textproduct: Pendleton

KEY MESSAGES

- Freezing morning lows Friday and near-freezing morning lows Saturday in the lowlands

- Warmer, drier this weekend

- Uncertainty in pattern details Monday and beyond

DISCUSSION

Satellite shows scattered to numerous CU across the forecast area beneath a cool, weakly unstable northwesterly flow aloft. Radar shows snow showers have developed this afternoon, mainly over the Blue Mountains where mid-level lapse rates of 8-9 C/km are present per SPC's RAP-based mesoscale analysis.

Breezy to locally windy westerly winds are present in the Columbia Basin and vicinity due to somewhat tight cross-Cascade pressure gradients (7-9 hPa difference between PDX and GEG) and a well-mixed boundary layer. Showers and breezy winds should taper off this evening and overnight as daytime convection wanes and the deep upper-level low continues to track east of the region.

An upper-level ridge will almost certainly (99 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 remains near- to sub-freezing temperatures for the lowlands, and Freeze Warnings have been issued. This set-up looks more favorable for mostly clear to clear skies and lighter winds relative to this morning, so radiational cooling should be more efficient. Moreover, afternoon surface dew points are in the upper teens and twenties across the region, and RAOBs show low PWATs of 0.15-0.40 of an inch; both of these are good indicators of efficient radiational cooling where winds slacken.

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. Most members keep the low offshore through early next week, a solution which would result in above-normal temperatures across the Inland Northwest down into central Oregon.

Precipitation chances increase Sunday for the Cascades, but expand eastward Monday through Wednesday in what is looking like a potential convective set-up for portions of the forecast area. Ensemble clusters show ~45 percent of members are advertising the upper low just off the OR/CA coast, a location that is favorable for convection. Another deformation band similar to what was observed earlier in the week is also looking like a potential outcome Tuesday through Wednesday should the closed low track inland along a supportive path, but confidence in that solution is currently low (10-20 percent).

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

VFR conditions currently across all sites, which will stay the course through the period. Widespread gusty conditions will persist through the remainder of the afternoon, with values between 20- 30kts. Winds will subside this evening as skies clear due to incoming high pressure. 75

Preliminary Point Temps/PoPs

PDT 30 57 34 69 / 0 0 0 0 ALW 34 57 38 68 / 0 0 0 0 PSC 33 62 34 72 / 0 0 0 0 YKM 29 61 37 67 / 0 0 0 0 HRI 32 61 34 71 / 0 0 0 0 ELN 29 57 33 63 / 0 0 0 0 RDM 20 57 27 70 / 0 0 0 0 LGD 27 54 32 60 / 0 0 0 0 GCD 23 54 31 63 / 0 0 0 0 DLS 34 63 39 71 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Freeze Warning from 11 PM this evening to 9 AM PDT Friday for WAZ026>029. OR...Freeze Warning from 11 PM this evening to 9 AM PDT Friday for ORZ044-507.