textproduct: Pendleton

KEY MESSAGES

- High confidence (99%) that a low-pressure system will track over the Pacific Northwest today into early Sunday, resulting in below-normal temperatures and widespread breezy westerly winds.

- Elevated fire weather conditions today due to breezy winds, but low confidence (<40%) in widespread Red Flag conditions.

- Very low to slight chance (5-15%) of thunderstorms today for the Washington Cascades and northeast Blue Mountains.

- Low-medium probability (20-50%) of near-freezing morning low temperatures in populated, cold-prone valleys of central and northeast Oregon on Sunday, except medium-high probability (50-75%) in Wallowa Valley.

DISCUSSION

Satellite imagery early this morning shows a closed upper-level low over northwest Washington and southwest British Columbia. Confidence is very high (99%) that the low will track inland over the Pacific Northwest today, then exit to the east through Sunday. Widespread breezy westerly winds are forecast today, strongest though the Cascade gaps. NBM probabilities suggest generally medium (30-70%) chances (locally higher) of reaching advisory-level wind gusts through our most wind-prone areas such as the Kittitas Valley and the eastern Columbia River Gorge and vicinity. Despite the breezy winds, chances of widespread Red Flag conditions are low (<40%) due to below-normal temperatures and seasonably low relative humidity.

Rain showers are very likely (up to 95% PoPs) along the Washington Cascade crest this morning into early afternoon as the low swings inland. Chances of showers and thunderstorms are lower (5-15%) over the Blue Mountains this afternoon, but still worth a brief mention.

Looking ahead, there are low-medium chances (20-50%) of near- freezing morning temperatures (lower to middle 30s) in populated, cold-prone valleys of central and northeast Oregon Sunday and Monday in the wake of the cold upper low, except for 50-75% Sunday morning for Wallowa Valley. NBM probabilities are likely too aggressive Sunday morning due to some lingering breeziness into the early overnight hours, though forecast PWATs (generally 0.4" or less) and temperatures aloft are supportive of chilly conditions. Thinking the coldest temperatures in some valleys will fall on Monday morning with light winds areawide under a shortwave ridge, something NBM probabilities do not highlight well. Did issue a Freeze Watch for Wallowa Valley, valid later tonight into Sunday morning.

Analysis of ensemble clusters suggests a continued troughing pattern for the Pacific Northwest by the middle of next week with all four clusters exhibiting some flavor of trough/upper closed low and near-normal or below-normal 500-hPa heights. Will the region see its first widespread wetting rain with the fall-like pattern? NBM probabilities are quite optimistic for the 48-hr period ending 5AM Friday. In general, it shows 40-70% chances of 0.10" of precipitation for non-mountain areas with 50-90% chances across the mountains (highest chances for the Cascades).

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

VFR conditions through the TAF period with mid to high FEW to OVC skies associated with a passing weather system. Breezy winds have developed through most of the sites, with top gusts reaching 20-30 knots. Strongest winds are currently peaking with the system moving through the region and I expect winds to weaken as we go through the late afternoon hours as the system pushes through. Will see some breezy wind gusts linger through the Central Oregon sites (BDN/RDM) but not expecting to be stronger than 20-30 knots for the most part.

Preliminary Point Temps/PoPs

PDT 73 43 77 44 / 0 0 0 0 ALW 74 49 77 50 / 0 0 0 0 PSC 78 47 80 48 / 0 0 0 0 YKM 75 49 81 53 / 0 0 0 0 HRI 75 48 81 48 / 0 0 0 0 ELN 68 43 76 46 / 10 0 0 0 RDM 72 35 79 40 / 0 0 0 0 LGD 74 40 79 43 / 0 0 0 0 GCD 76 41 80 46 / 0 0 0 0 DLS 74 52 81 55 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until noon PDT Monday for ORZ041-505-506- 509>511. Freeze Watch from late tonight through Sunday morning for ORZ050.