998
FXUS02 KWBC 300700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT FRI JUN 30 2023
VALID 12Z MON JUL 03 2023 - 12Z FRI JUL 07 2023
...MAJOR HEATWAVE FROM TEXAS THROUGH THE MID-LOWER MISSISSIPPI
VALLEY TO THE SOUTHEAST TO EASE NEXT WEEK...
...HOT TEMPERATURES FROM THE DESERT SOUTHWEST TO INTERIOR
CALIFORNIA INTO MONDAY...
..OVERVIEW
GUIDANCE IS SHOWING A FAIRLY TYPICAL SUMMERTIME PATTERN, WITH A
LOWER LATITUDE MEAN RIDGE ALOFT SETTLING TOWARD NEAR-AVERAGE
STRENGTH WITH A COUPLE PRIMARY FEATURES OF INTEREST FARTHER NORTH.
THE LEADING SYSTEM WILL BE A DIFFUSE EASTERN U.S./CANADA
SHORTWAVE AND ASSOCIATED WAVY FRONT, WHILE THE SOUTHERN PERIPHERY
OF A BETTER DEFINED CANADIAN TROUGH WILL PROGRESS FROM THE
NORTHWESTERN U.S. INTO THE MISSISSIPPI VALLEY. THIS LATTER TROUGH
WILL PUSH SOUTHWARD AND EASTWARD WITH TIME, LIKELY REACHING THE
EAST-CENTRAL STATES THROUGH SOUTH-CENTRAL PLAINS BY LATE IN THE
WEEK. EXPECT BOTH FRONTS TO PRODUCE EPISODES OF SHOWERS AND
THUNDERSTORMS WITH DIURNALLY FAVORED RAINFALL ALSO LIKELY OVER THE
SOUTH.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FOR THE MOST PART, LATEST MODELS AND ENSEMBLES HAVE BEEN OFFERING
BETTER THAN AVERAGE AGREEMENT. THE DIFFUSE TROUGH CROSSING THE
EAST HAS EMBEDDED SMALLER-SCALE DETAILS THAT HAVE LOWER
PREDICTABILITY. THUS IT IS LIKELY THAT IT WILL TAKE INTO THE
SHORT RANGE TIME FRAME TO RESOLVE SOME SPECIFICS FOR THE SHORTWAVE
AND ASSOCIATED SURFACE FRONT/WAVES. CURRENTLY THE MOST COMMON
THEME IS FOR A WEAK EMBEDDED UPPER LOW TO TRACK FROM NEAR THE
EASTERN GREAT LAKES TO JUST NORTH OF MAINE FROM EARLY MONDAY INTO
EARLY WEDNESDAY. BY DAYS 6-7 THURSDAY-FRIDAY THE 18Z GFS DROPPED
ITS UPPER LOW TO EAST OF NEW ENGLAND WHICH IS SOUTH OF MOST OTHER
GUIDANCE. THE NEW 00Z RUN HAS ADJUSTED BACK MUCH CLOSER TO THE
MODEL/MEAN MAJORITY. MEANWHILE A MODEL/MEAN CONSENSUS (MODEL
COMPOSITE EARLY AND THEN A MODEL/MEAN MIX AS MODEL DETAILS DIVERGE
SOMEWHAT) LOOKS GOOD FOR THE UPSTREAM CANADA/NORTHERN TIER U.S.
UPPER TROUGH AND LEADING COLD FRONT PUSHING SOUTH/EAST FROM THE
NORTHERN PLAINS. BEHIND THIS SYSTEM, GUIDANCE AGREES FAIRLY WELL
WITH THE IDEA OF A MODEST TROUGH DEVELOPING NEAR THE WEST COAST IN
RESPONSE TO A STRONG EASTERN PACIFIC RIDGE.
..WEATHER/HAZARDS HIGHLIGHTS
THE WAVY COLD FRONT PROGRESSING SOUTH AND EAST FROM THE NORTHERN
PLAINS OVER THE COURSE OF NEXT WEEK WILL LIKELY PRODUCE MULTIPLE
EPISODES OF SHOWERS AND THUNDERSTORMS, WITH SOME LOCALLY HEAVY.
