Area Forecast Discussion

KEY MESSAGES

- Warming and drying trend through Monday.

- Chance for mountain showers toward end of the week.

DISCUSSION

Current radar and visible satellite imagery shows dry conditions under mostly clear skies. This is in response to an upper level ridge axis centered over the Pacific Northwest. The ridge will continue to slowly track east, which enhances southwest flow aloft to allow for warmer air to advect into the region. Slightly above normal temperatures will result this afternoon as highs will reach into the upper 70s to low 80s across the Columbia Basin, Blue Mountain foothills, and Central Oregon. The warming trend persists on Sunday with highs in the mid-80s, peaking on Monday with afternoon temperatures reaching into the upper 80s across the aforementioned areas. Minimum humidities will also be on the decline during this timeframe, dropping into the mid- to upper teens across portions of Central Oregon and the John Day Basin Sunday and Monday. The trend shifts on Tuesday to cooler and more moist, which is associated with an upper level shortwave moving onshore over the central British Columbia coast. This trend will be slow and steady as high temperatures tick down 2-4 degrees each day through the remainder of the week. The improvement of humidities will lag slightly and trend slower, eventually staying in the low to mid-20s on Friday in relation to a second and more robust approaching system.

The first shortwave on Tuesday will struggle to dig into the Pacific Northwest due to the incumbent and slowly departing ridge of high pressure. Guidance strongly suggests the area staying dry as the system passes, with only 48% of ensemble members hinting at rain chances only over the John Day Highlands. The upper level ridge will rebuild slightly Wednesday and early Thursday ahead of the next system late Thursday into Friday. Guidance disagrees with the timing and strength of this system, which is expected to weaken quickly on its approach to the southern British Columbia and northern Washington coasts. Ensembles advertise light mountain showers beginning Thursday afternoon across the Cascades, with 56% of members suggesting widespread light showers Thursday night into Friday morning due to a stronger and earlier arriving system. Just 24 hours ago, it was the consensus that the system will be slower and keep showers more confined to the Cascade and Blue Mountains. The NBM is aligning more with the latter scenario of primarily dry lower elevations and 0.01-0.05" at higher elevations across our mountain zones. Due to the overall low confidence, the shifting of ensemble consensus from a slightly wetter to drier outcome over subsequent model runs is expected over the next 24 to 48 hours, with the primary outcome likely to align with light showers and minimal weather impacts. 75

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

VFR conditions to prevail through the period. Winds will be light, 12kts or less, and diurnally driven through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 49 83 50 84 / 0 0 0 0 ALW 54 84 56 85 / 0 0 0 0 PSC 52 86 53 87 / 0 0 0 0 YKM 54 84 54 85 / 0 0 0 0 HRI 51 86 53 86 / 0 0 0 0 ELN 52 80 52 81 / 0 0 0 0 RDM 43 84 45 84 / 0 0 0 0 LGD 49 83 51 85 / 0 0 0 0 GCD 49 85 50 86 / 0 0 0 0 DLS 57 88 59 87 / 0 0 0 0

PDT WATCHES / WARNINGS / ADVISORIES

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