textproduct: Pendleton

KEY MESSAGES

- Highs today forecast largely 10-15 degrees warmer than yesterday with above average highs by generally 5-10 degrees prevailing into mid-week.

- Chances for isolated to widely scattered thunderstorms anticipated tomorrow across central OR to the eastern mountains then including north central OR and south central WA Wednesday.

- Typical July dryness with low afternoon humidity today and tomorrow with light breezes promoting locally elevated fire weather conditions in the Gorge spilling into north central OR.

- Warmer than average temperatures more likely than not this upcoming weekend into early next week with low-end potential (5-20%) for thunderstorms across portions of south central WA Thursday.

DISCUSSION

Amplified large-scale pattern in place across the CONUS with yesterday's 00Z upper air plot showing broad high pressure centered across the northern High Plains and troughing across BC and southeast AK to well offshore the West Coast. Latest water vapor imagery shows a mid-level low offshore Baja California near 30 N -135 W and a shortwave trough well offshore the WA/OR border that is rotating eastward. Continued southerly flow prevails with monsoonal moisture being tapped into as its transported across CA into eastern OR. This is contributing to high clouds streaming across eastern OR with largely clear skies across much of central OR and south central WA. Limited sensible weather concerns today with highs rebounding 10-15 degrees from yesterday. Modest cross-Cascade surface pressure gradient will promote westerly breezes spilling out of the eastern Gorge and Cascade gaps. Limited fire concerns owing to light winds though they will be paired with typical seasonal dryness for this time of year. While very low-end chances for lightning/storms exist across the central OR mountains today and Wallowa (5-15%), activity is expected to be well south of the forecast area and more towards the OR/CA border if it materializes.

Looking ahead, a disturbance rotating northward from the aforementioned mid-level low in tandem with this stream of monsoonal moisture will promote better chances for thunderstorms across central OR into the eastern mountains. Decent signal captured in both HREF and REFS ensemble systems that increases confidence in this threat. Both systems show a signal with chances exceeding 30% for neighborhood probs for dBZ greater than 40 dBZ with the latter showing higher chances across the eastern mountains. Better surface and low-level moisture Tuesday should support marginal instability with MUCAPEs 500-1000 J/kg and MLCAPEs 200-500 J/kg based on deterministic guidance. Large scale forcing for ascent with orographic lift will promote isolated-widely scattered coverage. Character of storms should lean wet to a wet/dry mix given precipitable waters 0.75-1.10 with anomalies ~150-200% of normal based on the EPS. However, high-bases and inverted-V profiles will promote some dry storm risk, especially areas outside the main rain cores. A similar threat then presents itself on Wednesday with the lightning chances/thunderstorm potential spreading to also include north central OR and south central WA Wednesday.

There is increased uncertainty in the large-scale pattern Thursday-Friday as it relates to the evolution of the upper trough off the West Coast. Clustering guidance show a scenario with an ejecting disturbance tracking across the PacNW region bringing more unsettled weather and highs more typical to slightly above average. The other leading solution is a scenario with mean troughing that is more offshore and over the eastern North Pacific. The EPS ensemble system leans strongly (70% of its ensemble members) toward the former outcome with 50% of the grand ensemble (EPS, GEFS, GEPS) encompassing it overall. The latter solution would lead to a warmer outcome with this being captured by probabilistic HeatRisk. Of which, the best chances for major HeatRisk seen over the next 5 days is Thursday and Friday with chances 15-40%. This situation will bear monitoring considering the latter outcome with its high-end potential would support more heat impacts. Further ahead, highs are continue to be forecast above normal this weekend into early next week.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

VFR conditions area-wide with high clouds streaming across eastern OR into southeast WA, some smoke aloft is affecting central OR terminals. Largely low aviation concerns beyond smoke layers aloft affecting terminals in central OR and areas near wildfires in eastern OR. High clouds will continue to stream across the area. Meantime, light breezes with occasional gusts in central OR and in the eastern Gorge with gusts greater than 17 kts, mainly after 22 UTC. Highest peak gusts there today likely in the range of 20-25 kts (confidence >80%).

Preliminary Point Temps/PoPs

PDT 92 61 93 63 / 0 0 10 20 ALW 94 66 95 66 / 0 0 10 10 PSC 95 62 97 64 / 0 0 0 10 YKM 95 60 98 64 / 0 0 0 10 HRI 95 64 96 67 / 0 0 0 10 ELN 90 58 94 62 / 0 0 0 0 RDM 93 55 92 56 / 0 0 10 20 LGD 94 62 92 62 / 0 0 10 40 GCD 94 61 92 59 / 0 10 20 40 DLS 94 62 96 66 / 0 0 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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