textproduct: Pendleton

KEY MESSAGES

- High pressure through the week will keep the area dry and bring fog

- An incoming system over the weekend will bring mountain and low elevation precipitation

DISCUSSION

Current satellite shows mid level clouds moving across the region. Current webcams show many areas to be experiencing patchy fog with some areas having VIS to below 1/4 mile. This will be the case through much of the week as the high pressure settles overhead.

Models are in firm agreement with the high pressure ridge settling in over the region through Friday. This will bring increased chances for fog to develop overnight each night. Looking at the HREF raw ensembles, there is a 50-70% probability of the Basin, portions of Kittitas/Yakima Valleys and along the foothills of the Blues that will see VIS drop to below 3 miles through the evening. There are ground observations showing isolated locations already seeing VIS as low as 1/4 mile with the exception of portions of N. Central OR where there is widespread areas of dense fog. The fog is expected to linger through much of the morning before dissipating after noon. This will be the name of the game over the next few mornings with HREF and NBM ensembles showing 60-70% probabilities of the Basin and portions of the Blues seeing VIS of 3 miles or lower Thursday and Friday as well. NBM shows mixing heights to be mostly reaching 1000-2000AGL across much of the region, so the chances of air stagnation are low (20-30%) with the exception of central OR who has an air stagnation advisory out through Thursday morning. Otherwise, dry conditions will remain through Friday night into Saturday morning.

Models are in decent agreement with the next incoming system due in over the weekend. Clusters show the biggest difference will be with timing and or positioning of the next system. Regardless, all models and ensembles show the system to bring in precipitation across the region with highest amounts along the Cascades and the eastern mountains. Saturday will see perception mainly along the Cascades with NBM ensembles showing 40-60% 4 hour probabilities of 0.05 inches of accumulations. By Sunday, models show the precipitation to become more widespread with accumulations of up to 0.05 through the lower elevations to be 40-50% probabilities and 50-60% for the Blues. Storm total accumulations of near 0.5 inches along the Cascades is 70-80% and 50-60% for the Blues with 40-60% probabilities of 0.15 for the lower elevations and 50% for between 0.05-0.10 inches for the Basin and central OR. As the system moves in, snow levels will steadily decrease to near 5000 feet by the weekends end allowing for some of the precipitation to fall as snow above 5000ft by Sunday night.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

MVFR or lower conditions to prevail at most sites through the period. Low stratus has developed across the Columbia Basin and adjacent valleys/foothills this morning, and is expected to persist through the period (confidence 60-85%). CIG heights will mainly be less than 3kft at impacted sites, with heights fluctuating throughout the period. As for vsby, site PDT will continue to see IFR vsby through the morning, improving to VFR this afternoon; site PSC will see improvement to VFR by noon. Sites RDM/BDN will see VFR conditions through this evening, however there is growing confidence (40-65%) that site RDM will see stratus and fog develop by around 12Z, with low confidence (20-25%) in earlier/later development. Confidence was too low (<20%) to include mention of stratus/fog at site BDN. Winds will be light, 12kts or less, through the period. Lawhorn/82

Preliminary Point Temps/PoPs

PDT 33 47 33 51 / 0 0 0 0 ALW 36 47 36 50 / 0 0 0 0 PSC 34 48 34 50 / 0 0 0 0 YKM 33 50 33 50 / 0 0 0 0 HRI 34 48 33 50 / 0 0 0 0 ELN 31 46 31 47 / 0 0 0 0 RDM 28 57 26 58 / 0 0 0 0 LGD 37 57 36 57 / 0 0 0 0 GCD 34 59 33 59 / 0 0 0 0 DLS 36 50 36 52 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...None. OR...Air Quality Alert until 10 AM PST Thursday for ORZ506-509.