Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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316 FXUS66 KPDT 212309 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 409 PM PDT Fri Jun 21 2024 .Updated for Aviation... .AVIATION... 00Z TAFS...VFR conditions are expected through the TAF period. Winds of 10 kts or less can be expected at all sites through tonight and much of the day on Saturday. However, as a cold front approaches later Saturday, winds will increase at DLS, RDM and BDN towards the end of the TAF period and could gust as high as 25 kts. Winds could also pick up at PDT as well. Expect further increases beyond the end of the TAF period. && .PREV DISCUSSION... /issued 221 PM PDT Fri Jun 21 2024/ SHORT TERM...Tonight through Sunday...A dry westerly flow developing over the PacNW this afternoon has produced light winds, dry conditions, and hot temperatures. Meanwhile, satellite imagery is showing scattered cumulus clouds attempting to develop over the WA Cascades and higher peaks in the eastern mountains. Today and tomorrow, a thermal trough building in from the south will continue to bring a warming trend across the forecast area. Temperatures today are expected to be anywhere from 4 to 10 degrees warmer than yesterday, and another 2 to 5 degrees warmer on Saturday. While temperatures in the lower elevations Saturday will be in the 90s, the NBM does show a 20-35% chance that areas around Hermiston and the Tri-Cities could hit 100 degrees. With temperatures this warm, HeatRisk values are also increasing into the moderate category, with widespread moderate in the lower elevations today and Saturday. Beginning late tomorrow, a dry upper low with a surface cold front will approach the PacNW from the the Gulf of Alaska. This system will begin to tighten the cross Cascade pressure gradient Saturday evening, resulting in breezy winds developing through the Cascade gaps during the late afternoon and evening. By Sunday, the upper low will be swinging into southern BC while dragging the cold front across the PacNW. The main concern with this system passage will be the increased winds through the Cascade gaps into the Columbia Basin, where winds will be 15-25 mph with gusts mainly up to 40mph. That said, NBM probabilities of 24 hour max wind gusts greater than 45mph are 60-80% in the Kittitas valley, Simcoe Highlands, and the OR Columbia Basin. The increased winds will also coincide with critically low relative humidities across the Columbia Basin Sunday, resulting in elevated fire weather conditions. In the Cascade gaps, however, the cooler temperatures associated with the marine push/frontal passage will keep relative humidities above critical thresholds. Otherwise, there will be very little precipitation associated with this system, which will be mostly confined to the central WA Cascades. In this area, probabilities for only 0.01 inches of precipitation are only 40%-60%, highlighting the dryness of this system. Alluded to earlier, the cold front and upper low passage will help break down the surface thermal trough and bring relatively cooler temperatures back to the region, albeit afternoon temperatures will still be in the 80s. The best chances of reaching 90 degrees on Sunday will be around the Tri-Cities area, where the chance is only 20-30%. Lawhorn/82 LONG TERM...Monday through Friday...A zonal pattern remains over PacNW Monday before building into a ridge through Wednesday. Then, a trough will move inland PacNW late Wednesday into Thursday until exiting east when another ridge arrives off OR coast Friday. Models and ensembles are in great agreement with the weather pattern through Wednesday. However, there are some differences with Thursday`s pattern and the timing of Friday`s trough. 21% total members favor a zonal pattern whereas the majority agree with troughing for Thursday. And Friday, both GFS and ECMWF show the ridge occurring sooner than Canadian. Nonetheless, no major weather impacts will happen during the extended period due to dry conditions. Confidence remains low for mountain showers at the crest of WA/OR Cascades and the Blues late Wednesday through Thursday (<30%). The trough and cold front passage will have limited moisture. Seasonable temperatures will be Monday with the zonal pattern over the region. Tuesday into late Wednesday, temperatures warm up again from the transient ridge but decreases Thursday into Friday with the arrival of the upper trough off the coast. Wednesday afternoon will begin with wind gusts at 25-35 mph through early night along the lower Columbia Basin, Columbia River and Kittitas Valley (>70% chance). Confidence increases for increased wind gusts in these areas Thursday from the arrival of the trough. Breezy conditions will continue across the forecast area with wind gusts at around 30 mph or less through this remaining extended period (40-50% probability). Feaster/97 AVIATION...Previous Discussion...18Z TAFS...VFR continues for this TAF period with current light winds and clear skies. Periodic mid to high clouds will impact sites during the next 24 hours. Feaster/97 FIRE WEATHER...A Fire Weather Watch has been issued from Sunday 1pm to 8 pm for wind and low relative humidity for fire weather zones OR641 and WA691. An incoming dry cold front will result in breezy to gusty conditions developing in the Lower Columbia Basin, which will coincide with afternoon relative humidities in the teens. Strong winds through the Cascade gaps will also produce elevated fire weather concerns, but relative humidities are expected to remain above critical thresholds. Current confidence in elevated fire weather conditions Sunday is 60-70%. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 57 93 59 82 / 0 0 0 0 ALW 59 96 64 86 / 0 0 0 0 PSC 60 98 64 88 / 0 0 0 0 YKM 61 95 56 83 / 0 0 0 0 HRI 59 98 64 86 / 0 0 0 0 ELN 58 92 57 74 / 0 0 0 0 RDM 53 91 51 82 / 0 0 0 0 LGD 53 91 56 84 / 0 0 0 0 GCD 54 95 55 88 / 0 0 0 0 DLS 63 93 61 78 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Fire Weather Watch from Sunday afternoon through Sunday evening for ORZ641. WA...Fire Weather Watch from Sunday afternoon through Sunday evening for WAZ691. && $$ SHORT TERM...82 LONG TERM....97 AVIATION...77