textproduct: Pendleton

DISCUSSION

A ridge of high pressure aloft will continue to drive the sensible and impactful weather over the next week and beyond. A stagnant air pattern will lead to low mixing heights and weak winds as well as potential for valley and low land fog development each night.

Fog this morning hampered the Kittitas valley with areas with dense fog reducing visibility to a quarter mile but saw improving visibility at ELN by mid to late morning to about a mile as the dense fog advisory was allowed to be canceled early. The same sensible weather is likely to redevelop Tonight. Fog remains noticeable at the highest elevations of the Washington Cascades early This afternoon, and may redevelop in the Kittitas Valley again in earnest by around midnight once again based on the local gfs mos guidance trends. The probability for visibility to drop to one half mile or less spikes to about 60% in the Kittitas valley overnight, including the Ellensburg area, which can linger all day Tuesday based on the ensemble's trends.

A marked increase toward the 90th percentile for NBM winds was used across the Grande Ronde Valley as the surface pressure gradient between Baker and Meacham is fairly steady at around 6 to 7 mb which does not begin to weaken until early afternoon Tuesday. The wind advisory was extend for the Ladd and Pyles Canyons through 2 pm Tuesday.

ESAT (ensemble situational awareness table) shows that the high pressure over the area is at about the 2 standard for levels up through 500 ft through next weekend. The NBM was showing the stagnant conditions developing already by Tonight, with a window of opportunity for mixing heights to exceed 1500 ft across a broader area by Friday, An air stagnation advisory was posted for areas from Central Oregon into the Lower Columbia Basin, Eastern Columbia Gorge and north into the Kittitas valley until Friday morning. Additionally, fog may redevelop in the valley areas over the next few days especially in the Kittitas Valley and section of the Lower Columbia Basin of WA, a region of generally cooler air/lower dew point depressions.

AVIATION

VFR conditions currently at all sites, which will stay the course through the majority of the period. There is a potential for briefly reduced visibilities of 4SM mid-morning Tuesday at KYKM/KALW. Elsewhere, VFR conditions are expected under 25kft ceilings. Winds will stay light and below 8kts for all terminals through the period. 75

PRELIMINARY POINT TEMPS/POPS

PDT 35 54 30 46 / 0 0 0 0 ALW 40 54 33 45 / 0 0 0 0 PSC 35 51 30 44 / 0 0 0 0 YKM 35 52 32 48 / 0 0 0 0 HRI 32 50 30 44 / 0 0 0 0 ELN 36 47 30 45 / 0 0 0 0 RDM 28 59 25 57 / 0 0 0 0 LGD 32 49 32 53 / 0 0 0 0 GCD 32 55 34 57 / 0 0 0 0 DLS 37 51 34 48 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory from 7 AM Tuesday to 7 AM PST Friday for ORZ041-044-507-508-510-511.

Wind Advisory until 2 PM PST Tuesday for ORZ049.

WA...Air Stagnation Advisory from 7 AM Tuesday to 7 AM PST Friday for WAZ024-026>029-521.