textproduct: Pendleton

DISCUSSION

Fog is spreading across the Columbia Basin early this morning as the region remains under a high pressure pattern. This pattern will shift slightly heading into the weekend as the current ridge over the PacNW flattens, shifting the winds aloft into a more northerly flow regime that will invite cooler, drier air into the forecast area. Will this eat away at the developing fog layer? Generally these patterns help lift the fog slightly, but the expectation is that a low stratus deck will envelop the Columbia Basin over the next couple of days given the current and forecasted synoptic pattern, making for an overcast (for the lower elevations) and cold pattern through early next week.

Dense Fog Advisories remain in effect for the Yakima/Kittitas Valleys and the lower Columbia Basin of WA until noon Thursday. As of the writing of this discussion, overnight satellite imagery suggests that the lower Basin of OR, Walla Walla Valley, and Columbia River Gorge may also need advisories by the early morning as the fog layer spreads. Despite the ridge flattening, winds are expected to remain light, and model soundings suggest the inversion over the Basin isn't dissipating anytime soon. By the overnight period Thursday into Friday, am expecting this fog/low cloud layer to spread more toward the foothills of the Blues and even down into north central Oregon. Again, the oncoming northerly flow may help lift the layer slightly, but expect low clouds to persist in the Basin at the very least.

Otherwise, ensembles generally agree on some form of a ridge pattern influencing the PacNW through most of the next week. Expect Air Stagnation and Air Quality concerns to linger as a result. By the end of next week, some ensemble members do suggest a pattern shift in the form of a troughing pattern, but given that is over a week from now, confidence in the pattern that far out is pretty low (20% at best). 74

AVIATION...06z TAFs (Previous Discussion)

Most sites are VFR this evening, however, both YKM and PSC have gone LIFR in fog and stratus and conditions are expected to deteriorate at DLS and ALW toward morning. The other sites are expected to remain VFR. All sites should return to VFR by afternoon.

Winds are expected to be light.

PRELIMINARY POINT TEMPS/POPS

PDT 45 27 40 24 / 0 0 0 0 ALW 43 30 39 27 / 0 0 0 0 PSC 43 29 41 26 / 0 0 0 0 YKM 46 27 45 25 / 0 0 0 0 HRI 43 29 41 26 / 0 0 0 0 ELN 43 26 40 24 / 0 0 0 0 RDM 52 22 44 19 / 0 0 0 0 LGD 50 29 46 26 / 0 0 0 0 GCD 53 30 51 29 / 0 0 0 0 DLS 46 32 44 30 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 10 AM PST Friday for ORZ041-044- 507-508-510-511.

WA...Air Stagnation Advisory until 10 AM PST Friday for WAZ024- 026>029-521.

Dense Fog Advisory until noon PST today for WAZ026>028.