019
FXUS66 KPQR 090918
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
217 AM PDT TUE SEP 9 2025
SYNOPSIS
AREAS THAT OBSERVED SHOWERS AND THUNDERSTORMS YESTERDAY
ARE MOST LIKELY TO SEE MORE SHOWERS AND STORMS TODAY, WHILE LOCATIONS
THAT STAYED DRY YESTERDAY WILL MOST LIKELY STAY DRY. CHANCES FOR
SHOWERS AND THUNDERSTORMS CONTINUE ON WEDNESDAY, MAINLY OVER THE
CASCADES. CONDITIONS GRADUALLY TREND DRIER LATE IN THE WEEK WITH
SLIGHTLY WARMER TEMPERATURES. CONFIDENCE HAS DECREASED FOR WIDESPREAD
RAIN LATE SATURDAY INTO SUNDAY WITH A UPPER LEVEL TROUGH MOVING
INLAND, BUT REMAINS A DECENT POSSIBILITY (50-60% CHANCE).
SHORT TERM...NOW THROUGH THURSDAY NIGHT
CONDITIONS TODAY SHOULD BE
FAIRLY SIMILAR TO WHAT WAS OBSERVED YESTERDAY FOR MOST LOCATIONS,
WITH SHOWERS AND THUNDERSTORMS FOCUSING OVER THE SOUTHERN/CENTRAL
WILLAMETTE VALLEY AND OREGON CASCADES/FOOTHILLS. MEANWHILE, SOUTHWEST
WA AND THE OREGON COAST WILL MOST LIKELY REMAIN DRY. THE LATEST
HREF/REFS GUIDANCE SUGGESTS SHOWERS AND THUNDERSTORMS MAY MISS MOST
OF THE PORTLAND METRO AS WELL, HOWEVER AT LEAST SOME SHOWERS AND
STORMS CANNOT BE RULED OUT (40-50% CHANCE SHOWERS, 10-20% CHANCE
THUNDER). STRONGER SHOWERS AND STORMS WILL HAVE THE POTENTIAL TO
PRODUCE LOCALLY HEAVY RAIN. SIMILAR TO YESTERDAY, RAIN AMOUNTS WILL
BE HIGHLY VARIABLE ACROSS THE AREA DUE TO THE SHOWERY NATURE OF
PRECIPITATION. SOME LOCATIONS WILL SEE NO RAIN AT ALL, WHILE OTHER
LOCATIONS SEE OVER HALF AN INCH. THE OREGON CASCADES HAVE THE HIGHEST
CHANCE OF SEEING RAIN AMOUNTS OVER 0.5 INCHES BETWEEN 5AM WEDNESDAY
AND 5AM THURSDAY (15-20% CHANCE). PROBABILITIES RANGE BETWEEN 0-5%
FOR THE REST OF NORTHWEST OR AND SOUTHWEST WA. WHILE DEBRIS FLOWS
CANNOT BE COMPLETELY RULED OUT OVER THE EMIGRANT FIRE BURNING BETWEEN
OAKRIDGE AND TOKETEE FALLS, HOURLY RAIN RATES OVER 0.75 IN/HR WOULD
LIKELY NEED TO MATERIALIZE FOR THIS TO BE A CONCERN. AS OF RIGHT NOW,
THE HREF IS ONLY SHOWING A 10% CHANCE FOR HOURLY RAIN RATES OF THIS
MAGNITUDE TO OCCUR OVER OR NEAR THE BURN AREA BETWEEN 1-7PM TODAY.
THESE PROBABILITIES AND OVERALL CONFIDENCE IN PEAK RAIN RATES ARE NOT
HIGH ENOUGH TO JUSTIFY THE ISSUANCE OF A FLASH FLOOD WATCH FOR DEBRIS
FLOWS AT THIS TIME, HOWEVER THE CHANCE IS CLEARLY ABOVE 0% AND WORTH
MENTIONING.
