340
FXUS02 KWBC 091859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT FRI AUG 9 2024
VALID 12Z MON AUG 12 2024 - 12Z FRI AUG 16 2024
...EXCESSIVE HEAT LINGERS OVER PORTIONS OF TEXAS AND THE CENTRAL
GULF COAST STATES INTO MUCH OF NEXT WEEK...
..OVERVIEW
IT IS GENERALLY STILL THE CASE THAT A RATHER STAGNANT SUMMERTIME
UPPER PATTERN WILL BE IN PLACE ACROSS THE LOWER 48 NEXT WEEK,
COMPOSED OF A CENTRAL U.S. MEAN RIDGE AND MEAN TROUGHING IN THE
WESTERN AND EASTERN U.S. ON EITHER SIDE. THE SOUTH-CENTRAL U.S. CAN
EXPECT HIGH HEAT INDICES TO CONTINUE UNDERNEATH THIS UPPER RIDGE,
BUT TEMPERATURES FOR MANY OTHER AREAS OF THE COUNTRY ELSEWHERE
SHOULD GENERALLY BE NEAR TO BELOW NORMAL. 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.
THE NHC IS ALSO INDICATING POSSIBLE NEW TROPICAL SYSTEM
DEVELOPMENT OUT FROM THE TROPICAL ATLANTIC AND ANTILLES THAT
SUBSEQUENTLY OFFERS AN INCREASING SIGNAL OFF THE SOUTHEAST U.S.
AND BAHAMAS IN ABOUT A WEEK TO MONITOR.
..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. PREDICTABILITY SEEMS SLIGHTLY
ABOVE NORMAL IN THIS PERIOD. ONE SIGNIFICANT MODEL DIFFERENCE WAS
EVIDENT WITH THE 06 UTC GFS BY THE LATTER HALF OF NEXT WEEK. IT
MOVES WESTERN U.S. ORIGIN TROUGHING FARTHER INLAND THAN MOST 00
UTC GUIDANCE, EVEN INTO THE PLAINS BY NEXT FRIDAY, UNLIKE OTHER
GUIDANCE THAT MAINTAINS RIDGING THERE AS TROUGHING STAYS WEST. THE
12 UTC GFS/ECMWF ARE NOW MORE IN LINE WITH THE 06 UTC GFS, BUT THE
12 UTC CANADIAN HAS NOT TRENDED IN THAT DIRECTION. QUITE UNCERTAIN.
ACCORDINGLY, THE WPC FORECAST USED A DETERMINISTIC MODEL BLEND
MONDAY INTO WEDNESDAY WITH THE GFS/ECMWF/CANADIAN/UKMET. OPTED TO
SWITCH TO A COMPOSITE OF BEST COMPATIBLE GEFS AND ECMWF ENSEMBLE
MEANS DAYS 6-7 AMID NOTED GROWING FORECAST SPREAD AND UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
ABOVE NORMAL MOISTURE WILL BE DIRECTED INTO THE FOUR CORNERS
STATES AND NORTH AND EAST NEXT WEEK. MODERATE TO LOCALLY HEAVY RAIN
LOOKS TO BE MOST LIKELY ON MONDAY IN AREAS LIKE THE CENTRAL
ROCKIES AND CENTRAL HIGH PLAINS. BROAD MARGINAL RISKS ARE IN PLACE
ACROSS MUCH OF THE FOUR CORNERS STATES AND INTO SOUTHERN WYOMING
FOR MONDAY AND TUESDAY. SCATTERED CONVECTION IN THE SOUTHWESTERN
U.S. INTO THE ROCKIES SHOULD CONTINUE INTO LATER WEEK.
FARTHER EAST, MOISTURE ROUNDING THE UPPER RIDGE WILL SPREAD INTO
PARTS OF THE CENTRAL U.S., AND CONVECTION LIKELY IN THE FORM OF
MULTIPLE MESOSCALE CONVECTIVE SYSTEMS ARE FORECAST TO MOVE
GENERALLY WEST TO EAST. MARGINAL RISKS STRETCH ACROSS CENTRAL PARTS
OF THE PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY 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 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.
MEANWHILE, A WAVY FRONT STALLING FROM THE CENTRAL GULF COAST INTO
GEORGIA AND THE CAROLINAS COULD HELP SPARK/FOCUS SCATTERED TO
WIDESPREAD RAIN INTO MONDAY-TUESDAY. IN THESE AREAS, RECENT
EXCESSIVE RAINFALL FROM DEBBY HAS RESULTED IN FULLY SATURATED SOILS
THAT MAY ONLY PARTIALLY RECOVER BY THEN. MARGINAL RISKS ARE IN
EFFECT IN THIS PART OF THE SOUTHEAST FOR DAYS 4-5.
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 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.
TATE/SCHICHTEL
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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