textproduct: Pendleton

KEY MESSAGES

- Critical fire weather conditions in the OR Columbia Basin, locally elsewhere, Saturday afternoon

- Warm temperatures and dry conditions in the lower elevations, isolated thunderstorms in the eastern mountains Sunday through Tuesday

- Another round of elevated fire weather conditions Tuesday and Wednesday with return of breezy westerly winds

DISCUSSION

Today through Saturday: Satellite imagery this afternoon shows very little in activity across the forecast area. Currently, broad troughing across western Canada is placing the PacNW under a dry zonal flow aloft. While conditions are mostly quiet, breezy winds have developed throughout the morning and afternoon through the Cascade gaps, owing to a marine layer across western WA and northwest OR.

By tomorrow afternoon, a shortwave trough passing through southern BC will clip the PacNW, producing breezy winds through the Cascade gaps and into the OR Columbia Basin, with locally breezy winds elsewhere. Meanwhile, with lack of precipitation, and any moisture for that matter, afternoon relative humidities have been on a downward trend the last several days. This trend will result in widespread RHs into the teens and low 20s tomorrow afternoon. The breezy west winds and low RHs will overlap in the OR Columbia Basin tomorrow, resulting in critical fire weather conditions throughout the day. Localized areas of the Yakima/Kittitas valley, Warm Springs Reservation, and Hanford will also see a chance (20-45%) of critical fire weather conditions Saturday afternoon.

Sunday through Tuesday: Good agreement amongst ensemble cluster solutions that the Four Corners High will develop with broader upper level ridging developing along the Rockies. Meanwhile, a closed low in the Gulf of Alaska will slowly push south, with shortwaves rounding the low and reinforcing an upper trough offshore the PacNW. The PacNW will sit underneath a southwest flow aloft that will develop between those two features, resulting in a warming trend that will bring back widespread 90 degree temperatures in the lower elevations, light winds through the Cascade gaps and lower elevations, and mostly dry conditions (confidence 60-75%).

However, isolated thunderstorm chances will increase as shortwave impulses ride up the southwest flow Sunday through Tuesday. The development of the Four Corners High will bring increased surface moisture into portions of central OR and the eastern mountains, resulting in at least light rain cores (0.05 to 0.1 inches) to develop within any developing thunderstorm (confidence 45-60%). That said, with drying conditions and fuels, the threat of thunderstorm development will still result in elevated fire weather conditions. The southwest flow and ridging aloft will also bring increased surface instability with modest low to mid level lapse rates, supporting initial development of thunderstorms. Lastly, low to mid level shear will be enough (20-30kts) to help maintain thunderstorms that do develop during this period.

Tuesday, upper level troughing offshore will begin to move inland (confidence 60-75%), producing breezy winds through the Cascade gaps and into portions of the Columbia Basin Tuesday afternoon. Confidence is mod-high (60-80%) that critical fire weather conditions will develop across the OR Columbia Basin, Kittitas/Yakima Valleys, and portions of north central OR.

Wednesday and Thursday: Breezy to locally gusty winds will remain the concern through the middle of the week as ensemble cluster guidance shows the shortwave trough passing over the PacNW Wednesday, with zonal flow developing in it's wake for Thursday. (confidence 45-60%) Overall, conditions will remain dry across the forecast area, with temperatures dropping back to near normal (mid to upper 80s) in the lower elevations (confidence 45-50%). Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

VFR conditions accompanied by diurnally and/or terrain-driven winds are forecast through the period. Winds will be breezy during the afternoon and evening hours, strongest at DLS.

FIRE WEATHER

Breezy winds will continue through Saturday, while a low RH trend will continue through the week. Strong winds and low RH overlapping Saturday will bring critical fire weather conditions in OR Columbia Basin and localized areas along the Cascade East slopes and gaps. Breezy diurnal winds return Tuesday, with elevated fire weather conditions through the mid week. Isolated to widely scattered thunderstorm chances increase Sunday through Tuesday.

Preliminary Point Temps/PoPs

PDT 54 88 52 86 / 0 0 0 0 ALW 60 89 58 88 / 0 0 0 0 PSC 57 92 55 90 / 0 0 0 0 YKM 56 91 54 90 / 0 0 0 0 HRI 58 91 56 89 / 0 0 0 0 ELN 53 83 51 86 / 0 0 0 0 RDM 48 88 49 89 / 0 0 0 0 LGD 53 88 53 88 / 0 0 0 0 GCD 51 92 52 92 / 0 0 0 0 DLS 57 87 56 92 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...OR...Red Flag Warning from noon to 10 PM PDT Saturday for ORZ691.