textproduct: Pendleton

KEY MESSAGES

1. Isolated to scattered thunderstorms with abundant lightning and gusty outflow winds *Red Flag Warning In Effect*

2. Sunday continued southwest flow will bring chances of thunderstorms and showers.

DISCUSSION

Current nighttime satellite shows some mid level clouds lingering over the region. Radar shows a few returns along the eastern mountains but thunderstorms quickly teetered out earlier this evening. Overnight temperatures will be in mostly in the 50s with isolated areas in the Basin seeing low 60s.

Southwest flow aloft will continue over the region with a trough just off the coast. Models show a shortwave will make its way into the region bringing with it increased moisture form the south. this will lead to increased chances of thunderstorms and showers. Looking at forecasted RAP soundings, there are MUCAPE values between 250-400 J/kg, LIs of -3, lapse rates between 7.5-8 C/km and effective bulk shear of 18 kts. This is just enough instability to allow for isolated to scattered thunderstorms across central OR and the eastern mountains today with 30-55% chances. Also, the flow tilts enough to allow for moisture (PWATs 0.60-0.70 inches) to surge into the WA Cascades and again MUCAPE values above 300-500 J/kg, LIs of - 3, lapse rates above 8-9 C/km and shear of 15 kts. That coupled with orographic lift will lead to isolated thunderstorms along the eastern slopes of the WA Cascades this afternoon. Even with the increased chances of showers accompanying these storms, there is moderate confidence (60-70%) of elevated fire weather conditions developing due to lightning potential outside of rain cores and gusty outflow winds. Therefore a Red Flag Warning has been issued for these areas through & PM Friday.

Models show another shortwave is expected to move across the southwest flow bringing in another round of thunderstorm chances Saturday (30-50%). The flow will again allow for convection to occur over the WA Cascades. Forecast sounding show Saturday to have values above 250 J/kg, LIs of -1, lapse rates above 7 C/km and shear of 20 kts. While these are a bit weaker than Fridays values, we cannot rule out an isolated storm or two across central OR, the eastern mountains and the east slopes of the WA Cascades.

Sunday onward the models are phased slightly out of agreement with the overall synoptic pattern of an offshore closed low and where that low will go. However, mesoscale patterns show the area to continue to be under southwest flow aloft. This will allow continued moisture to be brought into the region. Chances of thunderstorms and showers will continue with 15-20% probabilities over the eastern mountains.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Smoke will have a marginal impact on the visibilities at area terminals this TAF period, Light winds under 12 knots are expected through the forecast with some risk of thunderstorms between 22 an 02z, especially around RDM/BDN where a TEMPO group is in place.

FIRE WEATHER

Increased moisture at the surface and incoming instability will increase the chances (30-55%) of isolated to scattered thunderstorms through the weekend. Abundant lighting is expected over the eastern mountains and the WA Cascades. Not only will abundant lightning be a concern, gusty outflow winds that develop will be a concern as well.

Preliminary Point Temps/PoPs

PDT 87 55 87 56 / 0 0 30 0 ALW 89 60 89 62 / 0 0 30 10 PSC 91 57 91 57 / 0 0 20 0 YKM 88 59 90 60 / 10 0 10 10 HRI 90 59 90 59 / 0 0 30 0 ELN 83 56 85 58 / 40 10 20 10 RDM 85 50 85 49 / 10 20 10 10 LGD 86 55 87 54 / 30 20 60 20 GCD 85 55 88 54 / 50 20 20 10 DLS 90 64 90 62 / 0 10 10 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 3 PM PDT this afternoon for WAZ026>030- 521>523. Red Flag Warning until 9 PM PDT this evening for WAZ695. OR...Air Quality Alert until 3 PM PDT this afternoon for ORZ041-049- 050-502-503-505-506-509>511. Red Flag Warning until 7 PM PDT this evening for ORZ694-695- 697-699.