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FXUS66 KPDT 180953 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 253 AM PDT Sat May 18 2024

SHORT TERM
Today through Monday...A broad upper-level low centered over western Canada continues to influence our weather in the form of mountain showers and gusty winds, as a jet associated with the southern flank of this system remains situated over the forecast area. If there's any solace from these prolonged windy conditions, it's that we're not quite expecting advisory-level winds anywhere in our area, however some localized areas could come close at times this afternoon.

Guidance has generally trended downward as far as wind gusts are concerned for Saturday afternoon, with even the bullish HRRR suggesting that wind gusts will largely remain in the 30-35 mph range across our typical wind-prone areas, including the Cascades Gaps and Oregon Basin. NBM probabilistic guidance is oddly pretty aggressive on the Oregon Basin and Simcoe Highlands achieving advisory level gusts, with values as high as 80% in some pockets.
That being said, the lack of a strong signal in the deterministic NBM, as well as the HRRR, and with 850 mb winds hovering right around 35 mph, just don't think the ingredients are quite there to pull the trigger on any headlines.

Precip will remain primarily over our mountain zones, as the airmass overhead is still dry with PWATs in the 0.3 to 0.5 range, leaving upslope flow as the primary mechanism for showers. 00z HRRR does suggest a few isolated showers may form over the Basin, likely due to upper-level support with the jet overhead, but rain will struggle to reach the surface outside of the mountains with how dry the boundary layer is. NBM did also paint some thunder potential over the central WA Cascades, but with how cool temps are expected today, opted to leave out any mention for thunderstorms.

Sunday looks to be dry as NNW flow prevails aloft, allowing for cool, below normal temps to settle in, with highs struggling to eclipse 70 degrees even in the lower Basin. Winds will remain breezy in spots, albeit much less so than today. Monday also looks dry for most of the forecast area, however an area of amplified northerly flow aloft on the back end of the departing Canadian low could trigger some isolated shower and thunderstorm activity across Wallowa County. Evans/74

LONG TERM
Tuesday through Friday...Several lows/troughs move through the region during the extended period. The first will be on Tuesday. There is already disagreement with the deterministic models, with the GFS having a much stronger low moving across the Pacific Northwest on Tuesday than the GFS. However, regardless of which solution is correct, there will be a trough over the area through Wednesday which will bring unsettled conditions. Rain, mainly over the mountains and possibly some thunderstorms over eastern areas are expected on Wednesday. However, there could even be some light QPF, generally a few hundredths, over lower elevation locations as well. THursday night should see decreasing precipitation as the trough moves eastward and then there is more uncertainty into Friday with the ECMWF having a flatter/drier solution and the GFS being stronger/wetter with the next system moving onshore. Obviously, a lot can change in a week, but the parade of systems will continue and timing ans strength will affect the upcoming holiday weekend.

Only about 32% of the ensemble clusters support the deeper GFS solution on Day 4/Wednesday and about 22% support it on Day 5/Friday. Additionally the ECMWF is ensemble mean is more in agreement with its deterministic run than the GFS leading to more support for the ECMWF solution as well.

High temperatures will be close to or slightly below normal through the extended generally from the upper 60s to the mid 70s.

AVIATION
12Z TAFS...High confidence (80-100%) in VFR conditions as the next upper low/trough moves across the area later today though Sunday. Winds will increase during the afternoon hours with gusts 25 to 30 kts at DLS, PDT, RDM and BDN and 20 to 25 kts elsewhere (90-100% confidence). Winds should decrease towards the end of the TAF period.

PRELIMINARY POINT TEMPS/POPS
PDT 66 39 63 39 / 0 20 0 0 ALW 69 42 65 43 / 0 20 0 0 PSC 72 46 71 46 / 10 10 0 0 YKM 68 39 68 41 / 10 10 0 0 HRI 71 44 70 43 / 0 10 0 0 ELN 62 38 63 39 / 10 10 0 0 RDM 65 33 57 31 / 0 0 0 0 LGD 65 38 58 36 / 0 10 0 0 GCD 67 36 58 34 / 0 0 0 0 DLS 66 45 66 44 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES
OR...None.
WA...None.

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