Pendleton, Oregon

• Near- to below-normal temperatures into next week.
• Periodic showers today, then more widespread precipitation this evening into Sunday morning, mainly for eastern Oregon and far southeast Washington.
• Low chance (30% or less, except for freeze-prone areas) of a season-ending freeze for the eastern Columbia River Gorge Monday.

Water vapor imagery shows a large, quasi-stationary low-pressure system located just offshore of the Pacific Northwest, centered in the vicinity of 45.2N, 129.5W. Middle and high cloud cover is present across much of central to eastern Oregon and southeast Washington, while mostly clear skies are noted over north-central Oregon and south-central Washington. Radar reveals isolated showers over the Columbia Plateau, mainly along a line from the Bend metro to the Tri-Cities metro. At the surface, most valley locations are nearly saturated at around 95-100% RH, and fog formation remains a concern for early morning. That said, low stratus and any widespread fog currently remains north and east of our forecast area of responsibility.

Over the weekend, the low is expected (99% confidence) to transition to an open-wave trough and move inland. While chances of precipitation have continued to trend downward, they are still medium-high (30-70%) across the majority of central/eastern Oregon and southeast Washington this evening into Sunday. The best chance of significant precipitation will be over northeast Oregon and southeast Washington where the NBM places a 20-50% chance (locally higher in eastern Wallowa County) of 0.25" through Sunday.

Ensemble solutions have coming to a concensus with regard to when the trough will exit to the east and upper-level ridging will build in from the Pacific; specifically, they suggest the trough will slide east late Sunday afternoon into Sunday night, and an amplified upper-level ridge will be overhead by Monday morning. Given clearing skies and dry conditions, this presents the best chance, albeit low at 30% or less, of a season-ending freeze for the eastern Columbia River Gorge in the next week. Freeze-prone portions of the Gorge do have somewhat higher chances of freezing (locally in excess of 50%), but at this time confidence remains too low to issue any watches.

Uncertainty in the 500-hPa pattern then grows Tuesday through the remainder of the week. Ensemble clusters show a range of solutions regarding a compact closed low Tuesday into Wednesday. Most members (~55%) take it into the Pacific Northwest across northern California or southern Oregon; the remaining members keep the low offshore or delay its inland transit. The majority of solutions (~80%) take the low too far south to produce significant precipitation for our forecast area, and mostly dry conditions (PoPs of 20% or less) are forecast to continue until Thursday when ensemble guidance hints at the return of some more active weather. Even then, chances of precipitation remain low (40% or less, highest for the Cascades) until Friday when a more robust low-pressure system is advertised.

Visibility reduced in FG/BR and/or ceiling restrictions persist this morning into the early afternoon at ALW/DLS. Confidence is low with respect to when these restrictions will finally improve on the day but DLS LAMP guidance suggests cig improvement after 20z, and as for ALW visibility will have to be monitored for short term trends. Light winds at all terminals. Shower chances increasing (about 15 to 25 percent confidence) after 01 UTC at RDM BDN, and after 12z more probabilistic 20 to 35 percent rain chances for PDT to ALW.

PDT  50  34  53  31 /  10  20  20   0
ALW  51  38  52  34 /  10  30  30   0
PSC  54  33  59  31 /   0  10  10   0
YKM  54  32  60  30 /   0   0   0   0
HRI  51  32  57  31 /  10  10  10   0
ELN  50  27  56  26 /   0   0   0   0
RDM  48  25  51  22 /  10  20   0   0
LGD  56  36  52  29 /  20  30  40   0
GCD  58  35  49  30 /  10  20  20   0
DLS  55  36  61  34 /  10  10   0   0

WA

None.

OR

None.