![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
966 FXUS66 KPDT 161703 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1003 AM PDT Fri Aug 16 2024 .UPDATED AVIATION...18Z TAFs...VFR conditions will persist through the forecast period with winds generally below 10 knots except 12 kts at PSC. Winds will increase at BDN/RDM around 22Z while the remainder of the TAF sites will become VRB. CIGs will be mostly FEW250 to CLR through the period as well.Bennese/90 && .PREV DISCUSSION... /issued 429 AM PDT Fri Aug 16 2024/ SHORT TERM...Today through Sunday...Skies are beginning to clear out across the forecast area after a day of scattered showers and thunderstorms over the eastern mountains. For today, we`ll be left in the wake of an upper-level low with dry SW flow aloft, before a more robust low pressure system centers itself off the PacNW coast over the weekend and advects moisture across the western half of the forecast area, while the eastern half sees more southerly flow, and thus an influx of hot and dry air. This will make for an active Saturday, with showers and storms across the Cascades and east slopes, as well as the potential for critical fire weather conditions across the southeastern portion of the area as winds pick up under a very dry air mass. For Saturday, as the aforementioned low drops down from the Gulf of Alaska, a band of amplified SW to S flow aloft accompanying it will usher in formidable moisture transport across the spine of the Cascades, while picking up on hot and dry desert air from the Great Basin and spreading it into eastern Oregon. We`ll have quite the stark contrast in the forecast as a result, with showers, potentially heavy at times, along with thunderstorms across the Cascades, spreading into the east slopes at times in the afternoon and early evening. Not particularly concerned about critical fire weather conditions across our Cascade zones with how wet storms will be (QPF guidance suggesting widespread >0.20 rain accumulations, thus the Flash Flood Watch for our WA Cascade burn scars), but more for our east slope zones like WA690 and parts of 691 should convective activity spread that far eastward. Confidence is too low to pull the trigger at this time, especially with the 06z HRRR suggesting limited activity outside of high terrain, and CAPE being limited enough as is. Instability won`t be a limiting factor across the mountains with how favorable the flow aloft is, but may be lacking once you trek further into the east slopes and beyond. Guidance has trended upward for temps across the eastern half of the forecast area, depicting more robust warm air advection as temps in the lower Basin flirt with the upper 90s. This can be seen in the drop in forecasted RHs as well, with the high terrain across south- central and southeastern Oregon bottoming out in the single digits. This, combined with potent flow aloft, will trigger breezy conditions and thus critical fire weather conditions in spots. Issued a Fire Weather Watch for OR 642 as a result. Winds don`t look to be quite strong enough elsewhere, but with the weather pattern shaping up to be as it is, unstable conditions for 642 and nearby zones cannot be ruled out as well. Once this low settles in off the coast, a blocking pattern keeps it in place for the next several days, however the upper-level flow backs off, leaving Saturday as the main day of impacts. Temps cool down on Sunday back towards seasonal norms, what with more mild SW flow aloft overhead. Evans/74 LONG TERM...Monday through Friday...Models continue to show very good agreement in having a persistent weather pattern over the western states next week at least through Thursday. A trough and strong closed low will be off the Pacific Northwest coast and a strong ridge will be centered over the Rockies and the Midwestern states. The trough will keep temperatures several degrees below normal and send a southwest flow over our area. Instability looks limited with NBM thunder probabilities no more than 10 percent through the period. The NBM does give 15-30 percent pops along the Washington Cascade crest and have a slight chance to chance of rain showers there each day Tuesday through Friday while the rest of the area remains dry. Monday will start out with the trough and its upper low a few hundred miles off the Olympic Peninsula and by Tuesday the low will be slightly weaker and will have moved south to the Oregon coast. Weather will be fairly similar each day. Temperatures will be a little warmer Monday with highs in the 80s to around 90 in the Tri- Cities while the mountains will be in the mid 70s to mid 80s. NBM probabilities give a 65-85 percent chance of 90 degree temperatures in the Columbia Basin and the Grande Ronde Valley, a 40-50 percent chance in the Blue Mountain Foothills but less than a 25 percent chance elsewhere. Tuesday will be a degree or two cooler. This drops the chances of 90 degree temperatures to 45-60 percent in the Columbia Basin and less than 30 percent elsewhere. The NBM gives a less than 10 percent of showers across the area Monday and most of Tuesday, but by late afternoon the low moves closer to the coast and this introduces a 20 percent chance of showers along the Washington Cascade crest with barely measurable amounts. Pressure gradients each day support a mild marine push through the Cascade gaps yielding 15-20 mph winds in the Columbia Gorge and Kittitas Valley. The chances for 25 mph winds in those areas are less than 20 percent both days. On Wednesday, models show the upper low moving ashore and getting absorbed into the main flow but at the same time, a shortwave will dive south out of British Columbia. This will restrengthen the trough overnight and Thursday after it briefly weakens Wednesday afternoon. So this will mean only minor changes in the weather. Temperatures both days drop to the upper 70s to mid 80s with 70s in the mountains. The Tri-Cities will have a 30-35 percent chance of 90 degree temperatures but the rest of the area will have less than 15 percent chance. Precipitation will continue to be limited to a slight chance of showers with very light amounts along the Washington Cascade crest. The Cascade gaps will have 15-20 mph winds Wednesday afternoon though chances of 25 mph winds are less than 20 percent. Winds will be lighter on Thursday. On Friday, models develop significant differences about the offshore trough. Model ensemble members are fairly evenly split about having a strong low, a weak low or one somewhere in between. They also vary the low location from about 200 to 700 miles offshore. Additionally, about 15 percent open the low into a wave and have a shallow trough centered over the Willamette Valley. The forecast follows the NBM and keeps temperatures similar to Thursday, maybe a degree or so in places. It keeps a slight chance of showers along the Washington Cascade crest once again while the rest of the area is dry. Perry/83 && .PRELIMINARY POINT TEMPS/POPS... PDT 82 54 92 55 / 0 0 10 20 ALW 86 58 97 60 / 0 0 10 20 PSC 87 59 97 64 / 0 0 0 30 YKM 84 54 91 56 / 0 0 10 70 HRI 86 57 96 60 / 0 0 10 20 ELN 84 54 91 58 / 10 0 0 60 RDM 81 49 86 47 / 10 10 20 50 LGD 83 51 93 52 / 10 10 10 10 GCD 84 53 93 51 / 10 10 0 10 DLS 83 60 93 60 / 0 0 20 70 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Fire Weather Watch from Saturday afternoon through Saturday evening for ORZ642. WA...Flash Flood Watch from Saturday afternoon through late Saturday night for WAZ522-523. && $$ SHORT TERM...74 LONG TERM....83 AVIATION...83