textproduct: Pendleton

KEY MESSAGES

- Warm, dry conditions today

- A low-pressure system and cold front are slated to arrive Monday afternoon and evening, ushering in widespread breezy to windy westerly winds and a slight chance of thunderstorms

- Shower and thunderstorm chances continue Tuesday through the week, but uncertainty remains in forecast details

DISCUSSION

Above-normal temperatures and dry conditions will continue today as the region remains under zonal flow aloft. Locally breezy winds coupled with widespread low afternoon relative humidity will lead to locally elevated fire weather concerns, but no headlines are in effect.

The next feature that will drive our weather Monday through the remainder of the week, a deepening closed low, is visible in water vapor imagery, located offshore in the vicinity of the Gulf of Alaska. Ensemble NWP guidance is unanimous in taking the closed low southeast along the Pacific coast into Monday. Ensemble solutions exhibit some subtle differences with regard to timing and location/track as it begins to move onshore Monday, but confidence in the low and its attendant surface cold front providing a pattern change late Monday is very high (99 percent).

Monday, flow aloft will turn southwesterly, and widespread breezy winds coupled with low relative humidity are forecast across central Oregon and the Eastern Mountains prior to the arrival of the cold front mentioned in the previous paragraph. This will lead to some elevated fire weather concerns, but none of our fire weather zones have been declared ready for Red Flag Warnings yet so no headlines are currently planned. Temperatures will be well above normal for the aforementioned region as well as portions of the Columbia Basin and Blue Mountain foothills.

By late Monday, the upper low and attendant surface cold front are slated to arrive, with the front sweeping from west to east from afternoon through late evening. NBM probabilities of exceedance suggest medium-high chances (40-85 percent) of reaching or exceeding advisory-level wind gusts across all of our non-mountain zones. Moreover, the NBM is advertising a chance (locally 30-60 percent) of exceeding warning-level gusts (58 mph or greater) across wind-prone portions of the Blue Mountain foothills as well as central Oregon, the Simcoe Highlands, the Yakima Valley, and the eastern Columbia River Gorge. Think the latter probabilities are too high relative to what raw guidance is showing; nonetheless, wind headlines may be needed.

In addition to the strong, gusty winds Monday afternoon and evening, there is a low (5-15 percent) chance of high-based showers and thunderstorms across the Columbia Basin, Blue Mountain foothills, and Blue Mountains (mainly the northern Blues). All deterministic guidance is highlighting some elevated instability, and synoptic-scale forcing appears to be supportive of kicking off some showers or thunderstorms given a sufficient mid-level moisture field. The NBM has yet to include a mention of these showers and thunderstorms in the forecast prior to 5PM PDT Monday, but does include showers across the region after 5PM as the front moves through.

Tuesday through the remainder of the week, shower and thunderstorm chances will continue, tied to the location of the upper-level low as it tracks inland across the Great Basin (likely Tuesday through Thursday) and eventually ejects north- northeast across the Great Basin, Pacific Northwest, or Rockies by Friday and Saturday. Ensemble cluster analysis suggests a pretty even split (40-60 percent, varying by day) regarding the low being in a location supportive (or along a supportive track) for showers, thunderstorms, and notable spring precipitation for the forecast area.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

VFR conditions are forecast for the next 24 hours, with sky cover ranging from SKC to BKN cirrus. Winds will be diurnally driven, strongest during the late morning through evening hours.

Preliminary Point Temps/PoPs

PDT 82 51 83 44 / 0 0 0 50 ALW 82 57 84 48 / 0 0 0 40 PSC 86 54 86 46 / 0 0 0 40 YKM 85 53 78 44 / 0 0 0 10 HRI 84 54 83 45 / 0 0 0 40 ELN 77 49 73 40 / 0 0 0 10 RDM 84 46 81 34 / 0 0 0 20 LGD 82 48 87 43 / 0 0 10 60 GCD 84 46 87 40 / 0 0 0 70 DLS 83 54 77 46 / 0 0 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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