Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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383 FXUS66 KPDT 231708 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1008 AM PDT Sun Jun 23 2024 Updated Aviation Discussion .AVIATION...18Z TAFS...VFR prevailing for this period. KDLS/KPDT/KYKM/KALW/KPSC currently have some clouds, but clear skies for KRDM/KBDN. As the system passes, increasing winds will be a concern for all sites sustaining at 12-20kts with wind gusts around 20-30kts. Wind conditions should improve later this evening. Feaster/97 && .MORNING UPDATE...No significant changes were made to the forecast this morning. Looking at observations across the PacNW, Day Cloud Phase Distinction RGB imagery reveals mostly clear skies across our forecast area. Meanwhile, a marine layer accompanied by stratus is evident along the Cascade crest westward. Onshore-directed surface pressure gradients are injecting this moist marine air through the Cascade gaps eastward into the Columbia Basin and along the Blue Mountain foothills. The result is surface dew points in the mid-40s to lower 50s and RHs in the upper 30s to upper 50s in the aforementioned region. As the day progresses, drier air from aloft will mix down to the surface, though 12Z HREF members are in excellent agreement that the boundary layer will not become sufficiently deep to tap into the driest air around 700 mb. If HREF members are correct, afternoon RHs will range from the upper teens to lower 30s across the Columbia Basin and along the Blue Mountain foothills. However, if the model depiction of boundary layer depth is too low, even by 500-1000 ft, afternoon RHs may plummet to the upper single digits and lower teens area-wide, except for areas most influenced by the marine layer such as Columbia River Gorge and upper Kittitas Valley. Multiple Red Flag Warnings remain in effect today across the lower elevations. Additionally, the Wind Advisory for the Kittitas Valley remains in place. Plunkett/86 && PREV DISCUSSION... /issued 224 AM PDT Sun Jun 23 2024/ SHORT TERM...Today through Tuesday night...Red flag conditions and strong winds will be the primary weather concerns today. The Red Flag Warning in effect for the Lower Columbia Basin of WA/OR (fire zones WA691 and OR641) will be expanded to include central Oregon (fire zone OR640) in effect this afternoon and evening. A wind advisory is in effect for the Kittitas Valley starting at 5 AM this morning through midnight. Winds have already increased across the Lower Columbia Basin and surrounding valleys. These winds are providing mixing of warm and dry air aloft to the surface, resulting in early morning temperatures in the lower 70s and RHs in the upper 20s and 30s. To give a feel for how dry it is aloft, the 00Z UIL sounding has a dewpoint spread of around 26C at 700mb. However, the depth of the marine layer at UIL is from the surface to 850mb. GOES nighttime microphysics shows the marine layer banked up along the west side of the Cascade Range. The marine layer will deepen as the day progresses with the passage of a shortwave trough and dry cold front. There will not be significant winds associated with the front with the exception of the Kittitas Valley where sustained winds around 30 mph gusting to 45 mph are forecast. Confidence is high for these winds to be observed, but gusts at 50+ mph have a much lower probability (0% from the HREF and 30% from the NBM). As far as fire weather concerns, the marine layer seeping through the Cascade gaps will keep RHs high enough along the Kittitas Valley and eastern CR Gorge despite the gusty winds. Deterministic models are in good agreement with Min RHs around 30% for these areas. RHs over the Lower Columbia Basin will be in the teens and 20s. Central Oregon will observe RHs in the teens as well with a few spots in the single digits. Since the winds are forecast to be a little stronger in central Oregon, a Red Flag Warning will be issued to include this zone. Winds aloft and at the surface will decrease tonight, and Monday`s winds will be considerably less than today. Afternoon highs on Monday will be about the same or a tad cooler than today and closer to seasonal average. No weather concerns are anticipated for Monday night through Tuesday night. However, the westerly flow will begin to back to the southwest on Tuesday as an upper level trough develops offshore. Afternoon temperatures will climb back into the 80s to mid 90s with the HeatRisk in the minor to moderate category. There are signs of elevated instability over eastern Oregon as well, but the threat of any thunderstorms is low...less than 15%. There is limited mid-level moisture but no indications of an upper level disturbance to provide the lift needed. However, I would expect cumulus buildups over the Blues and the John Day- Ochoco Highlands Tuesday afternoon and evening. Wister/85 LONG TERM...Wednesday through Sunday...Southwest flow expected over the region as an area of low pressure approaches the PacNW on Wednesday. Precipitation associated with this system has a slight to moderate chance (40-60%) of impacting the Cascade Mountains starting Wednesday. Additionally, temperatures will decrease on Wednesday by a few degrees, though values will generally still be around 5 degrees above normal. Wind will be the other consideration for Wednesday. Wind speeds will increase through the afternoon and evening hours, with the strongest wind favored to be across the Columbia Basin, Columbia River Gorge, and into the Kittitas Valley. In these locations, there is a 60-80% chance for winds of 25 mph with gusts of 30-35 mph on Wednesday afternoon and evening. Additional areas of Washington and Central Oregon will see 70-90% chance for winds around 20 mph with gusts near 25 mph for the same timeframe. Windy conditions will weaken slightly overnight. The area of low pressure continues to move through the area on Thursday, though models and clusters show variations in placement and related strength of the system`s influence on Thursday. The NBM has a return of gusty to breezy wind on Thursday afternoon, but keeps any threat of shower activity generally confined to the higher terrain. There are some solutions (GFS mainly) that do hint at the potential for showers across the lower elevations, though confidence in that development remains low. Further cooling temperatures anticipated Thursday with values landing around 5 degrees below normal. While wind will see another increase in the afternoon, winds are not expected to be as strong. The favored locations of the Columbia River Gorge and the Kittitas Valley remain, with most of these areas seeing a 70-90% chance for winds around 20 mph with stronger gusts. The presence of winds stronger than that is more isolated. The area of low pressure will generally move east of the forecast area by Friday, allowing a drier, northwest flow to influence the region. A warming trend in temperatures returns with values reaching near normal values on Friday with widespread dry conditions. This pattern will keep winds generally light. Similar conditions expected Saturday with additional warming. An approaching wave late Saturday into Sunday will turn flow southwesterly again, with a few showers present over the higher terrain. Branham/76 && .PRELIMINARY POINT TEMPS/POPS... PDT 81 48 81 51 / 0 0 0 0 ALW 85 52 85 54 / 0 0 0 0 PSC 87 52 86 55 / 0 0 0 0 YKM 83 46 83 51 / 0 0 0 0 HRI 85 52 86 55 / 0 0 0 0 ELN 74 47 81 51 / 0 0 0 0 RDM 82 43 83 47 / 0 0 0 0 LGD 83 47 81 51 / 0 0 0 0 GCD 89 47 87 52 / 0 0 0 0 DLS 77 52 84 55 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning from 1 PM this afternoon to 8 PM PDT this evening for ORZ640-641. WA...Red Flag Warning from 1 PM this afternoon to 8 PM PDT this evening for WAZ691. Wind Advisory until midnight PDT tonight for WAZ026. && $$ MORNING UPDATE...86 SHORT TERM...85 LONG TERM....76 AVIATION...97