textproduct: Pendleton

KEY MESSAGES

1. Showers and isolated afternoon thunderstorms today

2. Mountain snowfall, Significant snow Oregon Cascades, moderate snow Wa Cascades *Winter Storm Warning and Advisories Issued*

3. Breezy to windy conditions today through Thursday

DISCUSSION

Current radar showers showers steadily moving over the eastern portion of the Basin with showers beginning to develop over the Cascades. This mornings observation here in Pendleton recorded 0.03 inches of rain so far with other ground observations showing the last three hours have seen 0.01 inches along the eastern mountains and 0.06-0.09 through the Tri-Cities. Showers will continue to linger through the day today with 70-90% of the NBM raw ensembles showing 24 hour precipitation amounts nearing 0.15-0.25 inches by 11 PM. Along the leading edge of the incoming front, models show just enough forcing to pop off a thunderstorm or two. HREF ensembles show that 70% of the members are in agreement that there is 15-25% probability of the southeast and eastern portion of the CWA will see thunderstorms this afternoon and evening. The LREF ensembles showed the region could see CAPE values as high at 250 J/kg with 60% some confidence and also shear values nearing 25 to 30 kts and steepening lapse rates. Not only are there the risks of thunderstorms, but models also show the potential for outflow winds reaching 30-40 mph with 50% confidence.

Models show a robust upper level low with a front working its way onshore through the day today and into Thursday. This will continue to bring the lingering showers mentioned earlier as well as mountain snow. A Winter Storm Warning is in effect until 5 PM Thursday for the east slopes of the OR Cascades for total snow accumulations between 9 to 14 inches with 70-90% confidence. A Winter Weather advisory is in effect for the east slopes of the WA Cascades through 11 AM Thursday for up to 7 inches of snow with 60-80% confidence. NBM shows snow levels will drop to near 1500-2000 feet as the front tracks eastwards allowing for light snow accumulations to occur through the Ochoco-John Day Highlands and portions of central OR as well as the Grande Ronde Valley overnight with 30-50% confidence.

Models show a tightening of the surface pressure gradients and in house pressure gradient calculations have an 11 mb gradient that will form across the region. Highest winds will occur Thursday with 60-80% confidence of winds reaching 30-35 mph gusts along the wind prone areas and through the mountain gaps. Elsewhere will see breezy conditions with 20-25 mph gusts with 60-80% confidence.

Lastly, models are in relatively firm agreement with the next incoming system Friday. Clusters also show high confidence the the upper level ridge moving in over the weekend. Dry and warmer temperatures are expected peaking Sunday. 90

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

VFR conditions prevail this afternoon across the region. However, as rain redevelops, there could be some local MVFR CIGS especially if the rain is a bit heavier. For BDN and RDM some light snow could bring MVFR toward morning as well. Otherwise, any gusty winds this afternoon and early evening will decrease over the next few hours. However, gusty winds in the 20 to 25 kt range will develop in the late morning to early afternoon at all sites on Thursday.

Preliminary Point Temps/PoPs

PDT 34 50 32 59 / 100 60 10 0 ALW 37 50 37 59 / 100 60 20 0 PSC 38 58 35 63 / 90 30 0 0 YKM 31 56 32 61 / 60 20 0 0 HRI 36 55 34 62 / 90 30 0 0 ELN 32 49 32 57 / 80 30 0 0 RDM 26 47 22 61 / 70 40 0 0 LGD 32 45 29 58 / 100 80 40 0 GCD 29 43 26 57 / 90 80 20 0 DLS 36 55 35 64 / 70 30 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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