448
FXUS02 KWBC 270701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM 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 SOUTHERN
ROCKIES 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 REMAINED MOSTLY CONSISTENT ON THE
OVERALL SUMMERTIME UPPER-LEVEL PATTERN THROUGH MUCH OF THE MEDIUM
RANGE PERIOD, CONSISTING OF THE UPPER HIGH GRADUALLY MOVING EAST
ATOP THE SOUTH-CENTRAL U.S. WHILE A TROUGH AXIS PERSISTS OVER THE
NORTHEAST, AND MORE PROGRESSIVE FLOW WITH MULTIPLE ENERGIES IS
LIKELY FROM THE EASTERN PACIFIC INTO THE NORTHWESTERN AND
NORTH-CENTRAL U.S. AND SOUTHERN CANADA. WHILE THE GENERAL TREND OF
THE UPPER HIGH EASTWARD SHOWS GOOD AGREEMENT IN MODEL GUIDANCE,
THERE HAS BEEN SOME MINOR WAFFLING WITH JUST HOW FAST IT WILL
SHIFT EAST, ESPECIALLY BY AROUND MIDWEEK. THE 00Z GUIDANCE CYCLES
THE PAST COUPLE OF NIGHTS HAVE TENDED TO BE SLOWER THAN THE 12Z
CYCLES. THESE ARE RELATIVELY MINOR DIFFERENCES BUT THEY DO AFFECT
THE FLOW PATTERN FARTHER NORTH AS AN INITIALLY EASTERN PACIFIC
SHORTWAVE OR TWO TRACK EAST ACROSS SOUTHERN CANADA, POTENTIALLY
SUPPRESSING THE RIDGE STRETCHING NORTH. GFS RUNS HAVE BEEN ON THE
FASTER SIDE WITH WITH THE SHORTWAVE/SMALL CLOSED LOW EJECTING EAST
FROM THE PACIFIC NORTHWEST AROUND MONDAY-TUESDAY COMPARED TO OTHER
MODELS/ENSEMBLES. BUT BEYOND THAT ALL MODELS DIVERGE WITH NOT
REALLY CLEAR OUTLIERS OR FAVORED SOLUTIONS. MEANWHILE THE TROUGH
IN THE EAST IS QUITE AGREEABLE IN THE MODEL GUIDANCE, THOUGH
STARTS TO SHOW SOME DIFFERENCES BY WEDNESDAY-THURSDAY AS THE
SHORTWAVES APPROACH FROM THE WEST AND POSSIBLY THE NORTHWEST AS
WELL. IT REMAINS UNCERTAIN IF THIS WILL PUSH THE INITIAL TROUGHING
EAST AND ANOTHER TROUGH AXIS FORMS, OR IF AND WHEN THE SHORTWAVE
ENERGY GETS ABSORBED INTO THE ORIGINAL TROUGH. SOME SMALL-SCALE
ENERGIES COMING INTO THE WEST ARE LOOKING MORE FAVORABLE BY
MIDWEEK, WHICH WILL HAVE IMPLICATIONS ON MONSOON/OVERALL
PRECIPITATION ACTIVITY OVER THE REGION.
WITH THE BROAD REASONABLE AGREEMENT BUT WITH THE SMALLER-SCALE
DIFFERENCES NOTED ABOVE, THE WPC FORECAST WAS BASED ON A BLEND OF
THE 12/18Z DETERMINISTIC GUIDANCE EARLY IN THE PERIOD, WITH
INCREASING PROPORTIONS OF THE ENSEMBLE MEANS FROM THE GEFS AND EC
TO ABOUT HALF BY THE END OF THE PERIOD AMID INCREASING UNCERTAINTY.
..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. THERE ARE SOME MODEL DIFFERENCES WITH HOW FAR INLAND
ENHANCED RAINFALL TOTALS WILL MAKE IT, BUT THE RISK AREA STRETCHES
BACK INTO THE SOUTHERN APPALACHIANS IN CASE HEAVY RAIN FALLS IN
SENSITIVE MOUNTAINOUS AREAS. BUT IF MODEL GUIDANCE CONTINUES TO
TREND DOWN WITH RAIN TOTALS THERE, THE MARGINAL MAY BE ABLE TO BE
TRIMMED ON THE WESTERN SIDE TO FOCUS 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 FOR PORTIONS OF
GEORGIA AND FLORIDA AS THERE COULD BE HIGH RAIN RATES POSSIBLY
CAUSING EXCESSIVE RAINFALL. ANOTHER FRONT IS THEN LIKELY TO PUSH
THROUGH THE NORTHEAST AND MID-ATLANTIC BY TUESDAY-WEDNESDAY,
TRENDING PRECIPITATION CHANCES UPWARD IN THE REGION AT THAT POINT.
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 UNCERTAIN
AND VARY SOMEWHAT AMONG MODEL GUIDANCE, BUT MARGINAL RISKS COVER
THIS POTENTIAL FOR EARLY NEXT WEEK. 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. THUS RAINFALL
TOTALS MAY BECOME 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 SOUTHERN ROCKIES WILL FINALLY 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 EARLY
NEXT WEEK AND PERHAPS SHIFTING INTO THE INTERMOUNTAIN WEST CLOSER
TO THE MIDDLE OF NEXT WEEK. THE NORTHEAST SHOULD ALSO BE SLIGHTLY
BELOW NORMAL FOR TEMPERATURES AS A COUPLE OF COLD FRONTS PASS
THROUGH.
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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