Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
367 FXUS66 KPDT 041617 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 917 AM PDT Fri Jul 4 2025 .MORNING UPDATE...An upper-level low-pressure system centered just off the Oregon coast is inducing widespread cloudiness and precipitation over central and eastern Oregon this morning as the first of two shortwaves embedded within the broader low moves inland. Meanwhile, some clearing is evident on satellite imagery over south-central Oregon extending north into southern Deschutes County. Additional clearing across central Oregon and the Ochoco-John Day Highlands through morning and early afternoon should facilitate some modest (250-500 J/kg) surface-based CAPE by this afternoon. The second shortwave, currently just offshore, is expected to propagate onshore and move inland over south-central and eastern Oregon this afternoon. Coupled with falling heights aloft as the main upper low moves overhead, this should aid additional thunderstorm development primarily for Deschutes, Crook, Wheeler, and Grant counties. Of note, 12Z HREF neighborhood probabilities are highlighting up to a 70% chance of 3-hr precipitation exceeding 1 inch over last year`s burn scars in the Ochoco-John Day Highlands. The main burn scars of concern include those associated with the Wiley Flat, Rail Ridge, Crazy Creek, and Falls fires. After collaboration with BOI, have issued a Flash Flood Watch for the aforementioned burn scars, valid through 8PM PDT. Plunkett/86 && .FIRE WEATHER...Through this evening, a low-pressure system moving over the Pacific Northwest will facilitate widespread precipitation chances, highest for Oregon. Additionally, a chance of thunderstorms is forecast for central Oregon and the Blue Mountains. Chances of wetting rain through the evening are medium- high (50-80 percent for the Blue Mountains) with low-medium chances (30-60 percent) for the rest of central and eastern Oregon. No Red Flag Warnings have been issued due to the anticipated wetting rain, but frequent cloud-to-ground lightning is expected. Thunderstorms will be capable of producing locally heavy rainfall, small hail, and strong, gusty outflow winds in excess of 60 mph across southeast Deschutes, Crook, and Grant counties this afternoon and evening. Plunkett/86 && .PREV DISCUSSION... /issued 1037 PM PDT Thu Jul 3 2025/ .AVIATION...06Z TAFs...VFR with occasional MVFR conditions to prevail through the period. Remnant showers from earlier thunderstorms are currently impacting sites RDM/BDN, but are expected to clear out by 7Z. Tonight, shower/thunderstorm activity will redevelop across central and southeastern OR, then will propagate north throughout the morning and afternoon, but will be isolated to scattered. This has resulted in PROB30 groups for TSRA/SHRA being included at sites RDM/BDN between 10Z-16Z and between 17Z-22Z at sites PDT/ALW. Confidence is low (10-20%) in shower/thunderstorm activity impacting the remaining sites. However, cannot rule out gusty outflow winds impacting site PSC in the late afternoon. Otherwise, winds will mostly be 12kts or less...except at site DLS where winds 12-20kts with gusts to around 25kts will prevail through the period. Lawhorn/82 && .PREV DISCUSSION... /issued 206 PM PDT Thu Jul 3 2025/ .SHORT TERM...This evening through Saturday. Two distinct circulations are evident on satellite imagery this afternoon; the first is located off the southwest Oregon and northwest California coast, and the second is upstream in the northeast Pacific. These two lows are expected (>95% chance) to move onshore tonight through Friday night and facilitate widespread chances of precipitation. While the best chances (50-75%) of showers will remain over central Oregon and the Blue Mountains, low (15-40%) chances will encompass the rest of the forecast area. A chance (25+%) of thunderstorms is forecast over central Oregon and the Blue Mountains tonight through Friday evening, with the most robust convection anticipated Friday afternoon along the southern part of our forecast area in Deschutes, Crook, and Grant counties. Thunderstorms will be capable of producing small hail, locally heavy downpours, and strong outflow winds in excess of 50 mph. Drier conditions are forecast by Saturday as the low exits to the east and a drier zonal flow moves overhead. Plunkett/86 && .LONG TERM...Sunday through Wednesday...Confidence is increasing in warm to hot weather Monday through Wednesday as an upper-level ridge of high pressure builds over the Pacific Northwest. While ensemble clusters depict small differences in the 500-hPa height field over the region, roughly 80% of members show a robust ridge overhead. Forecast HeatRisk peaks at Moderate (level 2 of 4) to Major (level 3 of 4) for the lower elevations, and would support some form of heat highlights. Ensemble NWP is less confident in pattern details Tuesday through Thursday. While most members show a vorticity maximum diving southeast from the Gulf of Alaska and developing into a closed low off the northern California coast Sunday through Monday, its track as it rides over the ridge and moves onshore sometime between Tuesday and Wednesday will modulate shower and thunderstorms chances. Probabilities of showers and thunderstorms are currently too low (<10%) to have in the forecast. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 78 57 87 56 / 30 20 0 0 ALW 78 61 86 60 / 30 20 0 0 PSC 81 59 90 57 / 20 20 0 0 YKM 83 58 88 57 / 20 0 0 0 HRI 81 60 89 57 / 20 20 0 0 ELN 83 57 86 57 / 10 0 0 0 RDM 76 42 82 45 / 40 20 0 0 LGD 73 52 82 53 / 70 30 0 0 GCD 75 48 82 51 / 70 40 0 0 DLS 79 57 86 57 / 20 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Flash Flood Watch until 8 PM PDT this evening for ORZ506. WA...None. && $$ SHORT TERM...86 LONG TERM....86 AVIATION...82 FIRE WEATHER...86