155
FXUS02 KWBC 110658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT THU MAY 11 2023
VALID 12Z SUN MAY 14 2023 - 12Z THU MAY 18 2023
***FLASH FLOODING POTENTIAL STARTS TO ABATE SUNDAY ACROSS TEXAS,
AND AN EARLY SEASON HEATWAVE AFFECTS THE PACIFIC NORTHWEST***
..SYNOPTIC SCALE OVERVIEW
AN ANOMALOUS BUILDING NORTHWESTERN U.S./SOUTHWESTERN CANADA UPPER
RIDGE WILL LIKELY CLOSE OFF A HIGH OVER SOUTHWESTERN CANADA BY
SUNDAY AND THEN POSSIBLY OPEN UP AGAIN TO A RIDGE AXIS WHILE
PERSISTING OVER WESTERN CANADA THROUGH AT LEAST THE MIDDLE OF NEXT
WEEK. AT THE SAME TIME A WEAK UPPER LOW MAY RETROGRADE ACROSS THE
GREAT BASIN AND PACIFIC NORTHWEST, WITH SOME DEGREE OF UPPER
RIDGING POSSIBLY BUILDING OVER THE WESTERN U.S. IN ITS WAKE. THIS
PATTERN WILL RESULT IN AN EARLY SEASON HEATWAVE ACROSS THE
NORTHWEST AND TO A LESSER EXTENT OVER OTHER PARTS OF THE WEST. A
SYNOPTIC SCALE UPPER TROUGH EXTENDING FROM HUDSON BAY CANADA TO
THE EAST COAST DEVELOPS IN RESPONSE TO THE WESTERN CANADA RIDGE
WITH MULTIPLE SHORTWAVE PASSAGES, AND THIS WILL TEND TO FAVOR
COOLER CONDITIONS AND LOWER HUMIDITY OVER THE EAST DURING THE
FIRST HALF OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE AGREES WELL ON MOST ASPECTS OF THE SYNOPTIC
SCALE PATTERN GOING INTO SUNDAY AND MONDAY, WITH THE GFS ONLY
SLIGHTLY SLOWER WITH THE EMBEDDED UPPER LOW ACROSS THE
INTERMOUNTAIN WEST, SO A MULTI-DETERMINISTIC MODEL BLEND WORKS
WELL FOR A STARTING POINT IN THE FORECAST PROCESS. LOOKING AHEAD
TO TUESDAY, THE GFS WEAKENS THE WESTERN UPPER RIDGE A BIT MORE
THAN THE OTHER GUIDANCE, BUT IT IS OTHERWISE CLOSE TO THE
CONSENSUS ACROSS THE EASTERN U.S. WITH THE AMPLIFYING TROUGH. BY
THE END OF THE PERIOD THURSDAY, THE ECMWF BECOMES STRONGER WITH AN
UPPER LOW DROPPING SOUTH ACROSS CENTRAL U.S., THE CMC CONSIDERABLY
WEAKER WITH THE WESTERN U.S. UPPER RIDGE AND LOSES ENSEMBLE
SUPPORT, AND THE GFS IS A LITTLE SLOWER WITH THE ARRIVAL OF THE
NEXT SHORTWAVE TROUGH REACHING THE EAST COAST. TAKING THESE
FACTORS INTO ACCOUNT, THE FORECAST BLEND WAS PRIMARILY DERIVED
FROM ABOUT HALF OF THE ECMWF/GFS AND HALF OF THE ENSEMBLE MEANS
FOR WEDNESDAY AND THURSDAY.
