textproduct: Pendleton

KEY MESSAGES

- Dry weather today and tonight.

- Isolated thunderstorms Saturday and Sunday.

- Widespread rain Saturday through early Sunday.

- Below normal temperatures through the next week.

DISCUSSION

Westerly flow will be over the region today, which will bring dry weather. The flow will become more southwesterly tonight in advance of low pressure which will move south then southeast over the Pacific and then approach the Washington and Oregon coasts on Saturday.

The low will then move onshore in Oregon Saturday evening and move northeast towards southern Canada during Sunday, bringing rain. Precipitation should end from west to east during the day on Sunday, with all rain ended by Sunday evening/night.

Rainfall amounts during the day on Saturday will not be very much and mainly confined to the mountains. QPF amounts should mainly be 0.10 inches or less. The more widespread rain is expected to move in during the evening and overnight. QPF amounts vary widely between the models with the NAM being on the lower side and the GFS and ECMWF having some of the higher amounts, depending on location. Current forecast values have <=0.25 inches in central Oregon ).50 inches or less in most lower elevation locations 0.75 to 1 inch for the Blue Mountain Foothills. Amounts of 1 inch plus are forecast for the Washington Cascades and Blue Mountains.

However, there is considerable uncertainty in these numbers. The ECMWF EFI indicates that while these values are in the 90th to 95th percentile, it also shows a value of 5 for shift of tails, which shows the high uncertainty. Looking at the ensemble QPF clusters, the wettest pattern only has about a 25 percent chance of occurring, though the most likely scenario still does bring decent rains.

Another concern for Sunday, as the low moves across is gusty winds, especially in the Cascade Gaps, Kittitas Valley, Simcoe Highlands, Columbia Basin, Gorge and Foothills of the Blue Mountains. Winds look to gust in the 30 to 40 mph range, possibly as high as 45 mph. NBM wind gusts probabilities >=39 mph are >60 percent in many of these areas. Depending on how things develop, it is possible wind headlines may be needed at some point.

Dry northwest flow will then move in for Monday. Another low and trough will then drop down from Canada on Tuesday. There is some discrepancy as to how quickly this low exits the area, but it is expected to be dry or mainly dry at this time, but bears watching.

Temperatures will be below normal through the weekend and into next week, with Sunday being the coolest day. Temperatures will average 5 to 10 degrees below normal, but will probably be 15 degrees below normal on Sunday.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

VFR conditions are expected through the TAF period. Winds will mainly be 10 kts or less, except at DLS which will have some gusty winds to around 20 kts this morning before decreasing to 10 kts or less this afternoon.

Preliminary Point Temps/PoPs

PDT 72 46 72 45 / 0 0 10 100 ALW 74 52 74 50 / 0 0 0 100 PSC 77 49 77 46 / 0 0 0 90 YKM 74 52 73 49 / 0 0 20 90 HRI 76 47 76 45 / 0 0 0 90 ELN 70 48 69 44 / 0 0 10 90 RDM 74 39 66 35 / 0 0 40 80 LGD 73 46 76 44 / 0 0 30 100 GCD 75 46 77 43 / 0 0 30 90 DLS 76 53 74 51 / 0 0 20 80

PDT WATCHES/WARNINGS/ADVISORIES

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