textproduct: Pendleton

KEY MESSAGES

- High pressure returns to the region Tuesday

- Pattern change expected over the weekend

DISCUSSION

Current radar shows no returns as the shortwave warm front has traversed to the east. The nighttime satellite shows some fog forming through the Kittitas Valley with ground observations showing VIS to be decreasing along the I90 corridor. Patch fog will continue through the morning before clearing out later in the morning.

Models show the upper level ridge already building into the region. This will bring increasing stratus and potential fog back to the area over the next few days. While this pattern during winter does typically bring with it the potential for air stagnation, the NBM shows mixing heights to hover above 1500 feet and the abundance of low clouds expected through the period. However, fog will remain the daily concern through the period ahead of the next system. 50-60% of the raw ensembles show that Tuesday morning Kittitas, Yakima and a large swath through the Columbia Basin will see VIS drop as low as if not lower than 3 miles. By Wednesday, probabilities increase to 60-70% of 3 miles or less VIS through much of the Columbia Basin and Klickitat County along the Simcoe Highlands and along the Northern Blue Foothills. By Thursday models show the axis of the high to tilt and the back edge of the high will bring in southerly flow. This will bring in air warmer and has the potential to decrease the chances of fog forming overnight Thursday and Friday (60-70% confidence).

By Saturday models show the initial breakdown of the ridge as an upper level low begins to build in offshore bring increased precipitation chances (70-90%) to the Cascades and spreading to the eastern mountains Saturday night with 40-60% chances. Clusters and models are in decent agreement through the weekend, there is a telltale difference in the timing between models. The Euro has precipitation coming in ahead of the GFS. Regardless, precipitation and cooler temperatures are expected over the weekend. 90

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Sub-VFR conditions expected at all sites except BDN/RDM due to BR and low CIG decks. DLS will see MVFR conditions at 4SM due to BR and YKM will see LIFR conditions due to 900 ft CIG between 14-16Z (30-50% confidence). ALW will see VIS of 6SM and LIFR due to 900 ft cloud decks after 12Z and PSC will see 4SM due to BR with LIFR conditions due to again a 900 ft deck. Confidence in the low clouds and BR is 50-60%. after 18-20Z all TAF sites are expected to return to VFR conditions. 90

Preliminary Point Temps/PoPs

PDT 34 50 32 48 / 0 0 0 0 ALW 37 50 35 48 / 0 0 0 0 PSC 34 48 34 49 / 0 0 0 0 YKM 35 50 32 50 / 0 0 0 0 HRI 35 49 33 48 / 0 0 0 0 ELN 33 45 29 46 / 0 0 0 0 RDM 29 60 27 56 / 0 0 0 0 LGD 36 56 37 56 / 0 0 0 0 GCD 33 59 34 59 / 0 0 0 0 DLS 38 51 36 50 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.