textproduct: Pendleton

KEY MESSAGES

- Warming and drying trend through midweek

- Breezy winds Thursday across the Gorge and Kittitas Valley

- Afternoon thunderstorms expected Saturday

DISCUSSION

Current radar and infrared satellite imagery shows a light shower over eastern Wallowa county with some high level clouds moving in from the north as a system continues to depart to the east. In its wake, a transient upper level ridge will move over the region to promote clearing skies and warming temperatures. Highs are expected to increase about 5 degrees from Monday, reaching into the upper 70s to low 80s across the Columbia Basin, Gorge, Central Oregon, and the Blue Mountain foothills. This warming trend will persist on Wednesday as flow aloft turns from the northwest to the west, allowing high temperatures to bump up another 5 degrees - reaching near to slightly above normal averages for this time of year. Afternoon humidities will also be on the decline, dropping between 15-25% across Central Oregon and portions of the Eastern Mountains on Wednesday. Moderate overnight humidity recoveries will also be present Wednesday night into Thursday morning, with values in the 40-50% range across Central Oregon.

Near normal temperatures extend into Thursday as the transient ridge exits east. This is ahead of the next system that is dropping down the British Columbia coast, pushing inland north of Vancouver Island early Thursday morning. The upper level trough will infiltrate into the Pacific Northwest Thursday afternoon as a high pressure strengthens over the Four Corners region and shifts west. These two synoptic features will allow for a tightened pressure gradient to develop across the area, more specifically along the Cascades. As a result, breezy to windy conditions are likely through the Columbia Gorge, Kittitas Valley, and the Simcoe Highlands. Current guidance suggests that winds are expected to peak between 1 PM and 7 PM. Kittitas Valley should experience the highest winds on Thursday, with the NBM suggesting a 22% chance of reaching Wind Advisory criteria (45 mph or greater). This chance is expected to increase as the event nears as the GFS and NAM both highlight a 9-10 mb difference between Pane Field (PAE) and Pasco (PSC). In addition, there are only 20% of ensemble members that suggest a stronger transient ridge which would relate to slightly lower expected winds - with 68% of members highlighting slightly higher winds over the aforementioned areas. Thus, A Wind Advisory is probable (50-60%) over the Kittitas Valley Thursday afternoon, with lower chances for the Simcoe Highlands (30-40%) and the Columbia Gorge (25-35%).

Thursday's system effectively flattens the building Four Corners ridge and quickly ejects east, but a much stronger system follows shortly behind. This system drops more inland from Eastern Alaska and northwest British Columbia before shifting offshore just north of Vancouver Island. The offshore motion will allow it to strengthen and pull additional moisture from a closed low, located over the Eastern Pacific, on its way into the Oregon coast. It also provides enough time from the earlier system for a weak area of high pressure to attempt to build. These two factors will attribute to isolated afternoon thunderstorm chances across the east slopes of the Cascades, Central Oregon, and the Yakima/Kittitas Valleys on Saturday. Guidance is struggling with the timing and strength of these systems, but currently 56% of ensemble members showcase an earlier and stronger dropping system, which would provide widespread 150-300 J/kg CAPE values. These would also relate to a wetter scenario, with 56% of members bringing widespread rain amounts of 0.05-0.15". The remaining 44% of members keep rain amounts either limited to the east slopes of the Cascades or widespread rain amounts of 0.04" or less. Light, lingering showers are expected across Wallowa county on Sunday as the system slowly departs east into Monday. Both AI ECMWF and GFS guidance hints at northwest flow aloft persisting through early next week, with a weak, embedded system arriving Tuesday. 75

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

VFR conditions prevail with light winds with SKC to SCT cloud conditions. Most winds will be sustained less than 12 knots. Not expecting CIG or VIS issues.

Preliminary Point Temps/PoPs

PDT 76 47 84 51 / 0 0 0 0 ALW 77 52 84 58 / 0 0 0 0 PSC 80 50 86 54 / 0 0 0 0 YKM 79 53 84 56 / 0 0 0 0 HRI 80 49 86 54 / 0 0 0 0 ELN 77 49 82 55 / 0 0 0 0 RDM 75 41 87 45 / 0 0 0 0 LGD 74 46 84 50 / 0 0 0 0 GCD 76 47 87 51 / 0 0 0 0 DLS 81 56 87 58 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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