textproduct: Pendleton

KEY MESSAGES

- Mountain snow into Thursday

- Breezy to windy through Thursday

- Near- to sub-freezing morning lows Thursday and Friday for the lowlands

DISCUSSION

Satellite imagery shows a closed upper low centered over southwest British Columbia early this afternoon. Meanwhile, a robust cold front is trekking across eastern Oregon and far southeast Washington. In the wake of the front, skies have become clear to partly cloudy across much of the Columbia Basin and vicinity, with upslope convective showers noted across the Cascade crest. Winter weather headlines remain in effect, and confidence is high (80 percent) in an additional 2-6 inches of snowfall for the Washington Cascades and northern Blue Mountains, and 4-8 inches for the Oregon Cascades. While the bulk of the steady snowfall has ended for the Cascades -- and will end through this afternoon for the Blues as the front sags southeast -- snow showers will persist through tonight into Thursday morning as the aforementioned upper low moves over northeast Washington.

Breezy westerly to northwesterly winds have developed in the wake of the front and remain diurnally breezy to windy through Thursday. While winds of 20-30 mph coupled with gusts of 30-40 mph have developed in climatologically wind-prone locations, confidence in the need for any wind headlines is low-medium (30-60 percent), highest for the Kittitas Valley, eastern Columbia River Gorge, lower Columbia Basin, and foothills of the Blue Mountains. Winds will be locally stronger along exposed ridges within the Columbia Plateau region.

The cold air mass associated with the low has prompted concerns for near- to below-freezing morning temperatures. NBM calibrated probabilities still suggest medium-high chances (60-90 percent) of freezing temperatures for the Yakima and Kittitas valleys, medium probabilities (30-70 percent) along the foothills of the Blue Mountains, and low-medium (20-50 percent) for the lowest elevations including the eastern Columbia River Gorge and lower Columbia Basin. Freeze Warnings remain in effect for tonight into Thursday morning where chances of freezing are highest (Kittitas and Yakima valleys and the foothills of the northern Blue Mountains of Oregon). Will note there is still uncertainty in how much cloud cover will persist and how windy conditions will remain overnight into the morning hours, so confidence in widespread freezing temperatures is shaky (50-60 percent), but think areas of freezing temperatures still have a high enough chance of developing to retain the warnings.

An upper-level ridge will likely (90 percent confidence) build into the Pacific Northwest Friday into the weekend, yielding lighter winds and mostly dry conditions. The main headline- worthy consideration for Friday will be near- to sub-freezing temperatures for the lowlands. This set-up looks more favorable for mostly clear to clear skies and lighter winds relative to Thursday morning, so while the coldest air mass will have exited the region to the east, radiational cooling should be more efficient. Have not issued any Freeze Watches to avoid confusion given the existing Freeze Warnings for Thursday morning.

Uncertainty in the 500-hPa pattern grows through the weekend, but some flavor of a 500-hPa closed low is advertised by all ensemble clusters to be in the vicinity of the Pacific Northwest Saturday through the remainder of the period. Precipitation chances increase Sunday, but especially Monday and Tuesday, in what is looking increasingly like a potential convective set-up for portions of the forecast area. Another deformation band similar to what was observed earlier in the week is also looking like a potential outcome should the closed low track inland along a supportive path, but confidence in that solution is currently low (20-25 percent).

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

A cold front is moving across the area today, which will create gusty west wind and IFR ceilings in the vicinity of the frontal boundary, most notably at ALW and PDT early in the TAF period. Periods of light to moderate rain will obstruct visibility as low as 2 to 3SM in the vicinity of any of these aforementioned terminals and to around 3-5sm at BDN and RDM. Momentum behind the frontal boundary will maintain gusty winds of 20 to 30 knots into the evening hours.

Preliminary Point Temps/PoPs

PDT 31 53 32 57 / 30 10 0 0 ALW 34 54 36 57 / 50 30 0 0 PSC 34 61 34 63 / 20 0 0 0 YKM 30 59 31 61 / 10 0 0 0 HRI 32 59 34 62 / 20 0 0 0 ELN 29 51 30 57 / 10 0 0 0 RDM 22 48 21 57 / 40 10 0 0 LGD 28 46 29 54 / 70 40 10 0 GCD 25 45 25 54 / 70 40 0 0 DLS 35 56 35 63 / 40 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 11 PM PDT this evening for WAZ030-522. Freeze Warning from 11 PM this evening to 9 AM PDT Thursday for WAZ026-027. OR...Winter Weather Advisory until 11 PM PDT this evening for ORZ502. Freeze Warning from 11 PM this evening to 9 AM PDT Thursday for ORZ507. Winter Storm Warning until 5 AM PDT Thursday for ORZ509.