..WEATHER/HAZARDS HIGHLIGHTS
ALTHOUGH THE HEAVIEST RAINFALL IS LIKELY TO BE PRIOR TO SUNDAY
MORNING, THERE WILL LIKELY BE SOME LINGERING AREAS OF MODERATE TO
HEAVY RAIN GOING INTO DAY 4 SUNDAY ACROSS CENTRAL PARTS OF TEXAS
AND INTO OKLAHOMA, AND A SLIGHT RISK IS PLANNED FROM THE OK/TX
BORDER TO THE RIO GRANDE TO COVER THIS POTENTIAL. THE AREAL
EXTENT OF THE SLIGHT RISK IS SMALLER NOW GIVEN A MORE CONFINED
SIGNAL IN THE GUIDANCE, AND EVEN THOUGH THE RAINFALL WILL BE
TAPERING OFF, THE GROUND WILL LIKELY BE QUITE SATURATED FROM
RAINFALL IN THE DAY 3 PERIOD. GUIDANCE OFFERS MIXED SIGNALS FOR
HEAVY RAINFALL POTENTIAL OVER SURROUNDING AREAS INCLUDING THE
WESTERN HIGH PLAINS AND INTO OKLAHOMA/KANSAS, OWING TO DIFFERENCES
IN UPPER LEVEL DETAILS THAT HAVE FAIRLY LOW PREDICTABILITY SEVERAL
DAYS OUT IN TIME.
MEANWHILE LARGE SCALE EASTERLY FLOW ALOFT TO THE SOUTH OF THE
SOUTHWESTERN CANADA RIDGE SHOULD ADVECT INCREASING MOISTURE ACROSS
PORTIONS OF THE WEST DURING THE PERIOD. THE UPPER LOW FORECAST TO
TRACK THROUGH THE GREAT BASIN AND PACIFIC NORTHWEST DURING THE
WEEKEND AND EARLY NEXT WEEK, AS WELL AS OTHER POTENTIAL SMALLER
SCALE IMPULSES, COULD PRODUCE SCATTERED AREAS OF MAINLY LIGHT TO
MODERATE SHOWERS. GOING INTO THE MIDDLE OF THE WEEK, A DRIER
WEATHER PATTERN IS LIKELY FROM THE CENTRAL/NORTHERN PLAINS TO THE
EAST COAST, BUT THERE WILL STILL BE ENOUGH MOISTURE NEAR A
WEAKENING COLD FRONT OVER THE GULF COAST REGION TO GENERATED
SCATTERED SHOWERS AND STORMS FROM TEXAS TO THE SOUTHEAST STATES.
THE OTHER STORY MAKING WEATHER HEADLINES WILL BE THE EARLY SEASON
HEATWAVE CENTERED OVER THE PACIFIC NORTHWEST STARTING THIS WEEKEND
AND PERSISTING INTO NEXT WEEK AS THE ANOMALOUS UPPER HIGH BECOMES
ANCHORED IN PLACE OVER SOUTHERN BRITISH COLUMBIA. THE LATEST
TEMPERATURE FORECAST CALLS FOR HIGHS REACHING THE MIDDLE 80S TO
MIDDLE 90S FOR MANY OF THE LOWER ELEVATIONS IN WASHINGTON AND
OREGON, WHICH WOULD SET DAILY HIGH TEMPERATURE RECORDS. OVERNIGHT
LOWS WILL ALSO BE QUITE WARM WITH READINGS ONLY FALLING INTO THE
60S FOR MANY OF THESE SAME AREAS. THE WARM OVERNIGHT LOWS OVER
THE NORTHWEST AND SOME NEARBY AREAS COULD ALSO CHALLENGE SOME
DAILY RECORDS THROUGH AT LEAST MIDWEEK. IT WILL ALSO BE QUITE
WARM FOR THE CENTRAL VALLEY OF CALIFORNIA WITH HIGHS WELL INTO THE
90S THERE AS WELL. ELSEWHERE ACROSS THE NATION, THE HEAT AND
HUMIDITY ACROSS THE CENTRAL AND EASTERN U.S. SHOULD DECREASE SOME
GOING INTO EARLY NEXT WEEK AS A WEAK FRONTAL BOUNDARY CROSSES THE
SOUTHERN TIER STATES, AND A STRONGER COLD FRONT PASSES THROUGH THE
GREAT LAKES AND NORTHEAST BRINGING A MORE REFRESHING AIRMASS.
COOLER WEATHER OWING TO CLOUD COVER AND RAINFALL WILL LIKELY BE
THE CASE ACROSS MUCH OF THE SOUTHERN PLAINS WITH HIGHS RUNNING
5-15 DEGREES BELOW AVERAGE MOST DAYS.
HAMRICK
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
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