textproduct: Pendleton

KEY MESSAGES

- Light showers and afternoon isolated storms possible today.

- Breezy afternoon winds today and through week, peaking Friday. *Wind Advisories Issued*

- Cooling trend through Saturday, warming early next week.

DISCUSSION

Current radar and infrared satellite imagery showing pockets of light returns across Central Oregon as mid-to high level clouds slowly move across the Columbia Basin. This is in response to an approaching upper level shortwave that has tapped into some mid-latitude moisture to allow for light showers to extend east of the Cascades throughout the day. The best chances (30-50%) for showers will be along the east slopes of the Cascades and Central Oregon through this afternoon, and through Grant, Union, and Wallowa counties this afternoon through the evening. These counties will also experience the potential for isolated thunderstorms as the incoming shortwave erodes the backside of the exiting transient ridge. The HREF advertises surface CAPE values of 150-350 J/kg with 0-6km shear of 30-35kts, which is supportive of convective activity as also indicated by the Storm Prediction Center including the area in their General Thunderstorms (0 of 5) category. However, 700-500mb lapse rates do still look marginal (6-6.5C/km) and decrease through the afternoon and evening. Thus, it is expected that isolated, sub- severe thunderstorm cells will develop over our central and northeastern Oregon zones this afternoon and evening.

The incoming shortwave will also lead to the tightening of a pressure gradient along the Cascades, due to the interaction with the exiting transient ridge that brought warm and sunny conditions to the area on Tuesday. This enhanced gradient will impact much of the region with increased winds as the cold front passes mid-afternoon with gusts of 25-35 mph possible across the Blue Mountain foothills and the Columbia Basin. The highest winds will be experienced across the Simcoe Highlands and Kittitas Valley as west-northwest sustained winds of around 30 mph and gusts up to 50 mph will be possible. As a result, Wind Advisories have been issued from 1 PM today through midnight tonight. The NBM highlights a 70-80% chance of 45 mph gusts or greater through the Simcoe Highlands. In addition, the NAM and SREF indicate a 5-6mb pressure gradient between PAE and PSC, hinting to advisory-level winds through the Kittitas Valley.

Today's shortwave is spinning off a stronger upper level low pressure system currently located in the Gulf of Alaska. This low pressure will slowly move south along the coast of British Columbia Thursday and early Friday before moving onshore Friday evening and passing through the area on Saturday. Moisture looks to be lacking with this event and stays confined at elevation across the Cascades. However, a building upper level ridge to our east and associated surface high pressure will lead to windy conditions across much of the area. The GFS and NAM suggest a pressure gradient of 8-10mb between PQR and OTX, which would related to advisory-level winds across the Simcoe Highlands and north-central Oregon. The NBM shows a 70-80% chance of this occurring Friday afternoon and evening. Breezy winds are also expected across the Columbia Basin, Blue Mountain foothills, and Yakima/Kittitas Valley, but sub-advisory winds are currently expected. Consistency in guidance is improving as 59% of LREF ensemble members suggest winds near or slightly above the current forecast, with 41% of members hinting at an earlier or weaker incoming system. Another result of the dropping system will be cooling temperatures, as highs drop from the upper 70s to low 80s today into the upper 60s to low 70s Saturday across the Lower Columbia Basin, Blue Mountain foothills, and portions of Central Oregon. These Saturday values are 8 to 10 degrees below normal for this time of year. 75

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

VFR conditions currently across all sites, which will stay the course through the period. Ceilings will continue to drop this morning to around 5kft for all terminals, improving to 25kft through the evening. Breezy wind gusts of 20-30kts will impact KDLS/KPDT/KRDM/KBDN/KYKM this afternoon and evening. 75

FIRE WEATHER

Elevated fire weather concerns are anticipated on Friday across the Columbia Basin (Fire Weather zone WA691) due to a combination of breezy to windy conditions and afternoon relative humidity (RH) dropping to 20-25%. Compounding this threat is a dry baseline; Thursday afternoon's low RH (15-25%) will be followed by only moderate to good (50-65%) overnight humidity recoveries heading into Friday morning. Fuels in zone WA691 have been declared ready and receptive. While these compounding factors suggest a Red Flag Warning may be warranted for Friday, no official products have been issued at this time. 75

Preliminary Point Temps/PoPs

PDT 78 47 75 47 / 10 10 0 0 ALW 79 53 76 52 / 10 10 0 0 PSC 83 52 80 49 / 20 10 0 0 YKM 80 48 80 48 / 40 0 0 0 HRI 81 50 78 50 / 10 0 0 0 ELN 73 45 72 44 / 50 0 0 0 RDM 74 37 76 40 / 20 0 0 0 LGD 76 45 74 43 / 40 20 0 0 GCD 78 42 77 42 / 40 10 0 0 DLS 78 53 77 52 / 20 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 1 PM this afternoon to midnight PDT tonight for WAZ026-521. OR...None.