textproduct: Pendleton

KEY MESSAGES

- Extreme fire weather concerns today. *Red Flag Warnings Active* *Particularly Dangerous Situation (PDT) Red Flags Active*

- Windy conditions today. *Wind Advisories Active*

- Warming and drying trend next week.

DISCUSSION

Current radar and visible satellite imagery shows dry conditions as high level clouds are beginning to pass over portions of Central and Eastern Oregon. This is in response to the upper level low pressure system moving onshore over Southern British Columbia and an attendant dry cold front that will pass through the area this afternoon and evening. The RAP, GFS, and NAM all advertise a pressure gradient of 10-13mb across the Lower Columbia Basin, indicative of strong winds associated with this incoming system. The HRRR advertises 700mb winds of 40-50 mph extending across the Basin and peaking in intensity between 1 PM and 7 PM. with dewpoints expected to be between 35-45 degrees ahead of the front. The presence of such dry air over the pre- frontal environment will enhance the efficiency of elevated winds mixing down to the surface, further increasing confidence in the fire weather concerns. Thus, a Red Flag Warning is active across the Lower Columbia Basin, Eastern Mountains, and Central Oregon through 11 PM today. Due to the timing of the frontal system passing during peak heating hours in the afternoon, a Particularly Dangerous Situation (PDS) Red Flag has been included across the Lower Columbia Basin, Eastern Oregon, Blue Mountain, John Day Basin, and portions of Central Oregon through 8 PM as conditions may lead to rapid fire spread for new and existing fires.

Advisory level wind gusts (+45 mph) have already been experienced across the Kittitas Valley this morning, as observations near the Dalles and Hermiston have recorded several gusts between 40-45 mph. Guidance is having a tough time related to winds as the HREF and REFS both suggest a 10% chance or less of reaching 45 mph this morning. In addition, the NBM only highlighted a 10-20% chance of Ellensburg receiving a 45 mph gust this morning. This low bias related to guidance enhances confidence of elevated winds mixing down to the surface through the afternoon and evening as additional instability will be present along the passing frontal boundary. Thus, a Wind Advisory is active through 11 PM for the Lower Columbia Basin, Blue Mountain foothills, Eastern Columbia Gorge, and the Yakima/Kittitas Valleys.

The upper level trough continues to pass through the area on Sunday, keeping breezy conditions across the Kittitas Valley and Eastern Columbia Gorge with sustained west-northwest winds of 20-30 mph with gusts of 40-45 mph. This may warrant the issuance of a wind advisory, but will need further analysis over the coming 12-18 hours. The ECMWF and GFS AI ensembles show a thermal trough building along the coast Monday and Tuesday, producing a north-northeast wind across the area that ushers in a very dry airmass. Afternoon humidities are expected to hover in the mid-to upper teens as high temperatures peak Wednesday and Thursday in the low to mid-90s across the Lower Columbia Basin, Blue Mountain foothills, and Central Oregon. 75

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Predominantly VFR conditions are expected through the TAF period, though smoke from area wildfires will continue to be present and will have the potential to reduce CIGs/VSBYs, especially in the mornings. Additionally, a subset of CAMs within the HREF and REFS depict MVFR CIGs in low stratus (1.5-2.5kft AGL) overnight into Sunday morning at BDN/RDM. Confidence in persistent CIGs was low (<30%), but did include FEW025 to highlight the potential for low stratus.

Winds will continue to increase in magnitude through the afternoon, with breezy to locally windy westerlies (generally 15-25 kts with gusts of 20-35 kts) persisting at all sites through evening before slackening overnight into Monday.

FIRE WEATHER

A Red Flag Warning is currently active for fire weather zones across the Lower Columbia Basin, Eastern Mountains, and portions of Central Oregon as humidities are beginning to dip into the teens and winds of 20-25 mph and gusts of 30-40 mph are occurring. These conditions will persist through the remainder of the afternoon and extend into the evening associated with the passing of the dry cold front. Extreme conditions are expected through 8 PM, which has warranted a Particularly Dangerous Situation (PDS) designation for Red Flags across the Lower Columbia Basin, Kittitas Valley, Blue Mountains, Wallowa/Union Counties, and the Central Mountains of Oregon. Primary concerns are related to rapid fire spread over new and existing fires. Good to excellent overnight humidity recoveries are expected tonight in the wake of the passing system.

Breezy conditions will linger in Sunday across the Lower Columbia Basin zones, but afternoon humidities are expected to improve slightly and stay above red flag criteria. Dry conditions through Central Oregon with minimum humidities in the mid-teens, but winds are expected to be fairly light and around 10 mph from the north. Drying and warming conditions through the workweek, with north-northeast winds expected through Tuesday. 75

Preliminary Point Temps/PoPs

PDT 46 76 45 81 / 0 0 0 0 ALW 52 78 51 83 / 0 0 0 0 PSC 51 81 50 85 / 0 0 0 0 YKM 52 80 51 84 / 0 0 0 0 HRI 52 80 49 84 / 0 0 0 0 ELN 49 73 49 81 / 0 0 0 0 RDM 40 78 38 81 / 0 0 0 0 LGD 47 77 44 82 / 0 0 0 0 GCD 48 81 44 84 / 0 0 0 0 DLS 56 79 55 86 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning until 11 PM PDT this evening for WAZ690>693. Wind Advisory until 11 PM PDT this evening for WAZ024-026>029- 521. Air Quality Alert until 2 PM PDT Monday for WAZ028>030. OR...Red Flag Warning until 11 PM PDT this evening for ORZ691>704. Wind Advisory until 11 PM PDT this evening for ORZ041-044-507- 508-510. Air Quality Alert until 2 PM PDT Monday for ORZ044-049-050-502- 503-505>511.