textproduct: Pendleton

KEY MESSAGES

1. Dry and cool conditions this week

2. Trough will bring increased chances of precipitation midweek

3. Ridge over the weekend will bring back dry and warmer conditions

DISCUSSION

Current radar shows much of the precipitation is to the south moving across central OR through the Ochoco-John Day Highlands and into southern Wallowa. This is where the precipitation will stay for the remainder of today. Ground observations show the amounts to be light between 0.01-0.04 inches of rainfall. Some webcams show very light snow that is not sticking to the pavement. Light showers will continue through the day today bringing with it rain amounts nearing 0.07-0.09 inches with with 50-70% confidence.

Models show the front that just crossed the region to slightly rebound back into the area moving a bit farther north. LREF raw ensembles show that there is 50-60% of the members in agreement that this shift north will bring with it 15-25% chances of isolated thunderstorms through Grant and Cook counties Tuesday afternoon and 30-50% probabilities of rain through the Ochoco-John Day Highlands, even spilling over the Blues and into the foothills. Accumulations will be highest through the Highlands with accumulations nearing 0.10-0.20 inches with 50-70% of the NBM raw ensembles in agreement while lower elevations along the foothills will see 0.03-0.07 inches. Light snow showers will occur above 5500 feet with accumulations less than 0.2 inches with 70-80% confidence. Wednesday ahead of the front, LREF shows 15% probabilities of isolated thunderstorms along the leading edge of the front. Isolated thunderstorms would form along the western slopes of the eastern mountains.

Wednesday and Thursday models show a strong upper level low will begin to move in off the coast of B.C. and ahead of it will be another front. Models show this system to be robust with increased chances of mountain snow, low elevation rain and increased winds. Clusters do show some deviation with the models with timing, however, all models show a robust front making its way into the region Tuesday night/Wednesday morning. The front will move across the region bringing snow levels to near 2000 ft. This will allow for some snow showers across a good portion of the region with the highest amounts being along the Cascades. A Winter Weather Watch has been issued for the east slopes of the Or Cascades with models showing nearly 10-15 inches of accumulation along Santiam Pass with 50-80% of the raw ensembles are in agreement and Snoqualmie Pass could see 3-6 inches with 30-60% confidence as well as the higher peaks of the northern Blues around Tollgate. The eastern mountains could see up to 1-1.5 inches with 60-80% confidence. The lower elevations models are showing QPF amounts nearing 0.15-0.30 inches with 60-80% confidence. There is show shadowing showing up in the models runs and portions of the western Basin as well as through central and north central OR will only see 0.05-0.15 inches of rain Wednesday through Thursday with 50-70% confidence. Lastly, winds will become a bit breezy as the front moves through Thursday brining 70-80% probabilities of 25-30 mph gusts across the region.

Thursday night into Friday morning models show the next incoming system coming in from off the coast. An upper level ridge ill set up over the region bringing warmer and drier conditions. Clusters show that the main difference between the models will be positioning of the upper level ridge. Looking at in house model comparisons, temperatures will be anywhere from 5 to 10 degrees above seasonal normal through the Basin and adjacent valleys and 10-15 degrees above seasonal average for the Oregon potion of the CWA. Temperatures will start off in the low to mid 60s before increasing and seeing upper 60s to low 70s in some areas. Confidence in the temperatures is 50-70% peaking Sunday. 90

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Mostly VFR conditions to prevail through the period. A stationary front and upper system passage tonight will result in CIGs lowering to 500ft to 1kft tonight with a light rain/snow mix developing as well. CIGs will improve to 3.5kft or higher after 17Z. CIGs will lower to around 3.5kft at sites PDT/ALW between 12Z and 21Z. Winds will be light, 12kts or less, through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 30 52 38 57 / 10 30 30 90 ALW 32 51 41 57 / 0 30 30 100 PSC 29 55 39 58 / 0 10 20 90 YKM 28 54 35 53 / 0 0 20 90 HRI 30 54 38 58 / 10 20 20 90 ELN 26 49 33 47 / 0 0 20 90 RDM 31 54 36 54 / 50 40 30 90 LGD 30 54 38 54 / 30 70 60 100 GCD 36 56 37 53 / 80 90 60 100 DLS 34 55 42 55 / 10 20 50 100

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Winter Storm Watch from late Tuesday night through Thursday afternoon for ORZ509.