textproduct: Pendleton

KEY MESSAGES

- Widespread Moderate (Level 2 of 4) HeatRisk Tuesday

- Slight chance to chance (15-35%) of thunderstorms today for central Oregon, then slight chance (10-20%) of thunderstorms for central Oregon and the Blue Mountains Tuesday afternoon and evening

- Breezy to locally windy conditions coupled with low relative humidity for the Columbia Basin and Kittitas Valley Tuesday. Red Flag Warnings in effect 1 PM to 10 PM.

DISCUSSION

Satellite imagery shows a compact mid-level low churning over the Blue Mountains, tracking slowly northeast. Widespread partly cloudy to overcast conditions associated with the low are present from central Oregon through the Blue Mountains, though partial clearing has been noted in central Oregon as the low departs to the northeast. Over the Oregon Cascade crest, a CU field has developed, and isolated thunderstorms have formed, mainly south of Deschutes County. Ample surface-based moisture (dew points in the upper 40s to mid-50s) coupled with sufficient instability (surface-based CAPE of 500-1000 J/kg per 12Z HREF guidance) will facilitate additional shower and thunderstorm develop with widespread 25-35% chances of thunderstorms for the central Oregon Cascades and central Oregon. Highest chances are for fire weather zones OR705 and the southern half of OR700. Storms are expected to be predominantly wet due to their slow-moving nature, so no Red Flag Warnings have been issued. Storms will be capable of producing frequent cloud-to-ground lightning, small hail, and gusty outflow winds up to 55 mph. Farther east, partly to mostly cloudy skies have inhibited surface heating and instability, but forcing from the aforementioned closed low could still provide enough lift to generate an isolated thunderstorm or two across the Blue Mountains (10-20% chance).

Clearing skies are forecast Tuesday, so ample daytime heating is expected (90% confidence) across the majority of the region. Widespread Moderate (level 2 of 4) HeatRisk is forecast for the lower elevations. There is a low (10-35%) chance of afternoon high temperatures reaching or exceeding 100 degrees for the lower Columbia Basin and adjoining lower elevations.

Tuesday afternoon and evening, another slight chance (10-20%) of thunderstorms is forecast for the region stretching from central Oregon through the Blue Mountains. There are low (5-10%) chances for the Blue Mountain foothills and lower Columbia Basin. Confidence in exact location of thunderstorms remains low, partly due to the late afternoon and evening arrival of upper-level forcing from an incoming shortwave trough that is expected to pass over southern Canada.

Breezy to locally windy westerly to northwesterly winds coupled with low relative humidity will likely (70-90% confidence) result in areas of Red Flag conditions across the lower Columbia Basin of Oregon and Washington as well as through the Kittitas Valley Tuesday afternoon and evening. Red Flag Warnings are in effect from 1 PM to 10 PM Tuesday for OR691, WA691, and WA690. Confidence in reaching Red Flag criteria elsewhere is low (30% or less).

A quasi-zonal mid-level pattern is advertised by ensemble guidance through late week. This should keep periods of breezy to locally windy conditions and low relative humidity present, but confidence in overlap of wind and relative humidity is currently too low (50% or less) to have any additional watches or warnings in effect.

Ensemble clusters suggest a high probability (70-90%) of an amplifying mid-level pattern by the weekend, with troughing offshore and a building high over the Four Corners and/or Western CONUS.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

VFR conditions prevail with general light and variable winds, with the exception of RDM experiencing some slight breezy conditions. Otherwise, no CIG or VIS issues expected.

Preliminary Point Temps/PoPs

PDT 57 95 58 86 / 0 0 10 0 ALW 62 97 64 88 / 0 0 10 0 PSC 58 99 61 91 / 0 0 10 0 YKM 61 98 59 89 / 0 0 0 0 HRI 59 98 62 89 / 0 0 20 0 ELN 59 92 56 80 / 0 0 0 0 RDM 53 91 50 85 / 20 10 10 0 LGD 56 94 58 85 / 0 20 10 0 GCD 53 94 54 87 / 10 10 10 0 DLS 64 93 61 84 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning from 1 PM to 10 PM PDT Tuesday for WAZ690-691. OR...Red Flag Warning from 1 PM to 10 PM PDT Tuesday for ORZ691.