textproduct: Pendleton

KEY MESSAGES

- Scattered thunderstorms capable of strong/damaging gusts and isolated large hail will impact the forecast area this afternoon and evening

- Heavy downpours embedded within thunderstorms will bring an excessive rainfall threat to the Cascade east slopes today

- Breezy to locally gusty winds through the Cascade gaps and Lower Columbia Basin Friday

DISCUSSION

Severe convection an brief heavy rains are going to be the primary weather hazards today following afternoon low end heat risk (category 2) over the Washington Columbia Basin and Yakima Valley and Eastern Columbia River Gorge. Highs This Afternoon will peak in the low 90s in the and Lower Columbia Basin, and into the mid 80s across central Oregon and the Blue Mt Foothills. The category 2 heat risk (moderate) affects those who are sensitive to heat especially those without cooling/hydration and some health systems and industries.

Shallow convection has already developed across the northern periphery of the upper low, namely across Crooks into southern Deschutes counties with occasional dry lightning noted on ETLN 5 and 1 minute. Interestingly HRRR modeled updraft helicities are not very robust as the modeled convective elements move into the PDT CWA after mid afternoon which could limit the frequency of severe events (hail/damaging wind reports).

The general trend is for the southwest to northeast broken linear convection to spread into southern Oregon and the Blue Mountains from mid afternoon though about early evening before continuing north into a lower CAPE environment across the Washington Valleys and Upper Columbia Basin late this evening. The HREF Cams solutions with the most scenarios of longer lived and stronger rotating storms favors the Ochoco John Day Highlands and Deschutes County and the Oregon counties in general. Precipitation potential from the NBM mean ranges for up to one tenth of an inch over the Lower Columbia basin and expansion to one quarter inch across the rest of the forecast areas, with the exception of much higher rainfall amounts in three quarter of an inch to one inch range over central Oregon and the Oregon Eastern Slopes. Local flash flooding is possible in these areas especially over any preexisting burn scars over the last could of years with these rains upwards of an inch overnight.

Beyond the convective setup for look for stronger wind speeds and gusts especially though the Kittitas valley On Friday based on gap winds/gradient forgings.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

VFR conditions currently across all sites, which will stay the course through the period. However, there may be brief periods of MVFR for all terminals due to reduced visibilities associated with developing strong to severe thunderstorms this afternoon and evening. There has already been lightning reported near KRDM/KBDN this morning, with the potential intensifying through the remainder of the day. Windy conditions will also coincide with any developing storm cells as outflow boundaries could lead to brief wind gusts of around 40 kts. Brief heavy downpours and large hail (1+ inch diameter) will also be possible near any developing storm cells. Ceilings should stay around 5kft through the day, slowly improving to 10kft overnight. The thunderstorm threat diminishes tonight as storm activity shifts to our north. 75

Preliminary Point Temps/PoPs

PDT 51 69 42 67 / 60 10 10 0 ALW 57 72 47 68 / 50 10 10 0 PSC 54 75 45 73 / 70 20 10 0 YKM 57 73 43 72 / 90 40 10 0 HRI 54 70 44 70 / 60 20 10 0 ELN 54 66 40 64 / 80 40 0 0 RDM 42 59 32 62 / 90 60 10 0 LGD 48 72 42 64 / 60 50 10 0 GCD 42 69 37 65 / 60 60 20 0 DLS 55 67 45 69 / 90 40 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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