Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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249 FXUS66 KPDT 241714 CCA AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1013 AM PDT Mon Jun 24 2024 .AVIATION...18Z TAFs...VFR conditions expected over the next 24 hours. Breezy winds possible for DLS with a few breezes around 10-12 knots possible at DLS, with winds 10 knots or less all other sites. Bennese/90 && .Update...Minor changes made to the forecast for today and tonight. Main change was made for Wednesday when the next weather system will arrive. Expect a shortwave to pass over the forecast area early in the day with enough forcing and instability to trigger some showers and possible thunderstorms. By afternoon and evening the main focus of instability shifts to northeast Oregon and southeast Washington where the potential for showers and thunderstorms will continue. .SHORT TERM...Today through Wednesday night...There are a few weather concerns and forecast challenges in the short term, but nothing significant to require highlights at this time. The weather will be quiet over the next 24 hours, and Tuesday will be hot and dry. There is a slight chance (20%) of early morning thunderstorms on Wednesday over the northern Blues and an increasing chance (20-30%) of thunderstorms over northeast Oregon Wednesday afternoon and evening. The Cascades will have a 40-60% chance of showers Wednesday and Wednesday night, mainly near the crest. Unfortunately, the two large wildfires-- Slide Ranch near White Swan and the RV Long Bend near Maupin-- will have less than 10% chance of observing any precipitation during the short term. Winds have decreased behind yesterday`s cold front, and winds through Tuesday night will be relatively light. The westerly flow aloft today will keep pressure heights down and afternoon temperatures similar to yesterday. High pressure aloft centered over the four corner states will strengthen tonight and Tuesday, and the inverted surface thermal trough will make its appearance Tuesday afternoon and allow temperatures to climb into the 80s to mid 90s. The HeatRisk category will be minor to moderate. There are hints of elevated instability in eastern Oregon on Tuesday, but little to no moisture. However, as an upper level trough off the eastern Pacific nudges towards the coast and the upper flow shifts to the southwest Tuesday night, there will be increasing moisture combined with elevated instability that will bring a slight chance of early morning thunderstorms over the northern Blues (20%). The chance of thunderstorms increases over far northeast Oregon on Wednesday to around 20-30% as the offshore trough moves inland, and the upper flow increases from the southwest with embedded disturbances. CAPES are weak...less than 200 J/kg...but shear is very strong. 0-H5 bulk shear is as strong as 60 kts over most of eastern Oregon but 45 kts over Wallowa County. A 60-kt shear may result in cumulus tops being sheared off and cutting off any updrafts. But, Wallowa County will have the best chance for thunderstorms. NBM indicates 20% but the forecast will show 30% in the Wallowa Mountains where my confidence is a little higher. A tight pressure gradient will set up as the thermal trough is forced eastward towards the ID border and it will be breezy (locally windy). The afternoon RHs will not be critically low with the exception of southern OR, mainly south of John Day and Prineville, where forecast RHs are in the teens for Wednesday. This area has the best chance for elevated fire concerns but confidence that red flag conditions will be met is fairly low. Wister/85 .LONG TERM...Thursday through Monday...A semi-progressive pattern is on tap for the long term, beginning with a passing low pressure system that will stay just to our north, followed by transient ridging that will give way to another shortwave by the end of the period. This will keep our temperatures just below normal on Thursday, becoming closer to normal then through (mostly) the end of the forecast with periods of breezy winds and some showers and possible thunderstorms that should be primarily relegated to the high terrain of the region. The period begins with a deep upper low situated along the borders of Washington and Canada, quickly moving eastwards and exiting our area by Friday morning. Unfortunately this should equate to a lack of significant moisture making it into our region, keeping the bulk of any noteworthy precipitation along the mountains and in Northern Washington. The NBM only shows a 50% chance of QPF totals greater than or equal to a tenth of an inch for the Cascades in Kittitas County - anywhere else along the mountains including into the Blues has a 10% chance or less, with zeros for our lower elevation zones. Even our winds will be breezy but not at significantly impactful levels, with only a 30-80% chance of seeing gusts around or in excess of 35 mph for the lower Columbia Basin/Foothills of the Blues, Kittitas Valley, and Simcoe Highlands, hardly a strong for around here and not nearly enough to trigger a wind advisory. Noteworthy however will be temperatures, with highs descending into the 70`s for our population centers outside of the Columbia Basin where low 80`s are expected. This places us around 2-6 degrees below normal. Conditions are expected to be mostly benign for Friday and Saturday under transient ridging, with temperatures warming around 5 degrees each day. Sunday a quick moving shortwave will bring us back down around 3-5 degrees while winds breeze similarly to Thursday. Another round of mountain precipitation could occur, but this time with a bit more moisture and instability values around 500-800 J/kg in the Eastern Mountains of Oregon, a few thunderstorms can`t be ruled out. And with PWAT anomalies around 125-150% of normal, if any lightning does occur, hopefully there will be accompanying rain to help preclude a dry lightning risk as we continue to delve deeper into fire weather season. Into Monday the bulk of the precipitation exits as we should see similar temperatures to Sunday under westerly to northwesterly flow. Goatley/87 && .PRELIMINARY POINT TEMPS/POPS... PDT 82 52 92 59 / 0 0 0 0 ALW 85 55 95 62 / 0 0 0 0 PSC 86 56 95 63 / 0 0 0 0 YKM 85 53 92 59 / 0 0 0 0 HRI 86 55 96 64 / 0 0 0 0 ELN 82 52 91 59 / 0 0 0 0 RDM 84 49 92 54 / 0 0 0 0 LGD 82 53 91 58 / 0 0 0 0 GCD 88 54 96 57 / 0 0 0 10 DLS 85 56 94 62 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...85 LONG TERM....87 AVIATION...90