395
FXUS02 KWBC 271903
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
302 PM EDT THU JUL 27 2023
VALID 12Z SUN JUL 30 2023 - 12Z THU AUG 03 2023
...HOT TEMPERATURES AND HIGH HEAT INDICES ARE LIKELY ACROSS THE
SOUTH-CENTRAL PLAINS AND MISSISSIPPI VALLEY INTO THE SOUTHEAST
NEXT WEEK...
..OVERVIEW
THE PERSISTENT UPPER HIGH THAT HAS STAYED ATOP THE
SOUTHWEST/SOUTH-CENTRAL U.S. FOR WEEKS NOW IS FINALLY FORECAST TO
DRIFT EASTWARD NEXT WEEK, FINALLY BRINGING TEMPERATURES IN THE
DESERT SOUTHWEST CLOSER TO NORMAL (THOUGH STILL HOT). RIDGING
STRETCHING NORTH FROM THE UPPER HIGH WILL ALSO PROMOTE ABOVE
NORMAL TEMPERATURES ACROSS THE CENTRAL PLAINS TO MID-MISSISSIPPI
VALLEY WITH THE SOUTHEAST ALSO LIKELY TO WARM ABOVE NORMAL, WITH
HIGH HEAT INDICES. A "RING OF FIRE" TYPE OF PATTERN IS LIKELY IN
THE PRECIPITATION FORECAST, AS MONSOONAL MOISTURE LEADS TO
DIURNALLY DRIVEN CONVECTION IN THE FOUR CORNERS STATES AND
VICINITY, SHORTWAVES PUSH THROUGH NORTHWEST FLOW AND SPARK
THUNDERSTORMS IN THE NORTH-CENTRAL U.S., AND A COLD FRONT PRESSING
SOUTH AND THEN STALLING HELPS TO FOCUS RAIN AND STORMS AT LEAST
THE SOUTHERN HALF OF THE EASTERN SEABOARD. THERE IS A RISK OF
HEAVY RAINFALL AND FLASH FLOODING IN THESE AREAS WHERE HIGH RAIN
RATES OCCUR AND WHERE STORMS TRAIN/OCCUR OVER THE SAME AREAS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE HAS CONTINUED TO INDICATE THE MEDIUM RANGE
PERIOD WILL BEGIN IN THE MIDDLE OF MODERATE FLOW AMPLIFICATION AS
A STUBBORN UPPER-LEVEL HIGH OVER THE SOUTHWEST/SOUTH-CENTRAL U.S.
BUILDS A BIT NORTHWARD AND TROUGHING BUILDS SOUTHWARD OVER THE
UPPER-MIDWEST/NORTHEAST. THIS UPPER HIGH IS EXPECTED TO SHIFT
EASTWARD THROUGH THE PERIOD, AND WITH THIS EVOLUTION THERE MAY
CONSEQUENTLY BE SOME CORRESPONDING NORTHWARD ADJUSTMENT TO THE
TROUGHING ALONG THE EAST COAST. THIS EVOLUTION HAS ALSO REMAINED
THE MORE NOTABLE SOURCE OF GUIDANCE DISAGREEMENT OVER THE PAST
COUPLE DAYS. THE RECENT RUNS OF THE ECMWF, INCLUDING THE 00Z,
INDICATE THE UPPER-HIGH WILL COMBINE ONCE AGAIN WITH AN UPPER-HIGH
OVER THE WESTERN ATLANTIC FOLLOWING A BRIEF SPLIT AS THE
UPPER-TROUGH BUILDS SOUTHWARD OVER THE EAST COAST. HEIGHTS OVER
THE WESTERN ATLANTIC HAD BEEN A BIT LOWER IN THE GFS, THOUGH THE
00Z RUN DID BRIEFLY SHOW A SIMILAR PATTERN TO THE 00Z ECMWF,
BEFORE REVERSING A BIT AT 06Z. THE 00Z ECENS AND 00Z GEFS MEAN
FOLLOW A SIMILAR EVOLUTION TO THEIR RESPECTIVE DETERMINISTIC
COUNTERPARTS. OTHERWISE, SHORTWAVE ENERGY TRAVERSING NORTHWEST
FLOW OVER THE NORTHERN PLAINS/MIDWEST WILL LIKELY BE RELATED TO
ORGANIZED CONVECTION CHANCES DURING THE PERIOD, THOUGH WITH VERY
LOW PREDICTABILITY AT THIS TIME.
