textproduct: Pendleton

KEY MESSAGES

- A series of upper level low pressure systems will bring periods of rain, breezy westerly winds, and isolated thunderstorm chances through Friday.

DISCUSSION

Upper ridging at 500 mb will shift to a southwesterly flow aloft Today as and eastern Pacific trough shifts toward the WA/OR coast. The EC/GFS/HiRes models all show the lead shortwave spreading into nrn CA Tonight and northward toward the Snake River by midday Wednesday. Temperatures today look cooler by about 5 to 10 degrees across the gaps, central Oregon and warmer by about 5 degrees across the Yakima valley and parts of the Columbia Basin of Washington. More sky cover is expected today ahead of a changing synoptic pattern, however some periods of sun are forecast by NBM transitioning through the afternoon. Breezy to windy westerly surface winds across the central Oregon zones, Eastern Columbia Gorge, Simcoe highlands and the Kittitas valley can linger into the evening and overnight given the surface pressure gradients. The breezy winds, shift west southwest through late Wednesday as the initial shortwave spreads east of the region and the parent upper pacific low moves onshore Thursday night.

The pattern will bring a transition to wet conditions for midweek. For This afternoon, the HREF calibrated 4-hr probability of thunder is limited to a 10 to 25 percent chance range between about 20z and 03z over eastern Wallowa county and even lower chances for the same geographic area on Wednesday afternoon, so a low confidence forecast of isolated dry thunderstorms. Precipitation chances increase from there as the 48 hour expected NBM precipitation would put about one third to three quarters of an inch of rain by Wednesday overnight/Thursday morning. The extended period of the forecast looks near to cooler than normal and wetter than normal as the aforementioned upper low lingers over the PAC NW and Interior NW through around Tuesday or Wednesday of next week.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Scattered to broken high clouds across the region will continue Today with no expectations for lower ceilings developing. Most windy location will be DLS where gusts of of 25 to 30 kts will be common into the overnight. Breezy west to southwest winds at PDT developing in the mid afternoon. Light variable winds at BDN and RDM this morning turn the typical north in the early afternoon.

Preliminary Point Temps/PoPs

PDT 83 49 75 48 / 10 10 30 80 ALW 84 55 77 52 / 10 10 30 90 PSC 87 54 78 47 / 10 0 10 70 YKM 88 55 75 49 / 10 0 20 50 HRI 87 54 78 48 / 10 10 20 70 ELN 84 50 72 44 / 0 0 30 70 RDM 80 40 67 37 / 10 10 70 100 LGD 86 50 73 47 / 20 20 70 100 GCD 88 51 73 48 / 10 10 30 100 DLS 81 57 72 52 / 0 0 80 90

PDT WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 10 AM PDT Wednesday for WAZ026-522-523. OR...Air Quality Alert until noon PDT Wednesday for ORZ041-505-506- 509>511.