textproduct: Pendleton

KEY MESSAGES

- Breezy to windy westerly winds accompanied by patchy blowing dust this afternoon and evening. Wind Advisory in effect for Kittitas Valley.

- Near- to sub-freezing morning temperatures Saturday across much of the region. Freeze Warnings in effect for Central Oregon and Wallowa Valley.

- Widespread near- to sub-freezing morning temperatures continue early next week across the lower elevations.

DISCUSSION

Satellite imagery shows notable troughing over the Pacific Northwest region this afternoon: an upper-level closed low is centered over eastern British Columbia; meanwhile, a second vorticity maximum is diving southward along the Alaska panhandle and northwest British Columbia. A cold front is draped across our forecast area, and widespread breezy to windy westerly winds are present at the surface. Most areas have observed sub- advisory winds in the 15-25 mph range with gusts of 30-40 mph. However, especially wind-prone locations across the Columbia Plateau will continue to see sustained winds of 25-35 mph with gusts of 40-55 mph into this evening (80% confidence). Opted to issue a Wind Advisory for the Kittitas Valley, valid through 9 PM PDT this evening, where advisory-level winds have been most widespread. Patchy to localized areas of blowing dust have been observed across the Columbia Plateau from late this morning through early afternoon, and will likely continue into this evening (80% confidence). Have issued a Special Weather Statement for the threat of blowing dust, but areal coverage and intensity of visibility drops thus far has been too low to warrant a Blowing Dust Advisory.

The cold frontal passage will be dry for most areas, with low- medium (20-50%) chances of a wetting rain (0.10") for the northern Blue Mountains and Oregon Cascades. Elsewhere, a wetting rain has already occurred this morning into early afternoon in the Washington Cascades.

A colder, dry air mass (PWATs of 0.4" or less) is forecast in the wake of this afternoon's cold frontal passage, which will lead to some potential for overnight freezing temperatures. Confidence in areas or widespread near- or sub-freezing temperatures is highest (70-90%) for Central Oregon and Wallowa Valley; Freeze Warnings are in effect for those zones. Elsewhere, confidence in sub-freezing temperatures is medium (40-70%) in the Grande Ronde Valley, just a bit too low to issue a warning. In the Columbia Basin and surrounding valleys, confidence in reaching freezing temperatures is low (5-30%), highest for the Kittitas and Yakima valleys where skies are expected to be mostly clear overnight. On the subject of cloud cover, lingering clouds and northwest winds are the two variables that have the potential to spoil the forecast overnight freeze in northeast Oregon.

The aforementioned upper-level systems are expected (99% confidence) to track southward over the Pacific Northwest Saturday through Sunday, facilitating additional cold air advection into the region. While lingering cloud cover and breezy north to northeast winds associated with the low- pressure system remain sources of uncertainty, the region will see continued chances of near- or sub-freezing morning lows Sunday. Due to forecast lighter winds and mostly clear to clear skies, the best chance of widespread freezing morning lows for the lower elevations is Monday and Tuesday mornings, and additional Freeze Watches or Warnings may be issued in the coming days.

Warmer, mostly dry conditions are then forecast by mid-week as ensemble guidance indicates an upper-level ridge will likely deflect any notable weather systems to the north (60-80% chance).

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

VFR conditions throughout all sites, which is highly likely (greater than 70%) to continue through the TAF period. Reduced visibility from patchy blowing dust is possible at some terminals, with the best chance being KALW. Breezy winds currently occurring throughout most sites, with gusts of around 20-35 knots.

Winds are highly likely (greater than 70% chance) to weaken throughout the TAF period. There's currently moderate confidence that winds will transition to typical patterns by 16z (30-60% chance), although some sites may transition as early as around 12z. Clouds are also very likely to weaken alongside winds (greater than 70% chance), with clouds limited to at or above 25 kft after 12z for most sites.

Preliminary Point Temps/PoPs

PDT 35 58 33 56 / 20 0 0 10 ALW 39 58 36 57 / 30 0 0 10 PSC 38 63 37 61 / 0 0 0 0 YKM 36 61 39 60 / 0 0 20 0 HRI 38 61 36 60 / 10 0 0 0 ELN 32 54 32 55 / 0 20 30 0 RDM 27 54 24 51 / 0 0 0 20 LGD 31 54 32 51 / 30 0 0 10 GCD 32 55 28 51 / 20 0 0 0 DLS 42 62 40 64 / 0 0 10 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 9 PM PDT this evening for WAZ026. OR...Freeze Warning from 1 AM to 10 AM PDT Saturday for ORZ050-511.