textproduct: Pendleton

KEY MESSAGES

- Weak warm front Today

- High pressure returns Tuesday through Friday

- Likely pattern change by the weekend

DISCUSSION

A weak AR/warm front over western WA was creating warm and moist advection into central WA This Morning with numerous network obs reporting wetting rains (around one tenth of one inch) in the foothills/lower slopes of the WA Cascades. Lesser amounts (0.01 - 0.05) were observed across the Columbia basin and into se WA by early afternoon. With a stagnant pattern of high pressure returning and influencing the boundary layer, expect patchy fog to develop in some of the valleys and basins overnight. The confidence in development any one location however is low, with not a lot of support from the GFS Lamp guidance or HREF ensemble at least for this first night. Still this might be the most significant sensible weather impact over the next several days. Wednesday Night and Thursday Night should be a couple of degrees cooler, compressing the dew point depressions and favoring saturation and thus fog development.

The other risk to keep on eye on this week will, be potential for an air stagnation episode. We will definitely (100%) have sub 10 mph transport winds through the week, however the questions is the uncertainty in maintaining low (sub 1500 ft AGL) mixing heights through Thursday afternoon when the NBM brings deeper mixing, if only slightly.

The upper ridge will also act to keep the region precipitation free at least through the end of the week. Likely probabilities for precipitation (80-90%) return Saturday across the WA Cascades while still spreading lower end likely values, (55-65%) across the eastern mountains on Saturday Night through Sunday. Ensemble clusters all show this general precipitation pattern and cold air advection by Sunday as the NBM reflects this with decreasing snow level values through the latter half of the weekend.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

After a brief period of improved conditions this afternoon, the next round of fog will be developing this evening. MVFR to IFR with pockets of LIFR conditions will be possible after 03z for Washington terminals KPSC, KYKM, and KALW. The onset for the next round of fog is favored to be after 12z Friday for Oregon terminals KPDT and KDLS. As fog dissipates after 21z on Friday, building high pressure will bring a return of widespread VFR conditions.

Central Oregon terminals (KRDM and KBDN) are expected to remain VFR through the TAF period.Branham/76

Preliminary Point Temps/PoPs

PDT 35 50 32 50 / 10 0 0 0 ALW 38 49 36 51 / 20 0 0 0 PSC 33 49 34 49 / 10 0 0 0 YKM 33 49 35 50 / 10 0 0 0 HRI 33 50 34 49 / 10 0 0 0 ELN 33 44 33 45 / 30 0 0 0 RDM 29 58 28 59 / 0 0 0 0 LGD 34 54 35 55 / 10 0 0 0 GCD 32 57 33 58 / 0 0 0 0 DLS 38 52 37 52 / 10 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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