FXUS66 KPDT 162339 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 439 PM PDT Sun Jun 16 2024 Updated Aviation Discussion .AVIATION...00z TAFs...Expecting primarily VFR conditions this evening. Showers have formed along the east slopes of the Cascades late this afternoon, however rainfall has been very sparse and showers are very broken in nature. A few of these showers have produced lightning flashes, however these cells are expected to remain in high terrain, away from any TAF sites. YKM, DLS, BDN, and RDM are most likely to see any impacts from showers this evening, with the threat shifting more eastward to the rest of the TAF sites overnight, however expectation is that rainfall will be very light to minimal, and that the primary impact would be in the form of reduced cigs bkn-ovc around 4-7 kft. Winds will also remain breezy at many sites this evening, dying down overnight before picking back up once again by late tomorrow morning. Evans/74 && .PREV DISCUSSION... /issued 227 PM PDT Sun Jun 16 2024/ SHORT TERM...Tonight through Tuesday... Key Points: 1) Chance of showers and thunderstorms for our mountains, along with high elevation snow. 2) Breezy conditions expected again on Monday. 3) Cool temperatures continue through Tuesday before notable warming trend thereafter. Showers are beginning to form along the east slopes of the Cascades as the second in a series low pressure systems impacts our region. This low will sweep eastward and exit by Tuesday, bringing the continued chances of precipitation along with further cool temperatures and some breezy winds. For the precipitation - the aforementioned showers will continue to increase in coverage along the east slopes of the Cascades and into the Ochoco-John Day Highlands through this evening. Some modest instability is currently present along the Cascades, generally around 100-250 J/kg of CAPE, and models indicate we may reach up to around 500 J/kg, allowing for some strikes of lightning to be possible with this activity, but support is lacking for any sort of stronger activity. Into the mountains, this precipitation will also produce some snowfall, with snow levels at around 4500-5000 feet. With a lack of significant QPF, these amounts also remain on the lower side, with a few inches expected outside of the highest peaks. As the low continues its movement eastwards tomorrow, the pressure gradient tightens one more time for another round of breezy winds. Overall gusts are not expected as strong as they were on Sunday, with the NBM showing a 60-95% chance of gusts 39+ mph for our normal windy locations (Kittitas Valley, Simcoe Highlands, Columbia Basin, and Foothills of the Blues). If anywhere were to gust high enough to warrant a wind advisory (45+ mph), the Kittitas Valley would be the most likely location. Finally temperatures remain on the cool side, with highs still 5 to 10 degrees below normal Monday (60's to mid 70's for our population centers), increasing to around 2 to 8 degrees below normal for Tuesday (widespread 70's). Overnight lows tonight and Monday night still show widespread 40's to 30's. Some areas of frost for Central Oregon up through the Wallowas are likely, but there is low confidence (30%) that we will see further freezes. The Wallowa Valley is once again the most likely location for a freeze overnight tonight, but the NBM shows much less widespread freeze probabilities outside of the mountains leading to the lower confidence. Lows Tuesday night rise enough that freeze potential diminishes (widespread 40's), a signal that our cool streak is over and summer is on its way back. Goatley/87 LONG TERM...Wednesday through Sunday...Models are in fairly good agreement through the week but begin to have some timing issues next weekend. The Pacific Northwest will be under the influence of a weak and decaying upper level trough Wednesday into Thursday. The trough will dissipate allowing the flow to become westerly Friday and then amplify into an upper level ridge centered over the northern Rockies on Saturday as the next upper level trough approaches the coast. The arrival of this trough into the region is the timing issues as the GFS is slightly quicker than the ECMWF. As of now there is no convection showers in the forecast as probabilities are below 10%. However, as the flow aloft becomes more southwesterly late in the week due to the building ridge this could become an issue over the eastern mountains as probabilities begin to increase to 10-15%. Wednesday through Saturday will see a gradual warming trend with generally light winds. Hottest temperatures of the week will be Friday into Saturday with Saturday being the peak day. The probability of temperatures greater than 90 degrees these 2 days across the Lower Columbia Basin is 50-80% but the probability of greater than 100 degrees is less than 10%. So, primarily expecting high temperatures Friday and SAturday across the Lower Columbia Basin in the lower to mid 90s and 80s in the higher elevations. Main forecast concern comes over the weekend as the upper level trough approaches the coast. Past model runs were indicating a weak marine push possible late Saturday. Current runs are pushing this back making it more likely to occur overnight and into Sunday. This will usher in cooler temperatures on Sunday with temperatures lowering 5-10 degrees. Will see increasing westerly winds becoming 15 to 25 mph along the east slopes of the Cascades spilling out into the Columbia Basin which could pose an increased risked of fire spread in existing or new fire starts. && .PRELIMINARY POINT TEMPS/POPS... PDT 44 67 43 73 / 40 30 10 0 ALW 45 70 47 76 / 30 50 20 10 PSC 48 75 48 78 / 10 20 10 0 YKM 43 72 43 76 / 20 10 0 0 HRI 48 73 47 78 / 20 20 10 0 ELN 45 67 46 75 / 20 10 0 0 RDM 36 61 33 72 / 30 0 0 0 LGD 40 60 39 69 / 60 80 20 10 GCD 38 59 36 70 / 70 40 10 10 DLS 50 68 48 78 / 10 10 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...87 LONG TERM....91 AVIATION...74