textproduct: Pendleton

DISCUSSION

Patchy dense freezing fog will remain concentrated along the Columbia River through majority of the night, which led to issuing an Airport Weather Warning for KPSC reaching to a quarter mile or lower. Current Night Fog satellite imagery shows some patchy fog developing along I-84 at Boardman and upper parts of the Grande Ronde Valley. The models (HRW NSSL, HRRR, and NAM CONUS Nest) are aligned with the fog lasting through later this morning over the Columbia River. Visibilities around KPSC are currently observed with 1/4SM or less (>70% confidence), but conditions should begin improving during morning hours today.

As the 500-mb pattern becomes more zonal, precip activity will return later this morning/early afternoon as a frontal system makes its way to the PacNW. A weak atmospheric river (250-300 kg m/s) may influence more precip to develop along the WA/OR Cascades today. Precip may linger through Saturday across our forecast area before the lower elevations goes into a dry period Sunday with a tilted ridge. However, light precip may continue for the mountain areas. Storm total QPF amounts from this morning through early Sunday morning for the lower elevations will exceed 0.05 inch or more with 0.25 inch or higher for the Northwest Blues and WA/OR Cascades. For the remaining Sunday with lingering precip, QPF amounts for OR Cascades and Northwest Blues may exceed 0.10 inch or higher with Wallowa County at 0.10 inch or less. Snow accumulations of 2 to 5 inches will develop for the Northwest Blues, WA Cascades and southern parts of Wallowa County for Friday through Saturday (40-50% confidence). Sunday is when snow accumulations trend downward to an inch or less for these areas.

Monday through Thursday morning, we will start to see heavy snow accumulations over the mountain areas within a 72-hr period (12Z Monday through 12Z Thursday). Snow levels may drop below 3.5 kft Monday onwards where Winter Weather Advisories may be considered with WA/OR Cascades and the Northwest Blues seeing a 3-day Storm total snow exceeding 5 inches or more (50% confidence). The probability for snow amounts exceeding 10 inches or more is 50-70% Tuesday through Thursday for OR Cascades and Northwest Blues. Given that this snow forecast being 4+ days out, confidence will be low (<30%) at this time. Feaster/97

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

VFR conditions are currently in place for all sites except PSC which remains affected by freezing fog. Expecting (80 percent confidence) VSBY at PSC to improve by early afternoon. Elsewhere, CIGs will continue to lower through afternoon, with low (10-30 percent) chances of -RA by late afternoon and early evening east of DLS; at DLS, have prevailing -RA. Precipitation chances then increase to 30-50 percent at RDM/BDN/PDT/ALW overnight into Saturday morning. 86

Preliminary Point Temps/PoPs

PDT 37 47 34 47 / 30 40 70 20 ALW 40 48 37 47 / 40 60 80 40 PSC 36 51 34 51 / 30 20 50 10 YKM 32 47 31 46 / 40 20 20 10 HRI 37 48 36 49 / 20 30 60 10 ELN 30 42 28 41 / 50 20 20 10 RDM 30 45 28 46 / 20 40 30 10 LGD 35 47 34 50 / 30 80 70 50 GCD 35 48 33 50 / 10 70 40 20 DLS 38 48 37 48 / 60 50 50 20

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.