Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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077 FXUS66 KPDT 090329 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 829 PM PDT Sat Jun 8 2024 .SHORT TERM UPDATE...Strong to severe storms developed over Lake and Harney Counties this evening, and there have been some CG lightning associated with these large cells in far southern Crook and Grant Counties. We will continue to monitor these storms as they track to the northeast, but it looks like the stronger storms will skirt past our forecast area this evening with the exception of Grant County east of Seneca. The confidence is around 70% due the latest 00Z HREF composite reflectivity progs. The steering flow is very weak, and storms have only been moving around 8-15 mph based on KCBX storm motion and H7 winds around 10 kt. Foster Flat RAWS site in Harney County measured 0.64", so the slow moving storms will also bring heavy rain with eyes focused on the radar and observations. After midnight, the southwest flow aloft will increase ahead of an approaching shortwave trough. Showers and thunderstorms will increase over eastern Oregon, mainly Grant, Union and Wallowa Counties early Sunday morning. MUCAPES from CAMS go as high as 500 J/kg and mainly over southeast Oregon. There is elevated instability with negative theta-e lapse rates and DIV Q aloft. The chance of showers is around 30-50% for Sunday morning and the chance for thunderstorms is around 20-30%. Forecast was updated to reflect the current conditions and change the "chance" wording to "scattered" over our southeast zones. Otherwise, no updates needed. Wister/85 && .PREV DISCUSSION... /issued 500 PM PDT Sat Jun 8 2024/ SHORT TERM...Today through Monday... Bottom Line Up Front (BLUF) 1. Thunderstorms over south central OR and along the eastern mountains today and Sunday afternoon. 2. Warmer than average temperatures today before leveling towards normal. 3. Winds increase again Sunday. Hi-res models are in decent agreement with the upper level synoptic pattern through tonight. An upper level ridge has shifted east of the region as the leading edge of an upper level trough makes its way onshore. Mid level moisture will enhance as the southwesterly flow intensifies ahead of the the upper level trough. This synoptic set up will lead to thunderstorm probabilities across southern Deschutes, Crook and Grant Counties. The SPC has a marginal thunderstorm outlook over the southern portion of the CWA today then it switches to a general thunderstorm outlook along the eastern mountains on Sunday. Model derived soundings across the the aforementioned counties show MUCAPE values of 200-400 J/kg, lapse rates over 8.5 C/km, lifted index of -2 to -3, PWATs of 0.77 inches and bulk shear near 25 kts. As the upper level trough continues to push onshore, thunderstorm ingredients are projected to continue through Sunday and move along the Ochoco-John Day Highlands and across the eastern mountains into Wallowa County. Model derived soundings again show MUCAPE of 400-600 J/kg, lapse rates of 7.6 C/km, lifted index of -3 to -4, PWATs of 0.90 inches and bulk shear nearing 30-40kts. The strongest of the ranges being in Union and Wallowa Counties Confidence in these storms becoming severe is low from the SPC guidance, less than 5%. Even with the incoming frontal boundary and upper level trough, temperatures are going to remain slightly above to near normal. Models show the upper level trough to be mostly dry and `cooler`, only dropping the temperatures as few degrees Sunday. EFI is signaling above average temperatures for much of OR today and leveling back to near normal on Sunday through Monday. Over 80% of the raw ensembles show that today, much of the region will be in the upper 80s with some isolated 90s in the Basins, mid elevations like central and north central OR will be in the mid to upper 80s and the higher terrains will be in the high 60s to low 70s. Models then show the trough axis to be onshore Sunday which will push a frontal boundary across the Cascades allowing some `cooler` air to rush into the area. Temperatures will only cool by a few degrees with over 80% of the raw ensembles showing temperatures in the mid to upper 80s through the Basins, upper 70s to low 80s along the lower and mid elevations and low 60s along the higher elevation. Over 80% of the raw ensembles show Monday to be much the same as Sunday. There is an enhanced heat risk today for portions of the Basin where HeatRisk guidance is signaling moderate risk, so be mindful if outside and remember to drink plenty of fluids. Lastly, with the upper level trough pushing across the Cascades, model derived pressure gradient tool shows that there is a slight tightening of the surface gradients along the Cascades of 9 to 11 mb. While this is not wildly different from what is considered normal, it is elevated. Due to this, ensembles are picking up on increased winds, especially through our wind prone areas. There is over a 55-75% chance the Simcoe Highlands and portions of the Gorge seeing winds of 25 mph or greater, 70-80% through the lower Kittitas Valley and a 65-70% along the foothills of the Blues. Bennese/90 LONG TERM...Tuesday through Saturday...Westerly zonal flow on Tuesday will bring a low (20%) chance of some showers to the Washington Cascades into Tuesday night, while the rest of the are will be dry. A cold front will cross the region on Tuesday. Dry weather will continue into early Friday before southwesterly flow returns and so do precipitation chance, mainly to the Cascades through Saturday, again with most of the rest of the region remaining dry. There is considerable uncertainty as we head toward next weekend regarding the evolution of the pattern, with a trough expected to move onshore in the Pacific Northwest. The deterministic ECMWF is weaker and considerably faster with the trough than the GFS. As we approach the weekend, the ensemble clusters are a bit more supportive of the ECMWF solution (37%) by Friday, though at that time range there is general uncertainty anyway. There is definitely going to be a trough, it is more of a question of exactly when. By Saturday, the ECWMF has 36% of the clusters while the GFS has 32%, so not much difference. It will be breezy on Tuesday with the passage of the cold Front in the Columbia Gorge, Basin, Simcoe Highlands, Kittitas Valley. Wind gusts in the 25 to 35 mph range are anticipated. It will also be breezy around Friday (or whatever day this occurs) as the trough moves onshore, especially in the Basin, Gorge, Kittitas Valley. High temperatures will go from about 10 degrees above normal on Tuesday from the mid 80s to near 90 degrees in the Columbia Basin to about 5 degrees above normal on Wednesday with highs from the upper 70s to mid 80s. Thursda`s highs will be similar to Tuesday, as highs increase in southwesterly flow. By Friday, and especially Saturday, highs will be close to, or even slightly below normal due to the trough, though there is uncertainty. Highs will range from the upper 60s to upper 70s. AVIATION...00Z TAFS...BKN-OVC mid and high level clouds will remain through Sunday afternoon. Winds will also be 15 kt or less with strongest winds at KDLS, KRDM and KBDN before sunset. Thunderstorms have developed in south central Oregon...a little farther south than most of the CAMS advertised. The embedded wave triggering the isolated activity will travel to the northeast and bring showers and thunderstorms, but mainly over the eastern mountains and valleys. I included VCSH in the TAF for RDM and BDN for the early morning hours based on model QPF over central OR, but the VCSH may be removed based on the track of the weak wave. Wister/85 && .PRELIMINARY POINT TEMPS/POPS... PDT 59 80 56 83 / 0 20 10 0 ALW 61 83 59 85 / 0 20 10 0 PSC 62 87 60 89 / 0 10 10 0 YKM 59 86 53 87 / 10 30 10 0 HRI 62 87 59 88 / 0 20 10 0 ELN 61 82 55 81 / 10 30 10 0 RDM 56 80 47 82 / 20 30 0 0 LGD 57 76 51 79 / 20 40 10 0 GCD 56 78 49 82 / 30 40 10 0 DLS 64 83 56 84 / 10 10 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...90 LONG TERM....77 AVIATION...85