Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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849 FXUS66 KPDT 221614 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 914 AM PDT Wed May 22 2024 .UPDATE...Several advisory level wind gusts have occurred at the Pendleton airport this morning, which has warranted the extension of the Wind Advisory to include the foothills of the Northern Blue Mountains of Oregon through 5 PM this afternoon. The pressure gradient is forecast to tighten as guidance is in agreement with increasing winds through the early afternoon along the foothills as gusts of up to 50 mph will be possible. Otherwise, the early morning forecast package is on track and few edits were done with this morning`s update in regards to wind speeds along the foothills. 75 && .PREV DISCUSSION... /issued 412 AM PDT Wed May 22 2024/ SHORT TERM...Today through Friday...Satellite and radar imagery tonight shows the remnants of a warm front exiting into ID, with the associated broad band of precipitation draped across far eastern WA/OR. Behind this band of precip, cloud cover is becoming partly cloudy as water vapor shows a dry slot at the bottom of a closed upper low working it`s way into north central OR and south central WA. Today, the aforementioned upper closed low will drop southeast across the PacNW then exit into central ID later this evening, providing another active weather day across the forecast area. While precipitation yesterday was more stratiform, the combination of the upper low overhead and increasing surface instability will result in mostly showers through the evening hours. In the mountains, snow levels will be dropping to between 4.5kft-5kft, allowing showers at and above these elevations to consist of mostly snow or a rain/snow mix. Heaviest snow amounts (6+ inches) will be concentrated along the higher peaks across the Strawberry mountains, Wallowas, and the peaks along the Cascade crest(confidence 50-60%). Lighter amounts between 2-4 inches will accumulate in areas of the northern Blues from Tollgate north, as well as the central WA Cascades(confidence 40-50%). Increasing surface based instability and modest low level lapse rates will also provide enough forcing for isolated thunderstorms to develop in the Columbia Basin and the eastern mountains by the afternoon. Also to note, the cold core of the low aloft will also allow for graupel to be mixed in with the rain showers in the lower elevations. Westerly winds will be increasing through this morning into the afternoon across the much of the forecast area today, with high confidence (75-85%) of wind speeds 20-35mph and gusts 30-50mph, in which the strongest winds will be felt through the OR Columbia Basin and southern Blue mountain foothills where wind advisories are in effect. Late tonight through Friday morning, a drier northwest turning west flow will be settling across the PacNW resulting in widespread dry conditions through this period. That said, wrap- around moisture from the departing low will continue to aid in development of light rain/snow showers across Wallowa county into Thursday morning. Precipitation chances will return to the PacNW throughout Friday as a shortwave trough slides along the BC coast and across the region. Shower chances will mainly be confined to the mountain areas and immediate foothills throughout the day, while dry conditions will persist across the lower elevations. Rain amounts will be fairly light for Friday, with NBM probabilities only showing a 40-50% chance of 0.1 inches across the Cascade crest, northern Blues, and Wallowas. Modest cross-Cascade pressure gradients will result in breezy winds between 15-25mph and gusts up to 35mph developing through the Cascade gaps Friday, and locally breezy conditions across the lower elevations. Lawhorn/82 LONG TERM...Saturday through Wednesday...The forecast starts out with some uncertainty on Saturday in the location/track of an upper level low that will have an impact on the Pacific Northwest Weather. The GFS moves the low across Oregon while the ECMWF keeps it in southern Canada. The ensemble clusters favor a track more across Washington. Utilized the NBM for this forecast and it is producing a 30-40% chance of mountain showers for Saturday and 5-15% POPS elsewhere. There is a slim chance of thunderstorms (10-15%)over the eastern mountains Saturday afternoon but this chance will fluctuate based on the eventual track of the upper low, with higher probabilities with a more southern track. Regardless of the scenario surface based CAPE will be rather low (200 J/kg or less) so strong storms are not expected. QPF outside of locally heavier showers will be light with 50th percentile amounts from the NBM averaging 05-.10 inches. There is also the potential for breezy to windy west winds across the lower elevations especially the Cascade gaps on Saturday afternoon and evening. The NBM has a 20-40% chance for winds exceeding 45 mph in these areas Saturday afternoon. One of the windiest areas will be the Kittitas Valley. Most of the the 50 ECMWF ensemble members are forecasting peak wind gusts of 35-45 mph with a mean value of 40 mph Saturday afternoon at KELN. Once this weather system exits the region dry westerly flow will be over the region on Sunday and then the ensemble clusters are in general agreement that an upper level ridge will build northward centered roughly over the Rockies through Tuesday. This will result in a warming trend with high temperatures peaking Tuesday in the mid to upper 80s in the Columbia Basin. By Tuesday night and Wednesday there is considerable uncertainty in the pattern over our region with the clusters ranging from flat SWLY flow to a deep upper trough along the PACNW coast. The NBM increase pops to 10-20% across the lowlands and 20-30% across the mountains beginning Tuesday night. AVIATION...12Z TAFS...VFR conditions will prevail through the period with CIGS BKN-OVC 035-070 AGL. Beginning around 18Z and lasting until 03-05Z -SHRA will impact the KPSC, KALW, and KPDT terminals. Latest HREF guidance is showing a 50% chance of TSTMS at KPDT so have included VCTS in the TAF from 22-02Z. Winds will increase quickly at all sites after sunrise with 15-22 kt sustained winds and gusts 25-32 kt. Winds will tend to decrease late this afternoon and evening. 78 && .PRELIMINARY POINT TEMPS/POPS... PDT 55 41 65 42 / 70 70 0 0 ALW 57 44 68 47 / 70 40 10 0 PSC 63 49 73 50 / 50 30 0 0 YKM 60 43 73 45 / 30 20 10 0 HRI 60 45 72 46 / 60 60 0 0 ELN 55 43 68 43 / 30 10 10 0 RDM 51 32 64 38 / 20 10 0 0 LGD 51 39 61 39 / 80 60 10 0 GCD 50 37 60 38 / 80 80 10 0 DLS 60 47 70 48 / 50 10 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Wind Advisory until 5 PM PDT this afternoon for ORZ044-507-508. WA...None. && $$ UPDATE...75 && .SHORT TERM... .LONG TERM... && .AVIATION... SHORT TERM...82 LONG TERM....78 AVIATION...78