038
FXUS02 KWBC 310703
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EST SUN DEC 31 2023
VALID 12Z WED JAN 03 2024 - 12Z SUN JAN 07 2024
..OVERVIEW
THE MEDIUM RANGE PERIOD FEATURES A RATHER PROGRESSIVE FLOW PATTERN
WITH SYSTEMS OF MODEST AMPLITUDE MOVING WEST TO EAST ACROSS THE
LOWER 48. A SERIES OF UPPER LOWS/SHORTWAVES SHIFTING FROM THE
SOUTHWEST AND ACROSS THE SOUTHERN U.S. SHOULD HAVE THE BEST
MOISTURE TAP KEEPING THE BULK OF THE PRECIPITATION DURING THE
PERIOD CONFINED TO THE WEST COAST AND THE GULF COAST/SOUTHEAST
WHERE LOCALLY HEAVY RAIN WILL BE POSSIBLE IN SOME SPOTS. IN THE
NORTHERN STREAM, SHORTWAVES SHOULD TRAVEL ACROSS THE UPPER
MIDWEST/GREAT LAKES WITH POSSIBLE EVENTUAL INTERACTIONS WITH THE
SOUTHERN STREAM SYSTEMS OVER THE EAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DESPITE SOME MINOR TIMING/DETAIL DIFFERENCES, THERE IS GOOD
AGREEMENT THE FIRST HALF OF THE PERIOD REGARDING AMPLIFIED
TROUGHING ACROSS THE EAST AND THE FIRST OF TWO UPPER LOWS SLIDING
DOWN THE WEST COAST INTO THE SOUTHWEST. BY NEXT WEEKEND, THE
GREATEST FORECAST UNCERTAINTY SURROUNDS THIS UPPER LOW SHIFTING
INTO THE SOUTHERN PLAINS/SOUTHEAST WITH SOME POTENTIAL FOR EAST
COAST LOW PRESSURE DEVELOPMENT NEXT SUNDAY/DAY 7. THERE IS
INCREASING SUPPORT FOR A LOW PRESSURE SYSTEM LIFTING OFF THE EAST
COAST IN THE LATEST MODELS AND ENSEMBLES, BUT A LOT OF UNCERTAINTY
ON TIMING AND PRECIPITATION TYPE. THE GFS AND CMC ARE THE QUICKEST
TO LIFT THE SYSTEM OFF THE COAST, WHILE THE ECMWF IS NOTICEABLY
SLOWER. THE ENSEMBLE MEANS ARE A GOOD MIDDLE GROUND TIMING WISE,
BUT ARE NOTICEABLY WEAKER THAN THEIR DETERMINISTIC COUNTERPARTS
SUGGESTING A LOT OF SPREAD AND VARIABILITY STILL.
THE WPC FORECAST FOR TONIGHT USED A BLEND OF THE LATEST
DETERMINISTIC SOLUTIONS THE FIRST HALF OF THE PERIOD, WITH MORE
EMPHASIS TOWARDS THE ENSEMBLE MEANS LATE PERIOD, THOUGH WITH STILL
MODEST INCLUSION OF THE GFS AND ECMWF FOR SOME ADDED SYSTEM
DEFINITION.
..WEATHER/HAZARDS HIGHLIGHTS
AN INITIAL UPPER LOW/SHORTWAVE THROUGH THE SOUTHERN PLAINS INTO
THE SOUTHEAST SHOULD TAP GULF OF MEXICO MOISTURE AND SOME
INSTABILITY TO CONTINUE TO FUEL WIDESPREAD SHOWERS AND
THUNDERSTORMS ACROSS PARTS OF THE CENTRAL GULF COAST AND SOUTHEAST
ON WEDNESDAY. A MARGINAL RISK REMAINS IN THE FORECAST FOR THE DAY
4/WEDNESDAY EXCESSIVE RAINFALL OUTLOOK BUT THE LATEST GUIDANCE
SEEMS TO BE SUGGESTING THE HEAVIEST RAINFALL AND BETTER
INSTABILITY MAY REMAIN OFFSHORE SO COULD BE A MORE URBANIZED FLOOD
RISK. THE SECOND LOW FORECAST TO APPROACH THE WEST COAST BY
WEDNESDAY AND MOVE INTO THE SOUTHWEST BY THURSDAY MAY BRING
ORGANIZED PRECIPITATION TO THE WEST COAST AND SOME AREAS FARTHER
INLAND, WITH RELATIVELY HIGHER TOTALS MOST LIKELY OVER FAVORED
TERRAIN IN PORTIONS OF CALIFORNIA. THIS SHOULD ALSO EVENTUALLY
BRING HEAVY RAINFALL BACK INTO TEXAS AND THE GULF COAST LATE
WEEK/NEXT WEEKEND. DUE TO THE HEAVY RAINFALL EXPECTED EARLIER IN
THE WEEK ACROSS SOUTHEAST TX AND SOUTHWEST LA, THIS FOLLOWING
SYSTEM WILL ALSO NEED TO BE WATCHED FOR INCREASED FLOODING
CONCERNS. MODELS SHOW INCREASED SUPPORT FOR EAST COAST
CYCLOGENESIS WITH THIS LOW NEXT WEEKEND, WITH SOME SNOWFALL
POTENTIAL ON THE NORTH SIDE OF THE LOW, BUT HIGHLY DEPENDENT ON
THE EXACT TRACK OF THE SYSTEM DETERMINING WHERE AND HOW MUCH SNOW.
ELSEWHERE, NORTHERN TIER SYSTEMS MAY BRING LIGHT PRECIPITATION TO
PARTS OF THE GREAT LAKES/NORTHEAST PERIODICALLY NEXT WEEK, WITH
PRECIPITATION MOVING INTO THE PACIFIC NORTHWEST LATER IN THE WEEK
AS WELL.
THE BEST CHANCES FOR ABOVE NORMAL TEMPERATURE ANOMALIES SHOULD
FOCUS FROM THE NORTHERN PLAINS INTO THE NORTHEAST, WITH READING
GENERALLY 5-15 DEGREES ABOVE NORMAL. MODERATELY BELOW NORMAL
TEMPERATURES SHOULD BE CONFINED ACROSS THE SOUTHERN TIER TOWARDS
THE END OF THIS WEEK, ESPECIALLY ACROSS THE SOUTHEAST, BUT
INCREASE IN COVERAGE OVER THE WEST NEXT WEEKEND AS AMPLIFIED
TROUGHING MOVES INTO THE REGION.
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, 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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