HI-RES MODEL GUIDANCE SUGGESTS LINGERING CONVECTION WILL DISSIPATE
BETWEEN 7-11PM TODAY, BEFORE CHANCES FOR SHOWERS AND THUNDERSTORMS
INCREASE AGAIN WEDNESDAY MORNING INTO THE AFTERNOON FOR THE
CASCADES/FOOTHILLS, COLUMBIA RIVER GORGE, UPPER HOOD RIVER VALLEY AND
EASTERN PORTIONS OF THE PORTLAND/VANCOUVER METRO (30-60% CHANCE,
HIGHEST IN THE CASCADES). THIS TEMPORARY INCREASE IN PRECIPITATION
CHANCES IS IN RESPONSE TO WRAP-AROUND MOISTURE ON THE BACKSIDE OF A
CLOSED UPPER LEVEL LOW, WHICH LOOKS TO BE CENTERED OVER NORTHERN
CALIFORNIA AND NORTHWEST NEVADA AT THAT TIME. ON THURSDAY, MODELS
SUGGEST THIS LOW WILL PROGRESS EASTWARD INTO CENTRAL/EASTERN OREGON,
NORTHERN NEVADA AND SOUTHWEST IDAHO. THIS WILL MAINTAIN CHANCES FOR
SHOWERS WEDNESDAY NIGHT INTO THURSDAY, MAINLY OVER THE CASCADES.
CONDITIONS SHOULD DRY OUT FOR ALL LOCATIONS BY THURSDAY NIGHT AS A
SHORTWAVE RIDGE OVER THE COASTAL WATERS BEGINS TO PROGRESS EASTWARD
TOWARDS THE COAST. -TK
LONG TERM...FRIDAY THROUGH MONDAY NIGHT
FRIDAY AND SATURDAY ARE
SHAPING UP TO BE DRY WITH SLIGHTLY WARMER TEMPERATURES AND A GOOD
DEAL OF SUNSHINE DURING THE AFTERNOON HOURS. THIS PATTERN CHANGE WILL
BE IN RESPONSE TO A SHORTWAVE RIDGE THAT IS SET TO MOVE OVER THE AREA
FRIDAY INTO SATURDAY. EXPECT HIGH TEMPERATURES BETWEEN 75-80 DEGREES
OVER INLAND VALLEYS BOTH DAYS, AND HIGHS IN THE 60S AT THE COAST. IF
ENOUGH SUNSHINE OCCURS, HIGHS ABOVE 80 DEGREES WILL BE POSSIBLE,
ESPECIALLY ON SATURDAY WHEN NBM PROBABILITIES FOR HIGHS ABOVE 80
DEGREES RANGE BETWEEN 30-50% FOR INLAND VALLEYS. PROBABILITIES FOR
HIGHS ABOVE 85 DEGREES ARE AROUND 1%, SUGGESTING TEMPS IN THE LOWER
80S WOULD BE THE WARMEST POSSIBLE OUTCOME.
CONFIDENCE IN FORECAST TEMPERATURES, CLOUD COVER AND RAIN CHANCES
DECREASE SATURDAY NIGHT INTO SUNDAY. IN FACT, CONFIDENCE FOR
WIDESPREAD RAIN THIS WEEKEND HAS LOWERED COMPARED TO LAST NIGHT'S
FORECAST, AS OVERALL MODEL SPREAD HAS INCREASED WITH MORE ENSEMBLE
GUIDANCE NOW SHOWING VERY LITTLE TO NO RAIN AT ALL. NBM 24-HR POPS
BETWEEN 5PM SATURDAY AND 5PM SUNDAY HAVE DECREASED FROM 70-80% TO
50-60%, EXCEPT AROUND 75% IN THE OREGON CASCADES. IT APPEARS THE
DECREASE IN RAIN CHANCES AND FORECAST RAIN AMOUNTS IS DUE TO THE
EVOLUTION OF AN UPPER LEVEL TROUGH THAT WILL BE MOVING INLAND
THIS WEEKEND, AS MORE MODEL GUIDANCE NOW SUGGESTS THIS TROUGH WILL
SPLIT AND FORM A CLOSED UPPER LEVEL LOW THAT HEADS TOWARDS NORTHERN
CA, BRINGING DRIER WEATHER FOR NORTHWEST OR AND SOUTHWEST WA.
NEVERTHELESS, WIDESPREAD RAIN STILL REMAINS A GOOD POSSIBILITY GIVEN
HOW MANY ENSEMBLE MEMBERS DO NOT SHOW THIS TROUGH SPLITTING AND
DEPICT RAIN FURTHER NORTH. CURRENTLY, THE PROBABILITY FOR 0.25" OF
RAIN OR MORE THIS WEEKEND IS AT 40-50%. NOTE THE TEMPERATURE FORECAST
IS HIGHLY UNCERTAIN ON SUNDAY DUE TO THE UNCERTAINTY DISCUSSED ABOVE;
IF WIDESPREAD RAIN OCCURS, HIGHS WOULD LIKELY WIND UP AROUND THE NBM
10-25TH PERCENTILE (MID TO UPPER 60S). IF RAIN STAYS TO THE SOUTH AND
CONDITIONS END UP DRY AND SUNNY, HIGHS WOULD LIKELY MATCH THE
75TH-90TH PERCENTILE (UPPER 70S TO LOWER 80S).
