642
FXUS02 KWBC 011859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST MON JAN 01 2024
VALID 12Z THU JAN 04 2024 - 12Z MON JAN 08 2024
...HEAVY PRECIPITATION LIKELY TO IMPACT AREAS FROM THE GULF COAST
NORTHEASTWARD FRIDAY INTO NEXT WEEKEND...
..OVERVIEW
THE MEDIUM RANGE PERIOD FEATURES A RATHER PROGRESSIVE FLOW PATTERN
AS A PARADE OF STORM SYSTEMS TRAVERSES THE COUNTRY FROM WEST TO
EAST. ONE WILL BE EXITING THE EAST COAST AS ANOTHER MOVES THROUGH
THE SOUTHWEST ON THURSDAY, WITH POTENTIAL FOR ANOTHER ROUND OF
HEAVY RAIN ACROSS THE LOWER MISSISSIPPI VALLEY/SOUTHEAST BY
FRIDAY. AS THIS SYSTEM LIFTS UP THE EAST COAST NEXT WEEKEND, IT
HAS POTENTIAL TO BRING HEAVY PRECIPITATION (RAIN TO THE SOUTH,
SNOW TO THE NORTH) TO MUCH OF THE EAST. OUT WEST, THE NEXT SYSTEM
LOOKS TO MOVE IN NEXT WEEKEND AS WELL WITH ANOTHER ROUND OF VALLEY
RAIN AND MOUNTAIN SNOWS PROGRESSING FROM CALIFORNIA INTO THE FOUR
CORNERS REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE AGREES ON THE EXISTENCE OF THE TWO DOMINANT SYSTEMS OF
INTEREST, THE SYSTEM PROGRESSING FROM THE FOUR CORNERS THROUGH THE
EAST THURSDAY INTO THE WEEKEND AND THEN THE AMPLIFYING UPPER
TROUGH OVER THE WEST, BUT WITH SOME IMPORTANT DETAIL DIFFERENCES
ESPECIALLY FOR THE LEADING SYSTEM. THERE IS SOMEWHAT MORE SPREAD
FOR A POTENTIAL SMALLER SCALE SYSTEM APPROACHING THE PACIFIC
NORTHWEST AROUND FRIDAY.
FOR THE SYSTEM INITIALLY EMERGING FROM THE FOUR CORNERS ON
THURSDAY, THE MOST PRONOUNCED DIFFERENCE AMONG THE 00Z/06Z
GUIDANCE WAS THAT THE GFS WAS SOMEWHAT SLOWER THAN OTHER SOLUTIONS
PLUS TRACKED THE PRIMARY LOW INTO THE OHIO VALLEY WHILE DEVELOPING
A SECONDARY COASTAL/WESTERN ATLANTIC LOW--VERSUS THE OTHERS THAT
MAINTAINED A SINGLE SURFACE LOW FROM THE GULF COAST NORTHEASTWARD
THROUGH THE SOUTHEAST COAST AND BEYOND. WHILE THE 12Z/31 ECMWF
SHARED THE GENERAL 00Z/06Z GFS IDEA, 00Z TRENDS WERE PRONOUNCED
AWAY FROM THE GFS, WITH THE GEFS MEAN NUDGING MORE TOWARD THE
ECMWF/CMC/UKMET CLUSTER. THE 00Z ECMWF-INITIALIZED MACHINE
LEARNING MODELS STRONGLY FAVORED THE ECMWF/CMC/UKMET CLUSTER AS
WELL. IN THE NEW 12Z MODEL RUNS, THE GFS HAS COME IN MUCH CLOSER
TO THE MAJORITY WHILE A FASTER TREND IN THE UKMET STILL LEAVES
QUITE A BIT OF TIMING SPREAD. THERE ARE ISSUES WITH EXACT
NORTHWARD EXTENT OF THE TRACK AS WELL. MEDIUM TO SMALLER SCALE
SHORTWAVE DETAILS WITH LOWER PREDICTABILITY MAY HAVE A SIGNIFICANT
EFFECT ON THE SURFACE EVOLUTION, SO ADDITIONAL ADJUSTMENTS IN THE
GUIDANCE CONSENSUS APPEAR LIKELY.
