textproduct: Pendleton

KEY MESSAGES

- Mountain showers, isolated mountain thunderstorms, and breezy to gusty low elevation winds Today

DISCUSSION

A Pacific NW trough is driving a series of sensible weather impacts for the region including thunderstorm across the Cascades crest, increasingly windy conditions areawide This afternoon and a return to more normal temperatures for early May over the Inland Northwest. Numerous orographically forced thunderstorm have worked over the low CAPE environment along the Oregon cascade crest. Still HREF lightning probabilities show expansion after about 13-15 z across the Washington Cascade crest onto the eastern slopes and the Yakima/Kittitas valleys posing a lighting risk though the morning as colder air aloft spreads eastward. Also momentum transfer and a strong surface pressure gradient will cause strong westerly winds across the entire area resulting in the wind advisories and high wind warnings already posted for most of the non mountain forecast zones through midnight.

A more zonal flow aloft takes shape on the synoptic scale for days 2-4 before the LREF (ensembles) show another chunk of energy buckling the flow creating a mean 500 mb trough across the Inland NW/northern Great Basin regions where the largest differences are between clusters 2 and 4 (warmer vs colder/more amplified for our region). These differences seemingly have little impact on the sensible weather as forecast highs at PDT only vary by about 4 degrees between the 25th and 75th percentiles for Day5 (Sunday) highs. More meaningful differences (uncertainty) start showing up by Day 6 Monday, especially between clusters 2 and 3 (NW flow drier vs colder trough aloft and showery, tsra pattern, and the drier solution only represents about 18% of the ensemble members. Additionally clusters 2 and 4 represents about 45% of the ensembles that offer wetting rain to parts or much of the eastern mountains.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

VFR cloud bases (3-7 kft AGL) in showers will be found across the area Today with windy conditions. Winds will be strong enough to potentially create blowing dust in the basin, and valleys, which could impact MVFR vsbys in YKM/DLS/PDT/ALW. Look for winds gust commonly above 40 knots Today and lingering through the late evening, with only BDN and RDM having lower winds gusting less than 30 knots.

Preliminary Point Temps/PoPs

PDT 64 44 68 43 / 80 10 0 0 ALW 65 48 68 47 / 90 20 0 0 PSC 70 48 73 45 / 90 10 0 0 YKM 68 42 72 40 / 90 0 0 0 HRI 67 47 71 45 / 80 10 0 0 ELN 61 39 64 37 / 100 10 0 0 RDM 61 31 71 34 / 50 0 0 0 LGD 63 39 68 39 / 80 10 0 0 GCD 64 35 72 37 / 60 0 0 0 DLS 66 48 70 46 / 50 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 11 PM PDT this evening for WAZ024. Wind Advisory until 11 PM PDT this evening for WAZ026>029. High Wind Warning until 11 PM PDT this evening for WAZ521. OR...Wind Advisory until 11 PM PDT this evening for ORZ041. Wind Advisory until 11 PM PDT this evening for ORZ044-510. High Wind Warning until 11 PM PDT this evening for ORZ507-508.