textproduct: Pendleton

KEY MESSAGES

- Breezy westerly winds and light mountain precipitation today, with breezy northerly winds Sunday

- Below freezing morning temperatures in portions of Central OR, Grande Ronde valley, and Wallowa valley this weekend into early next week

- Chance for light precipitation early next week with colder than normal temperatures beginning next week

DISCUSSION

Nighttime satellite imagery tonight shows cirrus spreading east across the forecast area ahead of an approaching cold front and upper level trough.

Today through Sunday: Unsettled weather conditions will return to the PacNW today as a cold front and upper trough drop into the region from the north/northwest. The cold front boundary is expected to bring light showers to the central WA Cascade crest later this morning, with shower activity sliding south along the Cascade crest throughout the day. Showers will also reach the northern Blues, far northeast OR, and far southeast WA by this afternoon and evening, but otherwise dry conditions will persist elsewhere. Precipitation in the mountains will be fairly light, with chances of 0.1 inches in 24-hrs only between 25-45% in the Northern Blues, OR Cascade crest/east slopes, and southern portions of the WA Cascade east slopes; chances of 0.25 inches of liquid precip in the central WA Cascades will be closer to 70-90%. Snow levels will be on the decline to around 4-5kft later tonight, resulting in a 60-65% chance of 0.5 inches of snow accumulations along the higher elevations of the central WA Cascade crest. West to northwest breezy winds (15-25mph with gusts 30-40mph) will develop across much of the lower elevations with the cold front passage today, with strongest gusts up to 45 mph expected in portions of the Kittitas valley, Simcoe Highlands, and the eastern Gorge.

Saturday into Sunday morning, the upper trough will transition into an upper closed low as it descends into the PacNW from BC. As the upper low tracks south, light snow/rain showers will develop along the Cascade crest and portions of the eastern mountains. Accumulations of any snow will be limited to above 5kft, but even then chances of 0.1 inches of accumulations are 30-50% below 6kft along the Cascade crest and the Eagle Caps.

Sunday, the upper low will continue to dig south and exit the PacNW into northern CA, however upper troughing will remain over the region. While the precipitation chance will come to an end across the Cascade crest, a weak moisture plume riding up the back of the trough will clip the higher terrain of the eastern mountains, resulting in a chance (40-55%) of measurable precipitation (0.01 inches). Saturday night into Sunday, breezy north winds (15-20 mph with gusts to around 35 mph) will develop from the Columbia Basin into central OR with a push of cold air advection into the intermountain PacNW.

The cold front/upper low passage will promote much cooler conditions across the forecast area starting Friday night and continuing into early next week. Currently, a Freeze watch is in effect for the Wallowa valley, Grande Ronde valley, and central OR for Friday night as there is moderate confidence (60-75%) in freezing overnight temperatures developing. If not by Saturday morning, chances for freezing temperatures will increase in these areas and in the Kittitas valley and Blue Mountain foothills Saturday night as cold air advection continues into the region. Confidence is mod-high (65-85%) that freeze warnings will be needed for the aforementioned areas Saturday night. Lawhorn/82

Monday through Thursday: Cluster analysis of ensemble members depicts an upper-level trough with an associated closed low developing offshore the PacNW on Monday and propagating over the region in the next couple of days. Currently, there is temporal uncertainty with this trough of how fast it is moving and also uncertainty in the overall strength and placement of this upper- level trough and associated low. Along with this system, per model guidance of the NBM, there is the presence of a small shortwave on the backside of the trough that could bring a chance (20-30%) for light rain on Monday, but the greater chance for precipitation looks to be on Wednesday (50%), primarily along the Oregon Cascades and the Blues. As this system pushes through, we do have the chance (55-65%) for freezing morning temperatures Monday,Tuesday,and Wednesday morning for Central Oregon and the Wallowa Valley, with temperatures in the low 30s but greatest chance seems to be on Monday (65-70%).

After Wednesday, per cluster analysis, we see the development of a ridge pattern beginning Thursday into Friday and models are in good agreement with this pattern setup (65%), although there is some temporal uncertainty with this ridge pattern and uncertainty in the overall strength of it as well. There is a low chance (25-30%) for freezing morning temperatures Thursday, but temperatures should begin to warm up to the mid 60s-low 70s on Thursday.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

TAF sites DLS,PDT,RDM,BDN are expected to see mostly VFR conditions through the TAF period. CIGS at these TAF sites will remain mostly above 3000ft, but in the afternoon hours, CIGS will be as low as 5000-7000ft. VIS will remain mostly 6SM or above at these TAF sites. These TAF sites will see some breezy winds with gusts at least 25-30 kts in the morning-afternoon hours. Winds are expected to decrease during the evening. Ames/01

YKM/ALW/PSC: VFR conditions to prevail through the period. CIGs will descend to around 6kft AGL at site ALW this afternoon and overnight. A cold front passage will also bring a 30% chance of light rain to ALW between 00-03Z this evening. Breezy winds 15 to 20kts with gusts 25-30kts will develop at sites YKM/ALW/PSC today, with winds decreasing in the evening hours. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 71 35 58 35 / 10 20 0 0 ALW 72 40 59 39 / 20 20 0 10 PSC 75 38 63 37 / 0 0 0 0 YKM 70 36 61 40 / 10 0 0 40 HRI 72 39 61 36 / 0 0 0 0 ELN 63 32 55 32 / 10 0 10 50 RDM 71 28 54 25 / 0 10 0 10 LGD 74 32 55 33 / 0 30 0 10 GCD 78 34 55 30 / 0 20 0 10 DLS 70 42 63 40 / 10 0 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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