796
FXUS02 KWBC 090657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM 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 INTO MUCH OF NEXT WEEK...
..OVERVIEW
A RATHER STAGNANT SUMMERTIME UPPER PATTERN WILL BE IN PLACE ACROSS
THE LOWER 48 NEXT WEEK, COMPOSED OF A CENTRAL U.S. 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 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.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL GUIDANCE SHOWS REASONABLY GOOD AGREEMENT WITH THE
OVERALL PATTERN, WITH SOME TYPICAL DIFFERENCES IN SHORTWAVES THAT
TRACK THROUGH THE MEAN FLOW. THE MOST EGREGIOUS MODEL DIFFERENCE
AROSE WITH THE 12Z CMC BY THE LATTER HALF OF NEXT WEEK. IT MOVES
WESTERN TROUGHING FARTHER INLAND THAN OTHER GUIDANCE, EVEN INTO THE
PLAINS BY NEXT FRIDAY, UNLIKE OTHER GUIDANCE THAT MAINTAINS
RIDGING THERE AS TROUGHING STAYS WEST. FORTUNATELY THE NEWER 00Z
CMC SEEMS MORE IN LINE. BY LATER WEEK THERE IS ALSO SOME SPREAD
WITH HOW DEEP TROUGHING IN THE EAST MAY GET AND HOW PROGRESSIVE IT
IS, AFFECTING FRONTAL AND SURFACE LOW POSITIONS. THE WPC FORECAST
USED A DETERMINISTIC MODEL BLEND EARLY IN THE PERIOD FAVORING THE
12Z ECMWF AND 18Z GFS, GRADUALLY INCORPORATING AND RAISING THE
PROPORTION OF THE GEFS AND EC ENSEMBLE MEANS AS THE PERIOD
PROGRESSED TO OVER HALF BY DAYS 6-7, TO SMOOTH OUT SOME OF THE
SMALLER DETAILS OF THE INDIVIDUAL MODELS.
..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. IF MODELS STAY CONSISTENT WITH A
RAINFALL MAXIMUM IN NORTHEASTERN COLORADO, A SLIGHT RISK MAY BE
WARRANTED HERE IN THE DAY 4/MONDAY ERO, IF FLOODING IMPACTS WOULD
BE FELT. AS IT STANDS NOW, 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
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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