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Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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810 FXUS66 KPDT 162315 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 413 PM PDT Fri Aug 16 2024 Updated aviation discussion .SHORT TERM...Tonight through Sunday night...Latest visible satellite shows a moderate cumulus field over Wallowa County where their is a slim chance (10-15%) for a stray shower or brief TSTM through about 5 PM. Otherwise attention focuses on Saturday and Saturday night with the developing upper low off the coast impinging on the Cascades. Increasing southerly flow and large scale lift will lead to the development of numerous showers and thunderstorms along the east slopes...first in Oregon during the mid to late afternoon and then in Washington during the evening. Moderate to QPF is expected with this activity near the crest with rainfall amounts of .25 to .50 inches common and locally heavier amounts in the heavier storms. WPC has the Washington Cascade Crest in a Marginal Risk for excessive rainfall on Saturday and this matches very well with our current Flash FLood Watch for burn scars. With the copious rainfall expected will not issue fire weather highlights for areas near the east slopes though the threat for abundant lightning is high (75-85%). Did issue fire weather watches for the western portions of the Columbia Basin and Kittitas Valley where storms are more apt to be dry. Latest SPC fire outlook has an isolated dry tstm outlook in this area. Further, the SPC upgraded the Marginal Risk to slight risk along the Cascades for Saturday and this seems reasonable given the late afternoon/evening timing of a mid level shortwave and strong deep layer shear. Also on Saturday humidities will be near or below 10% in Oregon Fire Zone 642 with moderate southerly winds. A red flag warning is in effect from 1 pm-8 pm. Haines will also increase to 5 locally 6 during the day creating at least a moderate potential for plume dominated fires. The weather quiets down on Sunday and Sunday night with dry conditions and cooler temperatures. Highs on Sunday will be mostly in the 80s with 70s in the mountains. 78 Long Term...Wednesday through Sunday... Bottom Line Up Front 1. Dry pattern to start 2. Mountains showers and thunderstorms Wednesday 3. Seasonably cooler temperatures through the period Models are in relatively firm agreement with the upper level low creeping into the PacNW. Clusters do show a slight variance in the position with some models showing the low a bit farther off the coast while others have it closer. This will however, not affect the weather outcome through the beginning of the period. Dry and benign weather will prevail through Tuesday before a shift in the pattern will change things up a bit. Wednesday the models show the upper level low lifting off to the northeast and grazing the WA Cascades as it moves over the area. This will shift the flow to a southwest component allowing some mid level moisture to peruse over the WA Cascades. Models derived soundings are showing a bit of instability over the Cascades with values creating 500 J/kg, LIs of -4 and mid level lapse rates of over 7.5 C/km. However, bulk shear is very low and PWATs are below 0.65 inches. Orographic lift will assist these thunderstorms along the crests of the Cascades on Wednesday. With this, and looking at the raw ensembles, 10-15% show there to be thunderstorms over the Cascades so have left thunderstorm chances in the forecast for Wednesday. After Wednesday night, models show another upper level low making its way towards the PacNW and parking off the coast through the remainder of the period bringing with it southwest flow and continued chances of rain showers along the Cascade crests through Friday. The upper level lows will keep temperatures cooler over the region with the southwest flow coming off the coast and ushering continued cool air into the region. EFI is showing at or just below seasonal averages for this time of year with the NBM showing the average temperatures across the region to be in the mid to upper 80s for the lower elevations with some isolated 90s through the Basin to start the week before steadily decreasing into the low to mid 80s through the remainder of the week. Raw ensembles are a bit more widespread when it comes to the temperatures through the Basin with 53% saying the Basin will see over 90 degrees while the remainder of the region will see mid 80s on Monday. By Wednesday over 60% of the raw ensembles show the Basin and surrounding areas in the low to mid 80s and it remains as such through Friday. Bennese/90 && AVIATION...00Z TAFs...VFR conditions will persist through the forecast period with mostly clear skies and winds generally below 10 knots. && .PRELIMINARY POINT TEMPS/POPS... PDT 54 93 56 84 / 0 10 20 0 ALW 57 99 62 88 / 0 0 20 0 PSC 60 99 65 89 / 0 0 30 0 YKM 55 93 58 84 / 0 10 80 10 HRI 58 98 62 88 / 0 0 30 0 ELN 55 93 60 84 / 0 10 80 10 RDM 49 87 47 82 / 0 40 50 0 LGD 51 94 53 89 / 0 0 10 0 GCD 54 93 52 88 / 0 0 10 0 DLS 60 95 61 83 / 0 20 80 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Fire Weather Watch from Saturday afternoon through Saturday evening for ORZ641. Red Flag Warning from Saturday afternoon through Saturday evening for ORZ642. WA...Fire Weather Watch from Saturday afternoon through late Saturday night for WAZ691. Fire Weather Watch from Saturday evening through late Saturday night for WAZ690. Flash Flood Watch from Saturday afternoon through late Saturday night for WAZ522-523. && $$ SHORT TERM...78 LONG TERM....80 AVIATION...80