CURRENTLY THE GUIDANCE SIGNALS ARE NOT QUITE COHERENT/ORGANIZED
ENOUGH TO DEPICT ANY RISK AREA IN THE DAY 4 EXCESSIVE RAINFALL
OUTLOOK (MONDAY-MONDAY NIGHT), BUT THERE IS POTENTIAL FOR FUTURE
RUNS TO PROVIDE ENOUGH FOCUS TO SUGGEST AN AREA AT SOME POINT. BY
DAY 5 (TUESDAY-TUESDAY NIGHT) GUIDANCE GENERALLY SUGGESTS MORE
ORGANIZED ACTIVITY WITH GREATER LOCALIZED TOTALS, ALONG WITH AT
LEAST A MODEST INCREASE OF AVAILABLE MOISTURE. LOW LEVEL UPSLOPE
FLOW COULD ENHANCE RAINFALL TO THE NORTH OF THE FRONT. THUS THE
DAY 5 OUTLOOK PLANS TO DEPICT A MARGINAL RISK FROM PARTS OF THE
UPPER MIDWEST INTO THE NORTH-CENTRAL HIGH PLAINS. THE WESTERN
HALF OR SO OF THIS AREA HAS HAD THE MOST RAINFALL OVER THE PAST
COUPLE WEEKS AND WOULD BE MORE SENSITIVE TO ADDITIONAL RAIN. FROM
MIDWEEK ONWARD EXPECT THE AREA OF SHOWERS/STORMS TO CONTINUE
MOVING SOUTHWARD AND EASTWARD, EVENTUALLY REACHING AREAS FROM THE
GREAT LAKES/OHIO VALLEY TO THE SOUTH-CENTRAL PLAINS.
THE WEAKER WAVY FRONT CROSSING THE EAST EARLY NEXT WEEK SHOULD
ALSO PRODUCE SOME AREAS OF LOCALLY HEAVY RAINFALL GIVEN SUFFICIENT
MOISTURE AND INSTABILITY. GUIDANCE AGREEMENT IS NOT EXCEPTIONAL,
LIKELY CORRESPONDING TO THE LOW PREDICTABILITY OF IMPORTANT
SMALL-SCALE DETAILS, BUT ENOUGH SUPPORT REMAINS TO KEEP A MARGINAL
RISK AREA IN THE NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK. THIS AREA
IS CENTERED OVER MOST OF PENNSYLVANIA AND SOME SURROUNDING
LOCATIONS, CORRESPONDING TO A COMBINATION OF RELATIVELY LOWER
FLASH FLOOD GUIDANCE CURRENTLY AND RAINFALL FORECAST IN THE SHORT
TERM BEFORE THE VALID DAY. THE NORTHEAST SHOULD TREND DRIER
MID-LATE WEEK AS THE SYSTEM LIFTS AWAY BUT THE TRAILING FRONT MAY
LINGER FOR A TIME OVER THE CAROLINAS AND PROVIDE A FOCUS FOR
RAINFALL. MEANWHILE EXPECT MUCH OF THE SOUTH TO SEE TYPICAL
DIURNALLY ENHANCED SHOWERS/THUNDERSTORMS OF VARYING INTENSITY EACH
DAY.
EXCESSIVE HEAT ACROSS THE SOUTHERN TIER SHOULD BECOME LESS
WIDESPREAD NEXT WEEK AS UPPER RIDGING RETURNS TO A MORE
CLIMATOLOGICAL STRENGTH AND LATITUDE. PARTS OF THE
SOUTHEAST/CAROLINAS MAY STILL SEE HIGHS IN THE MID-UPPER 90S EARLY
IN THE WEEK ALONG WITH SUFFICIENT HUMIDITY TO SUPPORT HEAT INDICES
OF 105 TO SLIGHTLY ABOVE 110 DEGREES, WHILE THE WESTERN GULF COAST
REGION AND FAR SOUTHERN TEXAS IN PARTICULAR MAY CONTINUE TO SEE
HEAT INDEX VALUES REACH AT LEAST 110-115F ON MOST DAYS NEXT WEEK.
EXCESSIVE SUMMER HEAT OVER THE SOUTHWEST AND VICINITY SHOULD
CONTINUE INTO NEXT MONDAY WITH THE HOTTEST LOCATIONS REACHING THE
110-120F RANGE AND PARTS OF THE CALIFORNIA'S CENTRAL VALLEY
EXCEEDING 100F. AFTER MONDAY, THE SOUTHWEST SHOULD SEE
TEMPERATURES MODERATE WHILE THE PACIFIC NORTHWEST WILL BE A
LOCALIZED FOCUS FOR ABOVE NORMAL TEMPERATURES. ELSEWHERE, HIGH
TEMPERATURES OF 5-12F ABOVE NORMAL SHOULD PROGRESS FROM THE UPPER
MIDWEST INTO PARTS OF THE NORTHEAST AHEAD OF THE INITIAL PLAINS
COLD FRONT. BEHIND THE FRONT, EXPECT MUCH COOLER TEMPERATURES
WITH ONE OR MORE DAYS OF HIGHS 10-20F BELOW NORMAL OVER THE
NORTHERN INTO CENTRAL HIGH PLAINS.
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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