textproduct: Pendleton

KEY MESSAGES

- Warm temperatures and breezy conditions persist through week.

- Elevated fire weather concerns through Saturday.

- Warming trend expected next week, peaking Tuesday.

DISCUSSION

Current radar and infrared satellite imagery shows dry conditions under clear skies. This is in response to a weak, transient ridge developing ahead of another weak shortwave that will dissipate over the region today. The incoming shortwave will increase winds through the afternoon across the Columbia Gorge and Kittitas Valley as west-northwest winds of 20-25 mph with gusts of up to 35 mph are possible, peaking between 6-10 PM today. Zonal, upper level flow from the west will slightly drop high temperatures from Wednesday, but will still be a couple degrees above normal. The shortwave dissipating over the area is associated with an upper level low pressure system that has dropped from the Gulf of Alaska and will stall off the Central British Columbia coast near Graham and Moresby Islands later this afternoon. It continues its descent on Friday to Vancouver Island as an upper level high pressure off the southern California coast shifts toward the 4 corners region. These movements will allow flow aloft from the west to become southwest on Friday, bringing a slight warming trend across the area to wrap up the week. Winds will also increase slightly on Friday due to the incoming system along the coast, with west- northwest winds of 20-27 mph and gusts up to 40 mph through the Columbia Gorge, and Kittitas Valley. Elsewhere, winds of 15-20 mph with gusts up to 25 mph are likely.

Warm, dry, and breezy conditions will keep elevated fire weather concerns across the Columbia Gorge, Lower Columbia Basin, and Kittitas Valley areas through the remainder of the week. Critical conditions will be related to humidities today, with afternoon values dropping into the low to mid-teens across the Columbia Basin and in the low teens to single digits across Central Oregon. Wind becomes more the issue on Friday as afternoon humidities rebound slightly, but increased afternoon winds will extend further into the Basin and Blue Mountain foothills as a result of a stronger pressure gradient between the approaching low pressure offshore and ridge to our southeast. The offshore system is able to tap into marginal subtropical moisture to alleviate afternoon humidity values, as winds stay more confined to the Columbia Gorge and eastern slopes of the Cascades. Currently, the more concern resides on Friday as more widespread breezy conditions are anticipated.

The upper level low that stalls off the southern British Columbia coast will weaken late Saturday and slide over the high pressure ridge that traveled from the 4 corners area to the Dakotas on Sunday. Another low will drop along the British Columbia coast to take its place, coupled with remnants of a weak low pressure to its southwest in the Central Pacific. These features, along with the elongated upper level ridge spanning across CONUS, will lead to a warming trend that will peak on Tuesday. Guidance is in disagreement in how long the offshore upper level low will linger before riding up and over the CONUS ridge, which directly relates to how hot temperatures reach on Tuesday. Currently, 67% of ensemble members advertise highs at or above the current forecast, which relates to a stronger incoming low pressure system and staying offshore longer before riding up the CONUS ridge. High temperatures would reach into the mid-to upper 90s across the Lower Columbia Basin and Blue Mountain foothills with this solution. 75

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

VFR conditions to prevail through the period. Breezy winds (12-18kts with gusts around 25kts) will persist at site DLS through this evening, then redevelop tomorrow morning. Site PDT will see period gusts up to 18kts through this afternoon. Otherwise, winds will be light through period. Lawhorn/82

FIRE WEATHER

Elevated fire weather concerns for WA690, WA691, and OR691 are present through Saturday due to winds and low relative humidities. Critical humidities and winds are expected to stay isolated today, primarily over western OR691 and eastern WA690 between 1600-2000. Friday's concerns are more scattered across OR691 between 1400-2000, and may warrant a fire weather product during that timeframe. However, at this time confidence of Red Flag criteria being met is only 40-50%. This will have to be further analyzed over the next 24 hours. Elevated concerns over western portions of WA690, WA691, and OR691 materialize between 1600-2000 on Saturday, but look to stay isolated along the zone's borders.

Fire weather concerns relax Sunday onward as light winds are expected, but dry conditions will still be present as afternoon humidities hover around 20-25%. 75

Preliminary Point Temps/PoPs

PDT 88 56 90 55 / 0 0 0 0 ALW 90 61 92 61 / 0 0 0 0 PSC 92 59 95 60 / 0 0 0 0 YKM 92 59 93 57 / 0 0 0 0 HRI 91 60 93 59 / 0 0 0 0 ELN 85 56 86 53 / 0 0 0 0 RDM 88 50 88 48 / 0 0 0 0 LGD 89 54 93 55 / 0 0 0 0 GCD 91 53 95 53 / 0 0 0 0 DLS 89 59 87 59 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Heat Advisory from noon Friday to 7 PM PDT Sunday for ORZ050.