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 /06Z TAFS THROUGH 06Z SUNDAY/

VFR conditions will persist through the forecast period. Smoke has lifted and is not expected to affect any of the TAF sites through the day today. Winds will be diurnally breezy, strongest at DLS, with PDT, RDM, BDN seeing increased winds in the afternoon and the remaining sites will be under 10 kts.

Preliminary Point Temps/PoPs

PDT 73 42 76 46 / 0 0 0 0 ALW 74 48 76 51 / 0 0 0 0 PSC 78 45 78 46 / 0 0 0 0 YKM 75 47 79 50 / 0 0 0 0 HRI 75 46 78 46 / 0 0 0 0 ELN 68 43 74 45 / 10 0 0 0 RDM 72 33 78 38 / 0 0 0 0 LGD 74 39 78 42 / 0 0 0 0 GCD 76 40 79 44 / 0 0 0 0 DLS 74 51 79 53 / 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.