761
FXUS02 KWBC 042038
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 PM EDT MON SEP 04 2023
VALID 12Z THU SEP 07 2023 - 12Z MON SEP 11 2023
...IMPRESSIVE HEAT WILL MODERATE IN THE EAST LATE WEEK BUT PERSIST
ACROSS THE SOUTH-CENTRAL U.S AND SOUTHWEST...
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
RECENT MODEL GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT WITH THE
LARGE SCALE PATTERN CONSISTING OF MEAN TROUGHING ACROSS THE EAST,
AN UPPER HIGH/RIDGE REORIENTING ITSELF A BIT WESTWARD WITH TIME
INTO THE SOUTHWESTERN U.S., AND IMPULSES COMING INTO THE PACIFIC
NORTHWEST AND TRACKING EASTWARD TO THE NORTH OF THE RIDGE.
MEANWHILE THERE REMAIN SOME DIFFERENCES IN THE DETAILS OF
SHORTWAVE AND FRONTAL POSITIONS THAT ARE CERTAINLY WITHIN TYPICAL
SPREAD FOR THE MEDIUM RANGE PERIOD. THE LARGEST DIFFERENCES ARISE
WITH TIMING AND PLACEMENT OF AN UPPER TROUGH OR LOW OVER THE
EASTERN PACIFIC INTO THE WEST BY EARLY NEXT WEEK THAT WILL TAKE
ADDITIONAL TIME TO RESOLVE. THUS THE WPC FORECAST USED A
MULTI-MODEL DETERMINISTIC BLEND FAVORING THE GFS AND ECMWF EARLY
IN THE PERIOD, GRADUALLY INCLUDING AND INCREASING THE PROPORTION
OF THE GEFS AND EC ENSEMBLE MEANS WITH TIME TO HALF BY DAY 7. THIS
MAINTAINED GOOD CONTINUITY FROM THE PREVIOUS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
THE EMERGENCE OF AN AMPLIFIED UPPER TROUGH THROUGH THE MIDWEST
INTO THURSDAY/FRIDAY WILL ACT TO SUPPRESS UPPER RIDGING AND HIGH
HEAT ACROSS THE EAST, AFTER ONE MORE POTENTIALLY RECORD-BREAKING
DAY ON THURSDAY. UPPER TROUGHING WILL SETTLE OVER THE EAST THROUGH
THE WEEKEND 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
DRIFTS A BIT WEST INTO THE SOUTHWEST. WITH THIS RIDGE IN PLACE,
HOT LATE SUMMER TEMPERATURES WILL LINGER ACROSS THE SOUTH-CENTRAL
U.S. AND THE SOUTHWEST. TEMPERATURE ANOMALIES MAY BE STRONGEST
THROUGH LATE WEEK WITH SOME TEMPERATURES 15-20 DEGREES ABOVE
NORMAL IN THE SOUTHERN PLAINS, WELL INTO THE 100S. HIGH DEWPOINTS
AND HUMIDITY ESPECIALLY NEAR THE WESTERN GULF COAST WILL LEAD TO
DANGEROUS HEAT INDICES. ABOVE NORMAL TEMPERATURES BY ABOUT 10-15
DEGREES SHOULD PERSIST INTO THE WEEKEND AND EARLY NEXT WEEK ACROSS
THE SOUTH-CENTRAL U.S. AND INTO THE SOUTHWEST. WIDESPREAD 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.
MEANWHILE IN THIS PATTERN, THE EAST WILL BE 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. FOR THIS FORECAST CYCLE, ADDED A MARGINAL RISK INTO
THE ERO FOR FRIDAY FOR PARTS OF THE NORTHEAST/MID-ATLANTIC AS
CONVECTION LOOKS TO HAVE A RELATIVELY BETTER FOCUS NEAR/AHEAD OF
THE FRONT COMPARED TO THURSDAY. THE MARGINAL RISK ENCOMPASSES
LOWER FFGS IN PENNSYLVANIA INTO THE NORTHEAST BUT ALSO STRETCHES
SOUTH INTO THE DC/BALTIMORE AND RICHMOND METRO AREAS. THOUGH
ANTECEDENT CONDITIONS ON THE SOUTHERN SIDE ARE DRY, URBAN AREAS
COULD SEE A FLASH FLOODING RISK. RAIN CHANCES SHOULD GRADUALLY
DECREASE NEXT WEEK ALONG THE EASTERN SEABOARD AS THE FRONTS PUSH
EAST.
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 INTO THE PLAINS, WHICH WILL
CONTINUE TO BE MONITORED FOR SOME POTENTIALLY HEAVY TOTALS.
TATE/SCHICHTEL
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS,
SUN-MON, SEP 10-SEP 11.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST
AND THE MID-ATLANTIC.
- FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHEAST.
- HAZARDOUS HEAT ACROSS THE COASTAL PLAIN OF TEXAS INTO
SOUTHWESTERN LOUISIANA, THU-SAT, SEP 7-SEP 9.
- HAZARDOUS HEAT ACROSS PORTIONS OF LOUISIANA INTO EASTERN TEXAS,
THU-FRI, SEP 7-SEP 8.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE NORTHERN MID-ATLANTIC INTO
NEW ENGLAND, THU, SEP 7.
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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