704
FXUS02 KWBC 040700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE JUL 04 2023
VALID 12Z FRI JUL 07 2023 - 12Z TUE JUL 11 2023
...SOUTHERN TIER HEAT EXPECTED TO REBUILD DURING THE WEEKEND AND
PERSIST INTO NEXT WEEK...
...STRONG TO SEVERE STORMS ALONG WITH A HEAVY RAIN/RUNOFF THREAT
TO FOCUS OVER THE CENTRAL PLAINS INTO MIDDLE MISSISSIPPI VALLEY
FRIDAY-SATURDAY...
..OVERVIEW
EXPECT THE FRIDAY-TUESDAY PERIOD TO BE FAIRLY ACTIVE IN TERMS OF
SHOWER AND THUNDERSTORM ACTIVITY FROM THE NORTHERN-CENTRAL PLAINS
TO THE EAST COAST. FROM LATE WEEK INTO THE WEEKEND A LEADING
FRONT CROSSING THE EAST WILL BE ONE FEATURE HELPING TO FOCUS
RAINFALL, WHILE THE TRAILING PART OF THE FRONT ALONG WITH
SHORTWAVES EMBEDDED IN LOW AMPLITUDE FLOW ALOFT SHOULD PROMOTE
MULTIPLE EPISODES OF CONVECTION THAT WILL LIKELY PROGRESS FROM THE
CENTRAL PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY. THEN RECENT
GUIDANCE HAS BEEN SUGGESTING THAT THE MEAN TROUGH EXTENDING SOUTH
FROM CENTRAL CANADA MAY AMPLIFY TO SOME DEGREE OVER THE EASTERN
U.S. EARLY NEXT WEEK (WITH POSSIBLE SOUTHWARD SHIFT OF THE
EMBEDDED UPPER LOW IN CANADA), LEADING TO A REBOUND OF RAINFALL
OVER THE EAST ALONG/AHEAD OF WHAT MAY BE A COMPLICATED REFLECTION
OF SURFACE WAVES AND FRONTS. ONE OR MORE OF THESE FRONTS MAY
PRODUCE LIGHTER RAINFALL OVER THE CENTRAL U.S. FROM LATE WEEKEND
INTO NEXT WEEK. FARTHER SOUTH, AN UPPER RIDGE SHOULD PERSIST OVER
THE SOUTHERN ROCKIES/HIGH PLAINS THROUGH THE PERIOD AND STRENGTHEN
SOMEWHAT BY EARLY NEXT WEEK, LEADING TO SOMEWHAT HOTTER
TEMPERATURES OVER THAT PART OF THE COUNTRY. GUIDANCE MAINTAINS
THE IDEA OF MEAN TROUGHING ALOFT NEAR THE NORTHERN HALF OF THE
WEST COAST BUT WITH VARYING DAY-TO-DAY DETAILS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
GUIDANCE AGREES WELL ON THE OVERALL THEME OF THE PATTERN EVOLUTION
FROM THE ROCKIES EASTWARD, WITH A PERSISTENT MEAN RIDGE AXIS OVER
THE ROCKIES AND CYCLONIC FLOW DOWNSTREAM. FROM FRIDAY INTO THE
WEEKEND THE CYCLONIC FLOW WILL LIKELY BE FAIRLY LOW IN AMPLITUDE
AND CONTAIN MULTIPLE WEAK SHORTWAVES THAT WILL TEND TO MAKE
RESOLVING SURFACE DETAILS MORE DIFFICULT AFTER A WELL-DEFINED
FRONT REACHES THE EAST AND SOUTH LATE IN THE WEEK. FOR EARLY NEXT
WEEK THE MODELS AND ENSEMBLE MEMBERS HAVE BEEN DIVERGING AND
VARYING SIGNIFICANTLY FROM RUN TO RUN WITH RESPECT TO EMBEDDED
DETAILS WITHIN THE GENERAL AMPLIFYING TREND FOR THE CANADA INTO
NORTHERN/EASTERN U.S. MEAN TROUGH. THE CMC WAS THE MOST EXTREME
SOLUTION OF THE 12Z/18Z BATCH OF GUIDANCE, USING ENERGY IN THE
SOUTHWEST PART OF THE TROUGH TO FORM AN UPPER LOW THAT CROSSES THE
MIDWEST (LEADING TO 500MB HEIGHT ANOMALIES UP TO 3-4 STANDARD
DEVIATIONS BELOW CLIMATOLOGY OVER PARTS OF THE OHIO VALLEY). THE
NEW 00Z CMC DOES NOT HAVE THIS FEATURE AND NOW DROPS ITS MAIN
CANADA UPPER LOW INTO NORTHERN ONTARIO, WHICH IS SIMILAR TO THE
12Z ECMWF. THE 00Z GFS IS SIMILAR AS WELL, AFTER 12Z/18Z RUNS
WERE A LITTLE FARTHER NORTHWEST WITH THE DEEP UPPER LOW. LATEST
GEFS/ECMWF MEANS ARE HINTING AT THIS SOUTHWARD SHIFT OF THE CANADA
UPPER LOW VERSUS 24 HOURS AGO WHEN THE DOMINANT CLUSTERING WAS
NEAR NORTHERN HUDSON BAY (BUT SOME GFS RUNS WERE ALREADY PULLING
SOME OF THE ENERGY SOUTHWARD). ALONG THE NORTHWEST COAST THERE IS
REASONABLE AGREEMENT ON MEAN TROUGHING WITH ONE OR MORE EMBEDDED
COMPACT UPPER LOWS, BUT A FAIR AMOUNT OF SPREAD FOR SPECIFICS.