WELL BEHIND THIS SYSTEM, THERE IS A GENERAL CLUSTERING THAT FAVORS
A PROGRESSIVE SHORTWAVE AND COMPACT DEVELOPING SURFACE LOW NEARING
THE PACIFIC NORTHWEST AROUND FRIDAY. 00Z/06Z GFS RUNS WERE ON THE
DEEP SIDE WITH THE SURFACE LOW WHILE THE NEW 12Z RUN HAS TEMPERED
ITS DEPTH A LITTLE. THE 12Z GEFS MEAN HINTS AT THIS SYSTEM AND THE
UKMET IS FARTHER NORTH, WHILE CMC RUNS DO NOT REFLECT THIS SYSTEM.
OTHER GUIDANCE SUGGESTS THE 00Z ECMWF BECOMES TOO AMPLIFIED WITH
THE ASSOCIATED UPPER TROUGH ONCE IT REACHES THE PLAINS BY LATE
SATURDAY.
THE SUNDAY-MONDAY UPPER TROUGH AMPLIFYING INTO THE WEST CURRENTLY
SEEMS TO HAVE BETTER THAN AVERAGE PREDICTABILITY GIVEN ITS LARGE
SCALE AND FAVORABLE GUIDANCE CLUSTERING WHICH SUGGESTS AN EMBEDDED
UPPER LOW (WHETHER ACTUAL, OR IMPLIED AS IN THE ENSEMBLE MEANS)
TRACKING NEAR THE FOUR CORNERS AS OF EARLY MONDAY. A MODEL/MEAN
CONSENSUS LOOKS GOOD FOR THIS SYSTEM.
THE ABOVE GUIDANCE COMPARISONS LED TO UPDATING THE FORECAST WITH A
00Z/06Z MODEL BLEND EARLY AND THEN INCORPORATING SOME 06Z GEFS/00Z
ECENS MEAN GUIDANCE WITH THE MODELS LATER ON, THOUGH A FAIR AMOUNT
OF OPERATIONAL MODEL INPUT WAS ABLE TO BE MAINTAINED INTO DAY 7 IN
LIGHT OF ENSEMBLE MEAN SUPPORT FOR THE AMPLIFYING WESTERN UPPER
TROUGH/ASSOCIATED SURFACE SYSTEM. DUE TO CONSIDERATIONS FOR THE
SYSTEM AFFECTING THE EAST, GFS WEIGHT WAS KEPT A LITTLE LOWER THAN
WOULD TYPICALLY BE THE CASE.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION ACROSS THE FOUR CORNERS/SOUTHERN-CENTRAL PLAINS
STARTING BY THURSDAY SHOULD BECOME MORE WIDESPREAD AS THE FIRST OF
A SERIES OF UPPER LOWS TAPS GULF OF MEXICO MOISTURE TO FUEL
ANOTHER ROUND OF MODERATE TO LOCALLY HEAVY RAINFALL ACROSS THE
LOWER MISSISSIPPI VALLEY/CENTRAL GULF COAST STATES AND PERHAPS
NEARBY AREAS ON FRIDAY. THE DAY 5 EXCESSIVE RAINFALL OUTLOOK
MAINTAINS A MARGINAL RISK AREA ACROSS THIS REGION, WITH LATEST
GUIDANCE SUPPORTING SOME EASTWARD EXPANSION OF THE RISK AREA.
