932
FXUS02 KWBC 271901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EST WED DEC 27 2023
VALID 12Z SAT DEC 30 2023 - 12Z WED JAN 03 2024
...LOCALLY HEAVY PRECIPITATION POSSIBLE FOR NORTHERN CALIFORNIA
LATE THIS WEEK TRENDING LIGHTER SATURDAY...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW MEAN TROUGHING OVER THE EASTERN U.S.
INTO EARLY NEXT WEEK IN RESPONSE TO UPSTREAM RIDGING. WITHIN THIS
TROUGH, SOME COMBINATION OF SEPARATE ENERGIES AS OF SATURDAY
SHOULD DEVELOP LOW PRESSURE OVER/OFFSHORE THE NEW ENGLAND COAST,
FOLLOWED BY A SHORTWAVE DROPPING SOUTHEASTWARD FROM THE UPPER
MIDWEST AND LIKELY CROSSING THE EASTERN U.S. BY EARLY NEXT WEEK.
BEHIND THIS LATTER SYSTEM, AN EMERGING SEQUENCE OF PACIFIC
FEATURES SHOULD LEAD INTO WHAT APPEARS TO BE A MORE PROGRESSIVE
PATTERN OVER AN INCREASING PORTION OF THE LOWER 48. A DECENT
PORTION OF THE COUNTRY SHOULD BE DRY DURING THE PERIOD, WITH BEST
PRECIPITATION FOCUS ALONG THE WEST COAST ON SATURDAY AND NEXT
WEDNESDAY WHILE COVERAGE/TOTALS ARE UNCERTAIN OVER THE EASTERN
U.S. EARLY NEXT WEEK. THE SOUTHEAST WILL TEND TO SEE VARYING
COVERAGE OF BELOW NORMAL TEMPERATURES OVER THE COURSE OF THE
PERIOD WHILE MOST OTHER AREAS OF THE LOWER 48 SHOULD SEE NEAR TO
ABOVE NORMAL READINGS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MEDIUM RANGE PERIOD BEGINS THIS SATURDAY (D3) WITH GOOD MODEL
AGREEMENT IN THE WEST WITH THE EAST PAC TROUGH AND UPPER RIDGE
OVER THE ROCKIES. THERE'S SOME VARIANCE WITH RESPECT TO THE DEPTH
OF A SHORTWAVE TROUGH SPINNING THROUGH THE UPPER MIDWEST. THE 00Z
ECMWF AND 06Z GFS ARE IN AGREEMENT HERE WHILE THE 00Z
CMC/UKMET/GFS ARE CLUSTERED WELL ON A SIMILAR SOLUTION. THERE'S
SOME ADDITIONAL UNCERTAINTY AROUND THE EVOLUTION OF NORTHERN AND
SOUTHERN STREAM TROUGHS OVER THE EAST. THE UNCERTAINTY LIKELY
STEMS FROM THE POTENTIAL PHASING OF THE NORTHERN AND SOUTHERN
STREAM SYSTEMS. THE 06Z GEFS ENSEMBLE HAS PLENTY OF MEMBER SPREAD
REGARDING THE DEPTH OF THE UPPER TROUGH.
THE WEST COAST PATTERN IS A MESS ON SUNDAY (D4) WITH PLENTY OF
MODEL UNCERTAINTY REGARDING THE DEPTH AND TIMING OF THE AMPLIFIED
EAST PAC TROUGH. THE LAST FEW RUNS OF THE GFS HAVE BEEN SUPPRESSED
COMPARED TO THE OTHER GUIDANCE WITH RESPECT TO THE UPPER RIDGE
OVER THE ROCKIES AND PLAINS. THE 00Z CANADIAN IS MORE AGGRESSIVE
THAN THE REST OF THE MODELS WHEN IT COMES TO THE SOUTHERN STREAM
TROUGH PROPAGATING ACROSS THE SOUTHWEST AND SOUTHERN PLAINS AS
WELL AS THE NORTHERN STREAM SHORTWAVE SWINGING THROUGH THE
MIDWEST. THIS SOLUTION IS ACTUALLY MORE CONSISTENT WITH THE 00Z
AND 18Z GFS RUNS. THE 06Z GEFS HAS A NOTABLE AMOUNT OF TIMING
SPREAD FOR THE AFOREMENTIONED SHORTWAVE.
