textproduct: Pendleton

KEY MESSAGES

- Chances of isolated thunderstorms increase in the Eastern/Wallowa Mountains tomorrow.

- Breezy to windy conditions develop from North Central Oregon through the Kittitas Valley on Friday.

- Mostly dry set-up Thursdays onwards.

DISCUSSION

Radar and satellite shows a fairly clear and dry day across the region, with temperatures reaching the high 70s to low 80s. Dry conditions will continue through early Wednesday morning with a weak overhead ridge situated aloft. A shortwave will move onshore Wednesday morning, increasing thunderstorm chances with moist maritime air entering the area. GFS and ECMWF deterministic guidance brings dew points in the upper 40s to lower 50s across portions of the Wallowa mountains down to parts of the Oregon Blue Mountains late Wednesday morning through the late afternoon hours. This is the highest chance (10 to 20 percent chance) of isolated thunderstorm development in that region. NBM pin points highest values of CAPE at the surface (150 to 350 J/kg) in the same region by late morning/early afternoon Wednesday, along across the Kittitas Valley. Although sufficient lift is present in the Kittitas Valley, wind shear is not as strong in the Wallowas (5 to 15 knots compared to 20 to 30 knots) therefore any rain showers are unlikely to develop into an isolated storm though a 5 to 10 percent chance still remains for the Kittitas.

Overhead synoptic pattern becomes more zonal/ridge-like Thursday and Friday, leaving a mostly dry weather pattern to persist through the weekend. Another trough is expected to emerge from the Gulf of Alaska into the PacNW by Friday morning (>90 percent chance), although this next system will be mostly rain shadowed by the Cascade Mountains, secluding rain showers and light mountain snow to that region. The incoming trough will impact the lower elevation zones Friday via tight pressure gradient formation and a 850 mb 30-50 knot jet, leading to breezy to windy conditions Friday. Area of biggest concern for winds will be from North Central Oregon through the Kittitas Valley. NBM guidance advertises the chance of 45 mph or greater wind gusts through Friday as 10-30% chance in parts of North Central Oregon and the Kittitas Valley, with higher chances of 40-70% chances across the Simcoe Highlands. As of now, no wind highlights are expected but will be monitored as the event gets closer over the next few days.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

VFR conditions are forecast at all sites for the next 24 hours. Mostly clear skies today will transition to mostly cloudy to overcast skies consisting of mid/high cloud by Wednesday morning. Sustained winds of 12 kts or less are forecast today, albeit with higher gusts. Westerly winds will become breezy later Wednesday morning and afternoon. A low (10-30 percent) chance of light rain showers is forecast for all sites between Wednesday morning and afternoon.

Preliminary Point Temps/PoPs

PDT 51 78 48 76 / 0 20 10 0 ALW 55 80 54 76 / 0 20 10 0 PSC 54 83 52 81 / 0 20 10 0 YKM 56 80 48 80 / 0 30 0 0 HRI 53 81 51 79 / 0 20 0 0 ELN 53 74 46 72 / 0 50 10 0 RDM 50 74 38 75 / 0 10 0 0 LGD 47 76 45 74 / 0 30 20 0 GCD 47 77 42 76 / 0 40 10 0 DLS 63 78 54 77 / 0 10 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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