textproduct: Pendleton

DISCUSSION

Relatively unorganized showers will continue this afternoon through Thursday night as a broad area of low pressure churns just offshore. While some light mountain snow (generally one inch or less) is forecast, not anticipating anything worth an advisory.

Windy conditions are beginning to taper off across northeast Oregon and southeast Washington, so have allowed the High Wind Warnings to expire on schedule at 2 PM. Late tonight into early Thursday afternoon, expecting (80 percent confidence) another round of south to southeast winds of 20-35 mph with gusts of 30-45 mph along the slopes and base of the northern Blue Mountains. That said, have held off on issuing any wind highlights as an HREF-advertised 850-mb jet of 30-45 kts is marginally supportive of an advisory and NBM probabilities suggest a 50 percent chance or less of 45-mph wind gusts. Given the synoptic pattern, areas most prone to downslope winds such as along I-84 in the vicinity of Cabbage Hill will most likely (80 percent confidence) exceed 45 mph, but thinking areal coverage is too limited to justify an advisory. For reference, the HREF was forecasting a 50-70 kt 850-mb jet this morning, and this translated into maximum wind gusts of 60-80 mph along the base and slopes of the northern Blue Mountains.

Some patchy fog is forecast this evening and tonight across the forecast area, but confidence in coverage is too low to issue any headlines for it.

Looking ahead, an upper-level shortwave trough and attendant cold front will facilitate more organized precipitation Friday into Saturday. NBM probabilities suggest a 40-70 percent chance of advisory-level snowfall for the 24-hour period of 10 AM Friday to 10 AM Saturday across the northern Blue Mountains and OR/WA Cascades. Moreover, breezy to windy westerly winds are expected to accompany the system Friday and Friday night. NBM probabilities paint a 40-80% chance of advisory-level wind gusts (45 mph or greater) across the Columbia Plateau during the aforementioned period. Have held off on issuing any highlights for winter weather or wind given the long lead time.

By late Saturday, confidence is high (90 percent) that an upper- level ridge of high pressure will park itself over the Pacific Northwest, ushering in dry conditions areawide. Will we finally see a widespread cloudy cold pool event (stratus/fog in the Columbia Basin/Plateau)? It's too early to tell for sure, but have added a mention of patchy fog in the forecast.

AVIATION...00Z TAFs

As this system gradually moves out of our forecast area, KDLS/KPDT/KALW will be VFR until tonight with low clouds lingering for these sites thus making them MVFR or lower. Fog may return for KPDT/KALW tonight, possibly dropping VSBYs to 1/2SM or below (40-50% confidence). KPDT might see VSBY improving slowly Thursday morning hours, but will monitor for any fog development. KALW may see fog clear out around Thursday late morning as VSBY increase to 2SM or higher. The remaining sites will be VFR through this TAF period with KYKM having a 30% probability for light rain Thursday early morning. Winds have decreased from earlier and will be at 10kts or less for the rest of today and Thursday. Feaster/97

PRELIMINARY POINT TEMPS/POPS

PDT 33 51 35 49 / 20 30 30 60 ALW 36 51 37 49 / 30 30 50 80 PSC 31 45 32 49 / 10 30 40 50 YKM 28 42 30 43 / 10 50 30 30 HRI 32 47 32 48 / 10 30 40 50 ELN 25 37 26 37 / 10 70 40 50 RDM 28 50 28 45 / 20 20 20 40 LGD 37 49 36 45 / 30 40 50 80 GCD 35 50 35 44 / 20 40 50 80 DLS 35 45 36 46 / 20 60 50 70

PDT WATCHES/WARNINGS/ADVISORIES

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