FXUS66 KPDT 192245 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 345 PM PDT Fri Jul 19 2024 .SHORT TERM...This Afternoon through Sunday night...A weak shortwave passing over the forecast area this afternoon has led to slightly suppressed afternoon temperatures relative to yesterday, but temperatures remain 5-10 degrees above normal. Despite modest instability (MUCAPE of up to 500-1000 J/kg) accompanied by some weak synoptic forcing associated with the aforementioned shortwave, convection over the eastern mountains has been limited to a cumulus field, presumably due to very dry air aloft (visible on low/mid-level water vapor imagery). Tonight through Saturday, an anomalously strong mid- to upper- level ridge of high pressure will continue to rebuild over the Pacific Northwest with hot to very hot conditions Saturday through Monday. Excessive Heat Warnings and Heat Advisories are in effect. Saturday night into Sunday, a weak vorticity max/lobe riding up the coast coupled with increasing PWATs and mid-level moisture will facilitate some high-based showers. Confidence in thunderstorms for any given location is currently low, but confidence is medium-high (50-80% chance) in at least infrequent lightning for central OR and portions of eastern Oregon and south-central Washington. Currently, highest confidence in lightning is for central Oregon in Deschutes, Jefferson, and Crook counties, as well as western Grant County in eastern Oregon. Sunday evening, an approaching trough of low pressure will induce strengthening onshore-directed surface pressure gradients and a push of cooler marine air east of the Cascades, channeled through the Cascade gaps. This will persist through Sunday night and present elevated fire weather concerns for new and existing fires. The moister air mass will yield higher dew points and RHs which may limit widespread overlap of wind and RH criteria. Plunkett/86 && .LONG TERM...Monday through Friday... Key Messages: 1. Pattern change expected early in the long term 2. Possible thunderstorms over the eastern mountains on Monday 3. Much cooler than in recent days 4. Breezy afternoon winds through the Cascade gaps each afternoon Models are in good agreement in having a pattern change from the persistent strong ridge of the last couple of weeks to having a trough in control of the Pacific Northwest through the long term period. This will give us cooler temperatures through the week dropping to a few degrees below normal by Friday. The timing of the arrival of the trough is still a bit up in the air on Monday with the GFS bringing in cooler air earlier and the ECMWF giving us even warmer high temperatures than on Sunday. Monday will be a classic breaking down of the ridge situation and the GFS has ample instability over the eastern mountains so have kept a slight chance of thunderstorms with little if any rain Monday afternoon and early evening. Foresee no rain or thunderstorms after Monday. Pressure gradients will also tighten up with the trough and breezy winds through the Cascade gaps are likely each afternoon. Monday will have the most uncertainty as to the temperatures. The cooler GFS and NBM have temperatures in the 90s to about 103 in the lower elevations while the ECMWF has temperatures of 100 to 108 in the Columbia Basin and in the mid to upper 90s in the rest of the lower elevations. Have gone with the NBM temperature which are about 5 degrees cooler than Sunday with highs in the mid 90s to lower 100s and mainly 90s in the mountains. As mentioned above, have kept a slight chance of thunderstorms in the eastern mountains as the instability is there though front timing may keep it from happening. Afternoon winds will reach 15 to 25 mph in the Kittitas Valley, Columbia Gorge and the western Columbia basin and 10 to 20 mph elsewhere. Tuesday and Wednesday, the trough will move close to the coast while the ridge moves into the Rockies. Temperatures Tuesday will cool to the lower to mid 90s and in the 80s in the mountains. Wednesday will be a degree or two warmer. Afternoon winds will be a few mph lighter than Monday. Thursday will see the trough move ashore with a central low in British Columbia. This will bring in cooler air and temperatures will drop 5 or so degrees to the 80s and lower 90s. Friday will see the the trough axis move overhead, cooling temperatures a couple more degrees to the 80s with mid 70s to lower 80s in the mountains. Breezy west to northwest winds of 15 to 25 mph are expected each afternoon. Perry/83 && .AVIATION...18Z TAFs...VFR conditions will persist through the TAF period with clear skies. There will continue to be some lingering hazy conditions and locally smoky areas due to wildfires though TAF sites are not expected to drop below 6SM. KDLS will have sustained northwest winds around 15 kts with gusts to around 25 kts today. KRDM and KBDN could have some gusts to 20 kts this afternoon. Otherwise, winds are expected to remain below 12 kts for the next 24 hours. Perry/83 && .FIRE WEATHER...Hot, dry and unstable conditions are anticipated over the weekend as a robust mid- to upper-level ridge of high pressure amplifies over the Pacific Northwest. Red Flag Warnings are in effect from 11AM Saturday until 11PM Sunday for fire weather zones OR642 and OR644. Additionally, there are concerns for an elevated fire threat due to increasing winds late Sunday as cooler air associated with an approaching trough pushes into the region. This will produce sustained winds of 10-20 mph with minimum RH values in the teens and 20s. Through the remainder of the week, onshore gap flows are expected to redevelop each day. Plunkett/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 59 102 64 105 / 0 0 0 0 ALW 64 105 67 110 / 0 0 0 0 PSC 64 105 66 109 / 0 0 0 0 YKM 60 102 65 106 / 0 0 0 0 HRI 63 105 65 109 / 0 0 0 0 ELN 62 102 64 105 / 0 0 0 0 RDM 53 100 60 98 / 0 0 10 20 LGD 59 100 62 105 / 0 0 0 0 GCD 58 103 65 106 / 0 0 0 20 DLS 64 106 71 97 / 0 0 0 20 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning from 11 AM Saturday to 10 PM PDT Monday for ORZ041-044-049-050-502-503-505-507-508. Red Flag Warning from 11 AM Saturday to 11 PM PDT Sunday for ORZ642-644. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for ORZ506- 510-511. WA...Excessive Heat Warning from 11 AM Saturday to 10 PM PDT Monday for WAZ024-026>030-521. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for WAZ523. && $$ SHORT TERM...86 LONG TERM....83 AVIATION...83 FIRE WEATHER...86