textproduct: Pendleton

KEY MESSAGES

- Above-normal temperatures and mostly dry conditions through the week

- Breezy to windy each day Wednesday through Friday through the Cascade gaps and across the Columbia Basin and Blue Mountain foothills

- Periods of low relative humidity and 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 FEW-BKN mid-level clouds early this morning over the Columbia Basin and vicinity, with mostly clear skies elsewhere across the forecast area.

Zooming out to examine the bigger picture, water vapor imagery reveals a ridge of high pressure offshore extending over the Pacific Northwest and Canadian Rockies. Meanwhile, a closed low is present over the Southwest and broad troughing is visible downstream over the northern Great Plains and central to northern Rockies.

A switch to northerly to northeasterly winds is forecast by this afternoon across much of northeast Oregon and southeast Washington. Temperatures are generally expected to be several degrees cooler this afternoon relative to yesterday under the "cooler" northerly flow aloft, but are still forecast to be above normal for early May.

Regarding precipitation chances, 00Z and 06Z CAMs show isolated showers developing this afternoon over the Cascade and Blue mountains where modest instability (CAM-advertised MUCAPE of 250-750 J/kg) develops, but chances of measurable precipitation are very low (5-15 percent) for any location so they have not received a "slight chance" mention in the gridded forecast.

Looking ahead to Wednesday, NWP guidance is in good agreement that a weak shortwave will ride over the top of the ridge across British Columbia and the northern Rockies. 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 (40-80 percent) chance of reaching advisory-level wind gusts for climatologically wind-prone locations within the aforementioned region, with significantly lower chances elsewhere.

Another round of breezy, though likely (70 percent confidence) not windy, conditions is forecast Thursday as 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 (10-15 percent) is forecast.

By Friday, ensemble mean 500-hPa heights and vorticity show another shortwave from the Pacific entering the Pacific Northwest. While ensemble clusters show notable variance in strength and timing among solutions of the shortwave, confidence remains high (70 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 (10-15 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. By Tuesday, 00Z ensemble clusters suggest a low (25 percent) chance of a return to some flavor of troughing for the region.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

VFR conditions with some mid- and high-level clouds and diurnally/terrain-driven winds of 5-15 kts (gusty in the afternoon) are forecast for the next 24 hours at all sites.

Preliminary Point Temps/PoPs

PDT 78 50 83 54 / 0 0 0 0 ALW 78 53 82 56 / 0 0 0 0 PSC 83 51 88 54 / 0 0 0 0 YKM 83 53 87 52 / 0 0 0 0 HRI 83 51 85 55 / 0 0 0 0 ELN 78 50 79 49 / 0 0 0 0 RDM 78 43 81 43 / 0 0 0 0 LGD 73 46 78 49 / 0 0 0 0 GCD 75 45 78 46 / 0 0 0 0 DLS 83 56 83 54 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.