textproduct: Pendleton

KEY MESSAGES

- Showers today, with low thunderstorm chances, mainly over eastern areas.

- The next system will bring rain to the lower elevations and snow to the mountains Wednesday into Thursday.

- Temperatures will be about 5 to 10 degrees below normal Wednesday and Thursday before rising to near and possibly above normal later in the week.

DISCUSSION

An upper level low currently over northern California will weaken and gradually move inland through tonight. The broader upper trough will also move eastward through Monday, with the axis of the trough over the Great Basin by Monday night. Until the trough is east of the Pacific Northwest, unsettled conditions will continue.

Latest radar imagery showed a large area of showers, with some embedded thunderstorms over extreme southeastern Oregon and southwestern Idaho. Guidance has this area slowly pivoting northward and more developing northwestward around the larger circulation and through the remainder of today and into tonight. As this area moves northward, decent QPF is forecast across the Blue mountains and points eastward through Monday morning.

Lingering QPF is still expected over eastern areas on Monday, but with the trough moving out of the region, conditions should begin to improve by later Monday and drying is expected across most of the region, which will continue into Tuesday.

However, by later Tuesday into Wednesday precipitation chances increase as a low drops into the Pacific Northwest from Canada. This low will bring colder air and temperatures will be about 5 to 10 degrees colder than normal Wednesday and Thursday.

Overnight lows Wednesday night and Thursday night look to be quite chilly with temperatures below freezing in the Yakima and Kittitas Valleys and close to freezing along portions of the foothills of the Northern Blue Mountains. NBM probabilities of low temperatures <=32 degrees are 80 to 90 percent on both these mornings.

Furthermore, there will be breezy diurnal winds each day through Wednesday, in the Cascade Gaps and portions of the Columbia Basin and foothills of the southern Blue Mountains. Winds could gust in the 30 to 35 mph range and possibly as high as 40 mph.

Additionally, the low will bring at least some precipitation to all areas, with rain in the lower elevations (generally 0.15 inches or less) and snow in the mountains. Snow levels will drop from above 4000 feet on Wednesday to below pass level by Thursday morning. There is the potential for appreciable snow, especially above 5000 feet, but there are many caveats as well, including the time of year and the fact that any snow that falls during the day has a much more difficult time accumulating or is very wet in mid-April and the ground is warm.

This system will move out of the region by later Thursday and and ridging builds back in bringing dry conditions for the end of the week into the weekend. Another low may approach the Pacific Northwest for Sunday.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

VFR conditions currently at most sites, with KALW being the only terminal experiencing MVFR conditions due to reduced ceilings of 1800 feet. This is expected to persist overnight and through mid- morning Monday as light rain continues. Light rain is also occurring at KPDT, but should taper off into the early morning hours. However, decreasing ceilings should lead to MVFR conditions around sunrise before improving around noon.

Widespread breezy winds are anticipated overnight ant through the morning for all sites, with gusts of 20-30kts expected. KPSC/KYKM/KRDM/KBDN will see increased winds by mid-to late morning and extend through the period. 75

Preliminary Point Temps/PoPs

PDT 44 59 37 58 / 80 40 0 10 ALW 46 59 41 58 / 80 50 10 10 PSC 48 67 41 61 / 50 10 0 10 YKM 43 64 36 58 / 30 0 0 10 HRI 46 63 39 61 / 60 10 0 0 ELN 42 56 36 52 / 20 0 0 20 RDM 34 54 28 56 / 50 10 0 0 LGD 40 53 34 57 / 100 80 20 10 GCD 37 51 31 56 / 100 80 10 10 DLS 46 60 41 58 / 30 10 0 20

PDT WATCHES/WARNINGS/ADVISORIES

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