textproduct: Pendleton

KEY MESSAGES

- Shower and thunderstorm chances increase through Saturday, but linger into Sunday.

- Another system will impact the region around midweek and could bring some mountain snow.

- Rivers, especially the Naches and some points on the Grande Ronde are running high.

DISCUSSION

An upper level trough will move onshore in northern California this afternoon/evening as a large upper low approaches. This upper low will then move onshore in northern California Saturday night/Sunday morning and move eastward. As the low moves, its associated trough will move across the western states through Monday, which will keep unsettled weather over the area. Some weak ridging, then a more zonal flow will dry things out for later Monday into Tuesday.

Showers and isolated thunderstorms (20-30 percent) are expected this afternoon mainly over central Oregon and the John Day Highlands. On Saturday, there will be rain chances just about everywhere, with the highest probabilities (>60 percent) mainly in central Oregon and across the mountains. Thunderstorms chances are more widespread across the area as well the overall probabilities still remain generally 25 percent or less. As the trough migrates east on Sunday, the highest rain (and thunderstorm chances will mainly be over eastern Oregon and the John Day Highlands.

While CAPE values through Sunday are several hundred J/kg in areas and LI values are as low as -2 to -3 degrees Celsius. Questions remain as to how any cloud cover and any breaks in that cloud cover will play in to convective initiation.

Another low, this time dropping down from Canada will impact the region around midweek, bringing another round of precipitation, some late season mountain snow and temperatures about 5 degrees below normal.

Lastly, with the rainfall expected over the next few days, rivers, especially the Naches and a few points on the Grande Ronde, will continue to run high and are forecast to reach Action Stage. Other rivers will have significant in-banks rises but will remain below action stage.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Predominantly VFR conditions are anticipated for the next 24 hours. However, chances of sub-VFR VSBYs and/or CIGs in showers and/or thunderstorms increase this afternoon and evening to 30-50 percent for BDN/RDM with lower 10-30 percent chances of sub-VFR conditions for all other sites overnight into Saturday morning. Winds of 10 kts or less are forecast, though gusty outflow winds in the vicinity of showers and thunderstorms will likely (80 percent confidence) disrupt the background wind field such that confidence in details of the wind forecast is low- medium (30-60 percent) for any given site.

Preliminary Point Temps/PoPs

PDT 46 65 43 61 / 40 70 20 60 ALW 49 66 46 62 / 40 70 30 70 PSC 49 71 44 69 / 30 50 10 30 YKM 47 66 41 69 / 30 50 10 10 HRI 47 69 44 66 / 30 50 10 40 ELN 45 60 39 63 / 30 50 10 10 RDM 39 60 37 55 / 80 70 60 60 LGD 45 62 41 56 / 50 80 60 90 GCD 43 61 39 53 / 60 70 70 100 DLS 50 68 47 66 / 50 60 20 30

PDT WATCHES/WARNINGS/ADVISORIES

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