FXUS66 KPDT 190507 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1007 PM PDT Thu Jul 18 2024 .UPDATED AVIATION...06Z TAFs...VFR conditions will persist through the forecast period, however, there will be some lingering high level haze. DLS remaining breezy at 15 kts while the remaining sites are below 9 kts. Bennese/90 && .PREV DISCUSSION... /issued 444 PM PDT Thu Jul 18 2024/ AVIATION...00z TAFs...VFR. Dry conditions persist as the ridge progresses eastward. Gusty winds will remain present across KDLS, KRDM, and KBDN this evening in response to a tightened pressure gradient impacting western Oregon. Wind should weaken at these terminals after 08z tonight, with generally light wind (less than 15 kts) expected otherwise. Branham/76 PREV DISCUSSION... /issued 249 PM PDT Thu Jul 18 2024/ SHORT TERM...Tonight through Saturday...A deep high pressure ridge is expected to only strengthen it's grip on the inland PacNW over this weekend, once again burning us up with very warm temperatures and increased fire weather concerns. Heat advisories are expiring this evening, and although afternoon temperatures tomorrow will still be warm, highs should drop by a couple of degrees and overnight lows will be back into the 50's to 60's, allowing enough recovery that heat products will not be necessary tomorrow. Saturday is a different story though as we see widespread highs soaring back into the triple digits for our lower elevation population centers. And with even warmer temperatures on Sunday combined with overnight lows back into the upper 60's to low 70's, an excessive heat warning has been issued. The NBM shows all of our population centers at an 80-100% chance of exceeding 100 degrees on Saturday, giving very high confidence to this warning. Meanwhile, as flow turns more southerly from the ridge stretching into Canada, instability will be on the increase. This shouldn't come into effect until once again on Saturday when lapse rates across Southern and Central Oregon will rise. With relative humidities nearing the single digits alongside the hot temperatures and the Falls Fire ongoing, a Fire Weather Watch was necessary for hot, dry, and unstable conditions for zone OR-642 for the danger of extreme fire behavior. Thunderstorm potential may begin to materialize into early next week as this instability continues to overspread and moisture begins to advect back into the region. Goatley/87 LONG TERM...Sunday through Thursday...A strong high pressure ridge will prevail over the region on Sunday, before a low to our northwest noses its way in and breaks down the ridge. We'll see this prolonged heat come to an end as this ridge breaks down, but this will come at the cost of potential critical fire weather conditions, as the ridge's breakdown promotes breezy conditions across much of the forecast area for the early to middle of next work week. Sunday will be by far the hottest day of the period, with NBM probabilistic guidance depicting high chances (60-80%) of temps eclipsing 105 degrees across the Columbia Basin and adjacent valleys. Moderate odds exist for temps exceeding 110 degrees as well, primarily for the lower Columbia Basin (40-50%). Elsewhere, expect triple digit readings outside of our high mountain zones, with numerous daily high temperature records in jeopardy as a result of this particularly strong high pressure ridge. As the aforementioned low pushes into the PacNW, it will orient the winds aloft more SW, which may inject enough moisture to support thunderstorm development across primarily central Oregon and up along the east slopes of the Cascades. The 12z NAM highlights these areas in particular on Sunday, and seeing a signal this far out does inspire some confidence in the forecast, albeit on the lower end still (40%) given how hot and dry we'll be for the rest of the weekend. Better chances for storm development look to be on Monday, as the low really starts to move in and advect more moisture into the area, with chances spreading towards the eastern mountains as well (45% confidence). Ensembles are in good agreement on this low moving in by early next week, which will cool temperatures down by a good 10 to 15 degrees by the midweek with highs hovering right around averages for this time of year. Concern, however, then shifts toward an uptick in winds that could potentially spurn critical fire weather conditions. Confidence is only low/moderate based on what models are outputting for wind speeds (30-40% chance in Red Flag Conditions, at least for the east slopes of the Cascades and Columbia Basin), but based on pattern recognition alone, ensembles still key in on a classic ridge breakdown set-up that generally leads to gusty conditions while RHs remain below critical values after the heat we're expecting over the coming weekend. Evans/74 && .PRELIMINARY POINT TEMPS/POPS... PDT 62 96 59 102 / 0 0 0 0 ALW 67 100 65 106 / 0 0 0 0 PSC 68 101 65 105 / 0 0 0 0 YKM 62 99 61 103 / 0 0 0 0 HRI 67 101 64 105 / 0 0 0 0 ELN 65 97 62 104 / 0 0 0 0 RDM 53 93 53 100 / 0 0 0 0 LGD 60 95 60 103 / 0 0 0 0 GCD 58 98 59 105 / 0 0 0 0 DLS 64 96 64 105 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning from 11 AM Saturday to 10 PM PDT Monday for ORZ041-044-049-050-502-503-505-507-508. Fire Weather Watch from Saturday morning through Saturday evening for ORZ642. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for ORZ506- 510-511. WA...Excessive Heat Warning from 11 AM Saturday to 10 PM PDT Monday for WAZ024-026>030-521. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for WAZ523. && $$ SHORT TERM...87 LONG TERM....74 AVIATION...90