THERE'S EVEN LESS DETERMINISTIC AND ENSEMBLE GUIDANCE ON MONDAY
(D5). THE LAST FEW RUNS OF THE GFS HAVE BEEN FAIRLY CONSISTENT
WITH A DEEPER UPPER TROUGH ANCHORED RIGHT ALONG THE CALIFORNIA
COAST WHILE THE EURO HAS TRENDED CLOSER TO THE WEST COAST OVER THE
LAST FEW RUNS. THEREFORE, SOMETHING RESEMBLING THE GFS SOLUTION
MIGHT BE WHERE THE REST OF THE MODELS CONVERGE EVENTUALLY. THIS
MAY TRANSLATE TO SENSIBLE WEATHER IMPACTS FOR SOUTHERN CALIFORNIA.
IN THE EAST, ANOTHER PHASING SITUATION BETWEEN A PARENT LOW
CENTERED OVER EASTERN NUNAVUT AND ANOTHER OVER THE MIDWEST IN
ADDITION TO ENSEMBLE SPREAD WILL COMPLICATE THE PREDICTABILITY OF
SENSIBLE WEATHER IMPACTS ACROSS THE EAST AT THE START OF THE WORK
WEEK.
GUIDANCE APPEARS TO BE IN REASONABLE AGREEMENT REGARDING THE
WESTERN TROUGH AS IT MAKES ITS WAY ACROSS THE ROCKIES AND PLAINS
ON TUESDAY (D6). THE GFS/GEFS CONTINGENT HAVE CONSISTENTLY BEEN
MORE PROGRESSIVE WITH THIS SYSTEM AND ITS DIFFLUENT REGION
COMPARED TO THE REST OF THE GUIDANCE. THE RESULT OF THIS IS A MORE
MUTED QPF SIGNAL ACROSS THE GULF COAST/LOWER MISSISSIPPI
VALLEY/SOUTHERN PLAINS. THE UNCERTAINTY AROUND THE NOW EAST COAST
TROUGH INCREASES ON TUESDAY WITH PLENTY OF TIMING SPREAD IN THE
ENSEMBLES. THE OPERATIONAL GFS HAS KEPT THE UPPER TROUGH IN THE
EAST OR ALONG THE EAST COAST FOR THE LAST FEW RUNS WHILE THE
EUROPEAN AND CANADIAN DETERMINISTIC AND ENSEMBLE MEANS HAVE HAD IT
MORE OFFSHORE. THE DETERMINISTIC 00Z EC/CMC AGREE ON THE GENERAL
DEPTH AND LOCATION OF AN EAST PAC SYSTEM, WHILE THE 06Z GFS
DIVERGES A BIT ON ORIENTATION OF THE ASSOCIATED UPPER TROUGH. A
GENERAL MODEL BLEND WAS USED THROUGH DAY 4 WITH INCREASING
ENSEMBLE MEAN WEIGHTING BEGINNING ON DAY 5 AND CONTINUING THROUGH
THE END OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER TROUGH NEAR THE EAST COAST ON SATURDAY MAY PRODUCE SOME
LINGERING AREAS OF LIGHT PRECIPITATION FROM THE APPALACHIANS INTO
NEW ENGLAND, WITH BEST POTENTIAL FOR SNOW IN THE APPALACHIANS AND
NORTHERN NEW ENGLAND. THE WEAK SYSTEM CROSSING THE GREAT LAKES
THIS WEEKEND MAY PRODUCE A LITTLE LIGHT SNOW ALONG ITS PATH AND
PERHAPS A LITTLE RAIN JUST TO THE SOUTH. RAINFALL TOTALS ARE MORE
UNCERTAIN OVER THE GULF COAST AND SOUTHEAST, WITH SENSITIVITY TO
DETAILS OF SOUTHERN STREAM ENERGY EMERGING FROM THE SOUTHWEST AND
THE ORIENTATION/TIMING OF THE NORTHERN STREAM TROUGH. EVEN AMONG
THE FAVORED GUIDANCE CLUSTER FOR MASS FIELDS, AMOUNTS THERE COULD
RANGE ANYWHERE FROM FAIRLY LIGHT TO LOCALLY HEAVY. THIS SCENARIO
WOULD KEEP THE MIDDLE LATITUDES OF THE EAST DRIER THAN RECENT GFS
RUNS THOUGH.
