textproduct: Pendleton

KEY MESSAGES

- Above-normal temperatures and mostly dry conditions through this week into next week

- Wind Advisory in effect this afternoon and evening

- Periods of low relative humidity (10-20 percent) coupled with breezy to windy westerly winds Thursday and Friday through the Cascade gaps and across the Columbia Basin and Blue Mountain foothills

DISCUSSION

Satellite imagery shows mostly clear skies early this morning under an upper-level ridge of high pressure. Water vapor imagery reveals the ridge of high pressure extends from offshore northeast through the Canadian Rockies.

Later today, a weak shortwave will ride over the top of the ridge across British Columbia and the northern Rockies. Coupled with a cross-Cascade thermal gradient (warmer on the east side, cooler on the west side) due to an established marine layer (evident in Nighttime Microphysics RGB imagery as well as 00Z observed soundings at SLE and UIL) on the west side of the Cascades, this will induce a decently strong cross-Cascade pressure gradient (8-12 mb between PDX and GEG per latest guidance) and result in breezy to locally windy westerly winds through the Cascade gaps and across the Columbia Basin and Blue Mountain foothills. NBM probabilities of exceedance show a medium-high (50-95 percent) chance of reaching advisory-level wind gusts for climatologically wind-prone locations within the aforementioned region, with significantly lower chances elsewhere. Confidence was high enough (70-90 percent) that periods of advisory-level sustained winds and/or wind gusts will be met today, so went ahead and issued a Wind Advisory for multiple zones for this afternoon and evening.

Another round of breezy conditions is forecast Thursday as the shortwave exits to the east over the Rockies and upper-level ridging rebuilds over the Pacific Northwest. That said, a drier air mass is forecast to be present Thursday in the wake of the shortwave, and locally low relative humidity (10-20 percent) is forecast. Fuels are not yet ready for Red Flag Warnings, so no fire weather headlines have been issued.

By Friday, ensemble mean 500-hPa heights and vorticity show another shortwave from the Pacific entering the Pacific Northwest late morning through afternoon. Confidence is very high (90 percent) in another round of widespread breezy to windy westerly winds through the Cascade gaps and across the Columbia Basin and Blue Mountain foothills. NBM probabilities of reaching or exceeding advisory-level wind gusts are medium- high (40-80 percent) for wind-prone areas within the region outlined above. Similar to Thursday, the dry air mass (ensemble- advertised PWATs of 0.25-0.50") coupled with sufficient downward mixing during the daytime should facilitate some low relative humidity (10-20 percent) prior to the arrival of a more humid air mass by later Friday.

Taking a glance at the weekend into next week, ensemble NWP guidance shows little to no signal for organized precipitation until Tuesday as upper-level ridging remains the favored scenario for the bulk of the West. Periods of breezy westerly winds are favored as the ridge axis shifts inland Sunday through early next week and ensemble guidance shows potential for a couple additional shortwaves to ride over the top of the ridge.

To briefly touch on forecast temperatures, for most of our population centers high temperatures in the upper 70s to lower 90s coupled with lows in the upper 40s to lower 60s will present predominantly Minor (level 1 of 4) HeatRisk. This level of heat primarily affects those who are extremely sensitive to heat and without cooling/hydration.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

VFR conditions are forecast for the next 24 hours. Winds will be breezy to windy later this morning through evening at all terminals, strongest at DLS/PDT. Predominantly mid- to high- level cloud is forecast to increase in coverage by early afternoon.

FIRE WEATHER

Breezy to windy westerly winds are forecast today, and Wind Advisories are in effect for multiple zones. Locally low (10-20 percent) relative humidity is forecast to accompany breezy (Thursday) to windy (Friday) westerly winds across the Columbia Basin and surrounding lowlands. Poor to moderate overnight relative humidity recovery is anticipated Thursday night for ridgetop, mid-slope, and some basin locations. Above-normal temperatures are forecast this week and into next week, and significant precipitation is unlikely (90 percent confidence).

HYDROLOGY

The Naches River is forecast to remain near (Cliffdell) or above (Naches) action stage through the remainder of the week and into next week. Significant precipitation is unlikely (90 percent confidence) for the next week.

Preliminary Point Temps/PoPs

PDT 82 54 77 51 / 0 0 0 0 ALW 82 56 77 54 / 0 0 0 0 PSC 89 58 83 57 / 0 0 0 0 YKM 88 53 83 51 / 0 0 0 0 HRI 85 57 80 54 / 0 0 0 0 ELN 80 49 77 49 / 0 0 0 0 RDM 83 44 80 43 / 0 0 0 0 LGD 81 48 75 44 / 0 0 0 0 GCD 81 46 78 45 / 0 0 0 0 DLS 83 55 80 52 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 1 PM this afternoon to 1 AM PDT Thursday for WAZ024-026-521. OR...Wind Advisory from 1 PM this afternoon to 1 AM PDT Thursday for ORZ041-044-507-508-510.