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KEY MESSAGES

1. Moderate snow continuing into Tuesday WINTER WEATHER ADVISORY IN EFFECT 5 AM MONDAY THROUGH 8 AM TUESDAY

2. Heavy snow Tuesday night into Friday morning WINTER STORM WARNING IN EFFECT 5 PM TUESDAY NIGHT THROUGH 5 AM FRIDAY MORNING

3. Breezy winds will persist through the week

DISCUSSION

Current radar shows returns moving across the Cascades over Snoqualmie Pass through Hyak and into Easton. Current webcams shows snow build up along the shoulder and in the trees with ground observations reporting 3 inches of snow so far. Snowfall is expected to continue through the remainder of the day today and through 5 AM Tuesday morning. The Winter Weather Advisory remains in effect with an additional 2 to 6 inches of snow accumulations (70- 90% confidence).

Models show northwest flow aloft to continue to bring in bands of precipitation through the week. The strongest band will begin Tuesday night and an atmospheric river gets caught up in the flow around the Pacific high and flows directly into the PacNW. CW3E ensembles show a 90% probability of 250 kg/(ms) making its way across the Cascades bringing with it increased chances of heavy mountain snow. Models are in form agreement with the upper level system and WPC cluster are only showing the main variance to be is with the amplitude of the system. EFI also shows abnormally high amounts of snow and QPF in comparison to the seasonal averages with an EFI of 0.97 and a shift of tails of -5. This shows how abnormally strong and wet this system is for this time of year. Due to this, a Winter Storm Warning has been issued for the event with 70-90% confidence the event will bring 2 to 4 feet of snow to the WA Cascades. There will be a lull in heavy precipitation as the AR will bring in some slightly warmer air allowing the snow levels to increase and precipitation to turn to a wintery mix between 11 AM Wednesday and 5 AM Thursday. However, Thursday shows another cold air mass moving in bringing the snow levels back down to near 1500 feet and temperatures back to freezing.

Lastly, models show relatively tight pressure gradients to be associated with this system so breezy conditions are expected through the week. NBM raw ensembles show 50-70% probabilities of winds gusts 30-35 mph gusts across the area with localized areas seeing 20-25 mph such as the lower Columbia Basin, the Gorge, and central OR. 90

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

VFR conditions prevail for all sites. An embedded disturbance in mid-level zonal flow will continue bringing snow showers across the East Slopes of WA Cascades and portions of the Blue mountains. With that, KDLS may see light rain showers this early evening, but with a 30% probability. In addition to the zonal flow, breezy winds (20-30 kts) will linger through the evening hours for KPDT, KRDM, KYKM, and KPSC. However, winds may pick up again around Tuesday morning for KPDT, KALW, and KPSC. Feaster/97

Preliminary Point Temps/PoPs

PDT 29 47 33 57 / 20 20 20 40 ALW 31 47 36 56 / 40 30 40 60 PSC 31 52 36 60 / 10 0 10 20 YKM 26 48 29 54 / 10 10 50 60 HRI 31 51 36 60 / 10 10 10 20 ELN 24 42 28 46 / 20 20 60 70 RDM 23 42 28 54 / 10 10 10 30 LGD 26 42 28 49 / 50 40 40 70 GCD 23 41 27 53 / 10 30 10 40 DLS 31 49 36 54 / 40 50 70 80

PDT WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 8 AM PDT Tuesday for WAZ522. Winter Storm Warning from 5 PM Tuesday to 5 AM PDT Friday for WAZ522. OR...None.