textproduct: Pendleton

KEY MESSAGES

1. Showers and isolated afternoon thunderstorms through Wednesday

2. Midweek mountain snowfall, Significant snow Oregon Cascades *Winter Storm Warning and Advisories Issued*

3. Drier and warmer conditions over the weekend

DISCUSSION

Current radar shows much of the precipitation is traversing off to the north with a line of showers moving across the northern Basin and Yakima Valley. Ground observations are showing no accumulations with this line of showers so the showers are likely virga. Lingering showers are expected to persist through the evening with light accumulations along the foothills of the southern and northern Blues of 0.03-0.05 inches with 30-50% confidence while the eastern mountains will see 0.10-0.15 inches with 70-90% confidence and OR Cascades will see snow showers above 4500 feet with accumulations up to 2 inches with 70-90% confidence while the lower slopes will see 0.05 inches of rain. LREF raw ensembles show that there is 50-60% of the members in agreement that the northerly shift will bring with it 15-25% chances of isolated thunderstorms through Grant and Cook counties this afternoon. 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 through Grant, Cook and into southern Umatilla Counties.

Wednesday and Thursday models show a strong upper level low will 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 feet. This will allow for some snow showers across a good portion of the region with the highest amounts being along the Cascades. A Winter Storm Waning has been issued for the east slopes of the Or Cascades with models showing nearly 10-15 inches of accumulation along Santiam Pass with 60-80% of the raw ensembles are in agreement. A Winter Weather Advisory has been issued for the east slopes of the WA Cascades through Snoqualmie Pass due to the areas seeing up to 7 inches of snow 60- 70% confidence. Tollgate and portions of the northern Blues will see 4-6 inches of snow as well with 30-50% confidence. The eastern mountains will 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 some 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 25-35 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 will 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 THURSDAY/

A mix of conditions across sites through the period. A system approaching the region will brings periods of rain to all sites, with a frontal band producing light rain at sites PDT/YKM/ALW/PSC periodically between 10Z to 17Z. There will be a lull late in the morning, with the next round of light rain arriving between 20Z-22Z at these sites, and at sites RDM/BDN. Light rain will end around 00Z at site YKM, 03Z for sites RDM/BDN/PSC, and later in the evening for sites PDT/ALW. Site DLS will see consistent light rain between 10Z-23Z. CIGs are expected to become MVFR or lower with heavier rain bands at most sites, except RDM/PSC where VFR CIGs will prevail (confidence 65-80%). Winds will increase to 12-20kts with gusts 20-30kts at sites RDM/BDN in the afternoon and in the evening at site PSC. Winds will be 12kts or less at all other sites through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 38 58 35 52 / 40 100 90 50 ALW 41 57 37 52 / 40 100 100 60 PSC 38 58 38 60 / 30 90 90 20 YKM 36 54 32 57 / 40 90 60 10 HRI 38 59 36 57 / 30 90 90 20 ELN 32 48 32 50 / 40 80 80 20 RDM 36 55 27 49 / 40 90 80 30 LGD 38 55 32 46 / 70 90 100 80 GCD 37 53 30 44 / 70 100 100 90 DLS 41 55 37 56 / 70 100 70 30

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory from 5 AM Wednesday to 11 AM PDT Thursday for WAZ522. OR...Winter Storm Warning from 5 AM Wednesday to 5 PM PDT Thursday for ORZ509.