textproduct: Pendleton

KEY MESSAGES

- Breezy winds linger today. *Wind Advisory Active*

- Cooling into Friday, freezing morning temperatures Saturday

- Light mountain showers Sunday, including foothills on Monday.

UPDATE

Dry air and weak winds will bring abundant radiation cooling to bring freezing temperatures across parts of the Columbia Basin, Northern Blue Mountains, and Kittitas Valley Friday night into Saturday morning.

DISCUSSION

Current radar and visible satellite imagery very light returns across northern Columbia and Wallowa counties under mostly clear to partly cloudy skies. This is in response to an upper level trough to our northeast that will strengthen and extend south, bringing a cold front passage overnight tonight before slowly pushing east over the weekend. The frontal passage will bring breezy winds for the remainder of the evening, as well as cooler temperatures Friday as highs are expected to peak in the upper 50s to low 60s across lower elevations of the Columbia Basin and Central Oregon. Current wind gusts across much of the area are between 15-25 mph and will continue to slowly subside through the remainder of the evening. However, areas along the east slopes of the Washington Cascades, primarily through the Kittitas Valley, will experience more prolonged and heightened gusts of between 35-45 mph. Thus, a Wind Advisory has been issued across the Kittitas Valley until 9 PM this evening as gusts of up to 50 mph will be possible.

The cold front will pass to our south on Friday as the upper level trough continues to dip south, providing northern flow aloft. This will bring cooler temperatures on Friday under sunny skies. These clear skies will persist through the day and into Saturday, allowing efficient radiational cooling to occur as surface high pressure slides in behind the cold front. As a result, frigid morning temperatures are expected as morning lows will dip into the upper 20s to low 30s across the Lower Columbia Basin and Central Oregon. Confidence in these freezing Saturday morning temperatures is high as the NBM advertises a 70-90% chance through Central Oregon and Union county (Bend, Redmond, Madras, John Day), with a 40-70% chance over the Blue Mountain foothills and Kittitas Valley (Ellensburg, Pendleton, Walla Walla, Heppner, Condon) of experiencing morning temperatures of 32 degrees or lower. There is even a 45-65% chance of Central Oregon and Union county dipping into the upper 20s Saturday morning via the NBM.

The upper level trough will continue to dip south as an embedded shortwave approaches from the northwest on Sunday, bringing a return to mountain rain and high elevation snow chances to the area Sunday and Monday. The trough will dip south and tap into slight moisture Sunday to bring a 25-35% chance of showers to the Cascades, Blue Mountains, and John Day Highlands Sunday, with minimal amounts expected (<0.05"). The shortwave arrives on Monday to enhance rain chances (30-50%) and extend along the Blue Mountain foothills and the John Day Basin (20-40%). Monday's rain amounts are still expected to be minimal as the ECWMF AI Ensemble and GFS ensembles showcase Precipitable Water amounts of between 0.25-0.45" (80-90% of normal). Rain amounts over higher terrain across the Blue Mountains and Elkhorns may reach a wetting rain (0.10" or more), but lower elevations are likely to stay well below that amount with very little (less than 0.02") along the foothills. Snow levels will hover between 5000-6000 feet Sunday and Monday.

The trough begins to move east into Monday, opening the door to a slow moving upper level ridge and surface high pressure Tuesday onward. This will bring dry and warming conditions across the area as high temperatures reach into the upper 70s to low 80s through the Lower Columbia Basin on Friday. The NBM suggests a 45-60% chance of high temperatures reaching 80 degrees or above for the Tri-Cities area, Yakima, and The Dalles, and a 20-30% chance for Walla Walla and Hermiston Friday. Confidence in these chances are rather low as ensemble members struggle with the strength of the incoming shortwave that enhances southwest upper level flow to advect a warmer airmass into the region late in the week. Currently, 51% of ensemble members showcase the present ridge effectively shearing the incoming shortwave north versus the ridge shifting east and breaking down as the shortwave pushes inland earlier. Either way, the overall pattern aligns with warming and drying conditions through the workweek after light mountains showers Monday. 75

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

VFR conditions prevail with dry conditions persisting. Winds will be light in general. Still a bit breezy in PDT with 20 knot gusts going through the area, but will decrease going into the later morning hours. Otherwise, no CIG or VIS levels expected to drop below VFR status.

Preliminary Point Temps/PoPs

PDT 60 35 55 31 / 10 30 0 0 ALW 60 36 57 35 / 30 40 0 0 PSC 68 37 61 31 / 10 20 0 0 YKM 66 37 61 34 / 0 0 0 0 HRI 66 37 60 31 / 0 20 0 0 ELN 60 33 56 31 / 0 0 0 0 RDM 63 29 57 24 / 0 0 0 0 LGD 54 34 51 28 / 20 60 10 0 GCD 59 33 52 28 / 0 0 0 0 DLS 65 41 63 37 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Freeze Warning from midnight Friday night to 8 AM PDT Saturday for WAZ026-028-029. OR...Freeze Warning from midnight Friday night to 8 AM PDT Saturday for ORZ044-507.