640
FXUS02 KWBC 051926
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
325 PM EDT TUE SEP 05 2023
VALID 12Z FRI SEP 08 2023 - 12Z TUE SEP 12 2023
...HEATWAVE TO MODERATE IN THE EAST LATE WEEK, BUT PERSIST IN
EARNEST ACROSS THE SOUTH-CENTRAL U.S AND SOUTHWEST...
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN DECENT AGREEMENT ON MOST OF THE LARGE SCALE
DETAILS THROUGH THE FORECAST PERIOD. THE PERIOD BEGINS WITH A BIT
OF AMPLIFICATION TO THE PATTERN WITH A TROUGH DEEPENING OVER THE
EASTERN U.S. AND A RIDGE OVER THE SOUTHERN PLAINS/SOUTHWEST
EXPANDING/BUILDING A BIT WEST AND NORTHWARD. THE MAIN IMPLICATION
OF THIS SHIFT WILL BE FOR THE DEEPENING TROUGH/EMBEDDED SHORTWAVES
TO DRIVE A COUPLE FRONTAL SYSTEMS TO THE EAST AND GULF COASTS.
THEREAFTER, THE MAIN SURFACE FEATURES LOOK TO REMAIN RELATIVELY
STAGNANT THROUGH MOST OF THE PERIOD. SOME UNCERTAINTY ARISES
TOWARDS THE END OF THE PERIOD EARLY NEXT WEEK AS THE PATTERN
TRENDS LESS AMPLIFIED WITH THE RIDGE OVER THE SOUTHWEST FLATTENING
AS MORE NORTHERN STREAM ENERGY BEGINS TO DROP SOUTHWARD OVER THE
PLAINS. THE GFS HAD BEEN TRENDING A BIT MORE AGGRESSIVE IN
DEVELOPING A STRONGER CLOSED LOW OVER SOUTH-CENTRAL CANADA INTO
THE NORTHERN PLAINS/UPPER MIDWEST BEFORE THE 06Z GFS REVERSED
COURSE AND RETURNED TOWARDS A MORE SIMILAR SOLUTION TO THE
EMCWF/CMC, WHICH BRING AN OPEN NORTHERN STREAM WAVE SOUTHWARD.
THIS LEADS TO HIGHER UNCERTAINTY WITH THE RELATED CHANCES FOR
STORMS AND POTENTIAL FOR HEAVY RAINFALL OVER THE PLAINS DURING
THIS TIME FRAME. THE GOOD GUIDANCE AGREEMENT THROUGH MOST OF THE
PERIOD LED TO A SIMPLE CONSENSUS BLEND OF THE 00Z ECMWF/CMC/UKMET
AND 06Z GFS FOR THE UPDATED WPC FORECAST. A CONTRIBUTION FROM THE
00Z ECENS/GEFS MEANS IS ADDED FOR THE LATE PERIOD AS THE UKMET IS
TIME-LIMITED, BUT A REMAINING BLEND OF DETERMINISTIC GUIDANCE IS
OTHERWISE STILL SUFFICIENT GIVEN A REASONABLE CLUSTERING OF THE
SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
THE EMERGENCE OF AN AMPLIFIED UPPER TROUGH THROUGH THE
MIDWEST/OHIO VALLEY WILL ACT TO SUPPRESS UPPER RIDGING AND HIGH
HEAT ACROSS THE EAST BY FRIDAY. UPPER TROUGHING WILL SETTLE OVER
THE EAST THROUGH THE WEEKEND INTO EARLY NEXT WEEK AS ANCHORED BY
AN UPPER LOW OVER HUDSON BAY AND AS A SERIES OF WEAKER IMPULSES
RIDE OVER THE TOP THEN TO THE LEE OF THE TRANSITIONING UPPER RIDGE
AS IT STRENGTHENS OVER THE SOUTH AND EXPANDS WESTWARD INTO THE
SOUTHWEST. WITH THIS RIDGE IN PLACE, HOT LATE SUMMER TEMPERATURES
WILL LINGER ACROSS THE SOUTH-CENTRAL U.S. AND THE SOUTHWEST
THROUGH THIS WEEKEND. TEMPERATURE ANOMALIES WILL BE STRONGEST IN
THE SOUTHERN PLAINS LATE WEEK, WITH SOME TEMPERATURES 15-20
DEGREES ABOVE NORMAL, WELL INTO THE 100S. HIGH DEWPOINTS AND
HUMIDITY ESPECIALLY NEAR THE WESTERN GULF COAST WILL LEAD TO
DANGEROUS HEAT INDICES AS HIGH AS 115 DEGREES. ABOVE NORMAL
TEMPERATURES BY ABOUT 10-15 DEGREES SHOULD PERSIST INTO THE
WEEKEND BROADLY ACROSS THE SOUTH-CENTRAL U.S. AND INTO THE
SOUTHWEST. MANY DAILY RECORD HIGH MINIMUM AND MAXIMUM TEMPERATURES
ARE LIKELY TO BE SET, WITH PERHAPS EVEN A FEW MONTHLY RECORDS, IN
WHAT HAS PROVEN TO BE A SWELTERING SUMMER. UPPER-LEVEL ENERGY
TRENDING SOUTHWARD SHOULD HELP TO REDUCE THE STRENGTH OF THE RIDGE
AND BEGIN TO BRING TEMPERATURES TO STILL HOT BUT MORE REASONABLE
LEVELS EARLY NEXT WEEK.
