textproduct: Pendleton

KEY MESSAGES

- High temperatures in the mid 80s to mid 90s this afternoon.

- Isolated thunderstorms along elevated terrain in central and eastern OR this afternoon into the overnight hours

- Mountain showers, isolated mountain thunderstorms, and breezy to gusty low elevation winds Wednesday

DISCUSSION

Satellite imagery this afternoon shows a veil of cirrus over the forecast area, which ha limited heating across northern portions of the forecast area. Meanwhile, breaks in the cirrus have allowed central OR, Yakima valley, and the Gorge to warm into the mid to upper 80s. Otherwise, isolated areas of cumulus have begun to develop across elevated terrain south of the forecast area, but no sign of towering cumulus at this time.

Today, the upper ridge will begin to break down and push east, with deep southerly flow developing as a result. Instability across elevated terrain of central and eastern OR will increase as a result (MUCAPE 250-1250 J/kg), introducing a low chance (<15%) of isolated thunderstorms in these areas into the afternoon. CAMs and deterministic guidance are showing a shortwave impulse with a weak moisture plume riding up the southerly flow late Tuesday afternoon through the overnight hours. The combination of the shortwave, moisture, and instability will result in a continued low chance (10-15%) of isolated thunderstorms across the elevated terrain of eastern OR through late this evening, with a slight chance (15-25%) of isolated to scattered thunderstorms will develop throughout tonight along the OR/WA Cascade crest. Otherwise, expect mostly scattered showers along the Cascade crest throughout tonight as well. Temperatures will continue to warm through this afternoon, but locations under the cirrus will only warm into the lower to mid 80s, with areas outside of the cirrus coverage warming into the upper 80s to lower 90s.

Wednesday and Thursday: An upper low offshore will kick inland early Wednesday morning, which will transition into an open trough with a slight negative tilt. The trough passage will bring widespread shower chances and cooler temperatures across the region through Wednesday, with a slight chance (15-25%) of isolated to scattered thunderstorms continuing along the Cascade crest and WA Cascade east slopes through late Wednesday morning. Widespread winds 20-35 mph with gusts 35-55 mph will develop across the lower elevations, with winds approaching 40 mph and gusts up to 60 mph across portions of the Simcoe Highlands and the OR Blue Mountain foothills. High wind warnings and wind advisories have been issued for many lower elevation locations in and adjacent to the Columbia Basin.

The upper trough will exit the region Wednesday night allowing a broad upper ridge to slide over the PacNW with drier conditions. Light showers will retreat to the WA Cascade crest Thursday, with cooler temperatures persisting across the forecast area. Otherwise, tightened surface pressure gradients will persist into Thursday, bringing breezy winds (15-30mph with gusts up to 40mph) through the Cascade gaps into the Columbia Basin.

Friday through Monday: Ensemble cluster guidance is in great agreement through Saturday in a broad upper trough sliding over the PacNW, producing another round of mountain showers with breezy winds in the lower elevations (confidence 60-70%). The upper trough will bring much cooler conditions across the region, with high temperatures lowering into the upper 50s to 60s by Saturday (confidence 45-60%). The cooler airmass in the region will also result in snow levels dropping to the surface across the mountains, resulting a return of snow showers generally above 4kft to 4.5kft Friday night through Saturday.

Sunday into Monday, there is some disagreement amongst ensemble members in when a transient upper ridge will slide over the PacNW. A majority of members favor the ridge overhead by Sunday afternoon, with dry conditions developing and persisting into Monday, while remaining members delay the upper ridge arrival to Sunday night. Confidence is low-mod(25-40%) on end time of shower activity Sunday, while moderate (40-50%) for dry conditions Monday. Otherwise, temperatures will remain in the 60s Sunday, with warming into the lower 70s Monday (confidence 35-50%). Lawhorn/82

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Mostly VFR conditions to prevail through the period. An upper low approaching the region will produce showers and isolated to scattered thunderstorms starting late this afternoon through tomorrow. There is about a <10% chance of an isolated shower/thunderstorm impacting RDM/BDN later this afternoon, but otherwise shower chances will increase after 06Z and end around 18Z at these sites and site DLS. For sites PDT/YKM/ALW/PSC, shower chances will increase after 12Z, and will continue into the end of the period. After 18Z-20Z, showers will become more periodic. A prob30 for thunder was included at site YKM for the morning period. Winds of 15-25kts with gusts 25-45kts will develop at site DLS this evening, then develop at sites PDT/RDM/BDN/ALW/PSC after 13Z. Strong winds will persist through the end of the period. Lawhorn/82

FIRE WEATHER

Dry and warm conditions today but high pressure will breakdown late this afternoon. There is an isolated thunderstorm chance across the mountains in the late afternoon and evening. Breezy to gusty winds in the lower elevations and rain showers will develop early tomorrow morning as an upper low moves inland. Breezy winds will continue Thursday with min RHs in the teens in central OR. Mountain rain/snow showers will develop Friday and early Saturday, while winds will remain breezy.

Preliminary Point Temps/PoPs

PDT 51 65 44 68 / 0 70 10 0 ALW 55 65 48 68 / 0 80 20 0 PSC 55 70 47 73 / 0 70 10 0 YKM 53 68 43 71 / 10 80 0 0 HRI 53 68 46 71 / 0 70 0 0 ELN 47 61 39 63 / 20 90 10 0 RDM 42 62 32 72 / 40 60 0 0 LGD 50 63 40 68 / 10 80 20 0 GCD 48 65 37 71 / 20 70 0 0 DLS 52 67 48 70 / 40 70 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 8 PM this evening to 11 PM PDT Wednesday for WAZ024. Wind Advisory from 5 AM to 11 PM PDT Wednesday for WAZ026>029. High Wind Warning from 5 AM to 11 PM PDT Wednesday for WAZ521. OR...Wind Advisory from 8 PM this evening to 11 PM PDT Wednesday for ORZ041. Wind Advisory from 5 AM to 11 PM PDT Wednesday for ORZ044-510. High Wind Warning from 5 AM to 11 PM PDT Wednesday for ORZ507- 508.