textproduct: Pendleton

KEY MESSAGES

- Next chances for rain confined mainly to the mountains mid- week, late Tuesday/Tuesday night and late Thursday/Thursday night.

- Slight chance (10-20%) of thunderstorms over the Blue Mountains region Thursday and Friday.

DISCUSSION

Water vapor imagery shows an upper-level low exiting to the northeast leaving a moist northwesterly flow aloft. Upslope precipitation will continue to taper off over the Blue Mountains early this morning, with mostly dry conditions already in place elsewhere. Recent rainfall coupled with clearing skies and light wind has resulted in patchy dense fog formation, most notable in the Yakima Valley. Have issued a Special Weather Statement for the fog, but given its patchy coverage and intermittent presence at ASOS locations, have opted to forgo an advisory. Elsewhere, upslope stratus has induced low visibilities along OR 204 in the vicinity of the crest of the Blue Mountains.

Below-normal temperatures are forecast today as northwesterly flow aloft continues. Flow aloft is expected to transition to southwesterly by Tuesday afternoon and Tuesday night as a shortwave diving south along the Pacific coast cuts off over the Pacific Northwest. This low will provide our next chances (15-40%) of precipitation Tuesday afternoon and Tuesday night over the mountains, though confidence is just medium (50-60%) in the track of the low based on clustering of current 00Z ensemble solutions so anticipating some fluctuations in the PoP forecast until confidence increases in the track of the low. Roughly 75% of solutions cut the low off over southwest Oregon and northwest California, while the remaining take it farther east over eastern Oregon. A subset of members take the low far enough offshore of northwest California to keep the forecast area dry. Ensemble solutions keep the low in place through Wednesday before taking it inland on Thursday. Quite a bit of ensemble spread is evident by Thursday afternoon, with roughly 55% of members showing a closed low ejecting northeast over southern to eastern Oregon. The remaining members show the low transitioning to a weaker open-wave trough. The former scenario would result in better chances of convection over the Blue Mountains and central Oregon, while the latter would be drier. Currently have a slight chance (10-20%) of thunderstorms for the Blue Mountains on Thursday. Ensemble solutions remain split through Friday, though all clusters take the low farther inland. Chances of precipitation persist in 57% of members, and there is a low (10-15%) chance of thunderstorms Friday afternoon for the Blue Mountains should the aforementioned scenario materialize.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Breezy southwesterly to westerly winds will linger this morning at PDT/ALW; lighter winds are expected elsewhere. Stratus over DLS/PDT/ALW is forecast to remain VFR, though lighter winds and ample recent precipitation have enabled fog formation in the Yakima Valley. Anticipating YKM will continue to bounce between VFR and VLIFR as patchy dense fog sloshes around the valley early this morning; VFR conditions should return by mid- morning as fog lifts (80% confidence). There is low (30%) confidence in fog formation at RDM this morning.

Preliminary Point Temps/PoPs

PDT 70 44 67 47 / 0 0 0 20 ALW 70 49 69 50 / 0 0 0 10 PSC 74 45 70 46 / 0 0 0 10 YKM 69 47 66 47 / 0 0 10 10 HRI 73 44 70 46 / 0 0 0 10 ELN 65 43 61 43 / 0 0 30 10 RDM 71 36 70 38 / 0 0 0 30 LGD 69 41 72 44 / 0 0 0 20 GCD 70 42 75 45 / 0 0 0 30 DLS 74 50 73 53 / 0 0 0 10

PDT WATCHES/WARNINGS/ADVISORIES

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