textproduct: Pendleton

KEY MESSAGES

- Areas of dense fog and freezing fog today.

- Near- to below-normal temperatures into next week.

- Low chance (30% or less, except for freeze-prone areas) of a season-ending freeze for the eastern Columbia River Gorge Monday.

DISCUSSION

GOES satellite shows water vapor imagery showed a baroclinic leaf moving into The Mountain West as deep layer drier air associated with the upper trough moving over the Pacific and Inland Northwest was squarely centered over the PDT forecast area. This synoptic scale feature will be replaced by an upper ridge by sunrise Monday morning. The light winds and clearing skies may bring redeveloping fog in some of the fog prone valleys as well as bring an outside fort of freezing temperatures for the Columbia River Gorge by early Monday morning. The NBM less than 1 sm visibility probabilities are at 33 percent across the Kittitas Valley and 20 percents across the Northern Blue Mountains of Oregon Tonight into Monday morning additionally the HRRR does not develop low visibility in any of these zones while diminishing low visibility through the evening from mountains stratus layers through late Tonight.

With clearing sky, Monday morning should be noticeably colder than last night with the widespread cloudiness keeping the boundary layer warmer, and more notable in the eastern zones /Blue Mountain Valley floors like the Grande Ronde which may be up to 10 degrees colder and in the 20s. Based on NBM QMD , the minimum temperatures are of medium to high (50-70) confidence in a mid to upper 20s (25 to 28F window for overnight lows at LaGrande. The last forecast zones to yet have a true growing season ending freeze is in the the Eastern Columbia River Gorge, where the same 25 to 75 percentile QMD ranges from 35 to 37F for an overnight lows. Possibly some frost but not high enough confidence for a freeze (less than 25 percent).

Winds remain light through Monday night when winds become breezy over the southern and eastern Mountains and the Grande Ronde Valley into the overnight and though Tuesday. No appreciable warm up is expected as temperatures remain near to cooler than normal in the the 40s in the mountains and the 50s over the lower elevations. Dry through Wednesday with increasing chances for mountain rains Wednesday Night through Friday (20 to 60 percent confidence). A 20 percent chance for measurable precipitation exists across the Columbia Basin on Wednesday Night.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Fog and ceilings issues are diminishing as the upper trough slips east and an upper ridge becomes the dominant weather feature. That said clearing skies will allow efficient radiational cooling tonight. Any return of visibility of 1SM or less in BR or FG is at about 10% for PSC and PDT, and less than 10% at Yakima. Light winds at all terminals.

Preliminary Point Temps/PoPs

PDT 30 56 34 52 / 0 0 0 0 ALW 34 56 38 53 / 0 0 0 0 PSC 30 55 34 55 / 0 0 0 0 YKM 31 54 37 57 / 0 0 0 0 HRI 30 55 34 54 / 0 0 0 0 ELN 25 50 31 52 / 0 0 10 0 RDM 22 56 27 52 / 0 0 0 0 LGD 29 54 36 57 / 0 0 0 0 GCD 30 57 36 58 / 0 0 0 0 DLS 33 56 40 57 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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