Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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683 FXUS66 KPDT 240934 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 234 AM PDT Fri May 24 2024 .SHORT TERM... Today through Sunday night...A shortwave trough embedded in NW flow aloft will move across the area today and tonight. With daytime heating there will be modest airmass destabilization. The SPC HREF is indicating most unstable CAPE values reaching up to 500 J/kg along the Blue Mountains this afternoon. The CAMS are forecasting convective initiation around 19Z for areas from the Blue MTNS eastward with activity becoming more widespread through the late afternoon and early evening hours. The SPC HREF 1-hour calibrated thunder probabilities peak at 40% at 00Z this evening for Grant, Union, and Wallowa Counties. With storm motions around 20 kt and the potential for training, heavy rain will be the main threat from the storms. Scattered showers will continue into the overnight hours mainly in the far east with the TSTM threat ending by 03-06Z. Models and ensembles still disagree somewhat on the track of a small upper low for Saturday, but they are converging on a track that is mainly north of the forecast area. As a result shower chances will be more limited than earlier anticipated, and by Saturday afternoon it will be mainly dry. There will still be a cold frontal passage Saturday, and during the afternoon the pressure gradient between Portland and Spokane is forecast to reach 10 mb. This will result in windy conditions in the Cascade gaps and portions of the Columbia Basin (mainly Oregon portion). Probability of winds exceeding 45 mph in these areas is 20-40% around 2 PM Saturday afternoon based on the NBM. A westerly low level jet of 35-40 kt and steep low level lapse rates will help support gusty west winds. Winds will decrease Saturday evening and it will be rather chilly Saturday night. Lows will be in the upper 20s to lower 30s in the mountains and high plateaus, and in the mid 30s to mid 40s lower elevations. Ensembles agree on a ridging pattern on Sunday and Sunday night which will result in dry weather and a nice afternoon Sunday after a chilly start. 78 .LONG TERM... Monday through Thursday... A ridge will be over the Pacific Northwest on Monday. This will bring dry and warm weather over the region for Memorial Day. The ridge will move eastward during the day, which will allow for increasing southwesterly flow ahead of a trough offshore. The trough will move eastward and onshore by later Tuesday into Tuesday night and bring with it some shower and thunderstorm chances for later Tuesday into Tuesday night. The ECMWF EFI keys in on CAPE/thunderstorm chances across the Blue Mountains on Tuesday, with a broad area of 0.6 to 0.7 and a small area of 0.7 to 0.8. The trough will then move east of the area on Wednesday, allowing for a dry northwesterly flow which will prevail into Thursday. Overall, the guidance is in generally good agreement through midweek, then differences arise as the GFS is faster with the trough moving onshore. The ensemble clusters are fairly evenly split through the extended, so it is difficult to select a preference at this time. All of the guidance does have a trough, it is just more of a question of timing and strength as we go through the mid and late week period. As the trough moves through the region later Tuesday into Wednesday, and lingering into Thursday, there will be some breezy winds, especially in the Columbia Basin, Kittitas Valley and Simcoe Highlands. High temperatures will be above normal on Monday, mainly in the upper 70s to lower 80s. Tuesday will be a bit cooler, with highs in the mid 70s to lower 80s. With the trough moving onshore Wednesday, temperatures will be close to or even slightly below normal, mainly in the upper 60s to upper 70s. .AVIATION... 12Z TAFS...High confidence (90-100%) in VFR conditions at all TAF sites. Winds will increase and gust to around 25 kts later this morning or during the afternoon at all sites except YKM. DLS and PDT will then have gusty winds through at least 09-12Z Saturday. RDM and BDN will see decreases to around 10 kts around 25/03Z. PSC will see a decrease around 25/06Z. ALW will see a decrease to around 10 kts around 03Z. && .PRELIMINARY POINT TEMPS/POPS... PDT 68 43 61 39 / 10 20 10 0 ALW 71 47 65 44 / 10 30 10 0 PSC 75 49 70 45 / 10 20 10 0 YKM 71 40 68 38 / 20 10 0 0 HRI 73 46 67 43 / 10 10 10 0 ELN 67 43 62 41 / 30 10 0 0 RDM 66 37 58 33 / 10 20 0 0 LGD 66 42 58 36 / 50 60 20 0 GCD 67 40 59 34 / 70 60 20 0 DLS 69 48 64 45 / 10 10 10 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...78 LONG TERM....77 AVIATION...77