textproduct: Pendleton

DISCUSSION

Overnight satellite imagery shows a low stratus deck persisting over much of the lower elevation and valley zones of our forecast area. The region remains locked into a stagnant high pressure pattern that will gradually evolve during the later half of the work week, but for now, expect most of our population centers to continue to struggle seeing the sunlight. We are seeing some gradual retreat of the low cloud deck away from central Oregon early this morning, but this could very well return given how the synoptic pattern is expected to evolve through the midweek (30-40% confidence).

Looking at the big picture, a weak NW flow regime will remain in place through the midweek. This will allow the current stratus deck to persist where it is currently located, with any flux in its extent most likely to occur in central Oregon, which we've observed over the last few days. Otherwise, the stratus deck has more or less expanded to its maximum extent, so don't expect the Columbia Basin to see sun again until at least the end of the work week. What may finally break us free from the grasp of this gloom? Global models depict a large low pressure system over eastern Canada - so large that it introduces a weak open wave over the PacNW. Should note that confidence is still relatively low (30-40%) that this system will produce enough mechanical mixing to finally lift us out of this pattern, but it's still the most notable synoptic feature seen in the region over the last week and a half. At this point, we'll take anything just to see blue sky again.

Keeping an eye on webcams overnight, thus far fog coverage is patchy enough to preclude any advisories, but will keep an eye on north central Oregon in particular, where a few spots on US97 look pretty socked in. Precip wise, however, threats are pretty minimal until at least early next week, where ensembles hint at perhaps a more progressive pattern finally taking over. 74

AVIATION...12Z TAFS

Variable conditions currently across all sites, with VFR at KBDN, MVFR at KDLS/KYKM/KALW/KPSC, IFR at KPDT, and LIFR at KRDM due to reduced visibilities of 1/2SM due to freezing fog and ceilings of 100 feet. These conditions are expected persist, with dropping ceilings at KPDT leading to LIFR conditions and IFR ceilings at KALW developing later this morning. Elsewhere, conditions will stay constant through the morning before improving to VFR briefly for all terminals through the afternoon. Upper level ridging and surface high pressure extends through the period, keeping conditions dry and winds light (below 10 kts). 75

PRELIMINARY POINT TEMPS/POPS

PDT 31 23 32 21 / 0 0 0 0 ALW 32 26 32 23 / 0 0 0 0 PSC 36 25 35 24 / 0 0 0 0 YKM 37 24 35 21 / 0 0 0 0 HRI 34 25 33 22 / 0 0 0 0 ELN 32 22 33 20 / 0 0 0 0 RDM 38 19 39 18 / 0 0 0 0 LGD 39 19 40 22 / 0 0 0 0 GCD 47 22 47 25 / 0 0 0 0 DLS 36 29 37 26 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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

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