360
FXUS02 KWBC 271843
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
142 PM EST MON NOV 27 2023
VALID 12Z THU NOV 30 2023 - 12Z MON DEC 04 2023
..OVERVIEW
AN UPPER-LEVEL SHORTWAVE INITIALLY LOCATED OVER THE SOUTHWEST ON
THURSDAY WILL TRAVEL ACROSS THE MIDWEST AND INTO THE NORTHEAST BY
THIS WEEKEND. PERIODS OF MODERATE TO HEAVY RAINFALL WILL ACCOMPANY
THIS FEATURE AND ARE FORECAST TO IMPACT PARTS OF THE SOUTH,
SOUTHEAST, AND MID-MISSISSIPPI VALLEY. MEANWHILE, A COUPLE
QUICK-MOVING SHORTWAVES WILL MOVE INTO THE WEST LATE THIS WEEK,
PROMOTING AMPLIFIED MEAN TROUGHING THAT SHIFTS FROM THE WEST INTO
THE CENTRAL U.S. THIS WEEKEND INTO EARLY NEXT WEEK. AS THE PATTERN
AMPLIFIES, UPPER RIDGING WILL BUILD DOWNSTREAM OVER THE EAST
COAST. THIS SETUP WILL FAVOR WET, UNSETTLED WEATHER IN THE WEST
AND BRING ANOTHER ROUND OF POTENTIALLY HEAVY RAINFALL TO THE GULF
COAST AND SOUTHEAST OVER THE WEEKEND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN VERY GOOD AGREEMENT ON THE UPPER-LEVEL
PATTERN FOR THE MEDIUM RANGE TIME PERIOD. THE HIGHEST UNCERTAINTY
CONTINUES TO SURROUND ACTIVITY MOVING INTO THE WEST LATE IN THE
PERIOD. THERE IS A SIGNIFICANT AMOUNT OF RUN TO RUN VARIABILITY
WITH THE TIMING/LOCATION OF THE WESTERN SHORTWAVES, BUT THERE IS
AN OVERALL CONSENSUS ON A MORE AMPLIFIED AND ACTIVE PATTERN. FOR
THE AFTERNOON FORECAST PACKAGE, A PURELY DETERMINISTIC BLEND WAS
USED FOR DAYS 3-5 WITH SLIGHTLY MORE WEIGHT ON THE GFS AND ECMWF
THAN THE CMC AND UKMET. FOR DAYS 6-7, THE DETERMINISTIC GFS/ECMWF
WERE BLENDED WITH THEIR ENSEMBLE MEANS TO SMOOTH OUT SOME MODEL
DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
UPPER-LEVEL SHORTWAVE ENERGY WILL MOVE OVER THE MID-SOUTH WHILE A
WARM FRONT WILL LIFT NORTH OUT OF THE GULF OF MEXICO LATE THIS
WEEK, WHICH WILL SUPPORT WIDESPREAD MODERATE TO HEAVY RAINFALL IN
THE SOUTH AND LOWER MISSISSIPPI VALLEY. THERE IS A MARGINAL RISK
OF EXCESSIVE RAINFALL FOR THIS AREA ON THURSDAY-THURSDAY NIGHT.
MODELS HAVE CONSISTENTLY SHOWN THE HEAVIEST RAINFALL AMOUNTS IN
THE VICINITY OF THE EASTERN TEXAS GULF COAST AND WESTERN LOUISIANA
GULF COAST, WHICH MAY BE WHERE THE HIGHEST RISK OF FLASH FLOODING
WILL BE LOCATED. HEAVY RAIN MAY LINGER ACROSS THE CENTRAL GULF
COAST AND INTO THE SOUTHEAST ON FRIDAY, AND THERE IS A MARGINAL
RISK OF EXCESSIVE RAINFALL FOR THIS AREA. AMPLIFIED TROUGHING
SHIFTING OUT OF THE WEST THIS WEEKEND WILL PROVIDE A RENEWED SURGE
OF MOISTURE AND SUPPORT WIDESPREAD MODERATE TO HEAVY RAINFALL
ACROSS THE SOUTHEAST. OUT WEST, PRECIPITATION WILL INCREASE
THURSDAY THROUGH THE WEEKEND AS A COUPLE SHORTWAVES MOVE THROUGH
THE REGION, WITH SOME PRECIPITATION REACHING SOUTHWARD INTO
CALIFORNIA AND THE SOUTHWEST. THE HEAVIEST PRECIPITATION (COASTAL
RAIN AND MOUNTAIN SNOW) WILL BE ACROSS THE WASHINGTON/OREGON COAST
AND CASCADES NEXT WEEKEND WITH GENERALLY LIGHTER AMOUNTS FARTHER
INLAND.
THE INTERIOR WEST SHOULD STAY COOLER THAN NORMAL UNDERNEATH
REINFORCED TROUGHING THROUGH THE WEEKEND. TEMPERATURES FOR THE
REST OF THE COUNTRY SHOULD BE CLOSER TO NORMAL LATE THIS WEEK, BUT
TREND WARMER WITH TIME ACROSS THE NORTHERN PLAINS INTO THE MIDWEST
AND EVENTUALLY THE EAST BY THE WEEKEND. DAYTIME HIGHS COULD BE
5-10 DEGREES ABOVE AVERAGE ACROSS THIS REGION. THE WESTERN U.S.
MAY FINALLY TREND BACK TOWARDS NORMAL, OR ABOVE NORMAL IN SOME
PLACES, EARLY NEXT WEEK AS THE TROUGH MOVES EAST AND RIDGING
BUILDS BACK IN.
SANTORELLI/DOLAN
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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