881
FXUS02 KWBC 300646
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
146 AM EST SAT DEC 30 2023
VALID 12Z TUE JAN 02 2024 - 12Z SAT JAN 06 2024
..OVERVIEW
THE MEDIUM RANGE PERIOD FEATURES A VERY PROGRESSIVE FLOW PATTERN
WITH A COUPLE OF UPPER LOWS/SHORTWAVES MOVING FROM CALIFORNIA TO
THE SOUTHERN PLAINS/SOUTHEAST, WHILE IN THE NORTHERN STREAM WEAKER
SHORTWAVES MAINTAIN SOMEWHAT MEAN TROUGHING ACROSS THE NORTHEAST
AS A RESULT OF STRONG RIDGING ACROSS WESTERN CANADA. THIS TYPE OF
PATTERN KEEPS THE BULK OF THE PRECIPITATION CONFINED TO THE WEST
COAST AND THE GULF COAST/SOUTHEAST WITH LOCALLY HEAVY RAIN IN SOME
SPOTS. EXPECT MILDER TEMPERATURES ACROSS MAINLY THE NORTHERN
STATES WITH A TENDENCY FOR MORE BELOW AVERAGE TEMPS ACROSS THE
SOUTHERN TIER.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE GUIDANCE CONTINUES TO SHOW VERY GOOD AGREEMENT THROUGH THE
MIDDLE TO LATTER PART OF NEXT WEEK REGARDING A DEPARTING TROUGH
OFF THE EAST COAST, AN UPPER LOW SHIFTING FROM THE SOUTHWEST TO
THE SOUTHEAST TUESDAY-THURSDAY, AND A SECOND UPPER LOW DROPPING
DOWN THE WEST COAST INTO THE SOUTHWEST WEDNESDAY-THURSDAY. THERE
ARE SOME DETAIL DIFFERENCES, WHICH DOES HAVE IMPLICATIONS FOR
RAINFALL INTENSITY AND COVERAGE ACROSS THE GULF COAST, BUT AN
OVERALL BLEND OF THE DETERMINISTIC GUIDANCE SEEMED TO PROVIDE A
GOOD STARTING POINT. BY FRIDAY/DAY 6, THERE ARE SOME TIMING
DIFFERENCES WITH ADDITIONAL TROUGHING INTO THE WEST COAST, WHICH
LOOKS TO DEVELOP ANOTHER CLOSED UPPER LOW OFF WASHINGTON/OREGON BY
NEXT WEEKEND. THERE ARE ALSO STRENGTH AND TIMING QUESTIONS WITH
THE SECOND UPPER LOW AS IT MOVES INTO THE SOUTHERN PLAINS/GULF
COAST FRIDAY-SATURDAY, AND LOTS OF VARIABILITY WITH NORTHERN
STREAM ENERGIES THROUGH THE NORTHERN PLAINS INTO THE GREAT LAKES.
INTRODUCTION OF THE ENSEMBLE MEANS BY DAYS 6 AND 7 SEEMED TO HELP
SMOOTH OUT SOME OF THESE DIFFERENCES FOR NOW, WHICH DO SHOW A LOT
OF RUN TO RUN VARIATIONS/UNCERTAINTIES IN THE GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
AN INITIAL UPPER LOW/SHORTWAVE MOVING OUT OF THE SOUTHWEST SHOULD
BEGIN TO TAP GULF OF MEXICO MOISTURE AND SOME INSTABILITY TO FUEL
WIDESPREAD SHOWERS AND THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN
PLAINS/LOWER MISSISSIPPI VALLEY ON TUESDAY. THERE IS SOME OVERLAP
BETWEEN THE HEAVIER RAINFALL/QPF SIGNAL AND THE MORE SENSITIVE
AREAS DUE TO A RECENT WET PATTERN NEAR THE MIDDLE/UPPER TEXAS
COAST, SO A MARGINAL RISK WAS MAINTAINED ON THE NEW DAY 4/TUESDAY
EXCESSIVE RAINFALL OUTLOOK COVERING MUCH OF SOUTHEAST TEXAS AND
SOUTHWEST LOUISIANA. THIS ACTIVITY SHOULD SHIFT EAST ALONG THE
CENTRAL GULF COAST INTO THE SOUTHEAST ON WEDNESDAY, WITH ANOTHER
MARGINAL RISK THIS TIME CONFINED MAINLY ALONG THE COAST FROM NEW
ORLEANS TO THE FLORIDA PANHANDLE.
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 ON TUESDAY INTO EARLY
WEDNESDAY ACROSS SOUTHEAST TX AND SOUTHWEST LA, THIS FOLLOWING
SYSTEM WILL NEED TO BE WATCHED FOR INCREASED FLOODING CONCERNS.
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 GREATEST TEMPERATURE ANOMALIES DURING THE PERIOD SHOULD FOCUS
ACROSS THE FAR NORTHERN TIER NEAR THE CANADIAN BORDER AND INTO THE
GREAT LAKES/NORTHEAST WITH SOME LOCATIONS SEEING MULTIPLE DAYS
WITH READINGS 10-20F OR SO ABOVE NORMAL, WITH MORNING LOWS TENDING
TO BE FARTHER ABOVE NORMAL THAN DAYTIME HIGHS. MOST AREAS FROM
CALIFORNIA EASTWARD ACROSS THE SOUTHERN TIER, PARTICULARLY THE
SOUTHEAST, SHOULD SEE NEAR TO BELOW NORMAL HIGH TEMPERATURES
DURING THE PERIOD AS A SERIES OF UPPER LEVEL SYSTEMS MOVE THROUGH.
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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