textproduct: Pendleton

KEY MESSAGES

- Isolated showers and thunderstorms in the Eastern Mountains today, with greater & more widespread chances Wednesday and Thursday.

- Breezy winds across the region develop with the passing system.

- Temperatures cool tomorrow to fall like levels and last through at least this week.

DISCUSSION

Radar and satellite depicts precip and cloud cover secluded to the eastern mountain regions with low to moderate showers approaching at/near the Joseph and Enterprise area. A slight chance (up to 15%) of a thunderstorm or two will develop with low CAPE values (100-150 J/kg) and weak wind shear values. As the shortwave continues to move through the area, PoP's will increase as we head into the early morning hours through Thursday.

Wednesday: The shortwave continues to move towards onshore with increasing south/southwestern flow that will continue moisture transportation. NBM continues to advertise a maxima area of CAPE developing near Crook and Grant counties in the early morning hours around sunrise. Highest values develop up to 100-150 J/kg with weak wind shear, so any storms are expected to pulsing and not last a long time. Weather pattern appears to be more stratiform than convective in nature due to the lack of daytime heating and it being the time of the year with convection season dying down. Isolated thunderstorm development is mostly situated across parts of the Blue and Eastern Mountains (up to 15% chances). PoP's across the entire area increase up to 70-90% by the afternoon hours, with it being mostly stratiform with an occasional thunderstorm possible near the slopes and foothills of mountains (up to a 10% chance). Breezy winds with gusts up to 20 to 30 mph is expected throughout the Columbia Basin and Kittitas Valley, especially near the Cascade Gaps with this system.

Thursday: The pattern on Thursday is similar to Wednesday wet, breezy pattern with precipitation chances continuing in the 40-70% percent range with higher values in some of the mountain regions. The oncoming shortwave continues to push at/near the coast. CAPE values continue to be unimpressive with guidance developing up to 100-150 J/kg with weak wind shear. This suggests again that any storm development will not be long lived and pulsate throughout the day (70-90% chance). The Columbia Basin could see QPF amounts up to a quarter of an inch with amounts up to .75 to 1.0 inches in the mountain regions (60-80% chance). Parts of the Cascade and Wallowa crests can see locally higher amounts of up to 1.5" (50-70% chance).

Friday and beyond: Things become uncertain going into Friday and beyond, as clusters and guidance start to diverge on strength and timing of the weather system. By Friday, about 60% of solutions keeps the low closed and continue on the wetter pattern, while the other 40% opens up the wave and bring drier conditions across the area. Models are still almost evenly split going through the rest of the weekend with 57% (Clusters 1 and 3) still showing the wetter solution, with some timing issues between clusters 1 and 3. Regardless, no significant impacts are currently expected through Sunday (70-90% chance) and we will continue to monitor this evolving system.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

VFR conditions continue through the TAF period, but confidence in staying VFR goes down as we head into tomorrow morning, as a weather system continues to push into the area. Breezy winds through most of the sites with peaks occurring sometime this afternoon into the evening hours. Rain chances of 15-30% start entering the picture at 15Z at ALW/PDT/PSC with no anticipated thunderstorms expected. We'll see the system start to impact most/all TAF sites with moderate to heavy rain starting with the 00Z TAFs, but for now we captured the tail end of the dry period with the 18Z TAFs.

Preliminary Point Temps/PoPs

PDT 48 75 45 68 / 10 50 80 40 ALW 54 76 50 69 / 10 50 90 50 PSC 56 79 50 73 / 0 30 60 30 YKM 55 75 50 70 / 0 30 50 30 HRI 55 77 50 71 / 10 40 60 30 ELN 49 71 44 66 / 10 30 60 40 RDM 43 65 40 63 / 10 80 90 40 LGD 48 73 47 66 / 30 70 90 80 GCD 48 73 46 65 / 10 60 100 70 DLS 57 72 53 69 / 0 80 90 60

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.