textproduct: Pendleton

KEY MESSAGES

- Breezy and below normal temperatures through mid-week.

- Warmer and drier trend Thursday, peaking over the weekend.

DISCUSSION

current radar and visible satellite imagery shows very light and isolated returns across portions of Central Oregon under partly cloudy skies. This is in response to an upper level low pressure currently over Montana, that will continue to depart to the northeast and into southern Manitoba over the next 24 hours. A weak, transient ridge of high pressure is beginning to break up earlier cloud cover through the Columbia Basin, but an incoming shortwave will return clouds overnight into Tuesday. These synoptic features have also allowed a pressure gradient to develop along the Cascades to attribute to breezy conditions across the Columbia Gorge, east slope of the Cascades, Lower Columbia Basin, and the Kittitas Valley. The weak shortwave stalls along the coast overnight tonight before slowly passing through the area Tuesday followed by a second shortwave on Wednesday. The first shortwave will erode the backside of the transient high pressure ridge, which will provide enough instability for isolated thunderstorm development across the east and south edges of Grant, Union, and Wallowa Counties. Enough moisture should be present in any developing storm cells to provide wetting rain amounts (>0.10"). Wednesday's system is expected to be much drier as the shortwave stays further north and passes along the Canadian border. This should only lead to an uptick in cloud cover and afternoon winds.

Flow aloft turns from the northwest to more westerly Thursday, then more from the southwest Friday into Saturday, which initiates a warming and drying trend through the latter half of the week. Below normal high temperatures will become near to above normal values on Saturday, with highs breaking into the low to mid-90s across portions of the Lower Columbia Basin on Sunday. These high temperatures, coupled with overnight lows only dipping into the mid-to upper 50s, will attribute to isolated pockets of moderate HeatRisk across the Lower Columbia Basin and northern Blue Mountain foothills Sunday and Monday. However, guidance is not in full agreement regarding how enhanced the southwest flow aloft and upper level ridge will be over the weekend. At this time, 80% of ensemble members advertise a similar or slightly cooler outcome. The 20% warmer outcome is rather substantial though, suggesting Sunday's high temperature being 5 degrees warmer than the current forecast. This may be an outlier as 27% of ensemble members were suggesting this warmer outcome just 24 hours ago. Further analysis of this trend is necessary, which may lead to more areas of moderate HeatRisk Sunday. Stay tuned. 75

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

VFR conditions currently at all sites, which will stay the course through the period. Breezy conditions at most terminals as gusts of 20-30kts will be possible. KRDM/KBDN are the only sites that will experience lower winds of 5-15 kts. Winds subside through the evening, but will stay elevated between 15-25kts through Tuesday morning. 75

FIRE WEATHER

Minimal fire weather concerns this week as early week winds will be accompanied by afternoon humidities between 35-45% with excellent overnight humidity recoveries of 70-85%. There is a slight threat for isolated thunderstorms across Grant, Union, and Wallowa counties Tuesday, but chances are minimal as coverage is confined to the south and east of OR 693, 694, and 695. Minimum humidities trend lower toward the end of the week and through the weekend, but winds should stay rather light as upper level ridging develops. 75

Preliminary Point Temps/PoPs

PDT 52 75 44 75 / 10 10 0 0 ALW 56 77 51 76 / 10 10 0 0 PSC 56 81 49 80 / 0 10 0 0 YKM 55 82 49 81 / 0 0 0 0 HRI 54 78 47 78 / 10 0 0 0 ELN 51 73 45 73 / 0 0 0 0 RDM 40 73 34 74 / 0 0 0 0 LGD 50 75 42 75 / 10 10 0 0 GCD 47 76 39 76 / 10 10 0 0 DLS 54 72 50 73 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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