Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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693 FXUS66 KPDT 161736 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1036 AM PDT Mon Sep 16 2024 .Updated Aviation Discussion. .AVIATION...18Z TAFS...VFR conditions currently at all sites, which will stay the course through the period. An upper level system is tracking to our south, leading to extensive cloud cover across the region that will extend through the period with BKN-OVC ceilings of 7-12 kft. Breezy afternoon winds will occur for KRDM/KBDN as gusts of 15-20 kts are expected. Elsewhere, winds will stay below 10 kts through the period, with the exception of 20-25 kt gusts for KDLS toward the end of the period. There is a slight chance (<20%) of a light shower this morning into the afternoon hours, but did not mention any rain at any TAF site due to the low probability. 75 && .PREV DISCUSSION... /issued 248 AM PDT Mon Sep 16 2024/ SHORT TERM...Today through Wednesday...Radar returns tonight show light showers developing under a shortwave impulse pushing north across the eastern mountains. Precipitation amounts the last 6 hours have generally be under 0.1 inches. Otherwise, low to mid level cloud layers cover much of the forecast area, with some breaks in cloud cover across the Columbia Basin and north central OR. Today through Tuesday morning, an upper low over northern CA will swing across the Great Basin and into southern ID. While the track of the low will keep the best precipitation chances well to our south, deterministic and short-term high res ensemble guidance indicate another shortwave impulse rounding the low and across northeast OR and far southeast WA. That said, there is only moderate confidence (40-55%) in light showers reaching as far west as central OR and OR Cascade east slopes through Tuesday morning. While HREF members show a 50-60% chance of at least measurable precip, the NBM only depicts a 10-20% percent chance in those areas. Otherwise, the eastern periphery of the forecast area, including the Blues, will see rain showers through Tuesday morning. A slight chance of isolated thunderstorms will also be present along the Blues and Wallowas this afternoon through the evening, as CAPE values increase to around 300-400J/kg. Tuesday, the forecast area will be between two upper closed lows. The aforementioned low will continue to swing across the intermountain west, while a second low dives down the southern BC and PacNW coast. The eastern low will continue to support wrap around moisture into far northeast OR and southeast WA, while the western low will increase precipitation chances (30-60%) across the Cascade crest, central OR, and the eastern mountains. Precipitation chances will diminish throughout Wednesday as northerly flow develops aloft as both lows move out of the region. Only other concern through the next several days will be breezy to windy conditions developing late this evening through Tuesday. Surface pressure gradients across the Cascades will begin to tighten as an upper low descends along the BC coastline and the other upper low swings through the Great Basin. Winds will increase to 20-30mph with winds gusts up to 40mph through the Kittitas valley, eastern Gorge, and portions of the OR Columbia Basin; winds will generally be 15-25mph with gusts 30-35mph elsewhere. Confidence in wind gusts meeting or exceeding 45mph in the Gorge and the Kittitas valley is low(20-30%) owing to the lack of low level jet support in these areas. Lawhorn/82 LONG TERM...Thursday through Monday...Ensemble guidance does not have a strong grasp on the synoptic pattern in the long term, but does generally point toward weak NW flow trailing a blocking pattern that will settle in place over CONUS to kick off next weekend. Some ensemble members try to bring in a trough over the weekend, but deterministic guidance does not favor this approach. The beginning of next work week then looks benign, with weak zonal flow to perhaps ridging, before the synoptic pattern really falls apart across guidance beyond day 6. The highest forecast confidence lies in the first two days of the period, where models are in good agreement in a low cutting off and remaining stagnant over California, with another low centered over the eastern CONUS leading to an omega block that leaves us under weak NW to N flow. Expecting a dry forecast as a result Thursday and most of Friday, before the NW flow becomes more defined during the latter half of Friday and introduces shower chances to the WA Cascades. Beyond that, the pattern becomes murky as the deterministic GFS and ECMWF suggest weak NW flow with perhaps an embedded shortwave that may produce shower chances across the entirety of the forecast area, while the Canadian tries to bring in a full on NW low into the PacNW. NBM does suggest slight chance PoPs across most of the CWA, tapping into at least the potential for some kind of impulse, so will leave rain chances in for Saturday. The shift toward a zonal pattern Sunday onward would produce light PoPs across our high mountains, but otherwise Saturday looks to be the most impactful day of the period as far as precip is concerned. Expect generally mild temps with highs in the 70s and low in the 40s. Overall forecast confidence is medium (40-50%). Should note that both the deterministic GFS and ECMWF hint at the potential for an atmospheric river middle of next week, but confidence in this occurring is low (<20%) given how far out that is. Evans/74 && .PRELIMINARY POINT TEMPS/POPS... PDT 71 49 69 49 / 20 10 10 20 ALW 74 53 72 53 / 10 20 20 10 PSC 80 56 76 58 / 10 10 0 10 YKM 81 50 77 50 / 0 0 0 20 HRI 77 54 74 54 / 10 10 0 10 ELN 82 50 72 51 / 0 0 0 10 RDM 67 44 65 45 / 20 10 20 70 LGD 70 48 65 47 / 40 40 40 20 GCD 69 45 67 46 / 40 40 20 40 DLS 82 55 71 55 / 10 10 30 50 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...82 LONG TERM....74 AVIATION...75