524
FXUS02 KWBC 152032
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
431 PM EDT THU JUN 15 2023
VALID 12Z SUN JUN 18 2023 - 12Z THU JUN 22 2023
***EARLY SEASON HEAT WAVE TO PERSIST ACROSS MUCH OF THE
SOUTH-CENTRAL U.S. INTO EARLY NEXT WEEK AND BEYOND***
..SYNOPTIC OVERVIEW
FOR THE BEGINNING OF THE FORECAST PERIOD SUNDAY, A WELL DEFINED
NORTHEASTERN PACIFIC/GULF OF ALASKA TROUGH WITH EMBEDDED UPPER LOW
WILL BUILD SOUTHEASTWARD ACROSS THE WESTERN U.S. AND SOUTHWESTERN
CANADA AS A WEAK COASTAL LOW PRESSURE SYSTEM WILL BE EXITING NEW
ENGLAND. THE CORE OF THE UPPER RIDGE OVER SOUTHERN TEXAS AND
NORTHEASTERN MEXICO WILL PERSIST THROUGH THE FORECAST PERIOD,
MAINTAINING A SOUTH-CENTRAL U.S. HEAT WAVE THAT SHOULD EXTEND
THROUGH NEXT WEEK. MEANWHILE, THE PATTERN EVOLUTION SHOULD FAVOR
AN AREA OF ENHANCED RAINFALL FROM THE MIDWEST STATES INTO THE
SOUTHEAST U.S., WITH PORTIONS OF THE DEEP SOUTH LIKELY HAVING THE
HIGHEST TOTALS OVERALL. THE NORTHWESTERN U.S./NORTHERN ROCKIES
SHOULD SEE PRECIPITATION INCREASE EARLY NEXT WEEK AS THE WESTERN
SYSTEM MOVES IN, AND THE INITIAL UPPER TROUGH/LOW OVER THE
NORTHEAST WILL ALSO SUPPORT PERIODS OF RAINFALL THERE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MODEL GUIDANCE FOR THIS FORECAST UPDATE LOOKS TO BE IN GOOD
AGREEMENT WITH THE OVERALL EVOLUTION OF THE UPPER-LEVEL PATTERN.
THE PERIOD BEGINS DURING A BRIEF TRANSITION IN THE PATTERN AS
VARIOUS UPPER-LEVEL TROUGH/RIDGE FEATURES EVOLVE FROM THEIR
CURRENT PLACEMENT, BUT EVENTUALLY ARE REPLACED WITH A SIMILAR
BLOCKY PATTERN THAT HAS BECOME COMMON RECENTLY WITH MEAN TROUGHING
IN THE WEST, MEAN RIDGING IN THE CENTRAL U.S., AND A DEVELOPING
REX BLOCK OVER THE EAST. AN INITIAL SOUTHERN STREAM SHORT-WAVE
TROUGH WILL MOVE EASTWARD OVER TOP RIDGING OVER TEXAS AND
EVENTUALLY SETTLE INTO THE SOUTHEASTERN U.S., EXPECTED TO DEEPEN
INTO A CLOSED LOW. RIDGING OVER TEXAS WILL THEN BUILD NORTH AND
EVENTUALLY NORTHEASTWARD INTO SOUTHEASTERN CANADA, SETTING UP THE
EASTERN REX BLOCK AT THE END OF THE PERIOD. MEANWHILE, ANOTHER
DEEP, NORTHEASTERN PACIFIC/GULF OF ALASKA TROUGH WILL DIG
SOUTHWARD OVER THE WEST, COMPLETING THE RETURN TO A BLOCKY
PATTERN. MORE SUBTLE DIFFERENCES EXPECTEDLY ARISE WITH THE TIMING
AND MOVEMENT OF THE SHORTWAVE ENERGY THROUGH THE SOUTH, WITHIN THE
DEVELOPING TROUGH OVER THE WEST, AND THE DEGREE OF RIDGING THAT
BUILDS NORTHEASTWARD INTO SOUTHEASTERN CANADA. MORE SPECIFICALLY,
THE SOUTHERN STREAM SHORTWAVE IS A BIT OUT OF PHASE IN THE 00Z CMC
AND UKMET COMPARED TO A MORE SIMILAR EVOLUTION IN THE 06Z GFS AND
00Z ECMWF. THE MORE RECENT RUNS OF THE DETERMINISTIC GFS AND ECMWF
