textproduct: Pendleton

KEY MESSAGES

- Continued dry conditions through Friday

- Pattern change will bring mountain snow and low elevation rain

- Increased winds across the region will accompany pattern shift

DISCUSSION

Current satellite shows a large swath of the region under a stratus deck. Ground observations as well as webcams show many areas through central/n. central OR and along the foothills of the Blues plagued with fog/freezing fog with a dense fog/freezing fog advisory out until 10 AM. This will remain through the late morning.

Models show the ridge to be slowly moving to the east with the back edge bringing mainly south to south east flow aloft. By Friday afternoon/early evening, models show the ridge to be to the south east of the area and the leading edge of the upper level trough to be pushing onshore. Conditions will remain dry through Friday with another round of overnight fog reforming. HREF raw ensembles continue to show 60-80% of the Basin and adjacent valleys seeing fog reform with VIS of 3 miles or less Friday night and into Saturday morning.

Saturday models show the upper level trough to continue to push in from the west with models showing the precipitation to begin after 10 AM. Clusters show that the main discrepancy between the models is the timing with NBM, EURO and HREF split. Regardless, precipitation is expected to begin in the Cascades in the late morning with 70-80% confidence. As the day progresses, models show the system to continue to push east increasing rain chances for the lower elevations. By Sunday, models show the entire region will see increased chances of rain with 50-70% of the NBM raw ensembles having the Basin, adjacent valleys as well as central and n. central OR seeing up to 0.1 inches of rain through Sunday. However, with the more westerly/zonal flow, cooler temperatures will also move across the region and the NBM show snow levels to decrease to 3500 ft along the Cascades, east slopes, Gorge and portions of the western lower Columbia Basin and 4000-4500 to the east. Snow is anticipated to accumulates above 3500 ft Sunday with the NBM raw ensembles with 50-60% probabilities of up to near an inch Sunday along the WA Cascades and the Northern Blues. Models show precipitation to persist through Monday with another round of high mountain snow up to 1 inch (60-80%) and low elevations rain (70-80%) of between 0.05-0.10 inch.

Lastly, the upper level trough will also bring with it increased winds as it traverses the region. The region will begin to see an increase in winds Saturday morning steadily increasing through the weekend peaking Sunday. 40-60% of the NBM raw ensembles have winds between 10-15 mph sustained with gusts to 25 on Sunday. This coupled with the precipitation will assist in removing the air stagnation as well a ward off the fog.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Primary concern through much of the forecast period will again be low CIGs and VIS due to the stratus deck and fog. All sites are sub-VFR with RDM/BDN sub-MVFR. Models show the stratus deck to linger for RDM/BDN through much of the day keeping those sites LIFR through much of the period. PDT/ALW/PSC have brief times (14-17Z) where CIGs are expected to drop to IFR/LIFR due to CIGs (300-700ft) before lifting to MVFR after 20Z. Confidence in timing will be the most difficult to pin down as we move through the period. Confidence is high (60-80%) the CIGs and fog will linger overnight and through the late morning before lifting slightly after 20Z.

Preliminary Point Temps/PoPs

PDT 34 55 43 52 / 0 10 50 80 ALW 36 54 45 52 / 0 10 60 90 PSC 35 52 42 53 / 0 10 50 80 YKM 34 48 38 49 / 0 20 50 60 HRI 34 52 42 53 / 0 10 50 80 ELN 33 44 36 44 / 0 40 60 70 RDM 31 58 40 50 / 0 0 30 70 LGD 36 58 43 50 / 0 10 50 80 GCD 34 58 42 51 / 0 0 40 80 DLS 37 51 45 52 / 0 40 80 90

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until noon PST Saturday for ORZ506-509. Dense Fog Advisory until 10 AM PST this morning for ORZ507. Freezing Fog Advisory until 10 AM PST this morning for ORZ508- 510-511.