Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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716 FXUS66 KPDT 172333 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 433 PM PDT Tue Sep 17 2024 Updated Aviation Discussion .AVIATION...00Z TAFs...VFR conditions expected over the next 24 hours. Breezy winds expected DLS/RDM/BDN with gusts 20-35 knots through 03-04Z. PDT/ALW/YKM may see some gusts around 20 knots but has not been as gusty in these locations as expected. Cloud decks remain medium to high, 10-25k feet. A few showers may move near BDN/RDM during the 03-06Z timeframe, but should be scattered at best. Goatley/87 && .PREV DISCUSSION... /issued 258 PM PDT Tue Sep 17 2024/ SHORT TERM...Today through Thursday night... Key Messages: 1. Breezy to windy afternoon conditions each day, peaking today. 2. Light showers and isolated storms possible this evening. 3. Steady warm-up through period, eventually reaching near normal. Current radar and visible satellite imagery showing light returns along the northern Blue Mountains and foothills under partly to mostly cloudy skies east of the Hermiston/Boardman area. These conditions are in response to an upper level low pressure system to our southeast beginning to lift into eastern Idaho and western Wyoming. Another upper level system is approaching the coast, and a weak transient ridge has developed between these two upper level systems. This ridge has allowed clear to mostly clear skies to occur along the east slopes of the Cascades and the Gorge. The incoming system has also allowed a pressure gradient to develop along the Cascades, attributing to breezy to windy conditions through the Gorge, Blue Mountain foothills, and Kittitas Valley. Gusts of 44 mph and 38 mph out of the northwest have been reported this afternoon at The Dalles Airport and Ellensburg Airport respectively, which is expected to persist until 7 PM. Winds will slowly slacken this evening as the exiting system pushes into easter Montana and the coastal system digs south along the northern California coast. Sustained winds of 15-25 mph and gusts of 35-45 will be possible through 7 PM over these areas. Confidence in these wind values is moderate to high (60-80%) as the HREF and NBM showcase the probability of winds staying below advisory criteria (Sustained winds of 30 mph or greater and/or gusts of 45 mph or greater) of 20-40% over these areas. Elsewhere, winds will stay elevated with sustained winds of 10-20 mph and gusts of 20-30 mph. An upper level ridge will infiltrate into the area from the west on Wednesday ahead of a weak shortwave riding over the top of the ridge on Thursday, with both features providing windy afternoon conditions as a pressure gradient redevelops along the Cascades. Elevated winds are expected to be less than today and more confined to the Gorge and Kittitas Valley with sustained winds of 20-30 mph and gusts of 30-40 mph likely both days. The NBM is in agreement with this assessment, as the probability of sustained winds of 30 mph or greater is less than 10%, and gusts of 45 mph or greater is 10-20% for isolated areas of the Gorge and Kittitas Valley on only Thursday. These two upper level low pressure systems have kept periods of light showers occurring across the northern Blue Mountains and foothills through the morning and early afternoon. However, drier conditions will ensue through the remainder of the afternoon and into the evening as the system departs to our east. Only rain amounts of 0.01-0.03" are expected across the Blue Mountains and east slopes of the Oregon Cascades, with wetting rain only possible at higher elevations of the Elkhorns and eastern Wallowa County. There is still a potential for an isolated thunderstorm over these areas as the NBM shows surface CAPE of around 200 J/kg, but that chance is quickly dissolving as the departing upper level system loses its influence over the area. There has yet to be any lightning associated with today`s showers, but a strike or two will be possible (~15%) over the next couple hours for southern Wallowa county. Northwest flow aloft will turn more westerly on Wednesday before incurring a more southwest component on Thursday. This will allow temperatures to slightly increase through the period, with the greatest increase expected on Thursday. Even with this slight warm-up, high temperatures will only reach near normal or slightly above normal by Thursday with values breaking into the low 80s across lower elevations of the Basin and into the Yakima Valley. Confidence in highs breaking into the 80s for these areas is moderate to high (60-70%), as the NBM advertises a 50-70% chance. 75 LONG TERM...Friday through Tuesday...Models are showing better agreement through the long term period and are beginning to show some consensus for early next week. High pressure offshore and troughs to our east will promote a northwest flow over the area through much of the period though model clusters show varying degrees of ridging over the area with a persistent 10-15% of model solutions showing a more trough like solution rather than a ridge. The Extreme Forecast Index shows little in the way of significant weather aside from some marginally breezy winds through the Cascade gaps Friday afternoon. Temperatures will be near normal Friday and Saturday then will warm a few degrees to the mid to upper 70s Sunday through Tuesday. Friday will start out with high pressure in the eastern Pacific with a trough stretching from Alberta south to the desert southwest. The low pressure will be too far away to affect us other than to provide the pressure gradient for breezy winds around 20 mph in the Columbia Gorge and Kittitas Valley in the afternoon. The NBM shows both of those locations having a 65-70 percent chance of wind gusts greater than 25 mph. Temperatures will be in the lower to mid 70s with only the warmest locations in the Columbia Basin having as much as a 25 percent chance of reaching 80 degrees. Saturday will see the trough moving further east and this will allow the ridge offshore to strengthen and expand over our area though there are differences about the strength of the ridge. Temperatures will warm a degree or so. The northwest flow will create some light upslope showers along the Washington Cascade crest in the late afternoon and evening. Sunday will see the ridge continuing offshore though again there are differences. 65 percent of the model ensemble members have a strong ridge with a northwest flow overhead, 25 percent have a weaker ridge further offshore with a zonal westerly flow into our area and 10 percent have a trough riding over the ridge and through the area. The NBM favors a chance of rain along the Washington Cascade crest with just a few hundredths of an inch expected. The rest of the mountains and most of the Columbia Basin will have a slight chance of showers with minimal rain amounts. Temperatures warm a few degrees to the mid to upper 70s with mid 60s to lower 70s in the mountains. Monday will see the ridge axis move closer to the coast and this keeps showers out of the forecast with temperatures similar to Sunday. Tuesday the trough will be overhead according to 70 percent of the model ensemble members with the other 30 percent keeping it just offshore. It looks like another dry day aside from a slight chance of showers along the Washington Cascade crest. Temperatures will warm a few degrees to the mid to upper 70s with many lower elevation locations having a 50-75 percent chance of reaching 80 degrees. Perry/83 && .PRELIMINARY POINT TEMPS/POPS... PDT 48 74 45 76 / 10 0 0 0 ALW 53 76 50 79 / 10 0 0 0 PSC 57 79 53 80 / 10 0 0 0 YKM 50 79 46 80 / 0 0 0 0 HRI 54 78 50 80 / 10 0 0 0 ELN 52 74 48 79 / 0 0 0 0 RDM 43 71 40 77 / 20 0 0 0 LGD 46 72 44 77 / 10 0 0 0 GCD 43 71 42 77 / 10 10 0 0 DLS 55 78 51 79 / 10 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...75 LONG TERM....83 AVIATION...87