textproduct: Pendleton

DISCUSSION

Current satellite imagery shows a low stratus layer across the Columbia Basin area extending to Central OR. While majority of freezing fog has lifted over North-Central OR and Foothills-Southern Blue Mountain of OR, the webcams are currently showing ongoing freezing/dense fog along US-97 between Cow Canyon and Shaniko.

The northwesterly flow dominates the region with the upper ridge along the PacNW coast through work week. Thanks to the low stratus layer and temperature inversions, this will help keep high temps in the 30s and 40s. The boundary layer will remain dry from the ongoing subsidence, which will assist in lowering dewpoints and temps to near or below freezing during overnight hours. That said, freezing/dense fog could redevelop during early morning hours and night hours. Uncertainty still remain on the strength of the fog and extent, but we will monitor the forecast area and make any adjustments if need be. HREF raw ensembles show a 15-30% probability for visibilities less than 1/2SM but 30-40% prob during morning hours for tonight through early Tuesday morning, which might impact driving conditions.

With the ongoing inversions, stagnant air conditions will continue for the next few days with low low transport winds (10 mph or less) and mixing heights around 1.5 kft or lower. Any pollutants, haze, and/or smoke may still be trapped near surface level thus resulting poor ventilation, keeping Air Stagnation advisories in place until late Tuesday afternoon. Feaster/97

AVIATION...00Z TAFs

Low stratus with several sites <2000 feet of CIG continue to impact sites, with the Central OR terminals seeing initial IFR conditions. IFR conditions are expected to last much of the period as the surface high pressures continue to hold the low stratus in-tact for the majority of the TAF period. Guidance hinting that we'll get a break in the stratus in the last few hours of the period, but was cautious to include it for a longer duration given that guidance has not initial correctly for some of the terminals. We'll see how guidance evolves going into the 06Z TAFS, but for now sub-VFR conditions will prevail for the next few hours. Winds remain light and variable.

PRELIMINARY POINT TEMPS/POPS

PDT 22 35 21 34 / 0 0 0 0 ALW 25 34 23 34 / 0 0 0 0 PSC 24 38 22 36 / 0 0 0 0 YKM 22 39 20 37 / 0 0 0 0 HRI 23 35 22 35 / 0 0 0 0 ELN 21 35 20 35 / 0 0 0 0 RDM 20 45 18 41 / 0 0 0 0 LGD 24 43 22 43 / 0 0 0 0 GCD 25 49 26 49 / 0 0 0 0 DLS 26 39 26 39 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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

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