textproduct: Pendleton

DISCUSSION

Webcams show low visibilities across roads and interstates across the Yakima Valley and the Foothills of the Blues. Likely remain for the rest of the night as winds stay fairly light with limited cloud cover over the effected areas currently. Fog and freezing fog remain the primary story for tonight, as temperatures continue to fall below freezing with the efficient radiation cooling.

Mostly dry conditions will continue through Wednesday and through Thursday night with dry northwesterly flow aloft continuing from the offshore high pressure system (>90% confidence). Next weather system will begin sometime in the later part of Thursday morning as a shortwave with increased cyclonic vorticity aloft develops low valley rain with light mountain snow (50-80% confidence). Impacts start to increase Friday and towards the rest of the weekend with a positively tilted trough from the providence's of Manitoba and Saskatchewan digs further south enough to trigger multiple short waves across the Washington/Oregon area. Most of the main impacts will be felt from the heavy mountain snow and potential wind events at advisory level (20-60 percent chance across most of the region) with strongest winds looking to occur late Friday afternoon through mid Saturday morning. A warming trend will begin Thursday, giving us a break from the below freezing temperatures we've observed the past few days, with highs trending up into the low and mid 50s through the weekend. Clusters are in agreement with a generally narrative that we will continue to see valley rain and light mountain snow/wintry mix go through mid next week, although to the extent how strong/weak the system will be remains a bit uncertain with Day 7 and being in the autumn generally bring great uncertainty. NBM clusters are close to 50/50 to deliver a strong or weak ridge system, but every member does advertise some form of rain or wintry mix situation.

AVIATION...06Z TAFs

Most sites (KDLS/KPDT/KYKM/KALW/KPSC) will have low clouds arriving through the day Wednesday, though patchy fog lingers over KALW/KPSC overnight with KYKM joining in around 12Z (MVFR conditions or below). The fog will also drop VSBYs to 1/2SM or lower, bringing KALW/KYKM/KPSC to LIFR conditions. While the fog may dissipate late Wednesday morning (18Z/19Z) as VSBYs improve, low cloud decks will continue for these sites (KDLS/KYKM/KALW/KPSC) thus keeping them between MVFR and IFR. KPDT may see patchy fog/mist overnight (30-40% confidence), but mid to high clouds will start returning early Wednesday morning. KRDM/KBDN will be in VFR through this TAF period. Winds will be less than 10kts. Feaster/97

PRELIMINARY POINT TEMPS/POPS

PDT 41 29 42 36 / 0 10 70 70 ALW 39 31 41 36 / 10 10 80 70 PSC 38 28 40 31 / 0 10 60 40 YKM 38 28 42 29 / 10 10 40 30 HRI 39 29 41 34 / 0 10 70 50 ELN 38 27 41 30 / 10 20 40 40 RDM 45 25 47 34 / 0 10 40 30 LGD 41 26 41 36 / 0 10 80 80 GCD 42 26 43 37 / 0 0 70 80 DLS 44 37 47 42 / 10 20 70 60

PDT WATCHES/WARNINGS/ADVISORIES

OR...Freezing Fog Advisory until 10 AM PST this morning for ORZ507.

WA...Freezing Fog Advisory until 10 AM PST this morning for WAZ027- 029.