textproduct: Pendleton

KEY MESSAGES

- Cold, dry air mass continues to bring near-freezing to sub freezing morning temperatures into early this week

- Light rain-snow showers for the Wallowa Mountains and Southern Blue Mountains tonight into Monday morning

- Dry conditions, light winds, and above-normal temperatures prevail middle of next week through Friday

DISCUSSION

Breezy conditions this afternoon whit northeast wind trajectories and although no widespread blowing dust is expected, patchy blowing dust was added to the the weather grids for the balance of the afternoon. Overnight temperatures teetered around the freezing mark in t few of the valleys, certainly in the Wallowa valley as well as the foothills of the Blue Mts, aided there by some clearing sky overnight. Tonight's challenges will be of a similar nature, with at least some better confidence on cloud cover diminished altogether it he the northwest zones (Kittitas and Yakima Valleys) and a more likely band of a mix of low and mid level cloud lingering on the middle of the upper low/ cold pool aloft, which the HREF shows in a north to south axis with 50 to 70 percent coverage for both cloud levels. Additionally the NBM sprinkles 30 to 50 percent chances of precipitation across the higher terrain mountain zones of eastern Oregon (rain or rain/snow showers) which based on HRR trend could linger from about midnight though noon Monday. Similar to yesterday, the NBM has meaningfully colder temperatures across the board than the HREF data across the aforementioned zones as well as the Grande Ronde valley/and Wallowas. As the Wallowa valley saw freezing temps for an hour only at Enterprise, and Tonight looks about as cloudy or more so we will defer to Tuesday night where colder temps are anticipated by all of the probabilistic data (greater chances in areal coverage) for any freeze warnings in the the eastern zones. Freeze Warnings will be hoisted Tonight of the Yakima and Ellensburg areas. The upper low looks to pull into the Great Basin of Nevada and Utah by 12z Tuesday , leaving all of Washington and Oregon in a northerly flow aloft behind the system, and thus dry, clear with light winds. This will allow efficient long wave radiational cooling to bring the coldest temps of the week across a larger area. Much colder NBM lows temperatures and probabilities for reaching below freezing/32F at about 50-60 percent and up in many of the lower elevations points toward freeze watches for Monday Night and Tuesday Morning. Confidence leans higher in these instances as the widespread cloudiness of the last couple of nights will not be a factor.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Predominantly VFR conditions are forecast through the TAF period, albeit with some MVFR CIGs this morning at BDN/RDM. Ceilings are expected to gradually lift into the afternoon hours, with VFR conditions then forecast at all sites through the remainder of the period.

Winds will become breezy northerly to northeasterly at most sites today, then slacken this evening and tonight.

There is a low hourly chance (<30%) of light rain showers at PDT/ALW/PSC/RDM/BDN today, so omitted from the 18Z TAF, and will handle with amendments if necessary. Did include a PROB30 group for light rain showers early Monday at PDT/ALW where guidance suggests a 15-25% chance of precipitation.

Preliminary Point Temps/PoPs

PDT 32 57 30 63 / 10 20 0 0 ALW 36 57 36 64 / 20 20 0 0 PSC 35 62 31 66 / 0 0 0 0 YKM 34 63 34 65 / 0 0 0 0 HRI 34 60 30 66 / 0 10 0 0 ELN 29 59 30 63 / 0 0 0 0 RDM 22 55 22 64 / 0 0 0 0 LGD 30 54 26 62 / 30 10 0 0 GCD 28 54 25 64 / 20 10 0 0 DLS 37 68 36 71 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Freeze Watch from Monday evening through Tuesday morning for WAZ026>029-521. Freeze Warning from 11 PM this evening to 9 AM PDT Monday for WAZ026-027. OR...Freeze Watch from Monday evening through Tuesday morning for ORZ044-049-050-507-508-510.