Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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031 FXUS66 KPDT 180233 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 733 PM PDT Mon Jun 17 2024 .EVENING UPDATE...Latest radar imagery shows a band of scattered showers and thunderstorms moving across the Basin and into the Blue Mountains from the northwest. A deep trough that continues to envelop the PacNW is to blame, as this system charges the atmosphere with enough lift and moisture to create weak shower and thunderstorm activity across primarily the eastern half of our forecast area. Storm activity has been on the weaker end, however once cells start to further push into the mountains, the added lift may lead to more widespread storms. Bulk shear remains weak, however, so most storms that do form are still expected to be short lived. Winds will continue to trend downward through the evening and overnight hours as the trough shifts further east and drier, more benign W to NW flow aloft takes its place. The forecast Tuesday onward looks much drier as a result. Main changes to the forecast tonight were to expand thunderstorm potential into the Basin, as well as to up PoPs over there as well for this evening. Evans/74 && .PREV DISCUSSION... /issued 429 PM PDT Mon Jun 17 2024/ AVIATION...00z TAFs...VFR conditions expected for the period. Showers have developed over the Columbia Basin this afternoon, and may impact PSC, PDT, and ALW at times, however showers are scattered in nature and are tracking just a bit west of these sites, so confidence is low as to whether or not impacts will be seen. Gusty conditions continue at many sites as well, before lighter, terrain-driven winds are expected to prevail after nightfall. Skies will clear overnight as well, with quiet conditions expected to continue into Tuesday. Evans/74 PREV DISCUSSION... /issued 204 PM PDT Mon Jun 17 2024/ SHORT TERM...Tonight through Wednesday...Water vapor satellite imagery this afternoon shows an upper shortwave trough exiting into the northern Rockies. Shower activity associated with the trough passage has begun to increase this afternoon across far eastern WA/OR, while surface heating has provided enough instability for a few isolated thunderstorms to develop in northern Wallowa county and further east and north along the ID border. Shower activity will linger early into this evening across the northern Blues, but as the shortwave trough continues east, this activity will diminish and be mainly confined to the mountainous terrain of Wallowa county overnight. With the trough further east, winds will also weaken through the Cascade gaps and the lower Columbia Basin overnight. By tomorrow morning, the PacNW will be under a broad upper level troughing pattern with mostly light winds at the surface and dry conditions across much of the forecast area. That said, a weak shortwave impulse will move across the PacNW tomorrow afternoon, producing chances of light showers across the WA Cascades, northern Blues, and Wallowa county. Lingering surface instability with modest low-level lapse rates will also allow for an isolated thunderstorm or two to develop across Wallowa county Tuesday afternoon. With ridging developing across western Canada and troughing across the western US, a split flow will develop along the US/Canadian border Wednesday. This will continue to promote dry conditions and light winds at the surface. While the region is expected to be under a broad troughing pattern through the mid week, an inverted thermal trough developing through the Great Basin will lead to warming temperatures. By Wednesday afternoon temperatures will have warmed back into the 80s across the lower elevations, with 60s to 70s in the mountainous zones. Lawhorn/82 LONG TERM...Thursday through Monday...Models continue to be in fairly good agreement through the end of the week but some timing and placement issues remain on Sunday and Monday. The Pacific Northwest will be under the influence of a weak and decaying upper level trough Thursday. The trough will dissipate allowing the flow to become westerly Friday and then amplify into an upper level ridge centered over the northern Rockies on Saturday as the next upper level trough approaches the coast. This will produce a warming trend with generally light winds through the end of the week. Hottest temperatures of the week will be Friday into Saturday with Saturday being the peak day. The probability of temperatures greater than 90 degrees these 2 days across the Lower Columbia Basin is 60-90% but the probability of greater than 100 degrees remains less than 10%. So, primarily expecting high temperatures Friday and Saturday across the Lower Columbia Basin in the lower to mid 90s and 80s in the higher elevations then cooling Sunday and Monday. The arrival of the upper level trough into the region Saturday night and Sunday is in better agreement than yesterday. This will lead to then onset of a weak marine push Saturday evening becoming a full blown push on Sunday with breezy to windy conditions and winds 15 to 30 mph with higher gusts. This poses an elevated risked of fire spread in existing or new fire starts on Sunday. Temperatures will begin to cool Sunday with the arrival of the trough and then even cooler on Monday. Precipitation threat looks to remain focused along the crest of the Washington Cascades with some showers Saturday night through Monday. As of now there are no thunderstorms in the forecast as probabilities are below 10%. However, as the flow aloft becomes more southwesterly on Saturday due to the building ridge this could become an issue over the eastern mountains as probabilities begin to increase above 10%. && .PRELIMINARY POINT TEMPS/POPS... PDT 44 73 45 82 / 40 0 0 0 ALW 48 75 48 85 / 40 10 0 0 PSC 49 79 49 87 / 30 0 0 0 YKM 45 77 46 83 / 10 10 0 0 HRI 48 79 48 87 / 40 0 0 0 ELN 45 74 46 82 / 0 10 0 0 RDM 35 74 39 81 / 0 0 0 0 LGD 40 68 41 77 / 60 20 0 0 GCD 37 71 41 79 / 20 10 0 0 DLS 48 78 51 87 / 10 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...74 LONG TERM....91 AVIATION...74