THE FORECAST IS UNCERTAIN SUNDAY NIGHT THROUGH MONDAY NIGHT AS WELL.
CURRENTLY THERE IS A 20-30% CHANCE FOR RAIN SHOWERS DURING THAT TIME,
WITH HIGH TEMPERATURES MOST LIKELY IN THE 60S OR 70S, COOLEST AT THE
COAST. -TK
AVIATION
A LOW PRESSURE SYSTEM OFFSHORE OF THE OREGON COAST
WILL MAINTAIN SHOWERS ACROSS THE REGION THROUGH AT LEAST TUESDAY
NIGHT. CONDITIONS ARE MOSTLY DRY AS OF EARLY TUESDAY MORNING, BUT
SHOULD SEE SOME ISOLATED TO SCATTERED SHOWERS RETURNING LATER
TODAY. BREAKS IN THE RAIN AND CLOUDS ALONG THE COAST THIS MORNING
WITH CALM WINDS, CLEARING, AND RESIDUAL MOISTURE MAY LEAD TO
PATCHY FOG AND IFR/MVFR CIGS (ESPECIALLY AT KONP).
EXPECT MAINLY VFR CONDITIONS ACROSS THE REGION EXCEPT FOR BRIEF
PERIODS OF MVFR CONDITIONS IN HEAVIER SHOWERS. ADDITIONALLY, THERE
IS A 20-30% CHANCE FOR THUNDERSTORMS FROM 18Z TUE TO 00Z WED.
THEREFORE, ADDED PROB30S TO THE KSLE AND KEUG TAFS WHERE
THUNDERSTORM CHANCES ARE HIGHEST. LIGHTNING, ERRATIC WINDS, AND
HEAVY RAIN ARE THE MAIN THREATS WITH THE THUNDERSTORMS. TONIGHT,
HIGHER PRESSURE ALOFT ALONG WITH MOISTER CONDITIONS WILL SUPPORT A
MORE ROBUST MARINE LAYER WITH IFR/MVFR CIGS ALONG THE COAST.
KPDX AND APPROACHES...PREDOMINATELY VFR. INTERMITTENT SHOWERS AND
AND LIGHT WEST-NORTHWESTERLY WINDS UNDER 10 KT WILL CONTINUE
THROUGH THE TAF PERIOD. THERE IS A 15-20% CHANCE FOR THUNDERSTORMS
FROM 18Z TUE TO 00Z WED WITH LIGHTNING, ERRATIC WINDS, AND HEAVY
SHOWERS POSSIBLE. ANY HEAVY RAIN MAY LEAD TO BRIEF MVFR CIGS
AND/OR VIS. -ALVIZ/HEC
MARINE
HIGH PRESSURE OVER THE WATERS WILL MAINTAIN NORTHERLY
TO NORTHWESTERLY WINDS WITH GUSTS AROUND 10-12 KT OR LESS THROUGH
AT LEAST THURSDAY. SEAS REMAIN AROUND 2-3 FT AT 12-14 SEC TODAY,
BUILDING TO 4-6 FT AT 11-12 SEC WEDNESDAY TO FRIDAY WITH A WEST-
NORTHWESTERLY SWELL.
HEADING INTO THE WEEKEND, GUIDANCE IS SUGGESTING ANOTHER LOW
PRESSURE SYSTEM APPROACHING THE PACIFIC NORTHWEST. A FRONT
ASSOCIATED WITH THIS LOW WILL WEAKEN AS IT MOVES ACROSS THE WATERS
SATURDAY AND SUNDAY. THE WINDS WILL SHIFT SOUTHERLY AHEAD OF THE
FRONT ON SATURDAY, THEN NORTHERLY WITH AND BEHIND THE FRONT ON
SUNDAY. WINDS ARE NOT LOOKING TOO IMPACTFUL, WITH A 10-15% CHANCE
FOR WIND GUSTS OF 21 KT OR GREATER (SMALL CRAFT CONDITIONS)
ACROSS THE WATERS SATURDAY TO SUNDAY. SEAS ARE FORECAST AROUND 5-7
FEET AT 10-12 SEC THIS WEEKEND. -ALVIZ/TJ
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
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