textproduct: Pendleton

KEY MESSAGES

- Very low (5-15%) chance of thunderstorms today for central Oregon, mainly south of the Bend metro.

- Increasing chances of showers tonight (Thursday night) through Friday for central/eastern Oregon and southeast Washington. Highest chances for the Blue Mountains. - Slight chance to chance (10-30%) of thunderstorms over the Blue Mountains and vicinity Thursday. Lower chances (10-20%) for the northeast Blue Mountains region Friday.

- Temperatures will slowly warm to above normal by the end of the week, with above-normal temperatures and dry conditions persisting this weekend.

DISCUSSION

Water vapor imagery shows a closed upper low centered over southwest Oregon early this morning. East of the low center, showers are ongoing across south-central Oregon where forcing for ascent is co-located with ample moisture, mainly south of the Bend metro area. Showers will continue to taper off through morning as the low dives south-southwest, retrograding slightly as it moves over northwest California. Looking ahead to this afternoon, there is a very low to slight chance (5-15%) of afternoon and evening showers and thunderstorms across central Oregon, but most activity is expected to remain to our south in Klamath and Lake counties.

Shower activity is forecast to ramp again later tonight as moisture surges northwest, mid-level lapse rates steepen, and synoptic-scale forcing associated with the low moves overhead. Will note there is a low/slight (5-15%) chance of nocturnal thunderstorms tonight and again Thursday night.

Ensemble NWP guidance is in reasonably good agreement regarding the track of the low, but some uncertainty exists in timing/location as it moves across the region through Friday. In general, ensemble mean 500-hPa heights and vorticity show the low ejecting northeast across the Pacific Northwest Thursday through Friday, though clusters of ensemble solutions continue to show some differences in timing and magnitude of the low during this period. All clusters of ensemble solutions now advertise a scenario that would induce convection Thursday, with roughly half showing a solution that is conducive to convection persisting Friday for the Blue Mountains (mainly northeast Blue Mountains).

Chances of thunderstorms are highest on Thursday (10-30%), especially for the northeast Blue Mountains, with lower chances (5-15%) for the lower elevations of central Oregon, the Blue Mountain foothills, and even as far northwest as the lower Columbia Basin. Chances of thunderstorms drop to 10-15% for Friday, highest over Wallowa County, and will be heavily dependent on how quickly the low exits to the east; if the low lingers (solution favored more by the ECMWF ensemble) chances of showers and thunderstorms will continue over the Blue Mountains on Friday, but if the low exits more quickly (favored more by the GEFS and Canadian ensemble) we will see more showery weather that tapers off through the day.

All ensemble members indicate the low will exit to the east by Saturday, with transient shortwave ridging replacing it over the Pacific Northwest through the weekend. This would facilitate above-normal temperatures and dry conditions areawide.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

VFR conditions are forecast through the period for all sites except BDN where low stratus continues to produce MVFR CIGs early this morning. -RA in central Oregon is forecast to taper off by mid-morning, and have included a TEMPO for BDN for anticipated intermittent precipitation. Farther north at RDM, confidence in low stratus producing sub-VFR CIGs was lower (<30%). Low stratus will likely (70-90% confidence) lift at BDN and RDM by late morning to early afternoon, leaving mostly clear skies in its wake.

Sustained winds of 12 kts or less are forecast, though periodic higher gusts are expected during the afternoon hours. Strongest winds are forecast at RDM and BDN late morning through early evening, with gusts of 15-25 kts likely (80% confidence).

Otherwise, there is a very low (5-15%) chance of afternoon and evening showers and thunderstorms at BDN/RDM, though most activity is forecast to remain to the south and east of the metro area.

Preliminary Point Temps/PoPs

PDT 74 46 73 51 / 0 0 20 50 ALW 77 51 75 55 / 0 0 20 50 PSC 80 49 79 50 / 0 0 10 20 YKM 75 50 79 51 / 0 0 0 0 HRI 78 48 77 51 / 0 0 20 30 ELN 71 46 77 49 / 0 0 0 0 RDM 70 39 68 40 / 10 0 40 30 LGD 78 46 76 47 / 0 0 50 70 GCD 79 45 73 47 / 0 20 80 70 DLS 80 54 84 57 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...None.