769
FXUS02 KWBC 301859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT FRI AUG 30 2024
VALID 12Z MON SEP 02 2024 - 12Z FRI SEP 06 2024
..OVERVIEW
A FAIRLY PROGRESSIVE NORTHERN STREAM UPPER LEVEL PATTERN WILL BE
IN PLACE NEXT WEEK DURING THE MEDIUM RANGE PERIOD. ON THE LARGE
SCALE, UPPER RIDGING ACROSS THE SOUTHERN U.S. WILL EXPAND AND BUILD
INTO THE WEST AS SYSTEMS RIDE THE TOP OF THE RIDGE FROM WEST TO
EAST, PROVIDING MULTIPLE ROUNDS TROUGHING OVER THE GREAT LAKES AND
NORTHEAST. THIS PATTERN SHOULD PUSH A COUPLE OF FRONTAL BOUNDARIES
INTO THE CENTRAL AND SOUTHEASTERN U.S., WITH PERIODS OF STORMY
WEATHER EXPECTED TO ACCOMPANY THEM. MEANWHILE, EMBEDDED ENERGY
WITHIN THE LARGER SCALE UPPER RIDGE AND A PERSISTENT SURFACE TROUGH
AND EMBEDDED WAVES NEAR THE WESTERN GULF COAST SHOULD PROVIDE
FOCUS FOR HEAVY RAINFALL ACROSS PARTS OF TEXAS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS SHOW FAIRLY GOOD AGREEMENT ON THE OVERALL LARGE SCALE
PATTERN THROUGH MUCH OF NEXT WEEK, BUT THE TYPICAL DIFFERENCES IN
THE DETAILS OF INDIVIDUAL SYSTEMS CAUSE SOME NOTABLE DIFFERENCES IN
SENSIBLE WEATHER. ONE FEATURE OF NOTE IS THE SHORTWAVE ENERGY IN
THE SOUTHERN PLAINS OR SO THAT, ALONG WITH SURFACE TROUGHING/LOW
AND FRONTS IN THE VICINITY, WILL HELP FORCE CONVECTION IN TEXAS AND
SPREADING EASTWARD. BY AROUND WEDNESDAY, GFS AND TO SOME EXTENT
ECMWF RUNS ARE SLOW/WESTERN OUTLIERS WITH THE ENERGY AND KEEP
HEAVIER QPF IN WESTERN PARTS OF TEXAS, UNLIKE THEIR ENSEMBLES, AI
MODELS, AND THE CMC/UKMET (THROUGH ITS PERIOD) THAT TRACK HEAVY QPF
FARTHER EAST INTO THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST. A
WAVE ALONG THE SURFACE FRONTAL SYSTEM COULD ALSO PLAY A ROLE IN THE
CONSIDERABLE SPREAD WITH THE QPF THIS FORECAST CYCLE. THE NBM WAS
QUITE HEAVY IN THE LOWER MISSISSIPPI VALLEY/SOUTHEAST FOR
WEDNESDAY-THURSDAY, UNLIKE THE GFS, THOUGH THE ECMWF EVENTUALLY DID
CATCH UP A BIT WITH THE EASTERLY SHIFT OF QPF. THIS WAS QUITE A
CHANGE FROM CONTINUITY, SO DID TREND THAT DIRECTION BUT WAS NOT AS
AGGRESSIVE WITH THE TOTALS.
FARTHER NORTH, TROUGHING IN THE NORTHEAST SHOULD GRADUALLY LIFT
DURING THE FIRST HALF OF THE WEEK, WITH RIDGING IN THE CENTRAL U.S
ASIDE FROM THE EMBEDDED ENERGIES. MODELS AGREE A COMPACT UPPER LOW
WILL MOVE INTO THE PACIFIC NORTHWEST EARLY WEEK, BUT CONTINUE TO
SHOW VARIABILITY IN HOW THIS INTERACTS WITH ADDITIONAL NORTHERN
STREAM ENERGY. MOST DETERMINISTIC AND AI MODELS SHOW SOME TROUGHING
LINGERING IN THE NORTHERN GREAT BASIN INTO WEDNESDAY, EXCEPT FOR
THE 00Z ECMWF, WHILE THE NEWER 12Z MODELS ARE MIXED. MEANWHILE MOST
00/06Z GUIDANCE TRENDED SIGNIFICANTLY DEEPER WITH THE NORTHERN
STREAM TROUGHING AS IT MOVES FROM CENTRAL TO EAST-CENTRAL NORTH
AMERICA COMPARED TO THE PREVIOUS CYCLE. THE CMC WAS A FAST/WEAKER
OUTLIER WHILE THE 12Z CMC LOOKS BETTER.
