833
FXUS02 KWBC 100658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT SAT AUG 10 2024
VALID 12Z TUE AUG 13 2024 - 12Z SAT AUG 17 2024
...EXCESSIVE HEAT LINGERS OVER PORTIONS OF TEXAS AND THE CENTRAL
GULF COAST STATES INTO MUCH OF NEXT WEEK...
..OVERVIEW
AN UPPER RIDGE WILL BE IN PLACE ACROSS THE SOUTH-CENTRAL U.S.
THROUGH MUCH OF NEXT WEEK, LEADING TO HIGH HEAT INDICES THAT COULD
BE HAZARDOUS ACROSS THE SOUTHERN PLAINS TO GULF COAST. MONSOONAL
MOISTURE WILL MAINTAIN RAIN CHANCES ACROSS THE FOUR CORNERS STATES,
WHILE SOME MOISTURE MAKES IT FARTHER NORTH INTO THE NORTHERN
PLAINS TO MIDWEST, AND SOME ADVECTS EAST AROUND THE RIDGE FOR
ROUNDS OF MESOSCALE CONVECTIVE SYSTEMS THAT COULD FOCUS
PARTICULARLY IN THE MID-MISSISSIPPI VALLEY NEXT WEEK. MEAN
TROUGHING IS LIKELY TO SET UP ACROSS THE WEST COAST AND THE EAST,
WHILE AN UPPER RIDGE STARTS TO BUILD FARTHER WEST INTO THE FOUR
CORNERS STATES LATE WEEK. MEANWHILE, A TROPICAL SYSTEM THAT IS
LIKELY TO DEVELOP PER NHC COULD APPROACH THE BAHAMAS IN ABOUT A
WEEK, WHICH WILL CONTINUE TO BE MONITORED, THOUGH FORTUNATELY MOST
MODELS TAKE THE LOW SYSTEM AWAY FROM THE LOWER 48 AT THIS POINT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE STILL SHOWS REASONABLY GOOD AGREEMENT WITH
THE OVERALL PATTERN, WITH SOME TYPICAL DIFFERENCES IN SHORTWAVES
THAT TRACK THROUGH THE MEAN FLOW. UNFORTUNATELY THESE DIFFERENCES
THAT ARE ON THE SMALLER SIDE DO HAVE IMPACTS ON SENSIBLE WEATHER
LIKE RAINFALL AND FRONTAL PLACEMENT. THROUGH THE 12Z/18Z MODEL
CYCLE THAT WAS AVAILABLE FOR TONIGHT'S FORECAST, THE ECMWF, GFS,
AND AIFS FORMED A CLUSTER OF SOLUTIONS THAT WERE RELATIVELY
AGREEABLE WITH A SHORTWAVE TRACKING ACROSS THE NORTH-CENTRAL U.S.
THURSDAY INTO THE MIDWEST FRIDAY, ALONG WITH A WEAK SURFACE
LOW/FRONTAL SYSTEM. THIS TROUGH MAY DIG A BIT IN THE EAST-CENTRAL
U.S. INTO SATURDAY. WHILE UNCERTAIN, DID OPT TO LEAN TOWARD THIS
FAVORABLE CLUSTER OF GUIDANCE, AND FORTUNATELY INCOMING 00Z
GUIDANCE SEEMS TO SHOW THIS SAME GENERAL IDEA. BY LATE WEEK,
DEEPENING TROUGHING IN THE EASTERN PACIFIC MAY EDGE TOWARD THE WEST
COAST, AND RIDGING LOOKS TO BUILD FARTHER WEST IN BETWEEN THESE
TROUGH FEATURES. A MODEL/MEAN BLEND SEEMS REASONABLE WITH THAT.
THE TROPICAL CYCLONE THAT IS FORECAST TO DEVELOP IN THE TROPICAL
ATLANTIC COULD REACH WPC'S FORECAST DOMAIN BY NEXT WEEKEND. THE
BULK OF MODEL AND ENSEMBLE GUIDANCE INDICATES THE SYSTEM TURNING
NORTH NEAR THE BAHAMAS AND THEN NORTHEASTWARD ENOUGH TO TAKE IT OUT
TO SEA RATHER THAN INTO THE U.S., BUT WILL CONTINUE TO MONITOR AS
THE TRACK WILL DEPEND IN PART ON A POSSIBLE TROUGH AXIS ACROSS THE
EASTERN U.S./WESTERN ATLANTIC.
THE WPC FORECAST USED A MULTI-MODEL DETERMINISTIC BLEND HEAVILY
FAVORING THE 12Z ECMWF AND 12/18Z GFS RUNS FOR DAYS 3-4,
INCORPORATING THE EC AND GEFS ENSEMBLE MEANS BY DAY 5 AND
INCREASING THE MEANS TO HALF THE BLEND BY DAY 7 AMID GROWING
FORECAST SPREAD AND UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
ABOVE NORMAL MOISTURE WILL BE DIRECTED INTO THE FOUR CORNERS
STATES AND NORTH AND EAST ESPECIALLY INTO TUESDAY. A BROAD MARGINAL
RISK REMAINS IN PLACE FOR DAY 4/TUESDAY FOR MUCH OF THE FOUR
CORNERS STATES AND INTO SOUTHERN WYOMING. COVERAGE AND AMOUNTS OF
RAIN MAY TICK DOWN A BIT INTO WEDNESDAY, BUT LIKELY STILL
SUFFICIENT FOR A MARGINAL RISK FROM EASTERN ARIZONA INTO NEW MEXICO
AND COLORADO FOR THE DAY 5 ERO. SOME SCATTERED CONVECTION IN THE
SOUTHWESTERN U.S. INTO THE ROCKIES SHOULD CONTINUE INTO LATER WEEK,
EVENTUALLY FOCUSING WESTWARD A BIT (MORE INTO THE DESERT
SOUTHWEST) AS THE UPPER RIDGE RETROGRADES.
