textproduct: Pendleton

KEY MESSAGES

- A dry period through Friday however Fog will create visibility issues each morning

- A pattern change by the weekend could bring rains and mountain snow

DISCUSSION

Fog has been the primary challenge Today and will return over the next couple of overnights and mornings, primarily to the Kittitas and Yakima Valleys, and much of the Foothills of the Northern Blue Mountains. Even as visibility improved across the areas to above a mile from the dense quarter mile or less earlier the stratus remains anchored over the aforementioned areas including the entire Lower Columbia basin. It will be just a matter of time given the stagnant pattern that the boundary layer cools sufficiently for visibility to begin dropping once again for most of these microclimates. HREF data showed probabilities around 60% for one quarter mile or lower visibility based on rolling 4 hour increments through the next couple of days. NBMs Forecast High Temperatures are in the ball park of the 25th to 10th percentiles which seem reasonable given the fog and stratus expected. Advisories on fog for select forecast zones will be considered toward the end of this shift depending on forecaster confidence , and would lean toward the areas around Walla Walla deteriorating earliest as ALW still reports less than a quarter mile at noon.

By Sunday the GFS AR IVT shows about a 250-400 kg/ms AR dropping south across central WA, the remnants of a much more robust one that would dissipate across BC. Ran showers and high snow levels, above pass, will be the most probable early on however by late Sunday into Monday colder air will lead to snow levels below 4kft, which could spell some snow accums for White and Santiam passes. Russell/71

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Low ceilings contune to impact all sites except for the Central Oregon area (BDN/RDM). BDN/RDM will continue to be VFR through the forecast period, but we will see IFR to LIFR conditions develop overnight for the rest of the sites. PDT/ALW/PSC will see periods of a quarter mile to half mile visibilities in the overnight hours, but is forecasted to lift at around 18Z. Low ceilings will prevail for DLS/YKM but we'll see improvements in conditions at other sites.

Preliminary Point Temps/PoPs

PDT 33 48 32 47 / 0 0 0 0 ALW 38 49 36 48 / 0 0 0 0 PSC 35 48 33 49 / 0 0 0 0 YKM 35 49 33 50 / 0 0 0 0 HRI 34 47 33 47 / 0 0 0 0 ELN 34 46 30 47 / 0 0 0 0 RDM 30 61 26 57 / 0 0 0 0 LGD 36 56 36 57 / 0 0 0 0 GCD 34 60 33 59 / 0 0 0 0 DLS 38 51 36 50 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until 10 AM PST Thursday for ORZ506-509. Dense Fog Advisory until 10 AM PST Wednesday for ORZ510.