245
FXUS66 KPDT 071020
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
320 AM PDT TUE JUL 7 2026
KEY MESSAGES
- HOT, DRY, AND WINDY CONDITIONS ENHANCE FIRE WEATHER CONCERNS.
*RED FLAG WARNINGS ACTIVE*
- HEAT PEAKS TODAY, NEAR NORMAL TEMPERATURES BY THURSDAY.
- SLIGHT CHANCE (10-20%) FOR ISOLATED THUNDERSTORMS TODAY.
DISCUSSION
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS DRY
CONDITIONS UNDER MOSTLY CLEAR SKIES. THIS IS IN RESPONSE TO A
TRANSIENT UPPER LEVEL RIDGE BUILDING BRIEFLY IN THE WAKE OF THE
DEPARTING SHORTWAVE THAT BROUGHT SOME ISOLATED THUNDERSTORMS
ACROSS CENTRAL OREGON ON MONDAY. THE PRESENT RIDGE WILL LINGER
THROUGH THE BEGINNING OF THE DAY, AHEAD OF AN APPROACHING UPPER
LEVEL TROUGH THAT WILL MOVE ONSHORE THIS AFTERNOON. AS THIS
TROUGH NEARS, A PRESSURE GRADIENT WILL DEVELOP BETWEEN THE RIDGE
AND TROUGH, INCREASING WINDS ACROSS THE LOWER COLUMBIA BASIN
AND THE KITTITAS VALLEY. THE EARLIER RIDGE OF HIGH PRESSURE WILL
KEEP SKIES CLEAR THROUGH THE EARLY AFTERNOON TO ALLOW FOR
CONDITIONS TO DRY RAPIDLY AS TEMPERATURES SOAR. AFTERNOON
HUMIDITIES AS LOW AS 13% AND WEST WINDS OF 15-25 MPH WITH GUSTS
OF UP TO 35 MPH HAVE WARRANTED THE ISSUANCE OF A RED FLAG
WARNING ACROSS THE KITTITAS VALLEY (WA690) AND THE LOWER
COLUMBIA BASIN OF WASHINGTON (WA691) AND OREGON (OR691) BETWEEN
THE HOURS OF 1 PM AND 10 PM TODAY.
THE BUILDING OF THE TRANSIENT RIDGE AND APPROACHING TROUGH, AS
MENTIONED EARLIER, WILL ALSO ENHANCE SOUTHWEST FLOW ALOFT AND
ADVECT DRIER AIR FROM THE SOUTH. THE LINGERING HIGH LEVEL CLOUDS
OVERNIGHT HAVE LEAD TO MORNING LOWS OF AROUND 60 DEGREES,
SETTING UP POTENTIALLY THE HOTTEST DAY SO FAR THIS SUMMER AS
HIGHS REACH TO AROUND 100 DEGREES ACROSS THE LOWER COLUMBIA
BASIN AND ALONG THE BLUE MOUNTAIN FOOTHILLS. THE HREF ADVERTISES
A 40-60% CHANCE OF 100 DEGREE OR GREATER HIGH TEMPERATURES
ACROSS THE TRI-CITIES AREA TODAY, WITH A 20-40% CHANCE FOR
YAKIMA, HERMISTON, AND WALLA WALLA. THIS WOULD BE THE FIRST TIME
SINCE AUGUST 24, 2025 THAT TRI-CITIES REACHED 100 DEGREES, WITH
YAKIMA AS AUGUST 25, 2025, HERMISTON AS AUGUST 30, 2025, AND
WALLA WALLA AS AUGUST 23, 2025. DUE TO THE LACK OF OVERNIGHT
RELIEF AND HIGH TEMPERATURES ABOUT 10 DEGREES ABOVE NORMAL,
WIDESPREAD MODERATE HEATRISK (2 OR 4) EXTENDS ACROSS THE LOWER
COLUMBIA BASIN, BLUE MOUNTAIN FOOTHILLS, JOHN DAY BASIN, AND THE
YAKIMA/KITTITAS VALLEYS. THIS MODERATE CATEGORY PRIMARILY
RELATES TO CONCERN FOR MEMBERS OF HEAT-SENSITIVE GROUPS, BUT IT
ALSO EXTENDS TO THE GENERAL PUBLIC WHO ARE EXPOSED TO THE SUN
FOR LONGER PERIODS OF TIME. MAKE SURE TO STAY HYDRATED AND
REDUCE TIME OR MOVE EVENTS DURING PEAK AFTERNOON HOURS.
THE EARLIER MENTIONED SYNOPTIC FEATURES WILL ALSO LEAD TO A
SLIGHT CHANCE (10-20%) OF ISOLATED THUNDERSTORMS DEVELOPING
ACROSS PORTIONS OF THE AREA. THE BEST CHANCES WILL BE ACROSS THE
BLUE MOUNTAINS, CENTRAL OREGON, JOHN DAY BASIN, AND
UNION/WALLOWA COUNTIES. HOWEVER, CANNOT RULE OUT A ROUGE CELL
DEVELOPING ACROSS THE LOWER COLUMBIA BASIN, ALBEIT LOW
PROBABILITY (5-10%). SEVERAL INGREDIENTS FOR THUNDERSTORMS WILL
BE PRESENT, INCLUDING CAPE OF 200-300 J/KG IN THE BASIN AND
700-900 J/KG ACROSS HIGHER CHANCED AREAS, LOW LEVEL SHEAR OF
20-35 KTS, AND LAPSE RATES OF 7-8C/KM. THE LIMITING FACTOR
IS A DIRECT RESULT OF THE PRESENT TRANSIENT RIDGE THROUGH THE
EARLY AFTERNOON AND THE LATE ARRIVAL OF THE TROUGH THAT WOULD
BREAK UP THE WARM, STABLE AIR OF THE RIDGE. AS A RESULT, THERE
IS TOO MUCH CONVECTIVE INHIBITION (CIN) ACROSS THE BASIN AND NOT
ENOUGH OVER CENTRAL AND EASTERN OREGON. THE LOWER CIN DOES
PROVIDE ENOUGH ATMOSPHERIC FORCINGS TO INITIATE ISOLATED
THUNDERSTORMS EARLY IN THE AFTERNOON, BUT WILL STAY RATHER WEAK
IN NATURE AS THEY INCREASE CLOUD COVER AND COOL LOWER LEVELS OF
THE ATMOSPHERE. MAIN CONCERNS ASSOCIATED WITH ANY DEVELOPING
STORM CELLS WILL BE BREEZY WINDS AND LIGHTNING. ECMWF AI
ENSEMBLES AND GFS ENSEMBLES BOTH HIGHLIGHT PRECIPITABLE WATER
AMOUNTS OF 0.7-1.0", WHICH IS 130-160% OF NORMAL - SO ANY
DEVELOP STORM CELLS SHOULD PROVIDE A WETTING RAIN (=>0.10").