ARE ALSO BOTH A BIT MORE AGGRESSIVE WITH THE RIDGING BUILDING INTO
SOUTHEASTERN CANADA. HOWEVER, THE 06Z GEFS AND 00Z ECENS MEANS
BOTH ALSO SUPPORT THIS THIS EVOLUTION. DESPITE THESE DIFFERENCES,
A GENERAL MODEL BLEND FOR THE UPDATED WPC FORECAST IS APPROPRIATE
GIVEN THE SIMILARITY OF THE EVOLUTION IN THE PATTERN, WITH A BIT
MORE WEIGHT ON THE 06Z GFS/00Z ECMWF COMPARED TO THE 00Z CMC/UKMET
THROUGH THE EARLY PART OF THE PERIOD. A CONTRIBUTION FROM THE 00Z
ECENS MEANS IS ADDED TO REPLACE THE FORECAST TIME-LIMITED 00Z
UKMET FOR THE END OF THE PERIOD, WHICH RETAINED MORE DETAIL
SIMILAR TO THE DETERMINISTIC MODELS, ESPECIALLY WITH RESPECT TO A
STRONGER RIDGE BUILDING INTO SOUTHEASTERN CANADA AND DEEPER CLOSED
LOW OVER THE SOUTHEASTERN U.S. THIS FORECAST BLEND ALSO KEEPS
GENERAL CONTINUITY WITH THE PRIOR FORECAST SUGGESTING GOOD
CONSISTENCY IN THE GUIDANCE AND OVERALL FORECAST, WITH THE MAIN
CHANGES BEING A BIT STRONGER RIDGE OVER THE CENTRAL U.S. AND A BIT
DEEPER CUTOFF LOW OVER THE SOUTHEAST.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY SHOWERS AND STORMS ARE EXPECTED TO DEVELOP SUNDAY (DAY 4)
FROM MISSOURI INTO THE DEEP SOUTH AS THE SOUTHERN STREAM SHORTWAVE
PASSES OVER A NORTHWARD MOVING WARM FRONT, USHERING IN DEEPER GULF
MOISTURE SUPPORTED BY AN OVERNIGHT LOW-LEVEL JET. A SLIGHT RISK
OF EXCESSIVE RAINFALL IS IN EFFECT FOR PORTIONS OF THE MID-SOUTH
SOUTHEAST INTO MISSISSIPPI AND ALABAMA WHERE THERE IS A GROWING
SIGNAL FOR AREAL AVERAGE RAINFALL OF 1-3", WITH LOCALLY HIGHER
AMOUNTS. PORTIONS OF THIS REGION WILL ALSO LIKELY RETAIN WET
ANTECEDENT CONDITIONS GIVEN RECENT EPISODES OF HEAVY RAINFALL LATE
THIS WEEK AND INTO THE WEEKEND. GOING INTO THE DAY 5 PERIOD
MONDAY-MONDAY NIGHT, THE GUIDANCE SUGGESTS THE CORE OF THE
HEAVIEST RAINFALL MAY EXHIBIT MORE OF A BI-MODAL DISTRIBUTION
ACROSS THE SOUTHEASTERN U.S., WITH ONE MAXIMA OVER NORTHERN
GEORGIA AND THE SOUTHERN APPALACHIANS, AND ANOTHER MAXIMA NEAR THE
GA/FL BORDER. THE INHERITED SLIGHT RISK HAS BEEN EXPANDED
NORTHEASTWARD ALONG THE SOUTHERN APPALACHIANS AND SOUTH TO THE
GA/FL BORDER AS THE CLOSED UPPER-LOW BEGINS TO SETTLE IN AND
MOIST, ONSHORE FLOW FROM BOTH THE GULF AND SOUTHWEST ATLANTIC
SUPPORTS CONTINUED HEAVY AREAL AVERAGE RAINFALL. THIS HEAVY RAIN
WILL LIKELY CONTINUE INTO MID-WEEK AS A FRONTAL BOUNDARY LIFTS
NORTHWARD, SPREADING FURTHER NORTHEASTWARD UP THE COAST INTO THE
MID-ATLANTIC. TEMPERATURES ACROSS THE REGION WILL CONTINUE TO BE
BELOW AVERAGE WITH THE CLOSED-LOW OVERHEAD, INFLUENCE OF
CLOUDS/PRECIPITATION, AND COLD-AIR DAMMING SETTING UP ALONG THE
APPALACHIANS.
