textproduct: Pendleton

KEY MESSAGES

- Freeze watch is in effect for Friday night into Saturday morning.

- Breezy to windy conditions develop Friday.

- Patchy blowing dust possible Friday across the Columbia Basin.

DISCUSSION

A Freeze Watch is in effect for Grande Ronde Valley, Central Oregon, and Wallowa Valley for tomorrow night through Saturday morning.

Beginning tomorrow, an upper level trough is highly likely to move into the PacNW area from the Gulf of Alaska (over 90% chance). With it, the threat of freezing morning temperatures, gusty winds, and some rainfall are primary concerns. While confidence is high regarding the trough arrival and placement, its strength is still a subject of some uncertainty in ensemble guidance, particularly after Saturday. The extra-tropical transition of Hurricane Rachel presents some variability that could affect trough depth and impacts for next week.

As indicated with the freeze watch, there is moderate confidence of below-freezing temperatures throughout the weekend. NBM probabilities highlight higher elevation areas as being at risk starting Friday night into Saturday morning (50-75%), with lower elevation areas becoming progressively more likely to freeze as the weekend progresses into Monday morning. While the current freeze watch is limited to portions of Crook, Deschutes, Jefferson, Union, and Wallowa counties, additional products outside of these counties cannot be ruled out as conditions progress, especially Sunday through Tuesday.

Moderate confidence still exists for the potential of gusty winds, with the most widespread gusts occurring tomorrow and becoming more localized to the Columbia Gorge and southern Columbia Basin regions throughout Saturday and Sunday. Gusts in this region are likely to exceed 30 mph (greater than 75% chance) but unlikely to surpass 45 mph (less than 20% chance). Isolated patchy dust has been included in our forecast to reflect these winds, especially for areas not expected to receive rainfall.

Rain will likely be limited to NE Oregon/SE Washington per recent guidance (50-75%) chance of at least 0.01 inches within 24 hours). However any precipitation that falls will mostly be limited to below wetting-rain thresholds (at most 50% of exceeding 0.1 inches in 24 hours in isolated regions). Primary timing for rainfall is currently as early as tomorrow morning for the Washington Cascades (tomorrow afternoon/evening for surrounding areas) into Saturday and Sunday.

With the post-tropical transition of Rachel, there is a significant possibility of additional rain Monday through Wednesday (around 20- 40% chance), however variability of this is still very high. Ensemble clusters remain split regarding whether an embedded upper- level low will emerge and shift towards California/Nevada or whether it will stay as an open trough. In cluster scenarios with a deep upper low, ensemble guidance predicts lower rainfall totals compared to solutions with a more northerly placed low or trough. As such, rainfall odds for this time period are subject to change as guidance becomes clearer with the trough's arrival.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

VFR conditions to persist throughout the TAF period for all sites. Increasing winds and gusty conditions starting at 18z for KDLS, KPDT, KRDM, KALW, KPSC and KRDM, with light rain showers for KPDT, KALW, and KPSC.

Preliminary Point Temps/PoPs

PDT 49 71 36 58 / 0 10 10 0 ALW 56 72 41 59 / 0 20 30 0 PSC 48 75 39 63 / 0 10 0 0 YKM 50 70 37 61 / 0 0 0 10 HRI 49 73 39 62 / 0 10 0 0 ELN 48 63 33 55 / 0 10 0 30 RDM 40 71 28 54 / 0 0 10 0 LGD 45 73 35 55 / 0 10 30 0 GCD 46 77 36 56 / 0 0 20 0 DLS 53 70 42 63 / 0 10 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Freeze Watch from late Friday night through Saturday morning for ORZ049-050-511.