textproduct: Pendleton

KEY MESSAGES

- Near-freezing overnight/Sunday morning in the Columbia Basin and along the Blue Mountain foothills

- Slight chance of showers each day through Tuesday, mainly over the mountains

- Gradually warming to near or above normal through next week

DISCUSSION

Water vapor imagery shows a couple upper-level lows over or near the CONUS this afternoon. The most impressive low is a deep closed low over the Canadian Prairies and northern Great Plains. Meanwhile, a weaker low is located just offshore of central California. A shortwave trough embedded within northerly flow aloft on the west side of the aforementioned deep closed low is sliding south over the Pacific Northwest. Under the shortwave, clear to partly skies are present across the lower elevations, while the mountains have seen scattered to numerous cumulus develop. A few isolated showers are evident within the cumulus field, but not anticipating any robust convection today given the lack of any deep CAPE profiles.

Tonight into Sunday morning, there is a low-medium probability of observing freezing temperatures again across the Columbia Basin and along the Blue Mountain foothills. The best chances (30-60 percent) lie in the Pendleton area with lower (20-40 percent) chances extending outward across the rest of the aforementioned region including the Yakima and Kittitas valleys. Given that forecast cloud cover from CAMs is in the FEW-BKN range, confidence is a bit lower in a widespread freeze compared to this morning when mostly clear to clear skies were present, and have held off on issuing any freeze headlines. Have included a mention of frost in the forecast for areas with temperatures near or below freezing, though.

Looking ahead, ensemble NWP guidance is in agreement that additional weak shortwaves will dive southward through Sunday, providing additional weak forcing for showers, mainly over the mountains with lower chances (10 percent or less) extending across the lowlands. Flow aloft looks to turn more northwesterly by Monday and Tuesday, with a couple shortwaves and weak diurnally driven instability (CAPE of 500 J/kg or less) providing impetus for isolated to scattered showers, mainly over the mountains.

Wednesday through the remainder of the week, ensemble cluster analysis shows 500-hPa heights rising to near or above normal over the Pacific Northwest and vicinity, with roughly 80-90 percent of members placing dry conditions region-wide. Roughly half of members do show hints of a trough or closed low moving over southern Canada or the Northern Tier late Thursday or Friday, but confidence in it providing precipitation to the forecast area is low (10-20 percent). 86

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

VFR conditions currently at all sites, which will stay the course through the period. Winds will stay light and below 10 kts, with broken ceilings of 25kft this evening, dropping to 10-15kft for KDLS/KYKM/KRDM/KBDN Sunday afternoon. 75

Preliminary Point Temps/PoPs

PDT 33 62 39 64 / 0 0 10 10 ALW 38 62 42 65 / 0 10 10 20 PSC 36 67 40 70 / 0 0 10 0 YKM 37 67 38 69 / 0 10 10 0 HRI 34 66 40 68 / 0 0 0 0 ELN 33 62 36 62 / 0 10 10 10 RDM 26 59 29 61 / 0 0 0 0 LGD 30 57 33 59 / 0 10 10 40 GCD 28 56 32 58 / 0 10 10 40 DLS 40 69 43 67 / 0 10 10 10

PDT WATCHES/WARNINGS/ADVISORIES

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