textproduct: Pendleton

KEY MESSAGES

- Minor flooding into Thursday along the Umatilla River.

- Drier conditions return Thursday.

- Medium confidence (30-60 percent) in freezing temperatures for the Columbia Basin and Blue Mountain foothills Saturday morning.

UPDATE

Widespread precipitation has ended this evening as the upper- level low pressure system that brought ample precipitation to the region over the last 36 hours has exited to the east. CAMs continue to advertise low-medium potential (20-40 percent PoPs) for light upslope precipitation into the Blue Mountains overnight and Thursday, but as far as area streams and rivers are concerned, the bulk of the precipitation has already fallen.

Latest forecasts from the NWRFC have trended downward for many area rivers, based on latest QPE and QPF. The Umatilla River upstream/east of Pendleton is now forecast to remain at Minor flood stage overnight into Thursday, while in Pendleton the river is forecast to remain at bankfull/action stage. Elsewhere, the Naches River near Naches is at bankfull/action stage, and is forecast to remain so through Thursday, while other locations are now expected to remain below bankfull/action stage.

Opted to extend the areal flood advisory for the northern Blue Mountains through the night due to the ongoing minor flooding.

Winds remain breezy to locally windy, still quite gusty along the most wind-prone ridges within the Columbia Basin region, but are forecast to slacken overnight.

Looking ahead, an environment characterized by low PWATs (0.15-0.25 inches) coupled with mostly clear or clear skies and predominantly light winds has piqued my interest in freeze potential for Saturday morning. Mid-level cloud cover and locally breezy northeast winds may keep temperatures above freezing if they materialize. After collaboration with surrounding offices, held off on any freeze watches. Will keep a close eye on the set-up over the next couple days as confidence is already 30-60 percent in freezing temperatures, highest for low-lying and cold-prone portions of the Columbia Basin and Blue Mountain foothills. 86

DISCUSSION...issued 156 PM PDT Wed Apr 22 2026

Current radar shows a line of light to moderate rain continuing to fall in the Columbia Basin down through the Blue Mountains. The Kittitas and Yakima Valleys have dried out for the rest of the night with the line advancing ahead, though windy conditions persist with 40-50 mph gusts prevailing across the Kittitas Valley through the evening hours. Near the Northern Blue Mountains, strong orographic lift has enabled continuous moderate rainfall embedded with gusty 35-45 mph winds through the morning to afternoon hours. Observations from the past 12-hours shows that multiple sites already received 1 inch or greater of precip that include Meacham, Boiling Point, and Emigrant Springs. High confidence (>90% chance) that the Northern Blues will see at least an additional 1.7 to 2.7 inches of precip through tonight with the HREF 24-hour precip showing 1.3 to 1.5 inches in the 25th percentile. At the 75th percentile that jumps to 1.7 to 2.2 inches. Winds will continue to be breezy to locally windy across the OR Foothills, Kittitas Valley and Blues with winds decreasing below advisory level in the later evening hours (>90% confidence).

Synoptically, a ridge protruding into the PacNW & British Columbia area in a sideways rex pattern will tapper down PoPs through early next week. Model cluster support a cutoff low in the Alberta area will bring the area in-between the two systems with the ridge keeping most of the region dry while the low to the east will bring light snow showers into the Wallowas and parts of the Northern Blues. All of the LREF clusters tell a similar story through early next week with keeping the Columbia Basin dry with some light snow showers and rain across the mountainous regions (that includes Central Oregon). Not seeing anything in the way of any major impacts or highlights through early next week at this time with the ridge still present and preventing any major QPF systems to develop.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

VFR conditions are forecast at all sites for the next 24 hours as the low-pressure system that brought widespread rain and breezy to windy conditions departs to the east overnight.

Winds remain strong and gusty at PDT, but anticipating winds to diminish over the next several hours such that winds at all sites will be in the 5-15 kt range with gusts up to 25 kts through the remainder of the period.

CIGs in the 5-7 kft range are forecast at PDT/ALW/PSC overnight and Thursday as a second disturbance moves over the northern Rockies. Cloud coverage elsewhere is forecast to be more FEW-SCT should stratus develop. 86

HYDROLOGY...issued 156 PM PDT Wed Apr 22 2026

Rainfall has been less than forecast but has still been substantial. Rain amounts have been up to 2 inches in the Blue Mountains and up to an inch in the Blue Mountain Foothills so far and another half inch to inch of rain is possible through this evening. This has caused streams and rivers to rise. The Umatilla River at Gibbon is forecast to approach moderate flood stage this afternoon, though with reduced rainfall amounts, confidence is low to medium (30%-40%) of approaching moderate flood stage. Confidence is 70% to 80% that the Umatilla at Gibbon will reach minor flood stage. The Umatilla River at Pendleton is forecasted to reach minor flood stage by a few inches briefly between 9 PM and 5 AM tonight. Confidence is only about 50% of this happening. The Grande Ronde River at Troy, the John Day River at Service Creek and the Walla Walla River at Touchet River are all expected to exceed bankfull tonight and tomorrow. The first two only exceed it by a few inches. The Walla Walla River at Touchet gets to within a half foot of minor flood stage, but with rainfall trending lower than anticipated, do not believe it will reach minor flood stage. Elsewhere, the forecast for the Naches River at Cliffdell has been lowered to just below action stage. The Naches River at Naches is forecast to get about a half foot above bankfull tomorrow morning but should not cause any significant flooding. 83

Preliminary Point Temps/PoPs

PDT 39 59 37 56 / 30 10 20 0 ALW 42 59 38 57 / 40 30 40 10 PSC 42 66 38 62 / 10 10 20 0 YKM 39 67 38 60 / 0 0 10 0 HRI 40 64 38 60 / 10 0 10 0 ELN 40 60 34 56 / 0 0 10 0 RDM 26 63 29 58 / 20 0 0 0 LGD 36 55 35 52 / 90 20 50 10 GCD 32 57 33 53 / 90 0 10 10 DLS 41 65 42 63 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Flood Watch through Thursday evening for WAZ029. OR...Flood Watch through Thursday evening for ORZ502-507-508.