textproduct: Pendleton

KEY MESSAGES

- Isolated thunderstorm chances today.

- Warmer and drier trend through the weekend.

- Cooler through workweek, showers possible late in the week.

DISCUSSION

Current radar and visible satellite imagery shows light to moderate returns and building clouds over Wallowa, southern Union, and eastern Grant counties. This is in response to a slowly departing upper level low pressure system moving into southern Idaho this evening as an upper level ridge builds in its wake. The incoming high pressure is keeping skies clear across the Columbia Basin and Central Oregon, but also attributes to a potential for thunderstorms developing along the boundary between the departing low and incoming ridge. Towering cumulus clouds are currently being observed along this boundary, and is expected to lead to isolated thunderstorms into this evening across Wallowa, Union, and Grant counties. Both the HREF and REFS align with thunderstorm potential extending until 8PM as CAPE values peak between 200-400 J/kg before 4PM. The main concerns in and around any storm cells will include frequent lightning, small hail, and breezy and erratic outflow winds. Any storms that develop should be rather wet, as both the AI ECWMF and GFS ensembles showcase precipitable water amounts of 0.6-0.8" which is 120-140% of normal. Rain amounts within storms may reach to near 0.20", as little to no rain is expected outside of rain cores.

The upper level ridge continues to build and slowly shift east through the weekend, keeping skies sunny, conditions dry, and temperature warming as upper level flow enhances out of the west-southwest. High temperatures will peak Sunday and Monday, reaching into the mid-80s across the Columbia Basin and Central Oregon. Afternoon humidities will also dive into the mid-to upper teens across Central Oregon and the John Day Basin Sunday and persist through the week.

Guidance struggles with agreement Tuesday onward associated with a passing upper level shortwave moving across south-central British Columbia ahead of a stronger system that slowly drops along the British Columbia coast mid-to late in the week. The initial shortwave is expected to be weak, and merely advect a slightly cooler airmass into the region. 47% of ensemble members bring light showers across the Central Washington Cascades, with 26% of members extending light rain into higher terrain across the northern Blue Mountains. The main consensus is that mountains are to stay dry, but with cooler temperatures. The second system is plagued with timing concerns, with 59% of ensemble members advertising a slower system that brings moisture along the Cascades late Thursday before slowly extending along the east slopes and into the Columbia Basin through Friday afternoon. The slower scenario does allow for additional moisture and higher overall rain amounts Friday and Saturday. 75

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

VFR conditions will prevail through the TAF period. Overall, expect mostly clear skies and light winds. Elevated winds at DLS late this afternoon are forecast to gradually decrease to be light through this evening. The shower and storm activity currently concentrated to our southeast and east (over the Blue Mountains) is not expected to pose a risk to the PDT, PSC, and ALW terminals. This activity is forecast to dwindle through the night, with little to no showers/storms by Saturday morning.

Preliminary Point Temps/PoPs

PDT 47 78 48 81 / 0 0 0 0 ALW 53 78 53 82 / 0 0 0 0 PSC 51 82 51 84 / 0 0 0 0 YKM 52 81 52 82 / 0 0 0 0 HRI 51 81 50 83 / 0 0 0 0 ELN 50 77 51 78 / 0 0 0 0 RDM 39 78 41 82 / 0 0 0 0 LGD 47 79 48 82 / 0 0 0 0 GCD 46 79 49 85 / 0 0 0 0 DLS 54 85 56 87 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

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