PART OF THE DIFFICULTY IS UNCERTAINTY IN EXACT TIMING/SHAPE OF A
RIDGE THAT BUILDS TO ITS NORTH, ALONG WITH HOW UPSTREAM ENERGY
EXPECTED TO FILTER INTO THE MEAN TROUGH WILL INFLUENCE FEATURES
INITIALLY WITHIN THE TROUGH.
THE UPDATED FORECAST STARTED WITH A BLEND OF 12Z/18Z OPERATIONAL
MODELS TO REFLECT THE MOST COMMON IDEAS OF GUIDANCE DURING THE
FIRST HALF OF THE PERIOD. RECENT BEHAVIOR OF GUIDANCE LATE IN THE
PERIOD OVER CENTRAL/EASTERN NORTH AMERICA FAVORED A RAPID
TRANSITION TO A MORE CONSERVATIVE APPROACH BY DAY 7 TUESDAY WITH A
TOTAL OF 60 PERCENT TOTAL 18Z GEFS/12Z ECENS INPUT AT THAT TIME,
WHILE HOLDING ON TO SOME COMPONENTS OF THE 18Z GFS/12Z ECMWF. LOW
CONFIDENCE IN THE 12Z CMC SOLUTION FAVORED ELIMINATING IT FROM THE
FORECAST AFTER DAY 5 SUNDAY.
..WEATHER/HAZARDS HIGHLIGHTS
FROM LATE THIS WEEK INTO THE WEEKEND, THE CENTRAL PLAINS INTO
MIDDLE MISSISSIPPI VALLEY WILL BE THE MOST PROMINENT FOCUS FOR
POTENTIALLY STRONG/HEAVY CONVECTION DUE TO THE COMBINATION OF
SHORTWAVE IMPULSES ALOFT AND A SOUTH-CENTRAL PLAINS FRONT DRIFTING
SLOWLY NORTHEASTWARD. WHILE THERE IS TYPICAL UNCERTAINTY IN
DETAILS 4-5 DAYS OUT IN TIME, THERE SEEMS TO BE ENOUGH CLUSTERING
IN THE GUIDANCE TO FAVOR SLIGHT RISK AREAS IN THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS THAT COVER THE FRIDAY INTO EARLY
SUNDAY TIME FRAME. SOME REFINEMENT IN THESE AREAS IS LIKELY OVER
THE COMING DAYS BUT THE PATTERN APPEARS TO FAVOR THE OVERALL HEAVY
RAINFALL THREAT. FARTHER EAST, INSTABILITY AND ABOVE
CLIMATOLOGICAL MOISTURE ALONG AND AHEAD OF A FRONT PUSHING TOWARD
THE EAST COAST WILL FAVOR SOME AREAS OF HEAVY RAINFALL THAT COULD
POSE A FLASH FLOOD THREAT BUT THE FOCUS/RAINFALL MAGNITUDES ARE
LESS FOCUSED. THUS DAY 4 DEPICTS A BROAD MARGINAL RISK AREA FROM
NEW ENGLAND INTO PARTS OF THE SOUTHEAST, WITH A LINGERING MARGINAL
RISK ON DAY 5 OVER MOST OF NEW ENGLAND. REGARDING THE LATTER,
THERE IS A FAIR AMOUNT OF SPREAD FOR HOW MUCH MOISTURE WILL REMAIN
BUT THE AREA SHOWN CAPTURES THE BEST OVERLAP OF GUIDANCE AND THE
FACT THAT A FRONTAL BOUNDARY MAY PERSIST OVER THE REGION. AS
UPPER TROUGHING LIKELY AMPLIFIES EARLY NEXT WEEK, THE BEST FOCUS
FOR ENHANCED RAINFALL SHOULD MOVE FROM THE MISSISSIPPI VALLEY INTO
THE EAST. DETAILS REMAIN UNCERTAIN GIVEN HOW GUIDANCE HAS VARIED
THUS FAR. FRONTS MOVING SOUTH FROM CANADA MAY ALSO PRODUCE SOME
AREAS OF RAINFALL OVER THE CENTRAL U.S. FROM LATE WEEKEND INTO
NEXT WEEK, BUT WITH AMOUNTS AVERAGING SOMEWHAT LESS THAN THOSE
EXPECTED OVER THE EAST.
WITH GUIDANCE CONTINUING TO SHOW THE UPPER RIDGE OVER THE SOUTHERN
ROCKIES/HIGH PLAINS STRENGTHENING SOMEWHAT FROM THE WEEKEND INTO
NEXT WEEK, EXPECT GRADUAL EXPANSION OF HAZARDOUS HEAT ACROSS THE
SOUTHERN TIER DURING THE FORECAST PERIOD. GREATEST TEMPERATURE
ANOMALIES OF PLUS 10-12F FOR HIGHS SHOULD BE DIRECTLY UNDERNEATH
THE UPPER HIGH (WESTERN TEXAS AND SOUTHEASTERN NEW MEXICO) WITH
BROADENING COVERAGE OF HIGHS AT LEAST A FEW DEGREES ABOVE NORMAL
ELSEWHERE. LIKEWISE, EXPECT GRADUALLY INCREASING COVERAGE OF
MAXIMUM HEAT INDEX VALUES REACHING 110F OR GREATER OVER
SOUTHERN/EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY. PARTS
OF THE NORTHERN-CENTRAL PLAINS WILL SEE MULTIPLE DAYS OF BELOW
NORMAL HIGHS, WITH SOME LOCATIONS 10-12F BELOW NORMAL
FRIDAY-SATURDAY FOLLOWED BY A GRADUAL TREND CLOSER TO NORMAL. THE
NORTHEAST WILL START OUT WARM LATE THIS WEEK AHEAD OF AN
APPROACHING FRONT AND THEN TREND CLOSE TO NORMAL AS WELL.
RAUSCH
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, HEAT INDICES AND
KEY MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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