FARTHER EAST, MOISTURE ROUNDING THE UPPER RIDGE WILL SPREAD INTO
PARTS OF THE CENTRAL U.S., AND THUNDERSTORMS LIKELY IN THE FORM OF
MULTIPLE MESOSCALE CONVECTIVE SYSTEMS ARE FORECAST TO MOVE
GENERALLY WEST TO EAST OR NORTHWEST TO SOUTHEAST, WITH SHORTWAVE
ENERGIES NORTH OF THE RIDGE PROVIDING FORCING. MARGINAL RISKS
STRETCH ACROSS CENTRAL PARTS OF THE PLAINS INTO THE MIDDLE
MISSISSIPPI VALLEY (AND TENNESSEE VALLEY BY WEDNESDAY) TO COVER THE
FLASH FLOODING THREAT WITH THESE STORMS. CONVECTIVE STORMS LIKE
THESE "RIDGE RIDERS" ARE NOTORIOUSLY DIFFICULT TO PREDICT IN TERMS
OF EXACT PLACEMENT, BUT GIVEN THE POTENTIAL FOR HIGH RAIN RATES IN
AN UNSTABLE ENVIRONMENT, SLIGHT RISKS IN FUTURE CYCLES ARE
CERTAINLY A POSSIBILITY. THE MIDDLE MISSISSIPPI VALLEY MAY BE OF
PARTICULAR CONCERN INTO TUESDAY-WEDNESDAY IF STORMS REPEAT OVER
SIMILAR AREAS AS THE FORECAST CURRENTLY SUGGESTS. BY THURSDAY-
FRIDAY THERE IS A GENERAL TREND TOWARD CONVECTION MOVING EAST INTO
THE OHIO AND TENNESSEE VALLEYS TO SOUTHERN/CENTRAL APPALACHIANS. TO
THE NORTH, A COUPLE OF SHORTWAVES AND A FRONTAL SYSTEM OR TWO
SHOULD HELP TO FOCUS ROUNDS OF RAIN ACROSS THE NORTHERN PLAINS AND
UPPER MIDWEST NEXT WEEK. MODEL DIFFERENCES ABOUND WITH TIMING AND
AMOUNTS OF RAIN THERE IN THE NORTH-CENTRAL U.S., BUT DID DELINEATE
A MARGINAL RISK FOR DAY 5/WEDNESDAY ACROSS THE EASTERN DAKOTAS INTO
MINNESOTA WHERE WET ANTECEDENT CONDITIONS REMAIN FROM HEAVY RAINS
EARLIER THIS SUMMER.
MEANWHILE, A WAVY FRONT STALLING FROM THE CENTRAL GULF COAST INTO
GEORGIA AND THE CAROLINAS COULD HELP SPARK/FOCUS SCATTERED TO
WIDESPREAD RAIN LASTING INTO TUESDAY. IN THESE AREAS, RECENT
EXCESSIVE RAINFALL FROM DEBBY HAS RESULTED IN FULLY SATURATED SOILS
THAT MAY ONLY PARTIALLY RECOVER BY THEN. A MARGINAL RISK IS IN
EFFECT IN THIS PART OF THE SOUTHEAST FOR DAY 4/TUESDAY. THE CURRENT
FORECAST SHOWS LESS POTENTIAL FOR RAIN INTO WEDNESDAY AS THE FRONT
PUSHES SOUTH, BUT RAIN AND THUNDERSTORM CHANCES MAY RISE ONCE
AGAIN BY LATER WEEK FOR THIS AREA.
THE UPPER RIDGE AXIS OVER THE SOUTH-CENTRAL U.S. WILL MAINTAIN
TEMPERATURES UP TO 10F ABOVE (ALREADY HOT) NORMAL VALUES ACROSS THE
SOUTHERN PLAINS INTO THE CENTRAL GULF COAST. COMBINED WITH THE
HIGH DEWPOINTS IN MOST AREAS, HEAT INDICES ABOVE 110F ARE POSSIBLE,
AND EXPERIMENTAL HEATRISK SHOWS MAJOR TO EXTREME IMPACTS. NORTH OF
THIS REGION THOUGH, MOST AREAS SHOULD SEE NEAR TO SLIGHTLY BELOW
NORMAL HIGHS FROM THE WESTERN TO NORTH-CENTRAL TO EASTERN U.S., BUT
LOWS COULD BE A BIT ABOVE AVERAGE ESPECIALLY FOR THE INTERMOUNTAIN
WEST TO MIDWEST.
TATE
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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