textproduct: Pendleton

KEY MESSAGES

- Isolated thunderstorms over the Blue Mountains and their adjoining foothills this afternoon and evening. The environment is supportive of isolated strong to severe storms, capable of producing gusty outflow winds and hail.

- Breezy to windy this afternoon and evening, then breezy Friday.

- Predominantly above-normal temperatures likely (50-80% confidence) to persist through next week.

DISCUSSION

Water vapor imagery shows a deep closed low churning offshore in the vicinity of 45.6N, 126.5W this afternoon. Meanwhile, a broad ridge of high pressure is located over the western CONUS, leading to southerly to southwesterly winds aloft over the forecast area. Monsoonal moisture from the Southwest is still present over the region with RAP-based Mesoanalysis suggesting PWATs of 1-1.2" over the Blue Mountains and their adjoining foothills. Coupled with ample surface moisture (dew points in the upper 40s to lower 60s from surface observations), sufficiently steep mid-level (700-500 mb) lapse rates of 7-8 C/km, and modest synoptic-scale forcing associated with the upper low, the environment is primed for additional shower and thunderstorm development through the evening. The northern Blue Mountains, their foothills, and Wallowa County are under a Marginal risk of severe thunderstorms per SPC's latest forecast, with the main hazards being severe outflow wind in excess of 50 kts and hail up to 1" in diameter. DCAPE 1300-1500 J/kg is strongly supportive of gusty outflow winds with any stronger convection that develops.

A strong cross-Cascade temperature gradient (25-30 degrees), marine layer on the west side, and cross-Cascade pressure gradient should support widespread breezy to windy westerly to northwesterly winds through the Cascade gaps and into the western portion of the Columbia Basin through the evening and into the overnight period. Have issued wind advisories for the aforementioned area through 08Z tonight.

Looking ahead, confidence is very high (95%) that the upper low will lift northeast into British Columbia through tomorrow and into the weekend. Breezy winds will continue through the Cascade gaps each day, and lower RH on Friday may lead to localized overlap of critical wind/RH (see Fire Weather discussion below).

Heading into next week, there is still uncertainty in details of the 500-hPa pattern, but confidence is medium-high (50-80%) in predominantly above-normal temperatures across the forecast area as the region remains under the influence of a broad ridge of high pressure over the western CONUS.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

VFR conditions are forecast at all sites through the TAF period. Additional isolated thunderstorms are expected (80% confidence) to develop this afternoon over the Blue Mountains, but there is low confidence (30% or less) in SHRA/TSRA this afternoon affecting PDT/ALW/PSC. Overnight, there is a very low chance (10% or less) of additional high-based showers developing over PDT/ALW/PSC.

Winds will become breezy to windy this afternoon and evening, strongest at DLS. Periods of breezy winds are anticipated to continue overnight into Friday morning.

Some thin smoke from area wildfires is present across central Oregon and may reduce VSBYs overnight into Friday, but confidence was too low (<30%) to introduce in the 18Z TAFs.

FIRE WEATHER

Isolated thunderstorms are expected to continue through this evening, mainly over the Blue Mountains. Stronger thunderstorms will be capable of producing strong, gusty, and erratic outflow winds in excess of 60 mph.

Tonight into early Friday, there is a very low chance (15% or less) of additional high-based showers and isolated thunderstorms over the Blue Mountains and eastern half of the Columbia Basin.

Breezy to windy westerly to northwesterly winds of 15-30 mph with gusts of 25-45 mph will persist through the Columbia Gorge and into the Basin through early Friday, but RH should remain above critical values so no Red Flag Warnings have been issued.

Warm, dry, and locally breezy conditions are then forecast Friday through the weekend with very low chances (15% or less) of showers or thunderstorms. Portions of the eastern Columbia River Gorge and western half of the lower Columbia Basin of Oregon may (50% confidence) flirt with overlap of critical wind/RH Friday afternoon and evening.

Preliminary Point Temps/PoPs

PDT 56 90 57 91 / 0 0 0 0 ALW 63 92 63 93 / 10 0 0 0 PSC 61 94 60 95 / 0 0 0 0 YKM 59 93 59 94 / 0 0 0 0 HRI 59 92 61 94 / 0 0 0 0 ELN 56 88 56 86 / 0 0 0 0 RDM 46 89 50 91 / 0 0 0 0 LGD 58 93 57 93 / 20 0 0 0 GCD 54 96 54 95 / 0 0 0 0 DLS 58 87 60 90 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 1 AM PDT Friday for WAZ024. Heat Advisory until 9 PM PDT this evening for WAZ026>029. Wind Advisory until 1 AM PDT Friday for WAZ026. OR...Wind Advisory until 1 AM PDT Friday for ORZ041-510. Heat Advisory until 9 PM PDT this evening for ORZ044-049-050- 507. Wind Advisory until 1 AM PDT Friday for ORZ044.