Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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388 FXUS66 KPDT 101627 AAA AFDPDT Area Forecast Discussion...Updated National Weather Service Pendleton OR 927 AM PDT Fri May 10 2024 Updated aviation discussion .SHORT TERM...Today through Sunday night A ridge of high pressure continues to dominate over the region and will continue through the majority of the weekend. A weak shortwave will make its way across the upper level ridge breaking it down slightly bringing more seasonable temperatures back to the forecast area. Dry conditions will dominate even under the influence of shortwave makes its way across the WA Sunday evening. Models are in firm agreement with the upper level ridge over the forecast area with an upper level low still over the Four Corners remaining in tact through Sunday evening. This synoptic pattern has caused and will continue to cause the ridge to strengthen into what is called a Rex blocking pattern. This will bring dry and warming conditions through Saturday with temperatures reaching 15-20 degrees above normal by Saturday. High confidence in the forecast for temperatures cresting 90s with raw ensembles showing a 80% probabilities for the Columbia Basin and adjacent valleys, 60-70% for the lower Columbia Basin and the foothills of the Blues and the Gorge seeing temperatures in the mid to upper 80s. Sunday evening the models begin to show a weak shortwave making its way across the upper level ridge. This will cause a slight breakdown shifting the upper level flow to a more westerly component and increasing the winds, cooling the temperatures slightly and bringing a less 20% probabilities of rain to the far northern portion of WA Cascades. Otherwise, the remaining portions of the region will remain under dry and warm conditions with over 90% of raw ensembles showing the temperatures to be in the mid to upper 80s across the majority of the CWA with the higher elevations in the mid 60s to 70s. Winds are expected to increase as the cross Cascade gradient increases with the shift of the upper level flow. Ensembles show a greater than 60% probability of the lower Columbia Basin seeing sustained winds of 25 mph, 75-85% for the Simcoe Highlands and the Gorge, and over 90% for the Kittitas and Yakima Valleys. With the rise in temperatures, guidance has begun to pick up on a slight heat risk for Saturday through portions of the Columbia Basin. If you are outside on Saturday enjoying the warmth, please be mindful and wear sunscreen, drink plenty of fluids and remember that the rivers will be fast flowing and still dangerously cold. Bennese/90 .LONG TERM...Monday through Friday...Model agreement looks good through the first of the week with a weak shortwave passage Monday followed by the rebuilding of the ridge in the wake of its departure. However, from midweek onward uncertainty increases in both the ensemble and deterministic models as to whether the ridge will persist or a westerly flow develops and allows another trough passage late in the week. 00Z deterministic models highlight this uncertainty by having flipped in the past 24 hours. The GFS now builds a ridge over the western USA while the EMCWF has a trough passage occurring on Thursday which is the exact opposite from yesterday. Ensemble models also showing the differing solutions but to a lesser degree in the amplitude of the trough on Thursday. Overall this is causing the NBM to play middle of the road forecasting. Example, Thursday high temperatures probabilities range from mid 60s to mid 80s with actual forecasted highs in the mid 70s. Same for the chance of precipitation as it could either be dry or chance of precipitation, the NBM splits the difference with a slight chance of precipitation. So, current extended forecast will see cooler temperatures on Monday by 5 to 10 degrees as the trough passage ushers in some cold air advection. This produces some breezy to windy conditions which could reach wind advisory levels across portions of the Lower Columbia Basin. Could also see a few showers along the crest of the Cascades. Tuesday will see a reduction of the winds to just breezy and overall dry conditions as the trough departs and ridging begins to rebuild over the region. Beyond this point the high degree of uncertainly brings forecast confidence level to low. Will hold onto the NBM`s middle of the road temperature forecast but have under cut the NBM POPs restricting it to just a slight chance of showers along the Cascade crest late Wednesday through Friday. && .AVIATION...18Z TAFs...VFR conditions will prevail through the period. Skies will be clear with winds below 10 kts. Earle/81 && .PRELIMINARY POINT TEMPS/POPS... PDT 79 51 84 55 / 0 0 0 0 ALW 82 55 87 60 / 0 0 0 0 PSC 85 55 91 57 / 0 0 0 0 YKM 85 52 90 52 / 0 0 0 0 HRI 85 53 90 58 / 0 0 0 0 ELN 84 53 87 54 / 0 0 0 0 RDM 78 46 82 47 / 0 0 0 0 LGD 76 49 80 50 / 0 0 0 0 GCD 77 48 81 49 / 0 0 0 0 DLS 86 57 90 57 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...90 LONG TERM....91 AVIATION...80