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 /06Z TAFS THROUGH 06Z SUNDAY/

Light rain will continue to drift north across KDLS for the next few hours and then toward 12z, showers could be expanding across areas like ALW/PSC and YKM. Overall light winds (less than 10 knots) will be the rule at least until Saturday afternoon when chances for thunderstorms and locally erratic outflows could bring stronger gusts anywhere from BDN/RDM, northeast to the PDT/PSC/ALW terminals (mid to late afternoon and early evening).

Preliminary Point Temps/PoPs

PDT 47 65 42 60 / 50 50 30 70 ALW 50 65 46 60 / 50 70 30 80 PSC 49 71 44 66 / 30 40 10 40 YKM 48 67 42 68 / 30 40 10 20 HRI 47 69 44 63 / 40 40 10 50 ELN 45 60 39 63 / 30 50 10 20 RDM 40 61 37 54 / 80 70 70 60 LGD 45 62 41 55 / 50 90 60 100 GCD 42 61 40 52 / 60 70 70 100 DLS 50 67 47 64 / 60 60 30 40

PDT WATCHES/WARNINGS/ADVISORIES

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