316
FXUS02 KWBC 101839
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
239 PM 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/SOUTHEAST INTO MUCH OF NEXT WEEK...
..OVERVIEW
UPPER RIDGING 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/SOUTHEAST.
MONSOONAL MOISTURE WILL MAINTAIN RAIN CHANCES ACROSS THE FOUR
CORNERS STATES AND ADJACENT PLAINS, WHILE SOME MOISTURE MAKES IT
FARTHER NORTH INTO THE NORTHERN PLAINS TO MIDWEST, AND SOME ADVECTS
EAST AROUND THE RIDGE IN AN UNSTABLE AIRMASS FOR ROUNDS OF
MESOSCALE CONVECTIVE SYSTEMS THAT COULD FOCUS PARTICULARLY IN THE
MID- MISSISSIPPI VALLEY INTO THE OHIO 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/ROCKIES LATE WEEK. MEANWHILE, A TROPICAL SYSTEM THAT
IS LIKELY TO DEVELOP PER NHC COULD WORK FROM THE ANTILLES TO OFF
THE BAHAMAS IN ABOUT A WEEK, WHICH WILL CONTINUE TO BE MONITORED,
THOUGH FORTUNATELY MOST MODELS AND LATEST NHC GUIDANCE TAKES THE
LOW SYSTEM AWAY FROM THE LOWER 48 AT THIS POINT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS AND ENSEMBLES OFFER A REASONABLTY SIMILAR LARGER
SCALE SUMMER PATTERN EVOLUTION THROUGH MEDIUM RANGE TIME SCALES.
HOWEVER, GUIDANCE CONTINUES TO OFFER LESS THAN STELLAR FORECAST
SPREAD AND CYCLE TO CYCLE CONTINUITY VARIANCES WITH FLOW EMBEDDED
SMALL-MID SCALE SYSTEMS AND ASSOCIATED LOCAL WEATHER/CONVECTION
FOCUS. A COMPOSITE MODEL AND ENSEMBLE SOLUTION ALONG WITH THE
NATIONAL BLEND OF MODELS SEEMS TO OFFER A REASONABLE FORECAST
BASIS WITH DETAIL CONSISTENT WITH INDIVIDUAL SYSTEM PREDICTABILITY.
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.
..WEATHER/HAZARDS HIGHLIGHTS
IT GENERALLY REMAINS THE CASE THAT 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 THE CENTRAL
HIGH PLAINS. 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 AND LATEST
GUIDANCE HAS TRENDED SLIGHTLY MORE IN FAVOR OF THIS. BY THURSDAY-
FRIDAY THERE IS A GENERAL TREND TOWARD CONVECTION MOVING EAST INTO
THE OHIO AND TENNESSEE VALLEYS TO THE 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/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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