textproduct: Pendleton

KEY MESSAGES

- Extreme fire weather concerns Saturday. *Red Flag Warnings Issued* *Particularly Dangerous Situation (PDS) Red Flags issued*

- Windy conditions Saturday. *Wind Advisories issued*

- Dry conditions return early next week.

DISCUSSION

Current radar and visible satellite imagery shows dry conditions under smoky skies for much of the region. This is in response to a transient upper level ridge building today in the wake of the passing shortwave that brought additional cloud cover and breezy winds yesterday. The ridge is short-lived and is in front of a robust upper level low pressure system that will move onshore over the southern British Columbia coast Saturday morning and afternoon. A dry cold front at the surface is associated with this upper level low, and will pass through the Pacific Northwest from northwest to southeast through the afternoon and evening. This frontal passage is moving into a very dry air mass, and will bring with it strong winds out of the west. These parameters, coupled with additional instability associated with the frontal boundary and prolonged antecedent dry conditions, will promote extreme fire weather concerns which could lead to rapid fire spread for new and existing fires. Thus, multiple Red Flag Warnings have been issued from 11 AM to 11 PM across the Lower Columbia Basin, Blue Mountains, Central Oregon, John Day Basin, Grande Ronde Valley, Wallowa County, portions of the east slopes of the Oregon Cascades, and the Yakima/Kittitas Valleys. Expected high winds across the Lower Columbia Basin, Blue Mountains Wallowa/Union counties, Yakima/Kittitas Valleys, and portions of Central Oregon pose a Particularly Dangerous Situation (PDS) related to fire weather concerns, with the potential for catastrophic impacts related to wildfire spread. The NBM suggests a 60-90% chance of sustained winds of 25 mph in these areas, coupled with afternoon humidities in the mid-teens. Gusts are also expected to reach between 35-55 mph in these areas. Make sure to stay aware of the weather, and have multiple ways to receive or attain weather information.

The cold front will bring strong winds to the area, with highest winds expected to occur across the Kittitas Valley, Simcoe Highlands, Blue Mountain foothills, and the Lower Columbia Basin. Sustained winds of 25 to 35 mph with gusts up to 55 mph will be possible, peaking between 3PM-7PM. The GFS, SREF, and NAM all advertise a pressure gradient of 10-13mb between Portland and Spokane, which provides additional confidence in the wind forecast. Winds will stay elevated through the remainder of the evening before subsiding around midnight and continuing to drop overnight.

Conditions moderate on Sunday as a cooler and less dry airmass briefly moves over the region behind the exiting cold front and upper level low/trough. An upper level high pressure builds along the coast to allow for a thermal trough to develop. This will bring in a much drier airmass on Monday, dropping afternoon humidities into the low to mid-teens across Central Oregon - extending across the Columbia Basin by Tuesday. Diurnally breezy winds will result each day over the critically dry airmass, which may warrant the issuance of fire weather products over certain areas. 75

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

VFR conditions continue through the period with gusty winds developing Saturday morning/afternoon. Forecasting winds to gust 25 to 35 knots for DLS/PDT/ALW/PSC. Small chance (5 to 15 percent) of temporary MVFR conditions developing due to lingering smoke and haze.

FIRE WEATHER

RED FLAG WARNINGS have been issued for 11 AM to 11 PM Saturday for fire weather zones WA690-694 and OR 691-704. A Particularly Dangerous Situation (PDS) Red Flag has been issued for WA690-WA693, OR691-OR696, and OR700 between 2 PM and 8 PM. These zones included in the PDS could experience extreme fire weather resulting in rapid fire growth for new and existing fires. The ECMWF suggests 700mb winds of up to 50kts in the Basin with 40-45kts through Central Oregon. These elevated winds are moving into an airmass with precipitable water amounts of 0.4-0.6",60-80% of normal, which should allow for these winds to be more efficient at mixing to lower elevations. Guidance has also struggled with this unseasonal weather pattern, as observations highlight a higher bias related to model data. Thus, a trend toward drier and windier conditions is possible over the next 12 hours. 75

Preliminary Point Temps/PoPs

PDT 62 84 47 78 / 0 0 0 0 ALW 67 87 52 79 / 0 0 0 0 PSC 64 91 51 83 / 0 0 0 0 YKM 62 87 51 82 / 0 0 0 0 HRI 66 86 52 81 / 0 0 0 0 ELN 60 78 49 75 / 0 0 0 0 RDM 52 84 40 79 / 0 0 0 0 LGD 60 88 48 79 / 0 0 0 0 GCD 57 92 49 82 / 0 0 0 0 DLS 64 80 56 80 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning from 11 AM to 11 PM PDT Saturday for WAZ690>693. Air Quality Alert until 2 PM PDT Monday for WAZ028>030. Wind Advisory from 11 AM to 11 PM PDT Saturday for WAZ026. OR...Red Flag Warning from 11 AM to 11 PM PDT Saturday for ORZ691>704. Air Quality Alert until 2 PM PDT Monday for ORZ044-049-050-502- 503-505>511.