textproduct: Pendleton

KEY MESSAGES

- Warming trend into next week, peaking Monday. *Heat Advisories Issued*

- Breezy afternoon winds extend through midweek.

- Isolated fire weather concerns Sunday, widespread Tuesday.

DISCUSSION

Current radar and visible satellite imagery shows dry conditions and clear skies across the region. This is in response to an upper level ridge of high pressure offshore, that will continue to build through the weekend before slowly moving onshore early Monday. Clear skies and warming temperatures will persist as an inverted surface thermal trough builds along the coast associated with the upper level high pressure. As a result, high temperatures across the lower Columbia Basin, Central Oregon, Columbia Gorge, Blue Mountain foothills, and the Yakima/Kittitas Valleys will reach into the mid-to upper 80s today, upper 80s to low 90s Sunday, and in the mid-to upper 90s on Monday. Monday morning lows are expected to drop into the mid-50s and lead to widespread moderate HeatRisk (2 of 4) across the area. There are also isolated pockets of major HeatRisk (3 or 4) through the Columbia Gorge and the Yakima Valley. Thus, a Heat Advisory has been issued from 10 AM to 10 PM Monday for the Columbia Gorge, Central Oregon, and the Yakima/Kittitas Valleys. Temperatures will still be warm Tuesday with lows in the low to mid-60s and highs in the low to mid-90s, but a passing cold front in the afternoon/evening will bring relief overnight and into Wednesday as temperatures cool about 5 degrees.

As the ridge builds through the early part of the week, a shortwave ejects from an upper level system off the coast of Alaska, bringing an increase in cloud cover early Monday morning and breezy afternoon winds. The incoming shortwave approaches on Monday, helping to suppress the upper level ridge and tighten the pressure gradient between the two synoptic features. This pressure gradient is expected to peak late Tuesday morning and persist through the day as the GFS and SREF highlight a 10-14 mb gradient between PDX and GEG. This will lead to wind gusts of up to 55 mph across the Simcoe Highlands, north-central Oregon, and the Blue Mountain foothills, and up to 65 mph through the Kittitas Valley. The NBM advertises a 70-90% chance of advisory-level wind gusts (45+ mph) across the Simcoe Highlands, north-central Oregon, and the Blue Mountain foothills, and a 40-60% chance of warning-level wind gusts (58+ mph) through the Kittitas Valley. Confidence is improving in the likelihood of wind products being issued on Tuesday as only 19% of ensemble members hint at slightly higher wind values and 18% of members showcase slightly lower values due to variability related to the strength of the incoming shortwave trough and attendant cold front passage.

The heightened winds, hot temperatures, and low humidities will elevate fire weather concerns on Tuesday. Isolated concerns are present through Monday over north-central Oregon, but become more widespread on Tuesday. In fact, all fire weather zones (WA/OR691, OR700, OR704, and OR705) in where fuels are receptive for fire start and spread may have winds and humidity values that would correlate to the need for a red flag warning product. However, the incoming cold front should help in bringing cooler temperatures across the area that would increase humidities, but this aid may arrive later in the evening. 50% of ensemble members suggest either a faster incoming shortwave or a more suppressed ridge Tuesday afternoon/evening, which would relate to higher afternoon humidity values than currently forecast. Thus, this would need to be further analyzed as the event nears for more model consistency in the timing of the incoming shortwave.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

VFR conditions are forecast at all sites through the period. Skies are expected (95 percent confidence) to be clear to mostly clear, with some passing cirrus. Winds will be diurnally driven, mostly light overnight followed by breezy (10-15 kts) northerly to easterly winds with higher gusts (15-20 kts) during the afternoon and evening hours.

FIRE WEATHER

As stated in the above discussion, fire weather zones with fuels that are receptive to fire initiation and spread (WA/OR691, OR700, OR704, and OR705) may require fire weather products on Tuesday related to low afternoon humidities and high winds. There is good confidence (70-90%) that winds will be high enough to warrant concerns, but only marginal confidence (50%) is present when analyzing minimum afternoon humidities. Current timing of concern would be between 1000 and 2200 Tuesday.

Preliminary Point Temps/PoPs

PDT 50 87 53 92 / 0 0 0 0 ALW 54 87 57 92 / 0 0 0 0 PSC 56 91 57 96 / 0 0 0 0 YKM 57 91 60 98 / 0 0 0 0 HRI 54 90 56 95 / 0 0 0 0 ELN 53 87 59 94 / 0 0 0 0 RDM 47 86 49 92 / 0 0 0 0 LGD 48 84 49 89 / 0 0 0 0 GCD 45 86 47 91 / 0 0 0 0 DLS 61 93 64 99 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory from 10 AM to 10 PM PDT Monday for WAZ024-026- 027. OR...Heat Advisory from 10 AM to 10 PM PDT Monday for ORZ041-511.