THE WEST COAST STATES WILL LIKELY SEE RAIN AND HIGH ELEVATION SNOW
CONTINUE INTO SATURDAY WITH THE WEAKENING SHORTWAVE/SURFACE FRONT
REACHING THE REGION, BUT WITH TOTALS TRENDING LIGHTER COMPARED TO
FRIDAY. BEST FOCUS ON SATURDAY SHOULD BE OVER THE SIERRA NEVADA
AND SOUTHERN CALIFORNIA COASTAL RANGES. MOST OF ANY PRECIPITATION
MAKING ITS WAY FARTHER INTO THE WEST SHOULD BE ONLY LIGHT AND
SCATTERED. ANOTHER UPPER TROUGH MAY BRING SOME MOSTLY LIGHT
PRECIPITATION INTO CALIFORNIA BUT CONFIDENCE IS LOWER IN
SPECIFICS, WITH SOME GUIDANCE KEEPING MOST MOISTURE FARTHER
SOUTHWEST. EASTWARD PROGRESSION OF THIS TROUGH MAY HELP TO
DEVELOP RAINFALL NEAR THE GULF COAST BY NEXT WEDNESDAY. ALSO AT
THAT TIME A POTENTIALLY BETTER DEFINED SYSTEM MAY BRING ORGANIZED
PRECIPITATION TO THE WEST COAST, WITH BEST FOCUS CURRENTLY
EXPECTED TO BE OVER CENTRAL AND SOUTHERN AREAS.
CHILLY TEMPERATURES WILL LIKELY CONTINUE INTO THE WEEKEND OVER THE
SOUTHEAST, WITH FLORIDA SEEING THE BEST POTENTIAL FOR SOME
READINGS AT LEAST 10F BELOW NORMAL. LOW TEMPERATURES IN THE LOW
TO MID 30S MAY LEAD TO FROST OR FREEZES OVER PORTIONS OF NORTHERN
FLORIDA SATURDAY AND SUNDAY MORNING. A MODERATING TREND SHOULD
CONFINE NEGATIVE ANOMALIES JUST TO FLORIDA BY SUNDAY-MONDAY. A
FRONTAL PASSAGE EARLY NEXT WEEK MAY LOWER TEMPERATURES AGAIN OVER
THE SOUTH FOR NEXT TUESDAY INTO EARLY WEDNESDAY. IN CONTRAST,
PARTS OF THE FAR NORTHERN PLAINS AND UPPER MIDWEST (EXCLUDING
NORTH-CENTRAL PLAINS LOCATIONS THAT MAY STILL HAVE SNOW COVER)
WILL BE CONSISTENTLY ABOVE NORMAL WITH MULTIPLE DAYS OF PLUS 10F
OR GREATER ANOMALIES. ALSO THE NORTHEAST SHOULD SEE ABOVE NORMAL
MORNING LOWS THROUGH THE PERIOD. MOST OF THE WEST WILL SEE
MODERATELY ABOVE NORMAL READINGS DURING THE PERIOD BUT WITH A
GRADUAL COOLING TREND AS THE WESTERN U.S. MEAN RIDGE ALOFT WEAKENS
IN FAVOR OF PACIFIC SHORTWAVE TROUGHS. PARTS OF CALIFORNIA MAY
SEE SLIGHTLY BELOW NORMAL HIGHS. THE SOUTHERN PLAINS WILL BE ON
THE WARM SIDE DURING THE WEEKEND AND THEN TREND TO NEAR OR
SLIGHTLY BELOW NORMAL TEMPERATURES AFTER A FRONTAL PASSAGE.
KEBEDE/RAUSCH
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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