperatures, breezy to windy westerly winds, and periods of showery weather are very likely (99 percent confidence) as the closed low moves inland over the Pacific Northwest on Saturday before tracking inland Sunday into early next week.

Cluster analysis of 12Z ensemble members shows relatively small differences in timing/location and magnitude of the low during the period, so confidence is high in the current forecast of predominantly below-normal temperatures into early next week. However, even small differences in the track/timing of the low can have a significant impact on precipitation.

On the topic of precipitation, for the past several runs, deterministic and ensemble NWP guidance have been consistently advertising a couple shortwaves wrapping around the low Sunday and Monday. These will serve as the focusing mechanism for additional precipitation, with the best chances of noteworthy precipitation in Wallowa County; calibrated NBM probabilities indicate a 30-60 percent chance of 0.50" or greater during the period. Elsewhere, currently forecasting lighter precipitation (mountains and foothills) or isolated precipitation (lowlands).

Breezy to windy westerly winds will almost certainly (99 percent confidence) persist through the weekend and into early next week. Latest NBM guidance suggests low-medium (20-60 percent) chances of advisory-level wind gusts Saturday and Monday through the wind-prone regions of the Cascade gaps and lower elevations. Chances are highest (50-95 percent) on Sunday, and wind headlines may be needed.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

VFR conditions expected through the period. An upper low pressure system impacting the region will bring a Prob30 chance of showers to sites PDT/ALW into the early evening hours today. There is a 20% chance of showers impacting sites RDM/BDN through 03Z as well, but opted not to include in TAF at this time. Breezy winds will continue to develop and impact sites this late afternoon into the evening, becoming light overnight. The exception is site PDT where breezy winds will continue overnight. Expect breezy winds to redevelop mid to late morning tomorrow at sites DLS/RDM/ALW. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 47 69 46 71 / 50 0 10 30 ALW 53 71 51 71 / 30 10 10 50 PSC 52 75 50 79 / 0 0 0 10 YKM 50 74 50 79 / 0 0 0 0 HRI 50 73 48 75 / 10 0 0 10 ELN 46 67 46 70 / 0 0 10 0 RDM 40 62 35 66 / 10 20 10 10 LGD 47 63 44 63 / 90 30 30 70 GCD 43 62 39 63 / 90 70 40 40 DLS 53 70 52 72 / 10 10 10 10

PDT WATCHES/WARNINGS/ADVISORIES

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