THE EARLY PART OF THE WPC FORECAST USED A BLEND OF THE
DETERMINISTIC MODELS, BUT WITH THE INCREASING SPREAD AND EACH
DETERMINISTIC MODEL HAVING SOME ISSUES, TRANSITIONED TO A BLEND TO
OVER HALF ENSEMBLE MEANS LATE PERIOD. THE MAIN CHANGES TO
CONTINUITY WERE WITH QPF IN THE SOUTHEAST, AND WITH FRONTAL
POSITIONS IN THE NORTH-CENTRAL U.S. AND SOUTHERN CANADA THAT WERE
NEEDED BECAUSE OF THE DEEPER TROUGH MENTIONED ABOVE.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAIN HEAVY RAINFALL FOCUS DURING THE PERIOD WILL BE ACROSS THE
SOUTH AS SHORTWAVE ENERGY MOVES INLAND FROM THE WESTERN GULF.
PRECIPITATION COVERAGE AND TOTALS REMAIN HIGHLY UNCERTAIN, BUT THE
OVERALL DYNAMICS AND ANOMALOUS MOISTURE SUPPORT A HEAVY TO
EXCESSIVE RAINFALL THREAT WITH SLOW-MOVING STORMS. THIS IS COVERED
BY FAIRLY BROAD MARGINAL RISKS ON THE DAYS 4 AND 5 EROS (COVERING
MONDAY TO TUESDAY NIGHT), WITH A POSSIBLE FOCUS ACROSS THE GULF
COAST AND FARTHER INLAND ACROSS MUCH OF TEXAS, PERHAPS SPREADING
ACROSS THE CENTRAL GULF COAST AS WELL TUESDAY. MOISTURE ALONG A
FRONTAL BOUNDARY SAGGING SOUTH ACROSS THE CAROLINAS SHOULD SUPPORT
SHOWERS AND STORMS WITH A MARGINAL RISK OF FLASH FLOODING ON
MONDAY. FOR MIDWEEK AND BEYOND, FRONTS LINGERING ACROSS THE SOUTH
WITH SURFACE WAVES WILL PROMOTE ADDITIONAL RAIN AND LOCALLY HEAVY
DOWNPOURS. AMOUNTS AND LOCATIONS REMAIN VERY UNCERTAIN, BUT THE
TREND IS FOR INCREASED RAIN TOTALS FROM THE CENTRAL GULF COAST INTO
THE LOWER MISSISSIPPI VALLEY AND PARTS OF THE SOUTHEAST.
EVENTUALLY BY LATE WEEK, SOME MOISTURE MAY SPREAD INTO THE OHIO
VALLEY AND/OR EASTERN SEABOARD. MEANWHILE, SOME LIGHT TO MODEST
PRECIPITATION SHOULD ACCOMPANY A SHORTWAVE MOVING THROUGH THE
INTERIOR WEST, AND RAIN CHANCES COULD SPREAD INTO THE NORTHERN
PLAINS AND MIDWEST/GREAT LAKES LATER NEXT WEEK ALONG AND AHEAD OF A
FRONT.
MODESTLY ABOVE NORMAL TEMPERATURES ACROSS THE NORTHWEST ON MONDAY
SHOULD SHIFT EAST AND MODERATE INTO MIDWEEK. BY MID TO LATE WEEK,
INCREASING HEAT IS EXPECTED ACROSS MUCH OF THE WEST, WITH MODERATE
TO MAJOR HEATRISK THREATS ACROSS THE SOUTHWEST AND CENTRAL VALLEYS
OF CALIFORNIA. FROM THE SOUTHERN PLAINS TO THE MIDWEST AND THE
EAST, TEMPERATURES SHOULD BE NEAR OR BELOW NORMAL FOR THIS TIME OF
THE YEAR WITHIN A RATHER PLEASANT AIR MASS THROUGH MUCH OF NEXT
WEEK.
TATE/SANTORELLI
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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