964
FXUS02 KWBC 311934
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
334 PM EDT THU AUG 31 2023
VALID 12Z SUN SEP 03 2023 - 12Z THU SEP 07 2023
...HEAT FORECAST TO INCREASE ACROSS THE PLAINS, MIDWEST, AND
MID-ATLANTIC/NORTHEAST NEXT WEEK...
...WET PATTERN ACROSS THE WEST INTO EARLY NEXT WEEK, WITH FLOODING
POSSIBLE...
..OVERVIEW
THE EXTENDED FORECAST WILL FEATURE AN AMPLIFIED TROUGH OVER THE
WESTERN STATES AND AN UPPER RIDGE OVER THE CENTRAL U.S. THAT WILL
GRADUALLY SHIFT EASTWARD THROUGH THE WEEK. THIS PATTERN WILL
SUPPORT WELL ABOVE SEASONAL NORMAL TEMPERATURES ACROSS THE PLAINS,
UPPER MIDWEST AND THEN REACHING THE EAST. A VAST AREA OF SHOWERS
AND THUNDERSTORMS ACROSS THE WEST AND SOUTHWEST COULD LEAD TO
AREAS OF LOCALLY EXCESSIVE RAINFALL AND LOCALIZED FLOODING
CONCERNS. THE RAIN IS EXPECTED TO LIFT INTO THE NORTH-CENTRAL U.S.
IN ADVANCE OF COLD FRONT. SCATTERED SHOWERS AND STORMS COULD
PERSIST ACROSS THE GULF COAST REGION INTO FLORIDA ESPECIALLY EARLY
IN THE WEEK AS A SHORTWAVE AND FRONTAL BOUNDARY LINGER THERE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE HAS A DECENT HANDLE ON THE OVERALL PATTERN
SHOWING THE MAIN UPPER TROUGH WITH ITS AXIS OVER THE WEST COAST
STATES AND BROAD RIDGING FARTHER EAST. THERE ARE SOME SUBTLE
DIFFERENCES WITH THE UPPER STREAM ENERGY ENTERING THE WEST COAST
AND THEN WESTERN TROUGH EVEN ON DAY THREE. THE INTERACTION OF THIS
UPSTREAM ENERGY WITH THE PREEXISTING LOW SHOULD COMBINE WITH THE
TROUGH AT SOME POINT AND HELP PUSH IT EASTWARD. THE SPECIFICS OF
THIS FEATURE VARY WITHIN THE MODEL GUIDANCE AND GENERALLY ARE
WITHIN THE NORMAL NOISE AT THIS TIME. WITH TIME, THE GUIDANCE
SUGGEST THIS FEATURE BECOMES ABSORBED INTO THE TROUGH WHILE THE
RIDGE SHIFTS INTO THE EASTERN U.S. THE DETAILS OF THIS FLOW DO
HAVE IMPACTS FOR POSITIONS OF SURFACE FRONTS MOVING ACROSS THE
WEST AND BEYOND. THE TROUGH IS DEPICTED TO DEAMPLIFY A BIT AS IT
TRANSLATES DOWNSTREAM BY THE MIDDLE OF NEXT WEEK WHILE THE RIDGE
MOVES OVER THE EAST. ANOTHER TROUGH WILL APPROACH THE NORTHWEST BY
WEDNESDAY-THURSDAY, WHILE THE RIDGING IN THE EAST ERODES--HELPED
POSSIBLY BY ENERGY THAT WAS ONCE IDALIA. IDALIA'S TRACK IN THE
WESTERN ATLANTIC DOES BECOME UNCERTAIN AS MANY MODELS CURVE THE
STORM BACK TO THE WEST EVENTUALLY BY AROUND MIDWEEK, EVEN
APPROACHING (BUT NOT HITTING) THE NORTHEAST OR ATLANTIC CANADA.
THIS FEATURE WILL CONTINUE TO BE MONITORED.