TEMPERATURES BEGIN TO COOL AND NEAR NORMAL VALUES BY THURSDAY
BEHIND THE PASSING UPPER LEVEL TROUGH AND ACCOMPANYING WEST-
NORTHWEST FLOW ALOFT. ANOTHER UPPER LEVEL LOW SLIDES DOWN THE
BRITISH COLUMBIA COAST FRIDAY AS THE HIGH PRESSURE CENTER
STRENGTHENS OVER THE 4 CORNERS REGION TO BRING SOUTHWEST FLOW
BACK TO THE AREA. ECMWF AI ENSEMBLES AND THE GFS AI ENSEMBLES
BOTH SUGGEST THESE FEATURES WILL STALL AND SLOWLY DISSIPATE
THROUGH THE WEEKEND AND INTO NEXT WEEK. THIS WILL KEEP
TEMPERATURES SLIGHTLY ABOVE NORMAL AS DRY CONDITIONS PERSIST.
75
AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/
VFR CONDITIONS ACROSS ALL SITES, WHICH WILL STAY THE COURSE
THROUGH THE PERIOD. WIDESPREAD BREEZY WINDS OF 10-20KTS THIS
AFTERNOON, WITH KDLS/KPDT/KRDM/KBDN/KYKM GUSTING TO BETWEEN
20-30KTS THIS AFTERNOON AND EVENING. 75
FIRE WEATHER
A RED FLAG WARNING IS IN EFFECT BETWEEN 1 PM AND 10 PM TODAY
FOR FIRE WEATHER ZONES: WA690, WA691, AND OR691 DUE TO STRONG
WINDS AND LOW RELATIVE HUMIDITIES. WEST-NORTHWEST WINDS OF 15-25
MPH AND GUSTS UP TO 30 MPH AND HUMIDITIES AS LOW AS 13% IS
EXPECTED ACROSS THESE AREAS. CRITICAL FIRE WEATHER CONDITIONS
SHOULD MATERIALIZE FIRST ALONG THE WESTERN BOUNDARIES OF WA690
AND WA691, BEFORE INCLUDING WESTERN OR691 BY 1400 WITH CONCERNS
EXTENDING EAST THROUGH THE REMAINDER OF THE WARNING. THERE IS A
LOW, 5-10% CHANCE OF ISOLATED THUNDERSTORMS FOR THE BASIN, BUT
TIMING IS EXPECTED TOWARD THE END OF THE PERIOD - LIKELY AFTER
2000 WITH MINIMAL TO NO LIGHTNING EXPECTED.
ISOLATED FIRE WEATHER CONCERNS RETURN FOR OR690 AND WA/OR691 ON
WEDNESDAY AFTERNOON, BUT ARE CURRENTLY CONFINED TO THE EASTERN
AND NORTHERN BORDERS OF THE ZONES. AFTERNOON HUMIDITIES WILL BE
IMPROVED TO AROUND 20% WITH WINDS OF 10-20 MPH OUT OF THE WEST-
NORTHWEST. THESE ARE MARGINAL CONDITIONS AND WOULD RESULT IN
ELEVATED FIRE WEATHER CONCERNS - BUT MAY NOT REACH RED FLAG
CRITERIA. FURTHER ANALYSIS IS NECESSARY.
DUE TO THE OVERALL PATTERN LATE IN THE WEEK THAT PERSIST THROUGH
THE WEEKEND AND INTO NEXT WEEK, ELEVATED FIRE WEATHER CONCERNS
LINGER ACROSS THE COLUMBIA BASIN AND KITTITAS VALLEY. THIS IS
RELATED TO A STALLED OFFSHORE TROUGH AND INLAND HIGH PRESSURE
RIDGE THAT SLOWLY DISSIPATES THROUGH THE PERIOD. 75
PRELIMINARY POINT TEMPS/POPS
PDT 96 59 87 54 / 0 0 0 0
ALW 98 65 89 59 / 0 0 0 0
PSC 100 63 93 56 / 0 0 0 0
YKM 99 60 91 56 / 0 0 0 0
HRI 98 63 90 58 / 0 10 0 0
ELN 93 58 81 53 / 0 0 0 0
RDM 92 51 86 47 / 0 10 0 0
LGD 95 59 87 52 / 20 10 0 0
GCD 95 55 89 50 / 10 10 0 0
DLS 94 62 85 58 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 10 PM PDT THIS
EVENING FOR WAZ690-691.
OR...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 10 PM PDT THIS
EVENING FOR ORZ691.
DISCUSSION...75
AVIATION...75
FIRE WEATHER...75
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