Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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785 FXUS66 KPDT 061713 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1013 AM PDT Thu Jun 6 2024 Updated Aviation Discussion .AVIATION...18Z TAFS...VFR conditions prevail with current clear skies for this TAF period. Few high clouds will pass by tonight for KDLS/KALW and then Friday morning for KPSC. KDLS/KRDM/KBDN will experience gusty winds at 20-25kts with sustained winds at 10-15kts this afternoon before decreasing tonight (>50% confidence). Feaster/97 && .SHORT TERM UPDATE...Minor update made to the forecast to add a slight chance of showers and thunderstorms in our far southeast CWA this afternoon and evening, mainly covering southern Crook and Grant Counties. There have been isolated thunderstorms over Malheur County this morning, and CAMS are indicating more activity there this afternoon. Visible satellite shows some cumulus already developing in our SE zones. The instability is present with mid- level lapse rates around 7 C/km. SPC Mesoscale Analysis has yet to show any signs of CAPE at this time, but CAMs have CAPES as high as 500 J/kg. Despite the limited moisture and instability, what is lacking is anything to trigger storms. Weak vorticity will keep the isolated storms over southeast Oregon, therefore any probability for convection in our southeast zones is 15% or less. Wister/85 && .PREV DISCUSSION... /issued 423 AM PDT Thu Jun 6 2024/ SHORT TERM...Today through Saturday...High pressure with weak SW flow aloft continues to drive our weather, with clear skies and warming temps expected through the upcoming weekend. As more prominent ridging takes place Friday into Saturday, breezy east to northeast winds will pick up across the forecast area, impacting primarily the Basin down through central Oregon. Not expecting anything tremendously breezy (think 20 mph gusts at most), but enough to prevent the atmosphere from becoming too stagnant, thus putting a bit of a cap on warming. Still, highs are expected to climb into the 90s across our population centers both Friday and Saturday. An oncoming Pacific low will help work to amplify the SW flow aloft a bit more heading into the weekend, leading to a chance of showers and thunderstorms for primarily the eastern mountains. Models continue to tap into some mid-level moisture on Friday with some decent MUCAPEs in the 400-800 J/Kg range, however with the ridge axis overhead, am not too bullish on storm chances. That being said, the tail end of CAM runs, such as the 00z HREF, do put some weak reflectivity across the far southern portion of our forecast area, so did leave in a slight chance for isolated t-storms for Friday afternoon and evening across extreme southern Deschutes, Crook, and Grant Counties. Current thinking is that better chances for storms exist on Saturday, when a shortwave associated with the Pacific low begins to ease into the forecast area, allowing for more available moisture for showers and storms to fire off during the afternoon and evening hours. Evans/74 LONG TERM...Sunday through Thursday... Key Messages: 1. Thunderstorm potential Sunday afternoon and evening. 2. Warm, above normal temperatures through much of the week. The extended period is characterized by an initial upper level trough on Sunday, followed by several systems that keeps afternoon winds breezy and temperatures warm through much of the period due to persistent southwest flow aloft. However, the main weather concern resides with thunderstorm chances (15-30%) over Central and Eastern Oregon Sunday afternoon and evening as an upper level trough and associated cold front passes through the region from the southwest. This will effectively erode the incumbent upper level ridge that built over the region Friday and Saturday, allowing enhanced instability to be present along the boundary of the incoming airmass. The ECMWF EFI highlights 70-90% of ensembles showing above normal CAPE across Central Oregon, dropping to 50-70% of ensembles further northeast into the northern Blue Mountains and Wallowa County. The GFS suggests Most Unstable CAPE (MUCAPE) of 250-450 J/kg, 20-30 knots of low level shear, and low levels lapse rates of 6.5-7.5 C/km. These parameters are moderate for thunderstorm development via the GFS, but the ECWMF only shows isolated areas over Crook, Grant, and Wheeler counties exhibiting 100-150 J/kg of CAPE - which does coincide with locations of higher probability for thunderstorms (20-30%). These discrepancies are associated with the GFS anticipating a stronger incoming trough and weaker eroding ridge that the ECMWF, with the stronger trough solution currently represented by 60% of ensemble clusters. Along with the primary hazards of frequent lightning, hail, and gusty winds in the proximity of any developing storm cells, moderate to heavy rain may also be an issue as precipitable water (PWAT) amounts of 0.8-0.9" (130-170% above normal) are advertised by both the ECMWF and GFS. These could lead to a quick 0.05-0.15 of an inch of rain falling near a developed thunderstorm. Elsewhere, expected rain amounts are minimal as dry air (50-70% below normal PWATs) will follow closely behind the frontal boundary. Subsequent systems will continue to travel across the Pacific Northwest Tuesday and again on Thursday. As a result, a slight cooling trend will ensue, but it will be gradual as above normal high temperatures are expected to persist until late in the week. The current NBM suggests the area will approach normal high temperatures on Friday, with values dipping into the upper 70s to low 80s across lower elevations of the Basin and foothills. The slow trend will commence on Sunday, as highs drop 3 to 7 degrees from Saturday. These values drop another 2 to 3 degrees on Monday, 1 to 2 degrees on Tuesday, 2 to 4 degrees on Wednesday, and another 2 to 5 degrees on Thursday. These passing shortwaves are rather weak, as indicated by the slow and gradual decline in temperatures, which will keep dry conditions across the area as the bulk of each system passes to our north. Another consistency during this timeframe will be breezy afternoon winds as the passing shortwaves tighten isobars. This will lead to winds of 10-20 mph and gusts of 25-35 mph across the Basin, Gorge, Simcoe Highlands, and the Kittitas Valley each day, with directions primarily out of the west-northwest. 75 && .PRELIMINARY POINT TEMPS/POPS... PDT 84 54 88 59 / 0 0 0 0 ALW 85 57 90 60 / 0 0 0 0 PSC 88 59 93 62 / 0 0 0 0 YKM 88 54 91 58 / 0 0 0 0 HRI 88 56 92 61 / 0 0 0 0 ELN 84 53 89 58 / 0 0 0 0 RDM 85 51 89 57 / 0 0 0 0 LGD 83 51 86 57 / 0 0 0 0 GCD 89 54 91 59 / 10 10 10 20 DLS 89 58 93 64 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...74/85 LONG TERM....75 AVIATION...97