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 /06Z TAFS THROUGH 06Z SUNDAY/

VFR conditions continue to prevail, with no CIG or VIS issues expected. Radar currently shows a few showers across the east mountains not currently impacting any TAF sites. Breezy winds continue for DLS and PDT, while elsewhere will see their winds weaken to 10-15 knots by the early to late afternoon. Another round of light to moderate showers is possible in BDN and RDM with PROB30's occurring in the early afternoon hours.

Preliminary Point Temps/PoPs

PDT 47 69 46 72 / 20 10 10 10 ALW 53 71 51 73 / 20 10 10 10 PSC 52 76 50 80 / 0 0 0 10 YKM 50 74 49 80 / 0 0 0 0 HRI 50 73 48 77 / 0 0 0 0 ELN 46 67 46 71 / 0 0 10 0 RDM 40 62 34 67 / 20 20 20 0 LGD 47 63 44 65 / 100 40 30 40 GCD 43 62 39 65 / 90 70 40 20 DLS 53 70 51 72 / 10 20 10 0

PDT WATCHES/WARNINGS/ADVISORIES

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