textproduct: Pendleton

DISCUSSION

An upper level ridge impacting the region continues to support an extensive stratus layer from the Upper Columbia Basin down into Central OR and the John Day Basin. Most areas that have been under the stratus layer the past several days have seen dense fog lift, however visibilities less than half a mile persist in the Kittitas valley. Meanwhile, elevated areas of central and north central OR continue to see impacts from freezing fog, with visibilities a half mile or less as well. Other than fog/stratus, the only notable ongoings across the forecast area is an area of fine, light snow that has developed in an area between Walla Walla, Pendleton, and Cold Springs. At present, most surfaces are warm enough to prevent any accumulation, though a dusting is possible on the top of cars.

The stratus layer and inversion just above it will persist into the middle of next week as the PacNW stays under the influence of the upper ridge offshore. Uncertainty still remains around the redevelopment and strength of fog in areas around the Yakima Valley and Walla Walla the remainder of tonight. Otherwise, as the days progress, the chances of fog redeveloping steadily decreases across the remainder of the Columbia Basin and adjacent areas. For now though, have kept mention of patchy fog across areas under the stratus layer through Monday morning.

By Tuesday night, ensemble guidance is in good agreement in the upper ridge beginning to erode away as a trough dives down the continental divide. This will weaken the impacts from the upper ridge over the region, providing an opportunity to break the inversion/stratus layer over the inland PacNW Tuesday night into Wednesday, though conditions will remain for the better part dry across the forecast area. Late Wednesday into Friday, ensemble guidance is in decent agreement of troughing beginning to develop over the region, however there is great disagreement on the strength of the incoming trough, resulting in low confidence (10-20%) in precipitation amounts and type Thursday onward. Lawhorn/82

AVIATION

For 12z TAFS, Widespread stratus this morning will also have varying impacts. LIFR cat cigs are going to persist though the morning at RDM/BDN/YKM. MVFR cigs are expected to continue at PSC/DLS. Fog or Freezing fog will continue to reduce visibility between one quarter to three quarters of a mile. Diurnally improving conditions later by late morning though the afternoon will be short lived as the boundary layer cools and allows ceilings to again deteriorate as well as fog redevelop This Evening.

PRELIMINARY POINT TEMPS/POPS

PDT 34 25 34 23 / 0 0 0 0 ALW 35 29 34 25 / 0 0 0 0 PSC 38 27 36 25 / 0 0 0 0 YKM 35 27 38 24 / 0 0 0 0 HRI 35 26 35 24 / 0 0 0 0 ELN 35 26 37 23 / 0 0 0 0 RDM 37 23 42 19 / 0 0 0 0 LGD 46 31 47 25 / 0 0 0 0 GCD 52 32 52 28 / 0 0 0 0 DLS 40 30 40 27 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 4 PM PST Tuesday for ORZ041-044- 507-508-510-511.

Freezing Fog Advisory until noon PST today for ORZ510-511.

WA...Air Stagnation Advisory until 4 PM PST Tuesday for WAZ024- 026>029-521.

Freezing Fog Advisory until noon PST today for WAZ026-027.