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 /18Z TAFS THROUGH 18Z SUNDAY/

VFR conditions across all TAF sites through much of the period. BDN/RDM will see a decrease to MVFR due to low CIGs moving in after 11Z. Today, most TAF sites will see light rain to PROB30 chances of thunderstorms after 20Z, especially sites in Central OR and sites along the Foothills of the Blues. Although there's no below VFR conditions through the start of the period, the PROB30 chances include temporary MVFR conditions in the heaviest storms that will develop mainly affecting the VIS in heavy rain. 90

Preliminary Point Temps/PoPs

PDT 43 58 43 57 / 30 80 80 50 ALW 46 60 45 57 / 20 90 80 60 PSC 44 65 47 66 / 10 60 60 30 YKM 42 67 44 65 / 10 40 30 10 HRI 44 62 45 62 / 20 70 60 30 ELN 38 64 42 56 / 10 30 20 10 RDM 37 54 35 54 / 60 70 60 20 LGD 41 54 40 51 / 60 90 90 70 GCD 40 51 38 49 / 70 90 80 80 DLS 46 62 47 60 / 30 60 50 10

PDT WATCHES/WARNINGS/ADVISORIES

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