textproduct: Pendleton

DISCUSSION

Key Messages:

1. Windy conditions tonight, returning late Tuesday night. *Wind Advisories Active*

2. Significant rainfall leading to flood concerns through week. *Flood Watch Issued*

Current radar and visible satellite imagery showing moderate to heavy rainfall west of the Cascades, with isolated showers passing through the Columbia Basin under mostly cloudy to cloudy skies. This is in response to an upper level shortwave and associated cold front that is passing through the area this evening. The passing cold front will also tighten the pressure gradient across the Columbia Basin, providing breezy winds tonight through the morning hours on Tuesday. The RAP, GFS, and NAM advertise a gradient of 9.5-11.5 mb between Portland (PDX) and Spokane (GEG), which relates to sustained southwest winds of 25-35 mph with gusts of up to 60 mph, peaking between 8PM tonight and 3AM Tuesday morning. Confidence in these wind speeds is high (75-90%) as the NBM advertises a 70-95% chance of 50 mph gusts or greater across the Simcoe Highlands and southern Blue Mountain foothills and a 50-80% chance of 45 mph gusts or greater through the northern Blue Mountain foothills, Yakima Valley, and the Lower Columbia Basin. Thus, a Wind Advisory has been issued through 7 AM Tuesday for the aforementioned areas. Winds will slowly taper off through Tuesday morning and afternoon before a second cold front passage occurs late Tuesday night through Wednesday morning, promoting a return to breezy conditions. This second frontal system is not as strong as tonight's, as the GFS and NAM indicates a pressure gradient of 8-10 mb. These values relate to sustained southwest winds of 15-25 mph and gusts up to 40 mph, which is below the wind advisory threshold (45 mph or greater).

The early week system will not only bring windy conditions across the region, but substantial and widespread rainfall is anticipated through Wednesday associated with a strong atmospheric river (AR) event. The ECMWF and GFS ensembles show Precipitable Water (PW) amounts of around 1 inch, which is 225-250% above normal. The fetch associated with this AR extends to the date line (~170W), effectively tapping into subtropical moisture and temperatures. As a result, snow levels have soared into the 7000-9000 foot range as high temperatures are breaking into the upper 50s to mid-60s through the week, which is about 15-25 degrees above normal for this time of year. These warm temperatures and rain-on-snow potential due to elevated snow levels will allow rivers and streams to reach flood levels, especially for the Naches and Yakima Rivers as the current forecast reaches action stage over the next 24 hours and peaks in moderate flood stage for the Naches River near Naches and the Yakima River near Parker and Kiona Thursday and Friday. Reaches further upstream are expected to reach minor flood stage over the next 24 hours. As a result, a Flood Watch has been issued and is in effect through Friday morning. The Yakima River at Easton has already reached into action stage, with low-lying and flood prone areas already experiencing localized flooding. This has warranted the issuance of a Flood Advisory for the Elk Meadows area near Cle Elum as flooding is ongoing via contact with the public. In addition to the Yakima and Naches Rivers, the Klickitat River near Pitt and the Umatilla River near Gibbon both reach action (bankfull) stage Wednesday morning. River levels are expected to subside slowly over the weekend with all reaches currently forecast to fall below minor flood stage by early Monday morning. 75

AVIATION...00Z TAFs

Weather disturbance continues to bring light showers into some sites. Current conditions at all airports are at VFR. Main highlight will be the strong winds, which will/has already impact all airport sites. Most sites will see 20 to 30 mph+ gusts over the next 24 hours, with decreasing strength headed into the later morning hours/early afternoon tomorrow. VFR conditions will continue with some LAMP guidance suggesting MVFR conditions with lower ceilings over the second part of the period. Was only confident to give BDN MVFR conditions with RDM, ALW, and PDT not far behind in confidence (they will have a 5 to 15 percent chance for brief MVFR conditions due to low CIGs).

PRELIMINARY POINT TEMPS/POPS

PDT 48 56 46 63 / 60 100 90 60 ALW 49 55 48 62 / 80 90 100 70 PSC 50 57 46 64 / 40 80 90 40 YKM 42 52 39 62 / 80 70 100 70 HRI 50 58 46 64 / 40 90 90 50 ELN 37 45 36 54 / 90 70 100 70 RDM 45 57 45 62 / 50 80 50 20 LGD 45 51 43 58 / 90 100 100 70 GCD 45 52 46 58 / 50 90 70 30 DLS 51 56 49 63 / 90 100 100 80

PDT WATCHES/WARNINGS/ADVISORIES

OR...Wind Advisory until 7 AM PST Tuesday for ORZ041-510.

Wind Advisory from 4 PM this afternoon to 7 AM PST Tuesday for ORZ044-507-508.

WA...Wind Advisory until 7 AM PST Tuesday for WAZ024-521.

Flood Watch through Friday morning for WAZ026-027-521>523.

Wind Advisory from 7 PM this evening to 7 AM PST Tuesday for WAZ027>029.