textproduct: Pendleton

KEY MESSAGES

- Shower and thunderstorm chances continue today, and decreased chances on Sunday.

- Another system will bring precipitation back to the region later Tuesday into Wednesday.

DISCUSSION

An upper low was approaching northern California and will move inland early Sunday morning. The low will then weaken and move east northeastward through Monday as a broad upper trough remains over the western CONUS. By later Monday, into Tuesday, this trough will move eastward and weak ridging will move into the area, followed by a more zonal westerly flow.

Guidance has continued to show that the best chances for thunderstorms this afternoon and evening is along a diagonal line from central Oregon through the Blue Mountain Foothills and into eastern Oregon. Latest satellite imagery showed some cumulus field development and a lot of clouds but also enough breaks in the clouds for thunderstorms to develop. There is certainly enough CAPE (200-500 J/kg) and supportive LIs (-1 to -3 degrees Celsius). However, temperatures are cooler than they were at this time yesterday and so far thunderstorms have struggled.

Any thunderstorms should decrease this evening. On Sunday, both the shower and more limited thunderstorm threat will move eastward and mainly be confined to eastern portions of the area.

Drying will move in from west to east on Monday and continue into most of Tuesday.

By later Tuesday into Wednesday, an area of low pressure will drop down from Canada and bring another chance of precipitation, including the potential for late season snow to the mountains. This next system looks to being over 0.75 inches of liquid equivalent QPF to the mountain crests and at least some snow. It is very difficult for snow to accumulate during the day this time of the year, but certainly it can happen at night, but at least several inches of snow is possible, and snow levels will be below pass level. At lower elevations, generally 0.25 inches of rain or less is expected.

Temperatures will average about 5 degrees below normal Wednesday into Thursday, and there could be some below freezing mornings especially in the colder valleys. NBM probabilities are as high as 80-90 percent for lows <=32 degrees Thursday morning in the Yakima and Kittitas Valleys.

Drier weather is then expected for the end of the week.

It will also be a bit breezy Tuesday and Wednesday mainly in the normally breezy locations, with wind gusts of 30 to 35 mph, and possibly as high as 40 mph. NBM probabilities of wind gusts >=39 mph are between 60 and 80 percent, especially across portions of the Columbia Basin and Foothills of the southern Blue Mountains.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Another round of precipitation for the area spreading south to north associated with the cold/moist conveyor belt and weak isentropic lift from and approach low pressure off the Pacific. VFR conditions are anticipated although brief MVFR visibility and cigs can occur on Sunday in rain. Primary time window is from around 14z through 23z, and high enough confidence (greater than 50 and upwards to 80%) for using prevailing rain.

Preliminary Point Temps/PoPs

PDT 65 43 58 44 / 50 30 80 80 ALW 65 46 60 46 / 50 20 80 80 PSC 71 44 66 47 / 30 10 50 60 YKM 67 42 67 44 / 40 0 30 20 HRI 69 43 62 45 / 30 20 70 70 ELN 61 38 64 43 / 50 10 20 20 RDM 61 37 52 35 / 70 60 80 70 LGD 62 41 55 41 / 80 50 90 90 GCD 61 40 51 37 / 50 80 90 90 DLS 68 47 62 46 / 60 20 60 50

PDT WATCHES/WARNINGS/ADVISORIES

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