THE WPC FORECAST FAVORED A MULTI-MODEL APPROACH THAT USED THE 00Z
ECWMF/CMC/UKMET/GEFS MEAN/EC ENSEMBLE MEAN AND 06Z GFS. THE USE OF
THE MEANS WERE SLOWING INTRODUCED AND INCREASED AS THE FORECAST
PERIOD PROGRESSED. THIS APPROACH WAS SIMILAR TO CONTINUITY FROM
THE PREVIOUS FORECAST PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
MUCH OF THE WEST WILL HAVE RAINY CONDITIONS INTO SUNDAY THANKS TO
THE AMPLIFIED UPPER TROUGH IN PLACE OF THE WEST COAST. STRONG MEAN
SOUTHERLY FLOW TO THE EAST OF THE TROUGH AXIS WILL CARRY MONSOONAL
MOISTURE WITH PRECIPITABLE WATER VALUES WELL ABOVE NORMAL AND
INSTABILITY INTO THE INTERIOR WEST. ON SUNDAY, THE HEAVIEST
RAINFALL IS FORECAST FOR NORTHERN UTAH INTO EASTERN IDAHO AND
WESTERN WYOMING, AND A SLIGHT RISK REMAINS IN PLACE IN THE ERO FOR
THESE AREAS WITH A WIDER MARGINAL RISK ACROSS PARTS OF THE GREAT
BASIN AND ROCKIES. BURN SCARS, SLOT CANYONS, AND URBAN AREAS WILL
BE PARTICULARLY VULNERABLE TO FLOODING. AS THE TROUGH CONTINUES TO
SHIFT INLAND, PRECIPITATION SHOULD EXPAND/PUSH INTO THE NORTHERN
PLAINS BY MONDAY WHILE LINGERING OVER PARTS OF THE INTERMOUNTAIN
WEST AND CENTRAL UTAH. A MARGINAL RISK IS PLACE FOR MONDAY ACROSS
THE NORTHERN ROCKIES/HIGH PLAINS AND INTO CENTRAL UTAH AS MOISTURE
LEVELS REMAIN ABOVE NORMAL, BUT NOT QUITE TO THE SAME EXTENT AS ON
SUNDAY. SHOWERS AND STORMS ALSO MAY BE MOVING FASTER THAN ON
SUNDAY. SO A SLIGHT RISK IS NOT PLANNED INTO MONDAY FOR NOW, BUT
AN UPGRADE IS NOT OUT OF THE QUESTION IN FUTURE FORECAST UPDATES
IF BETTER MODEL AGREEMENT IN RAINFALL POSITIONS AND FOR HEAVIER
TOTALS OCCURS. RAIN CHANCES ARE EXPECTED TO SPREAD EAST INTO THE
MIDWEST BY TUESDAY-WEDNESDAY AS THE UPPER TROUGH AND COLD FRONT
MOVE EASTWARD. FARTHER SOUTH, A SHORTWAVE IS FORECAST TO HOVER
OVER THE LOWER MISSISSIPPI VALLEY, WHICH IN COMBINATION WITH A
FRONTAL BOUNDARY WILL PROVIDE SUPPORT FOR SCATTERED SHOWERS AND
STORMS. RAINFALL AMOUNTS DO NOT LOOK TO BE AS HEAVY AS IN THE
SHORT RANGE PERIOD THOUGH. SIMILARLY, SOME SHOWERS ARE POSSIBLE
ACROSS ESPECIALLY THE SOUTHERN PART OF THE FLORIDA PENINSULA.
HEAT IS FORECAST TO BUILD ACROSS PARTS OF THE CENTRAL AND EASTERN
U.S. NEXT WEEK UNDERNEATH UPPER RIDGING. TEMPERATURES 15 TO 25
DEGREES ABOVE SEASONAL AVERAGE ARE EXPECTED ACROSS THE
NORTH-CENTRAL STATES AND RECORD WARM MAXIMUM AND MINIMUM
TEMPERATURES COULD BE WIDESPREAD. HIGHS WILL BE WELL INTO THE 90S
IF NOT POSSIBLY EVEN HITTING THE 100F MARK THERE, WITH LOWS
POTENTIALLY STAYING IN THE MID-70S FOR LIMITED OVERNIGHT RELIEF.
THE NORTH-CENTRAL U.S. SHOULD SEE SOME RELIEF WITH COOLER
TEMPERATURES PUSHING WEST TO EAST BY TUESDAY-THURSDAY AS AN UPPER
TROUGH AND SURFACE COLD FRONT MOVE THROUGH. BUT THIS WILL PUSH
ABOVE NORMAL TEMPERATURES INTO THE OHIO VALLEY AND GREAT LAKES
REGION AND THE MID-ATLANTIC AND NORTHEAST, WITH ANOMALIES AROUND
10-15 DEGREES. FARTHER SOUTH, TEMPERATURES GENERALLY 10-15 DEGREES
ABOVE AVERAGE (AROUND 100F FOR HIGHS) WILL EXTEND SUMMER FOR THE
SOUTHERN HALF OF THE PLAINS THROUGH NEXT WEEK. THE WESTERN U.S. ON
THE OTHER HAND LOOKS TO BE ON THE COOL SIDE ESPECIALLY FOR HIGH
TEMPERATURES PARTICULARLY EARLY IN THE WEEK, WITH SOME MODERATION
BY MIDWEEK.
CAMPBELL/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE CENTRAL
GREAT BASIN, THE NORTHERN PLAINS,
THE NORTHERN ROCKIES, THE CENTRAL ROCKIES, AND THE NORTHERN GREAT
BASIN, SUN-MON, SEP 3-SEP 4.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHEAST AND THE
MID-ATLANTIC.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST
AND THE GREAT LAKES.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY
AND THE SOUTHERN PLAINS, SUN-THU,
SEP 3-SEP 7.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE GREAT
LAKES, THE UPPER MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS,
SUN-MON, SEP 3-SEP 4.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE MID-ATLANTIC, THE
NORTHEAST, AND THE CENTRAL APPALACHIANS,
MON-WED, SEP 4-SEP 6.
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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