textproduct: Pendleton

KEY MESSAGES

- High temperatures in the upper 80s to mid 90s Tuesday

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

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

DISCUSSION

Tonight through Tuesday: Little to talk about on satellite this afternoon as skies are mostly clear with very thin cirrus decks moving across the forecast area.

Clear conditions and light winds today will continue overnight into tomorrow as an upper level ridge persists over the region. By late tomorrow morning, 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 (<10%) 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 central and eastern OR through Tuesday night. The upper ridge and southerly flow aloft will also result in temperatures climbing into the upper 80s to mid 90s Tuesday afternoon.

Wednesday and Thursday: Guidance has come in much better agreement in the last 24 hours in an upper low offshore kicking inland Wednesday morning, which will transition into an open trough with a slight negative tilt. There is high confidence (80-90%) that the trough passage will bring mountain shower chances and cooler temperatures across the region Wednesday, while there is mod-high confidence (65-85%) that widespread winds 20-35 mph with gusts 35-55 mph will develop across the lower elevations. The strongest winds are expected through the Columbia Basin/Gorge and adjacent valleys/foothills, including north central OR and the Simcoe Highlands...mod-high confidence (70-85%) that wind advisories will be needed in most of these areas Wednesday.

While guidance is in mostly good agreement, there remains uncertainty on timing of the trough crossing inland, which will impact the extent of isolated thunderstorm chances for Wednesday morning through the afternoon. If the trough lags and comes in later in the morning, then areas from OR Cascades to the eastern mountains will see slight chances (~15%) of isolated thunderstorms embedded with shower chances, whereas if the trough arrives earlier the isolated thunderstorm chances will be limited mainly to the elevated terrain of northeast OR. Confidence on forecast thunderstorm extent is moderate (50-65%).

Ensemble cluster guidance is in great agreement of a broad flat ridge developing behind the trough exit late Wednesday through Thursday, resulting in shower chances being limited to the Cascade crest. Otherwise, breezy winds will continue in the lower elevations throughout Thursday.

Friday through Sunday: Ensemble cluster guidance is in good agreement through the weekend that a broad upper trough will slide over the PacNW, producing another round of mountain showers with breezy winds in the lower elevations (confidence 45-60%). By Sunday, there is decent agreement in the forecast area sitting between an upper ridge to the northwest and upper trough to the east, keeping the lower elevations dry with locally breezy winds and light showers across the Cascades and northern Blues.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

VFR conditions will persist through the forecast period. Winds will be diurnally driven through the period under 10 kts with the exception of DLS which will see increased winds around 4Z of 16G25kts. Towards the end of the period around 6Z Tuesday, BDN/RDM could see an isolated thunderstorm or two. 90

FIRE WEATHER

Dry and warm conditions continue through Tuesday. A breakdown in high pressure aloft will bring increasing unstable conditions Tuesday afternoon and night, with a low chance (<15%) of isolated thunderstorms in central and eastern OR. Breezy to gusty westerly winds in the lower elevations and mountain showers will develop Wednesday. Isolated thunderstorms will be possible Wednesday morning into the afternoon. Breezy winds and isolated mountain showers continue Thursday. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 48 85 52 66 / 0 0 0 60 ALW 51 88 56 66 / 0 0 0 70 PSC 50 91 56 71 / 0 0 0 60 YKM 50 87 55 70 / 0 0 20 70 HRI 48 88 54 68 / 0 0 0 60 ELN 45 83 48 63 / 0 0 20 80 RDM 45 90 42 62 / 0 0 40 70 LGD 45 91 51 64 / 0 0 0 80 GCD 47 94 48 66 / 0 0 10 60 DLS 53 88 53 67 / 0 0 40 60

PDT WATCHES/WARNINGS/ADVISORIES

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