textproduct: Pendleton

KEY MESSAGES

- Red Flag Warnings in effect for abundant lightning today into Friday morning.

- A convective weather pattern will continue through at least Saturday with daily shower and thunderstorm chances. More uncertainty in pattern details Sunday into next week.

- Near-seasonal temperatures through the week.

DISCUSSION

Water vapor imagery reveals a shortwave trough over the Pacific Northwest, with an embedded circulation noted over northeast Washington. Forcing associated with the aforementioned circulation has likely been the catalyst for convection that developed yesterday afternoon across the Washington Cascades and remains ongoing northeast of our forecast area. Meanwhile, the Blue Mountains remain beneath the entrance region to a subtle mid/upper jet. Coupled with modest vorticity advection and mid- level moisture, some weak showers are developing early this morning. Not anticipating any robust convection, but observations are consistent with what NWP guidance has been advertising: modest synoptic-scale forcing coupled with sufficient mid-level (700-500 hPa) moisture and negative mid- level (700-500 hPa) theta-e lapse rates typically facilitate some weak nocturnal convection (predominantly showers with isolated embedded thunderstorms).

The circulation mentioned above will then exit to the northeast into the northern Rockies through the day, but a second vorticity lobe is expected to dive southeast into the Pacific Northwest today, reinforcing the shortwave trough. Additional convection is expected (95 percent confidence) to develop this afternoon across the mountains, and the previous day shift issued Red Flag Warnings for multiple fire weather zones in Oregon due to forecast scattered thunderstorms and abundant lightning. Note that the warnings for much of the Blue Mountains continue Thursday night for nocturnal convection.

Looking ahead, ensemble NWP guidance suggests continued southwest flow aloft and additional reinforcing shortwaves through at least Saturday. This will keep a convective pattern in place resulting in daily shower and thunderstorm chances, mainly over the mountains. Additional Fire Weather Watches or Red Flag Warnings may be needed if confidence in abundant lightning increases for Friday afternoon or over the weekend.

Sunday into next week, uncertainty in pattern details burgeons due to model differences in the development and evolution of a deep closed low in the Pacific. Ensemble cluster analysis indicates concensus that the low will develop, but roughly equal chances (40-60 percent) of either the deep closed low remaining well offshore into the middle of next week or a somewhat more progressive pattern with a weaker open wave trough over the Pacific Northwest in addition to a weaker offshore low. Either solution puts the forecast area under a pattern that is favorable for some periods of convection, but chances of convection have trended downward since yesterday's discussion for Sunday into early next week. Broadly, still have 10-25% chances of precipitation for the mountains with lower chances for non-mountain areas.

Lastly, Air Quality Alerts/Advisories issued by air quality agencies remain in effect for the majority of our forecast area due to wildfire smoke from ongoing regional wildfires.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

VFR conditions prevail with more elevated smoke in some areas. Couple of TAF sites are on the borderline with visibilities down to 6 miles. May see some MVFR conditions develop but not in a prolonged way. May see some smoke settle down to the surface overnight, but chances of that happening are small at 5 to 15 percent. No breezy winds anticipated with most sustained winds at less than 12 knots with most gusts not exceeding 20 knots.

Preliminary Point Temps/PoPs

PDT 85 54 87 57 / 0 0 0 0 ALW 87 59 88 62 / 0 0 0 0 PSC 89 58 90 58 / 0 0 0 0 YKM 88 61 88 59 / 0 10 10 0 HRI 88 59 90 60 / 0 0 0 0 ELN 83 57 82 56 / 10 20 30 0 RDM 84 49 85 49 / 0 10 10 10 LGD 86 55 86 55 / 0 30 30 10 GCD 87 54 86 54 / 10 60 40 20 DLS 90 63 91 63 / 0 0 10 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 3 PM PDT Friday for WAZ026>030-521>523. OR...Air Quality Alert until 3 PM PDT Friday for ORZ041-049-050-502- 503-505-506-509>511. Red Flag Warning from 1 PM this afternoon to 5 AM PDT Friday for ORZ696>699. Red Flag Warning from 1 PM this afternoon to 9 PM PDT this evening for ORZ700-705.