Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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230 FXUS66 KPDT 140921 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 221 AM PDT Tue May 14 2024 .SHORT TERM...Today through Thursday...Short term forecast will be dominated by an upper level ridge positioned over the eastern Pacific Ocean. This will keep the Pacific Northwest under a warm and dry northwest flow pattern through Wednesday. High temperatures today will be at or slightly above Monday`s highs followed by and increase of around 5 degrees on Wednesday with highs in the 80s in the lower elevations and 70s in the mountains. Winds will be relatively light but there will be a weak marine push through the gaps of the Cascades late this afternoon and evening producing some locally breezy conditions along the east slopes of the Cascades. This pattern repeats on Wednesday afternoon and evening. On Thursday the high pressure over the eastern Pacific begins to shift westward away from the coast which allows an upper level low over Alaska to move into western Canada. This will push the jet stream south over the Pacific Northwest and combine with an increasing west to east pressure gradient to increase westerly winds through the day and persist through the night. .LONG TERM...Friday through Tuesday...Guidance is in broad agreement on a light to moderate NW flow pattern over the region, before introducing the chance for broad troughing to envelop the forecast area by the end of the period. Net effect will be generally seasonable temps, periods of breezy conditions, and some occasional chances for light orographic shower activity, primarily across the central Washington Cascades. Looking at model ensemble clustering, discrepancies really don`t start to show up until around Monday next week. Until then, guidance shows a cutoff low off the SoCal coast helping to initiate a NW flow pattern over the PacNW. Deterministic guidance shows a more amplified band of NW flow Friday, with those upper-level winds looking to mix down to the surface during the day. NBM probabilistic guidance already showing widespread likely (>70%) chances for gusts to exceed 30 mph, however chances drop down considerably when measuring for advisory-criteria winds. Despite the amplified flow aloft, however, PoPs are low, as deterministic guidance shows PWATs only in the 0.3 to 0.5 range, leaving only slight chances for the high mountains, namely across the WA Cascades. This amplified pattern persists through much of the weekend, however the wind forecast trends downward as the NW flow aloft slackens a bit heading into Sunday. Monday onward is when ensembles start to produce diverging solutions, mainly due to the timing of an oncoming broad trough originating from the NNW. Adding to that, some cluster groups favor a continuation of NW flow rather than the arrival of any kind of trough. Across deterministic guidance, the GFS seems to favor the troughing solution, while the ECMWF brings down a weaker trough while keeping the persistent NW flow pattern in place. Should the trough materialize, expect a drop in temps as it brings in colder Canadian air, however precip chances will likely be limited, due to how dry the oncoming airmass will be. We`re reaching the time of year where, outside of idealized conditions, the boundary layer across the forecast area is simply too dry to support widespread precip under cooler, drier NW flow patterns. Overall forecast confidence through the weekend is high (80%), while Monday onward is moderate (50%). Only real sensible weather impact expected through the long term will be periods of gusty conditions under the NW flow pattern. Evans/74 && .AVIATION...12z TAFs...VFR conditions expected for the period. Skies will be mostly clear outside of some light cirrus. Winds will be breezy at times for DLS, but elsewhere, expect generally W/NW winds less than 12 kts, becoming terrain-driven overnight. Evans/74 && .PRELIMINARY POINT TEMPS/POPS... PDT 74 47 80 51 / 0 0 0 0 ALW 77 51 82 55 / 0 0 0 0 PSC 81 54 87 57 / 0 0 0 0 YKM 81 49 87 51 / 0 0 0 0 HRI 80 50 86 55 / 0 0 0 0 ELN 76 49 81 53 / 0 0 0 0 RDM 73 43 80 47 / 0 0 0 0 LGD 71 44 77 48 / 0 0 0 0 GCD 73 44 79 47 / 0 0 0 0 DLS 80 52 85 54 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...91 LONG TERM....74 AVIATION...74