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Area Forecast Discussion
Issued by NWS Pendleton, OR
Issued by NWS Pendleton, OR
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916 FXUS66 KPDT 102142 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 242 PM PDT Wed Jul 10 2024 .SHORT TERM...Tonight through Friday night...The heat has reached its peak, and the Excessive Heat Warnings and Heat Advisories are set to expire at 11 PM. Unfortunately, our forecast area will remain in the minor to moderate HeatRisk through Friday. Additional heat related statements may be issued for the upcoming weekend as confidence is high (80%) that we will be pushing in the moderate or even major HeatRisk category. No significant cooling is in sight for the next several days. Red Flag Warnings are in effect for most of the forecast area--dry and unstable conditions along the Blues, Wallowas, and the John Day-Ochoco Highlands and wind/RH threats for the Lower Columbia Basin, Kittitas Valley, the eastern CR Gorge, and central Oregon. The warning was expanded to include fire zone OR610 which covers the east slopes of the northern Oregon Cascades, including the Warm Springs area. These are in effect through 11 PM this evening with the exception of fire zone 690 which covers the Kittitas Valley which is in effect until 8 PM Thursday. The upper level ridge has shifted eastward with the axis along the northern Rockies. WA/OR are on the backside of the ridge and under a southwest flow aloft. The weakening ridge has enhanced the instability with dry air at the surface and aloft. At the surface, the inverted thermal trough east of the Cascades has strengthened the cross-Cascade gradients with breezy winds observed through the CR Gorge and Cascade gaps. Fortunately, this is not a strong onshore flow and marine push as evident by the lack of stratus clouds along the coastline. Otherwise, there would be much stronger wind speeds that would result in more pronounced red flag conditions. The pattern changes little through Friday, therefore winds will be locally breezy in central and north central Oregon. Wister/85 .LONG TERM...Saturday through Wednesday... Bottom Line Up Front 1. Breezy conditions return along Cascade east slopes and through the Cascade Gaps could leave to fire weather concerns. 2. Thunderstorm potential Saturday and Sunday. 3. Dry and warm conditions remain in place. Models are in firm agreement with the upper level high perched over the Four Corners and an upper level low sits off the coast of California. This synoptic set up will cause west to south west flow aloft. This will create the tightening of the surface pressure gradients across the Cascades. A diurnal wind pattern will set itself up each day with winds becoming breezy along the east slopes of the Cascades especially through the Cascade Gaps. NBM is showing a near 88% probability of the Columbia River Gorge, foothills of the southern Blues and the lower Columbia Basin will see daily sustained wind speed averaging between 10 to 15 mph. 60-80% of the raw ensembles are in agreement with what the NBM is showing. Moving on to the Kittitas and Yakima Valleys, NBM in showing 90% probabilities of sustained winds of 15 to 20 mph with 90 to 100% of the raw ensembles in agreement. Daily daytime relative humidities will be in the teen with a few scattered locations being in the 20s. With the elevated winds, dry RH values and the incoming instability, fire weather concerns may become elevated as the event draws nearer. As of right now, confidence in fire weather conditions is low (10-20%). Models remain in firm agreement through the period with the synoptic patter with the upper level low remaining off the coast of California and the upper level high over the Four Corners. However, models show the low to strengthen just a bit and the high to move slightly southward a touch. Just enough that there is some upper level moisture that gets wrapped around the high and ushered into the region Saturday night with the majority ushering in Sunday. This set up will allow for thunderstorm probabilities through central OR and along the Ochoco-John Day Highlands before spreading across the rest of the eastern mountains and into Wallowa County. Model derived soundings for Deschutes and Grant counties show MUCAPE values cresting 500 J/kg, lapse rates of 9.5 C/km, lifted index of -2 and bulk shear of 49 kts. PWATs within the sounding is 0.63 inches and with the dry layer beneath the moisture, these thunderstorms on Saturday will be dry. The ingredients are there for thunderstorms on Saturday, however, raw ensembles are only showing a probability of 15% due to the model variances in the amount of moisture that will make its way into the region. Sunday shows a tad more promise with raw ensembles showing upwards of 25% probabilities for thunderstorms with model derived sounding showing a much more moist and unstable atmosphere. Model derived sounding along the eastern mountains have areas where MUCAPE values are cresting over 500 J/kg with some locations seeing values as high as 900 J/kg, lapse rates of 8.9 C/km, lifted index of -4 and bulk shear of 50 kts. PWATs are still in the 0.65 inch range and with the continued dry and warm surface conditions, any rain associated with these storms will again be light to nil. This will also lead to some potential fire weather concerns and will be monitored as the event draws nearer. Lastly, even with the synoptic pattern shift, models are still showing the region to be under dry and warm conditions through the long term period. EFI is showing temperatures to remain above normal through the beginning of the long term before slowly teetering more towards climatological normal by mid work week. 90% of the raw ensembles have the Pendleton area back in the mid to upper 90s, 62% has the Basin, Gorge, Yakima Valley and central OR to be in the upper 90s and into the 100s. Temperatures will steadily decrease through the long term period before leveling off by Wednesday. Bennese/90 && .AVIATION...VFR conditions will prevail through the period. Winds will be the primary concern across all TAF sites except ALW/PSC. Sustained winds will be between 15 to 20 kts, slightly higher at DLS with gust nearing 30 kt possible. Winds will settle in the evening and overnight period as they will be mostly diurnally driven. CIGs will remain SKC. Bennese/90 && .PRELIMINARY POINT TEMPS/POPS... PDT 61 96 60 97 / 0 0 0 0 ALW 66 99 65 100 / 0 0 0 0 PSC 65 100 64 101 / 0 0 0 0 YKM 62 98 61 99 / 0 0 0 0 HRI 65 100 63 101 / 0 0 0 0 ELN 64 94 62 99 / 0 0 0 0 RDM 53 95 55 96 / 0 0 0 0 LGD 60 95 59 98 / 0 0 0 0 GCD 59 98 60 102 / 0 0 0 0 DLS 64 95 63 98 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning until 10 PM PDT this evening for ORZ041- 044-505-507-508-510-511. Red Flag Warning until 11 PM PDT this evening for ORZ610-639>645. Heat Advisory until 10 PM PDT this evening for ORZ049-050-502- 503. WA...Excessive Heat Warning until 10 PM PDT this evening for WAZ024- 026>029-521-523. Red Flag Warning until 11 PM PDT this evening for WAZ691>693. Heat Advisory until 10 PM PDT this evening for WAZ030. Red Flag Warning until 8 PM PDT Thursday for WAZ690. && $$ SHORT TERM...85 LONG TERM....90 AVIATION...90