textproduct: Pendleton

KEY MESSAGES

1. Mountain showers and high elevation snow

2. New pattern will bring slightly below seasonal temperatures

3. Widespread chances of precipitation at the start of the week

DISCUSSION

Current satellite is showing clouds moving across the region. Radar shows a band of moisture is also moving across the Cascades with ground observations at or above 5400 feet seeing snowfall. Temperatures through the pass are marginal in the low to mid 30s, but expecting some accumulation along the Chinook Pass through the remainder of the day before the system moves east and dissipated. Otherwise, rain will be the primary form of precipitation below 5400 feet.

The change in the synoptic pattern will lead to below seasonal average temperatures continuing with the coolest day being tomorrow (Monday). Deterministic guidance models show an upper level low off the coast of the PacNW and a rain band along the leading edge which is causing some rain/snow along the Cascades. Models are in good agreement with the initial low making its way fully onshore by Monday afternoon. This will bring with it below seasonal average temperatures with in house calculations showing nearly 5-10 degrees below normal across central OR, eastern mountains and the foothills of the Blues while the Gorge Basin and adjacent valleys will see temperatures 1-5 degrees below seasonal normal. Monday HREF raw ensembles show 70-80% chances of the Basin seeing mid to upper 50s while the remainder of the region will see temperatures in the mid 40s. Temperatures will steadily trend downward through the week with the coolest day being Friday.

Not only will this upper level low bring cooler temperatures, but models are also showing increased chances of precipitation. Current radar shows a precipitation band along the northern Cascades of WA. The rain will continue to spread across the region through Monday becoming widespread between 11 AM and 5 PM. Looking at the HREF raw ensembles for the 24 hour period, the ensembles show a 60-80% chance the eastern mountains, Blues, foothills and the eastern slopes of the Cascades will see near 0.05 inches of rain with higher peaks above 5400 feet seeing near 0.5 inches of snow. The remaining locations will see 0.01-0.04 inches of rain. As the low continues to move to the east, clusters and deterministic models begin to diverge. NBM shows rain showers continuing on Wednesday while the variance between the models differ in timing and precipitation amounts.

After Wednesday the models begin to diverge slightly with the trajectory of the next upper level low. Clusters show a position/timing variance. Timing is mostly linked to the incoming QPF with the EURO brining in precipitation as early as Wednesday morning across the region while the GFS has the precipitation locked in along the Cascades. Regardless of the timing of the QPF, precipitation is expected to continue through the week with the potential for snow levels to drop below 4000 feet by Friday.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Low pressure will spread rain across RDM/DLS/BDN over the next few hours, and reaching farther east terminals at PDT/ALW by around 18z. Ceilings are not expected to get into the IFR area, as HRRR models soundings show cigs around 4-5 kFT AGL. Winds mostly from a southwest trajectory and under 10 knots with downslope gusts from 15 to 20 mph possible at BDN/RDM late Monday morning into the afternoon.

Preliminary Point Temps/PoPs

PDT 33 53 37 54 / 0 40 40 40 ALW 39 54 42 54 / 0 50 50 50 PSC 36 57 39 59 / 10 10 10 10 YKM 38 56 35 57 / 20 20 10 0 HRI 34 56 40 57 / 0 30 20 20 ELN 32 53 31 53 / 30 40 10 0 RDM 31 47 32 48 / 40 50 20 30 LGD 39 54 36 52 / 0 90 70 70 GCD 35 50 34 49 / 0 70 40 50 DLS 41 58 42 59 / 40 70 50 20

PDT WATCHES/WARNINGS/ADVISORIES

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