THE UPPER HIGH BUILDING NORTH ALSO LOOKS TO SHIFT MEAN TROUGHING
OVER THE PACIFIC NORTHWEST COAST NORTH/WESTWARD AS THE PATTERN
OVER THE WEST BEGINS TO AMPLIFY A BIT AS WELL, WITH SOUTHWEST FLOW
IN PLACE OVER PORTIONS OF THE WEST OVERALL. SUBTLE SHORTWAVE
ENERGY MAY TRANSLATE THROUGH AND HAVE SUBSEQUENT EFFECTS ON
PRECIPITATION CHANCES IN A MONSOONAL PATTERN THOUGH ANY DETAILS
ARE EXPECTEDLY HARD TO PREDICT AT THIS TIME RANGE. THE MORE RECENT
RUNS OF THE CMC AND GFS HAVE BEEN THE MOST ENERGETIC, BUT THIS IS
NOTED IN THE ECMWF AS WELL. THE UPPER HIGH OVER THE SOUTHERN TIER
LOOKS TO BUILD A BIT BACK OVER THE SOUTHWEST/NORTHERN MEXICO IN
THE LATEST 00Z AND 06Z GFS/00Z ECMWF RUNS AND 00Z ECENS/GEFS
MEANS, BUT NOT SO MUCH IN THE CMC. HEIGHTS OVERALL REMAIN THE MOST
EXPANSIVE ACROSS THE ENTIRE SOUTHERN TIER IN THE 00Z ECMWF/00Z
ECENS MEAN AND 00Z GFS COMPARED TO THE OTHER GUIDANCE (00Z CMC/00Z
GEFS MEAN) AT THE END OF THE PERIOD.
GOOD CLUSTERING OF THE GUIDANCE THROUGH THE EARLY PERIOD LENDS
ITSELF TO A GENERAL MODEL BLEND IN THE UPDATED WPC FORECAST. THE
00Z GFS IS FAVORED OVER THE 06Z GIVEN THE NOTED SIMILARITIES TO
THE ECMWF AND ECENS MEAN WITH RESPECT TO HEIGHTS OVER THE
SOUTHEAST. THE CONTRIBUTIONS FROM THE MEANS ARE NATURALLY
INCREASED TOWARDS THE END OF THE PERIOD WITH THE 00Z GFS/00Z ECMWF
AND 00Z ECENS FAVORED IN THE BLEND OVER THE 00Z CMC AND 00Z GEFS
MEAN GIVEN THE BETTER CONSENSUS ON THE OVERALL EXPANSION OF THE
UPPER HIGH OVER THE SOUTHERN TIER COMPARED TO THE OTHER GUIDANCE.
IT SHOULD BE NOTED THE UPDATED 12Z GFS WAS MORE SIMILAR TO THE 06Z
IN TERMS OF HEIGHTS OVER THE SOUTHEAST, THOUGH WAS STILL MORE
EXPANSIVE ACROSS THE SOUTHERN TIER COMPARED TO THE 00Z CMC/00Z
GEFS MEAN.
..WEATHER/HAZARDS HIGHLIGHTS
SHORTWAVE ENERGY IN NORTHWEST FLOW ALOFT FROM THE NORTH-CENTRAL
U.S. TO THE EASTERN U.S. WILL CARRY SHOWERS AND THUNDERSTORMS
ACROSS THOSE REGIONS EARLY TO MID-NEXT WEEK. IN THE EAST, BY
SUNDAY THE NORTHEAST SHOULD BE POST-FRONTAL AND DRY, WHILE A COLD
FRONT PRESSING SLOWLY SOUTH IN THE MID-ATLANTIC TO CAROLINAS
SHOULD HELP SPARK CONVECTION THERE. A MARGINAL RISK IS IN PLACE
FOR THIS MORE FOCUSED ACTIVITY IN AN UNSTABLE AND MOIST
ENVIRONMENT. FORECAST QPF HAS REMAINED RATHER LOW OVER WESTERN,
MOUNTAINOUS AREAS OF THE REGION, AND DESPITE HEIGHTENED
SENSITIVITY TO ANY LOCALLY HEAVY DOWNPOURS, LOW CONFIDENCE IN
SPATIAL CONVERGE HAS LED TO AN UPDATED MARGINAL RISK AREA FOCUSED
FARTHER EAST. THE COLD FRONT SHOULD PUSH EVEN FARTHER SOUTH MONDAY
FOR A CONVECTIVE FOCUS OVER THE SOUTHEAST. A MARGINAL RISK HAS
BEEN DRAWN UP IN THE DAY 5 ERO FOR PORTIONS OF GEORGIA AND FLORIDA
AS THERE COULD BE HIGH RAIN RATES POSSIBLY CAUSING EXCESSIVE
RAINFALL. THE COMBINATION OF AN ADDITIONAL FRONTAL PASSAGE AS WELL
AS THE SOUTHERN FRONT RETREATING BACK A BIT NORTHWARD IS THEN
LIKELY TO BRING PRECIPITATION CHANCES BACK UP THE EAST COAST MID
NEXT WEEK.