THERE IS SOME QUESTION ABOUT HOW FAR NORTHWARD INSTABILITY MAY
EXTEND, BUT ANOMALOUS MOISTURE AND A LEADING FRONT FORMING NEAR
THE GULF COAST TO PROVIDE A FOCUS, PLUS FAIRLY WET ANTECEDENT
CONDITIONS FROM SHORT-TERM RAINFALL, SEEM TO SUGGEST SOME FLASH
FLOODING POTENTIAL. HEAVY PRECIPITATION WILL SPREAD ACROSS THE
SOUTHEAST/MID-ATLANTIC AND POSSIBLY THE NORTHEAST NEXT WEEKEND,
WITH INCREASING POTENTIAL FOR SNOW TO THE NORTH AND WEST OF THE
LOW. EXACT AMOUNTS AND PRECIPITATION TYPE FOR SOME OF THE MAJOR
EAST COAST CITIES REMAINS HIGHLY UNCERTAIN AT THIS POINT, BUT DOES
NEED TO BE WATCHED. THE WPC WINTER WEATHER OUTLOOK PROBABILITIES
HIGHLIGHT THE BEST POTENTIAL FOR AT LEAST 0.25" LIQUID IN THE FORM
OF SNOW OVER THE CENTRAL APPALACHIANS. JUST TO THE EAST, GUIDANCE
TRENDS HAVE LED TO SOMEWHAT HIGHER PROBABILITIES VERSUS THE
PREVIOUS 12-HOURLY ISSUANCE (FOR EXAMPLE, FROM 10 PERCENT TO 30
PERCENT) NEAR THE DC-NYC CORRIDOR. IT MAY TAKE SOME TIME TO
RESOLVE IMPORTANT DETAILS GIVEN THE CURRENT SPREAD FOR SURFACE LOW
TIMING/TRACK.
A SMALLER-SCALE SYSTEM MAY BRING A BRIEF FOCUS OF ENHANCED
RAIN/MOUNTAIN SNOW TO THE PACIFIC NORTHWEST AROUND FRIDAY. THEN
EXPECT BROADER COVERAGE OF MODERATE TO LOCALLY HEAVY PRECIPITATION
FROM THE WEST COAST/CALIFORNIA AND INTO THE INTERIOR WEST BY NEXT
MONDAY. THERE IS A DECENT SIGNAL FOR MEANINGFUL MOUNTAIN SNOWS
ACROSS PARTS OF THE CASCADES, SIERRA NEVADA, AND INTERIOR MOUNTAIN
RANGES/SOUTHERN ROCKIES. SURFACE CYCLOGENESIS ACROSS THE
SOUTH-CENTRAL PLAINS EARLY NEXT WEEK SHOULD ALLOW PRECIPITATION TO
MOVE INTO THE CENTRAL U.S., WITH POTENTIAL FOR SNOW TO THE NORTH
OF THE LOW TRACK.
ABOVE NORMAL TEMPERATURES SHOULD BE MOSTLY CONFINED TO THE FAR
NORTHERN TIER WITH ANOMALIES GENERALLY PLUS 5-15F FOR HIGHS, AND
PERHAPS AS HIGH AS PLUS 15-25F FOR MORNING LOWS OVER PARTS OF
MINNESOTA/WISCONSIN DURING THE WEEKEND. SOME MODERATELY ABOVE
NORMAL TEMPERATURES MAY RETURN TO THE SOUTHERN PLAINS/LOWER
MISSISSIPPI VALLEY EARLY NEXT WEEK. THE SOUTHERN TWO-THIRDS OF THE
WEST SHOULD SEE BELOW NORMAL TEMPERATURES LATE THIS WEEK, WITH
SOME COOLER ANOMALIES AT LEAST 10F BELOW NORMAL FOR HIGHS
SPREADING ACROSS THE WEST INTO THE HIGH PLAINS BY SUNDAY-MONDAY AS
UPPER TROUGHING MOVES OVER THE REGION. NORTHERN PARTS OF THE WEST
SHOULD TREND BELOW NORMAL AS WELL. MOST OF THE EAST WILL LIKELY
SEE NEAR TO BELOW NORMAL TEMPERATURES LATE WEEK INTO THE WEEKEND,
PERHAPS REBOUNDING TOWARD NORMAL BY NEXT MONDAY.
RAUSCH/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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