Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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121 FXUS66 KPDT 222358 AAA AFDPDT Area Forecast Discussion...UPDATED AVIATION. National Weather Service Pendleton OR 458 PM PDT Sat Jun 22 2024 .SHORT TERM...Tonight through Monday...An inverted thermal trough continues to extend across the Great Basin and into eastern OR/WA this afternoon, resulting in temperatures warming into the lower 90s so far this afternoon. Meanwhile, mid to upper level moisture ahead of an approaching trough is moving across WA, resulting in scattered cloud decks developing mainly across the northern half of WA. These cloud decks have limited some heating across portions of the WA Columbia Basin and adjacent valleys, but the expectation is for these areas to continue to warm into the mid to upper 90s over the next several hours. Later this evening, an upper trough and surface cold front will approach the PacNW, resulting in a marine push across the western half of the region up to the Cascade crest. With the thermal trough on the east side and a marine airmass developing on the west side, pressure gradients will tighten across the Cascades, resulting in breezy winds through the gaps and eastern Columbia River Gorge. As the upper trough travels along the US/Canadian border tomorrow, the marine airmass will deepen, and the subsequent marine push through the Cascade gaps will result in breezy to windy conditions in the Columbia River Gorge and the Kittitas valley. In fact, sustained winds of 30mph and gusts up to 50mph will develop through the Kittitas valley, which has warranted the issuance of a wind advisory (confidence 80-85%). The winds associated with the marine push and cold front passage tomorrow will spread into the Columbia Basin and the remainder of the lower elevation locations across the forecast area, with winds generally between 15-25mph and gusts up to 40mph (confidence 70-85%). While the marine push will result in cooler temperatures and relatively higher RHs through the Cascade gaps tomorrow, water vapor imagery shows a very dry airmass at the bottom of the trough. Model guidance depicts this very dry airmass at 700mb mixing down along the cold front passage in the Columbia Basin and adjacent foothill areas tomorrow(confidence 85%). With the anticipated dry conditions and breezy winds, Red Flag Warnings were issued for the Lower Columbia Basin for Sunday afternoon through the evening. Though the system will be fairly dry, there are chances (20-35%) of light rain showers developing along the Cascade crest as early as tonight through tomorrow evening. Otherwise, the thermal trough over the area will breakdown, bringing temperatures back into the upper 70s to 80s across the lower elevations. Monday, pressure gradients will relax as westerly flow aloft evolves into a broad, shallow ridge over the PacNW. That said, locally breezy winds will develop in the afternoon through the Gorge and the Kittitas valley. Temperatures will continue to be in the upper 70s to 80s Monday afternoon, with otherwise quiet conditions across the forecast area. Lawhorn/82 .LONG TERM...Monday night through Saturday. The ridge axis will move across the region early on this extended period. A trough then arrives to the PacNW Wednesday through late Thursday, bringing increased winds and cool temperatures across the forecast area. Mountain showers are also possible at the crest of the WA/OR Cascades but, confidence remains low due to limited moisture associated with trough and cold front (<30%). Temperatures will cool late Wednesday through Thursday with the arrival of the trough but an arrival of the ridge Friday through Saturday will bring warm temperatures across the forecast area. High chances (>70%) for wind gusts occurring late Wednesday afternoon at 25-35 mph through early night along the lower Columbia Basin, Columbia River and Kittitas Valley. Confidence remains high for increased wind gusts in these areas Thursday as the trough passes. Friday onward, locally breezy conditions will continue across the forecast area with wind gusts at around 20 mph or less (40-50% probability). Feaster/97 && .AVIATION...00Z TAFS...Limited aviation concerns with the main forecast challenges revolving around winds and a cold front that will advance across the area overnight. VFR conditions currently area-wide with few-sct cu seen across portions of the eastern mountains and limited mid-high clouds across portions of south central WA. These latter clouds will push off east with clear skies taking hold overnight. A tight gradient cross-Cascade pressure gradient will sharpen early tomorrow in tandem with a moderate belt of upper-level winds that will be spreading across the area tonight and remain in place through tomorrow. While light breezes will persist at most TAF sites overnight, winds will start ramping up area-wide late morning tomorrow. The exception will be KDLS overnight where there winds will continue to be elevated (gusts around 20-25 kts at times). High confidence (> 80%) in all TAF sites seeing frequent gusts in the 25- 30 kt range tomorrow outside central OR. Of which, strongest gusts anticipated at the KDLS terminal with ~35 kts expected to be common. Timing for uptick in gusts around 17-20 UTC, latest in central OR. Most likely 24-hr daily peak gusts are expected to be strongest at the KDLS, KPDT, and KPSC terminals with magnitudes in the 35-40 kts range (highest at KDLS). && .FIRE WEATHER...A Red Flag Warning is in effect from 1 PM to 8 PM PDT Sunday for wind and low relative humidity for fire weather zones OR641 and WA691. A marine push and cold front passage will result in winds of 15 to 25 mph tomorrow in the lower elevations. A dry airmass aloft will mix down the cold front boundary in the Lower Columbia Basin, resulting in critically low relative humidities coinciding with the elevated winds in this area. Current confidence is high (80-85%) in critical fire weather conditions being met tomorrow afternoon and early evening. Elevated fire weather conditions will also be a concern through the Cascade gaps, including the eastern Columbia River Gorge and the Kittitas valley, where the strongest winds are expected. Lawhorn/82 && .PRELIMINARY POINT TEMPS/POPS... PDT 59 81 48 81 / 0 0 0 0 ALW 62 85 52 84 / 0 0 0 0 PSC 63 87 53 85 / 0 0 0 0 YKM 56 82 48 82 / 0 0 0 0 HRI 63 85 53 86 / 0 0 0 0 ELN 55 71 48 78 / 0 0 0 0 RDM 51 82 43 82 / 0 0 0 0 LGD 56 84 48 81 / 0 0 0 0 GCD 55 89 48 86 / 0 0 0 0 DLS 61 77 53 83 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Red Flag Warning from 1 PM to 8 PM PDT Sunday for ORZ641. WA...Red Flag Warning from 1 PM to 8 PM PDT Sunday for WAZ691. Wind Advisory from 5 AM Sunday to midnight PDT Sunday night for WAZ026. && $$ SHORT TERM...82 LONG TERM....97 AVIATION...80 FIRE WEATHER...82