MEANWHILE, THE NORTH-CENTRAL U.S. CAN ALSO EXPECT SCATTERED STORMS
AS SHORTWAVES TRACK THROUGH THE REGION AND MOISTURE INCREASES. A
HEAVY RAIN/FLASH FLOODING THREAT WILL LIKELY BE TIED TO THE
POTENTIAL FOR ORGANIZED CONVECTIVE SYSTEMS IN THE NORTHWESTERLY
FLOW. DAY TO DAY POSITIONS OF HEAVY RAIN AND MCSS ARE VERY
UNCERTAIN AT THIS POINT WITH NOTABLE QPF FOOTPRINT CHANGES
RUN-TO-RUN IN THE GUIDANCE. BROAD MARGINAL RISKS HAVE BEEN
INCLUDED ON BOTH DAYS 4 AND 5 TO COVER THIS POTENTIAL, WITH THE
EXPECTATION THAT THEIR AREAL COVERAGE MAY LIKELY STILL NEED SOME
FURTHER ADJUSTMENT, AND EVENTUAL MORE CONCENTRATED SLIGHT RISKS
POSSIBLE. THE FOUR CORNERS STATES AND INTO WYOMING ARE LIKELY TO
SEE DIURNALLY DRIVEN CONVECTION EACH DAY AS MONSOONAL MOISTURE
COMES IN, AND AS THE UPPER HIGH SHIFTS EASTWARD WITH TIME THIS MAY
INCREASE MOIST SOUTHERLY FLOW AND ALLOW FOR ADDITIONAL SHORTWAVE
ENERGY TO COME IN. THERE IS ALSO A NOTABLE TREND OF QPF BECOMING
MORE WIDESPREAD AND LOCALLY HEAVIER AS THE WEEK PROGRESSES, AND
MARGINAL RISKS ARE IN PLACE AND BECOME BROADER WITH TIME.
BY EARLY NEXT WEEK, THE PERSISTENT UPPER HIGH THAT HAS BEEN
CENTERED OVER THE SOUTHWEST/SOUTH-CENTRAL U.S. WILL START DRIFTING
EASTWARD, ALLOWING FOR HIGH TEMPERATURES IN THE DESERT SOUTHWEST
TO FINALLY EASE TO NEAR NORMAL. HIGHS SHOULD STILL BE OVER 100F IN
MANY AREAS BUT AT LEAST THERE SHOULD BE MINOR RELIEF COMPARED TO
THE PAST FEW WEEKS. MEANWHILE WITH THE CORE OF THE UPPER
HIGH/RIDGE TRACKING EAST, TEMPERATURES ARE LIKELY TO INCREASE TO
ABOVE NORMAL WITH IT. THE MOST PERSISTENT/GREATEST ANOMALIES
SHOULD BE IN THE CENTRAL PLAINS TO THE MID-MISSISSIPPI VALLEY,
WHERE ABOVE NORMAL TEMPERATURES BY 5 TO 15 DEGREES ARE LIKELY AS
ACTUAL TEMPERATURES NEAR OR EXCEED 100F. THE SOUTHERN PLAINS TO
LOWER MISSISSIPPI VALLEY AND SOUTHEAST MAY SEE SLIGHTLY LOWER
ANOMALIES OF 5-10F ABOVE NORMAL, BUT THE HEAT COMBINED WITH HIGH
DEWPOINTS WILL LEAD TO HEAT INDICES SOARING ABOVE 105F, EVEN ABOVE
110-115F IN SOME AREAS. RECORD HOT HIGHS AND WARM MINIMUM
TEMPERATURES ARE POSSIBLE IN THESE REGIONS. SLIGHTLY COOLER THAN
AVERAGE TEMPERATURES ARE POSSIBLE IN THE PACIFIC NORTHWEST THIS
WEEKEND/EARLY NEXT WEEK BEFORE SHIFTING INTO THE INTERMOUNTAIN
WEST CLOSER TO THE MIDDLE OF NEXT WEEK AS UPPER-RIDGING BUILDS
NORTHWARD AND PRECIPITATION CHANCES INCREASE OVER THE
INTERMOUNTAIN WEST. THE NORTHEAST SHOULD ALSO BE SLIGHTLY BELOW
NORMAL FOR TEMPERATURES AS A COUPLE OF COLD FRONTS PASS THROUGH.
PUTNAM/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, 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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