Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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052 FXUS66 KPDT 191729 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1029 AM PDT Sat Oct 19 2024 .UPDATED AVIATION DISCUSSION... .AVIATION...18Z TAFS...VFR conditions will prevail throughout this period. Winds at KPSC will elevate to 15 kts with gusts up to 25kts due to increased westerly flow. Conditions will improve starting this evening. Otherwise, winds will be less than 12 kts for the remaining sites. Feaster/97 && .MORNING UPDATE...Radar reveals a region of light -RA across much of Morrow, Umatilla, Benton, Franklin, and Walla Walla counties early this morning, likely facilitated by subtle mid-level WAA coupled with weak upper-level PVA. Updated the forecast to include a slight chance (15%) mention of -RA for the aforementioned area since the PSC ASOS and web cameras indicate some precipitation is reaching the ground. Elsewhere, reduced PoPs in the lee-side valleys of Yakima and Kittitas counties to exclude anything above a slight chance (15-24% PoPs) mention of -RA. Plunkett/86 && .PREV DISCUSSION... /issued 323 AM PDT Sat Oct 19 2024/ .SHORT TERM...Today through Monday night...No major concerns are anticipated in the short term period...at least nothing that requires highlights. Rain and high elevation snow will bring additional relief to some of our current wildfires, and the Cascades and Blue Mtns will have moderate rainfall amounts with a quasi-stationary cold front Sunday night and Monday (confidence 80%). Western WA and northwest OR are observing widespread precipitation, and some of the showers have spread to the Cascade east slopes. In the Kittitas County, several RAWS have measured 0.2-0.3" of precipitation over the past 24 hours. Additional amounts up to 0.10" are likely (60%) in northwest Kittitas County, but the probabilities decrease significantly for amounts greater than 0.1". This is associated with a warm front lifting north today with precipitation north of the forecast area by the afternoon. Doppler Radar is also detecting isolated showers over the northern Blue Mtns associated with orographic lift in a westerly flow aloft, and this will be included in the forecast for the early morning hours. Otherwise, it will be a dry day and warmer compared to yesterday due to weak ridging taking place over WA/OR. The westerly flow over the eastern Pacific will buckle in response to a developing trough over the Gulf of Alaska. A southwest flow will increase over the forecast area tonight and Sunday. Sunday will be partly to mostly cloudy and unseasonably warm due to increasing heights and the southwest flow aloft. Meanwhile, a fairly strong surface low off the WA coast will send a warm front over northwest WA and into BC with little effect for our forecast area. However, a cold front will sag southward Sunday night and Monday for the next round of precipitation. PoPs will be 60-90% for nearly all forecast zones on Monday. The upper level support associated with the left exit region of an upper level jet and a weak AR advertised by both the ECMWF ENS and GEFS increase confidence that wetting rainfall (i.e. 0.1") will be widespread. In a nutshell, moderate rainfall amounts of 0.25-0.5" are forecast for the Cascade east slopes and the Blue Mountains, but 0.5-0.75" of rain cannot be ruled out. NBM shows 80% of 0.25" or more along the Cascade Range and the Blue Mountains...40-60% in Wallowa County and along the Blue Mtn Foothills. There is a 60% chance for 0.5-0.75" and a 30% probability for amounts greater than 0.75" along the Cascade crest and the Blue Mtns north of Ukiah. No wind concerns are anticipated, but it will be locally breezy with gusts 20-30 mph during the short term. The Grande Ronde Valley will have continuous southerly winds gusting to 25-35 mph as a lee side low sets up on the west side of the northern Blue Mtns. Wister/85 .LONG TERM...Sunday through Saturday... Bottom Line Up Front 1. Mostly dry conditions to start the period 2. Precipitation returns Friday 3. Seasonal temperatures through the period Remnants of the the upper level system will allow for some high mountain showers Tuesday while the remainder of the forecast area will be under dry conditions. Models show an upper level low beginning to build off the coast. This is shifting the upper level flow to a more westerly to southwesterly flow. Clusters are in decent agreement with the main variance being in the positioning of the upper level low. Models show the low to begin to shift south allowing a ridge to begin to build in over the PacNW. Models begin to diverge from one another beginning Tuesday night with regards to the amplitude of the ridge. ECMWF has the upper level flow flattening and becoming westerly while the GFS and Canadian keep the ridge in place overhead. Confidence in the solution is moderate (50- 60%). Regardless of the solution of westerly flow or the ridge, models and ensembles show the solution to be dry. Models continue to diverge from one another through the remainder of the period. Clusters are struggling with the timing and positioning of the incoming system with regards to whether it will be a closed low or an open wave and when the precipitation will essentially occur. With that, NBM has been populated and shows precipitation to be over the region beginning Thursday morning. Confidence in the solution is low (30-40%). 10-20% of the raw ensembles show precipitation reaching the Cascade crests Thursday afternoon with light precipitation amounts of near 0.01 inches of rain. 60-70% of the ensembles show that by Friday afternoon, the Cascades will see near 0.20 inches of additional rain, 30-40% show the lower Columbia Basin, foothills of the Blues, central OR and portions of the Ochoco- John Day Highlands will see near 0.05 inches of rain. Again, confidence in the forecast that far out remains low. Temperatures through the long term are expected to remain seasonal with the EFI showing temperatures to be at or near seasonal. 66% of the raw ensembles show the majority of the region seeing temperatures in the upper 50s with a few isolated locations in the Basins seeing near 60 Tuesday. As the ridge settles overhead, temperatures will increase ever so slightly with nearly 50% of the ensembles putting the majority of the norther portion of the region in the 60s, while the souther and south eastern portions seeing near the 70s. By Friday, ensembles become spread and show almost equal chances of temperatures being in the upper 40s or 50s. Confidence in the temperatures beginning Friday is again low (30-40%) as the solutions vary which will ultimately cause temperatures to vary greatly as well. Bennese/90 && .PRELIMINARY POINT TEMPS/POPS... PDT 72 44 75 46 / 20 0 0 60 ALW 75 49 79 48 / 20 0 0 60 PSC 74 50 77 53 / 20 0 0 60 YKM 70 40 73 41 / 20 10 10 70 HRI 74 47 77 50 / 20 0 0 60 ELN 68 43 72 41 / 20 20 20 70 RDM 73 41 75 44 / 0 0 0 50 LGD 68 43 71 43 / 10 0 0 40 GCD 71 41 76 45 / 0 0 0 20 DLS 72 46 75 50 / 20 10 20 90 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ MORNING UPDATE...86 SHORT TERM...85 LONG TERM....90 AVIATION...97