MEANWHILE IN THIS PATTERN, THE EAST OFFERS A MAIN AREA FOR
PRECIPITATION TO FOCUS, GIVEN MOISTURE (HIGHER PRECIPITABLE WATER
VALUES THAN AVERAGE IN THE NORTHEAST AT LEAST) AND INSTABILITY
POOLING AHEAD OF THE TROUGH AND FRONTAL SYSTEM. WHILE RAIN AMOUNTS
SHOULD BE MAINLY MODERATE, THE INGREDIENTS WILL BE IN PLACE FOR
LOCALIZED HEAVIER RAIN TOTALS ESPECIALLY BECAUSE STORMS MAY BE
SLOW-MOVING AND RELATIVELY PARALLEL TO THE FRONT, ALLOWING FOR
POTENTIAL TRAINING OF STORMS. THE WPC DAY 4/5 EXCESSIVE RAINFALL
OUTLOOKS (EROS) DENOTE "MARGINAL" RISK AREAS FOR FRIDAY AND
SATURDAY FROM THE NORTHERN MID-ATLANTIC INTO THE NORTHEAST AS
CONVECTION LOOKS TO HAVE A RELATIVELY BETTER FOCUS NEAR/AHEAD OF
THE FRONT AND FAVORABLE RIGHT ENTRANCE REGION UPPER JET SUPPORT.
THE MARGINAL RISK ENCOMPASSES LOWER FFGS FROM PENNSYLVANIA INTO
THE NORTHEAST AND INCLUDES FAVORED TERRAIN OF THE POCONOS AND
CATSKILLS TO THE ADIRONDACKS AND GREEN MOUNTAINS. RAIN CHANCES
SHOULD GRADUALLY DECREASE INTO NEXT WEEK ALONG THE EASTERN
SEABOARD AS THE FRONTS PUSH EAST OFF THE COAST.
FARTHER WEST, SCATTERED CONVECTION IS ALSO LIKELY NEAR A WAVY
TRAILING FRONT ACROSS THE LOWER MISSISSIPPI VALLEY AND VICINITY
THROUGH LATE WEEK, THOUGH THE PLACEMENT OF HEAVIER RAINFALL TOTALS
REMAINS UNCERTAIN. ADDITIONALLY TO THE NORTH, A SERIES OF
SHORTWAVES LOOKS TO WORK FROM THE PACIFIC THROUGH THE
WEST/NORTHWEST AND INLAND ACROSS THE INTERMOUNTAIN WEST/ROCKIES
THROUGH THE PERIOD, ALBEIT IN A PATTERN WITH LIMITED PRECIPITATION
INITIALLY. BUT BY THE WEEKEND INTO EARLY NEXT WEEK, CONVECTION MAY
START TO BECOME MORE WIDESPREAD AND BETTER ORGANIZED IN THE
NORTHERN ROCKIES BEFORE WORKING DOWN THROUGH THE PLAINS, WHERE
SOME HEAVY RAIN TOTALS LOOK PLAUSIBLE BUT UNCERTAINTY REMAINS ON
TIMING/LOCATION.
PUTNAM/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE
SOUTHERN PLAINS, SUN, SEP 10.
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC AND THE
NORTHEAST, SAT, SEP 9.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST
AND THE MID-ATLANTIC.
- FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHEAST.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE SOUTHERN PLAINS, AND THE
SOUTHWEST, FRI-SUN, SEP 8-SEP 10.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHERN PLAINS AND THE
SOUTHWEST, SAT-SUN, SEP 9-SEP 10.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY
AND THE SOUTHERN PLAINS, FRI, SEP
8.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page