textproduct: Pendleton

KEY MESSAGES

- An upper level low will move onshore Thursday and remain over the Pacific Northwest through much of the weekend.

- Widespread shower chances through early Thursday, with isolated thunderstorm chances each afternoon through Friday. Low (<30) shower and thunderstorm chances, mainly over the mountains through the holiday weekend.

- Below normal temperatures through the remainder of the week and into the weekend.

DISCUSSION

An area of low pressure off the British Columbia coast will move southeastward and inland over Washington and Oregon on Thursday. This upper low will keep the weather unsettled over the next few days.

As this low approaches, strong southerly flow ahead of it will bring a fairly widespread rainfall across the region this evening into early Thursday. Most locations, except the Columbia Basin and possibly central Oregon should get wetting rain and the mountain locations should get significantly more, with mountain locations receiving at least 0.25 inches and possibly 0.50 inches or more. As the low moves across the region Thursday and Friday, the precipitation will largely be confined to the mountains, where additional wetting rains are possible. The highest rain total look to be for areas from the northern Blue Mountains eastward. With instability from the upper low in place, isolated (<20%) thunderstorms are possible, mainly over the mountains. Over the holiday weekend, precipitation chances still exist but will be lower, generally (<30%).

Finally, by Monday, the low begins to move eastward and drier weather will move in from later Monday through the midweek period.

Winds will also gust 20 to 30 mph this afternoon and evening as the low approaches.

High temperatures will mainly be in the 60s and 70s through the weekend. This is 7 to 10 degrees below normal on average. Lows will mainly be in the 40s, with some 30s as well, which are also about 7 to 10 degrees below normal. The ECMWF EFI indicates some areas mainly in central Oregon where departures are below normal are greater than the 90th percentile with some locations even in the 95th percentile below normal for high temperatures. By midweek, temperatures return closer to normal.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

An upper-level low will generate unsettled weather across the forecast area through the period. Widespread rain will likely (70-90 percent confidence) persist into the night at PDT/ALW/PSC with rain expected to taper off over the next several hours at DLS/RDM/BDN/YKM.

Confidence in persistent MVFR CIGs/VSBYs was too low (<50%) to include in the 06Z TAFs, but periods of RA or +RA at PDT/ALW may (30-50% chance per 00Z HREF guidance) result in temporary MVFR conditions (CIGs and/or VSBYs) overnight. Chances of sub-VFR conditions are low (<30%) elsewhere.

Included some PROB30 groups for showers or rain Thursday afternoon and evening for all sites except PSC/YKM.

Sustained winds of 10 kts or less are forecast through the period, but anticipating periodic gusts of 12-18 kts at BDN/RDM during the mid/late morning and early afternoon.

Preliminary Point Temps/PoPs

PDT 49 68 42 68 / 90 10 40 30 ALW 52 69 46 68 / 100 20 40 30 PSC 51 73 43 73 / 80 0 10 20 YKM 48 70 45 71 / 50 10 10 20 HRI 50 71 43 71 / 80 0 20 10 ELN 45 66 40 66 / 70 30 20 40 RDM 39 64 31 63 / 90 20 40 50 LGD 49 66 41 66 / 100 80 80 60 GCD 47 63 39 65 / 100 80 70 40 DLS 51 70 47 72 / 80 30 30 20

PDT WATCHES/WARNINGS/ADVISORIES

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