ELSEWHERE ACROSS THE U.S., THE UPPER TROUGH/LOW DIGGING INTO THE
WEST WILL LIKELY INCREASE THE COVERAGE AND INTENSITY OF
PRECIPITATION OVER THE PACIFIC NORTHWEST AND ESPECIALLY THE
NORTHERN ROCKIES FROM SUNDAY INTO TUESDAY. SOME LOCALLY HEAVY
RAIN MAY FALL OVER AREAS IN THE NORTHERN ROCKIES THAT COULD BE
SENSITIVE DUE TO WELL ABOVE NORMAL RAINFALL OVER THE PAST FEW
WEEKS. NOTICEABLY COOLER TEMPERATURES WILL ALSO BE USHERED IN BY
MONDAY AS THE TROUGH BEGINS TO SETTLE IN ACROSS MUCH OF
CALIFORNIA, NEVADA, WASHINGTON, OREGON, AND IDAHO. AFTERNOON HIGHS
SHOULD GENERALLY BE 5 TO 15 DEGREES BELOW AVERAGE, WITH THE
GREATEST ANOMALIES MONDAY-TUESDAY OVER THE NORTHERN GREAT BASIN,
WHERE HIGHS COULD BE UP TO 20 DEGREES BELOW AVERAGE. A FEW PLACES
COULD CHALLENGE DAILY RECORDS FOR COOL HIGHS.
THE EXCESSIVE HEAT WILL CONTINUE INTO NEXT WEEK ACROSS MUCH OF
TEXAS AND INTO PORTIONS OF LOUISIANA, OKLAHOMA, AND NEW MEXICO,
WITH WIDESPREAD 100S AND EVEN SOME 110S ACROSS CENTRAL AND
SOUTHERN PORTIONS OF TEXAS, AND 90S COVERING MUCH OF THE DEEP
SOUTH AND THE CENTRAL PLAINS. MANY DAILY RECORD HIGH TEMPERATURES
ARE POSSIBLE, AND SOME MONTHLY RECORDS MAY EVEN BE CHALLENGED.
HEAT INDICES AS HIGH AS 115-120 DEGREES ARE POSSIBLE FOR PARTS OF
SOUTHERN AND SOUTHEASTERN TEXAS WHERE THE GREATEST COMBINATION OF
HIGH DEWPOINTS AND TEMPERATURES WILL LIKELY EXIST. AS MEAN RIDGING
EXPANDS FURTHER NORTH, ADDITIONAL MUCH ABOVE AVERAGE TEMPERATURES
ARE FORECAST FOR PORTIONS OF THE NORTHERN PLAINS, PARTICULARLY ON
MONDAY-TUESDAY, WITH HIGHS REACHING INTO THE MID- TO UPPER 90S. A
COLD FRONT MOVING INTO THE REGION WEDNESDAY-THURSDAY WILL BRING
COOLER TEMPERATURES AND A CHANCE FOR LOCALLY HEAVY RAINFALL.
PUTNAM/HAMRICK
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF TENNESSEE VALLEY, SOUTHERN
APPALACHIANS, THE DEEP SOUTH, UPSTATE NORTH AND SOUTH CAROLINA,
AND THE INTERIOR SOUTHEAST, AND THE EASTERN GULF COAST, SUN-MON,
JUN 18-JUN 19.
- HEAVY RAIN ACROSS MUCH OF THE MID-ATLANTIC INTO PORTIONS OF THE
CENTRAL AND SOUTHERN APPALACHIANS, AND INTO THE INTERIOR
SOUTHEAST, TUE-WED, JUN 20-JUN 21.
- HEAVY RAIN ACROSS PORTIONS OF THE EASTERN GULF COAST, TUE, JUN
20.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHERN PLAINS TO THE CENTRAL
HIGH PLAINS, WED-THU, JUN 21-JUN 22.
- SEVERE WEATHER ACROSS PORTIONS OF THE MID-SOUTH, SUN, JUN 18.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN
PLAINS, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN.
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN PLAINS.
- EXCESSIVE HEAT ACROSS THE SOUTHERN PLAINS INTO THE LOWER
MISSISSIPPI VALLEY, SUN-THU, JUN 18-JUN 22.
- EXCESSIVE HEAT ACROSS PORTIONS OF THE NORTHERN PLAINS, MON-TUE,
JUN 19-JUN 20.
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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