750
FXUS02 KWBC 042013
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
412 PM 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...
...HEAVY RAIN/RUNOFF CONCERNS AND POSSIBLY A SEVERE WEATHER THREAT
SHOULD FOCUS OVER THE SOUTH-CENTRAL PLAINS AND MISSISSIPPI VALLEY
FRIDAY-SUNDAY...
..OVERVIEW
EXPECT THE FRIDAY-TUESDAY PERIOD TO BE FAIRLY ACTIVE IN TERMS OF
SHOWER AND THUNDERSTORM ACTIVITY FROM MUCH OF THE 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/LOWER 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. THESE
DIFFERENCES ALSO IMPACT THE QPF POSITION/AMPLITUDE. THIS FORECAST
CYCLE TRENDED DRIER ACROSS THE OHIO VALLEY AND WETTER FARTHER
SOUTH ACROSS THE MID-SOUTH PER THE LATEST GUIDANCE, BUT
PREDICTABILITY REMAINS ON THE LOWER SIDE FOR THE DETAILS,
ESPECIALLY IN THE OHIO VALLEY. THE NBM THROUGH 13Z SEEMED TO BE
LAGGING A BIT ON THIS SOUTHERN TREND COMPARED TO THE MULTI-MODEL
CONSENSUS OF QPF FARTHER SOUTH.
INTO EARLY NEXT WEEK, 00/06Z MODEL GUIDANCE AND THE INCOMING 12Z
CYCLE AT LEAST AGREES BETTER WITH A GRADUAL DRIFT SOUTH OF THE
HUDSON BAY LOW FOR MORE WELL-DEFINED TROUGHING OVER THE
EAST-CENTRAL U.S. BUT DIFFERENCES ARISE WITH ITS CENTROID POSITION
AND POTENTIAL FOR ELONGATION OF THE LOW IN SOME DIRECTION, CAUSING
TROUGH AXIS DIFFERENCES. THE 06Z GFS WENT SO FAR AS TO SPLIT THE
LOW BY MONDAY-TUESDAY WHILE NORTH-SOUTH-ORIENTED ENERGY THAT WAS
MORE AGGRESSIVE THAN IN OTHER GUIDANCE/OTHER GFS RUNS TRACKS
ACROSS THE EAST COAST.
MEANWHILE IN THE WEST, SHORTWAVES/COMPACT UPPER LOWS IN MULTIPLE
STREAMS SHOULD LEAD TO MEAN TROUGHING THROUGH MUCH OF THE PERIOD,
BUT WITH 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.
GIVEN THE ABOVE CONSIDERATIONS, THE WPC FORECAST UTILIZED A BLEND
OF THE DETERMINISTIC GUIDANCE PARTICULARLY FAVORING THE 00Z ECMWF
AND 06Z GFS FOR THE EARLY PART OF THE FORECAST PERIOD. AS THE
FORECAST PROGRESSED, INCREASED THE PROPORTION OF THE EC AND GEFS
ENSEMBLE MEANS AT THE EXPENSE OF THE INDIVIDUAL MODELS (ESPECIALLY
THE GFS), REACHING ABOUT HALF BY THE END OF THE PERIOD NEXT
TUESDAY AMID THE INCREASING UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
FROM LATE THIS WEEK INTO THE WEEKEND, SOUTHERN AND CENTRAL PARTS
OF THE PLAINS AND MISSISSIPPI VALLEY WILL BE THE MOST PROMINENT
FOCUS FOR POTENTIALLY STRONG CONVECTION WITH HEAVY RAINFALL DUE TO
THE COMBINATION OF SHORTWAVE IMPULSES ALOFT AND A SOUTH-CENTRAL
PLAINS FRONT OR TWO MEANDERING ACROSS THE REGION. WHILE THERE IS
TYPICAL UNCERTAINTY IN DETAILS 4-5 DAYS OUT IN TIME, MAINTAINED
SLIGHT RISKS IN THE DAYS 4-5 (FRIDAY-SUNDAY MORNING) EXCESSIVE
RAINFALL OUTLOOKS GIVEN THE PATTERN SHOULD SUPPORT A HEAVY
RAINFALL THREAT WITH AMPLE INSTABILITY AND ABOVE AVERAGE MOISTURE
IN PLACE. THERE HAS BEEN SOME SHIFT IN THE GUIDANCE SOUTH WITH THE
AXIS OF HEAVIEST RAINS OVER THE PAST COUPLE OF CYCLES; THUS THE
SLIGHT RISK AND THE QPF PARTICULARLY ON DAY 5 SHIFTED A BIT SOUTH
AS WELL TO INCLUDE SOME OF THE LOWER MISSISSIPPI VALLEY. 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 POSITION/RAINFALL MAGNITUDES ARE LESS FOCUSED. THUS DAY 4
DEPICTS A BROAD MARGINAL RISK AREA FROM NEW ENGLAND INTO THE
SOUTHEAST. DAY 5 CONTINUES TO SHOW CONSIDERABLE SPREAD ACROSS THE
EAST-CENTRAL TO EASTERN U.S. IN TERMS OF THE RAINFALL AXES, WITH
SOME MODELS FAVORING THE OHIO VALLEY MORE THAN OTHERS. AT THIS
POINT THERE IS A LARGE MARGINAL RISK IN PLACE TO COVER MOST OF THE
HEAVY RAINFALL THREATS, BUT THIS MAY BE ABLE TO SHRINK WITH TIME
IF MODELS CONVERGE WITH THEIR SOLUTIONS. 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.
THE WEST IS LIKELY TO REMAIN PERSISTENTLY DRY.
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. LOW
TEMPERATURES IN THE UPPER 70S TO 80F WILL NOT PROVIDE MUCH RELIEF
OVERNIGHT AND COULD EXACERBATE HEAT STRESS AS WELL AS CAUSE SOME
RECORDS FOR WARM MINIMUM TEMPERATURES. MEANWHILE PARTS OF THE
NORTHERN-CENTRAL PLAINS SHOULD 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.
TATE/RAUSCH
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI VALLEY, AND THE SOUTHERN
PLAINS, FRI, JUL 7.
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI
VALLEY, THE SOUTHERN PLAINS, AND THE OHIO VALLEY, SAT-SUN, JUL
8-JUL 9.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA AND THE SOUTHWEST,
FRI-TUE, JUL 7-JUL 11.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE
SOUTHEAST, THE LOWER MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND
THE SOUTHWEST, SAT-TUE, JUL 8-JUL 11.
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 FORECAST, 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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