281
FXUS02 KWBC 120712
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 AM EST FRI JAN 12 2024
VALID 12Z MON JAN 15 2024 - 12Z FRI JAN 19 2024
...HAZARDOUS AND RECORD-BREAKING COLD FROM AN ARCTIC AIRMASS WILL
SPREAD ACROSS THE NORTHWEST INTO THE CENTRAL AND EAST-CENTRAL U.S.
NEXT WEEK...
...POTENTIAL FOR AN IMPACTFUL STORM SYSTEM NEAR THE EAST COAST
NEXT TUESDAY-WEDNESDAY...
..OVERVIEW
GUIDANCE IS PERSISTENT WITH A DEEP AND BROAD MEAN TROUGH ALOFT
OVER MUCH OF THE LOWER 48 WHILE THE UPSTREAM MEAN RIDGE OVER THE
EASTERN PACIFIC DRIFTS TOWARD THE WEST COAST THROUGH NEXT WEEK.
THIS UPPER PATTERN AND ARCTIC HIGH PRESSURE FILTERING IN AT THE
SURFACE WILL SUPPORT VERY COLD TEMPERATURES OVER AREAS FROM THE
NORTHWEST THROUGH MUCH OF THE PLAINS/MISSISSIPPI VALLEY INTO
MONDAY AND TUESDAY, WITH NUMEROUS DAILY RECORDS FOR COLD
LOWS/DAYTIME HIGHS. IN MODIFIED FORM, COLDEST ANOMALIES SHOULD
FOCUS OVER THE EASTERN HALF OF THE COUNTRY BY MIDWEEK WHILE THE
WEST TRENDS WARMER. LOW PRESSURE FORMING ON THE SOUTHERN PERIPHERY
OF THE ARCTIC HIGH MAY SPREAD SNOW ACROSS PORTIONS OF THE
MID-SOUTH MONDAY AND INTO THE MID-ATLANTIC/NORTHEAST TUESDAY. THE
WEST SHOULD ALSO SEE INCREASING PRECIPITATION CHANCES TUESDAY AND
BEYOND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS QUITE AGREEABLE WITH THE LARGE AND DEEP UPPER
TROUGH COVERING THE EASTERN TWO-THIRDS OF THE NATION NEXT WEEK.
HOWEVER, THERE ARE TWO PROMINENT UNCERTAINTIES IN THE FORECAST,
BOTH DURING TUESDAY-WEDNESDAY: DETAILS OF A POTENTIALLY IMPACTFUL
STORM SYSTEM NEAR THE EAST COAST, AND NORTHEASTERN PACIFIC/WESTERN
CANADA EVOLUTION ALOFT THAT WILL AFFECT PRECIPITATION SPECIFICS
OVER THE WEST.
RECENT MODELS REMAIN AGREEABLE WITH SHOWING SHORTWAVE ENERGY
PIVOTING THROUGH THE SOUTHERN SIDE OF THE BROAD AND DEEP TROUGH
SERVING TO FORM A SURFACE LOW NEAR THE EAST COAST TUESDAY INTO
WEDNESDAY. 12/18Z AND NOW THE 00Z MODEL GUIDANCE GENERALLY SHOWS
LOW PRESSURE DEVELOPING NEAR THE SOUTHEAST COAST BY EARLY TUESDAY,
BUT WITH SOME SPREAD IN THE FORMATION/TRACK THAT IS AMPLIFIED BY
THE FACT THAT EVEN RELATIVELY SMALL DIFFERENCES WOULD HAVE
CONSIDERABLE SENSIBLE WEATHER DIFFERENCES. WITH THE 12/18Z SUITE
OF MODELS, THE GEFS AND EC MEAN SHOWED SIMILAR LOW TRACKS
NORTHWARD ACROSS THE WESTERN ATLANTIC AND A FAIRLY STRONG SYSTEM
REACHING NEW ENGLAND OR THE CANADIAN MARITIMES BY EARLY WEDNESDAY.
12/18Z GFS RUNS WERE MOST LIKE THE MEANS, SO FAVORED THAT CLUSTER
FOR THE WPC FORECAST. THE 12Z AND NOW THE 00Z ECMWF DETERMINISTIC
RUNS ARE MORE OFFSHORE WHERE HARDLY ANY PRECIPITATION IS ONSHORE
OF THE EAST COAST. THIS SEEMS UNLIKELY BASED ON OTHER GUIDANCE AND
THE EC ENSEMBLE MEAN AND MEMBERS, BUT UNFORTUNATELY THE
ECMWF-INITIALIZED MACHINE LEARNING MODELS DID NOT SEEM TO RUN FOR
THE 12Z CYCLE, SO WE LACK THAT PIECE OF INFORMATION THAT COULD
HELP WITH THE MODEL DIAGNOSTICS. MEANWHILE THE 12Z CMC SHOWED
REASONABLE ALIGNMENT IN THE TRACK THOUGH A BIT FASTER THAN
PREFERRED, BUT NOW THE 00Z CMC HAS A TRACK CONSIDERABLY INLAND
THAT WOULD SPREAD RAIN TO SOME MID-ATLANTIC AREAS. THE 00Z GFS
ALSO SHOWS DIFFERENCES FROM ITS PREVIOUS RUNS, WITH A DUAL
STRUCTURE TO THE LOW EARLY WEDNESDAY WITH SOME LOW PRESSURE
HANGING NEAR THE DELMARVA, AND NOT CONSOLIDATING UNTIL LATER
WEDNESDAY. OVERALL, THE FORECAST DETAILS REMAIN LOW CONFIDENCE AS
THE STORM TRACK SPREAD IS STILL HIGH.
MEANWHILE THE QUESTION MARK FARTHER WEST INVOLVES THE DEGREE TO
WHICH A TROUGH CROSSING OVER/SOUTH OF ALASKA (AND POSSIBLY ENERGY
TO THE SOUTH) ULTIMATELY DENTS THE EAST PACIFIC/WEST COAST UPPER
RIDGE AROUND TUESDAY-WEDNESDAY, BEFORE CONSENSUS RETURNS TO A MORE
AGREEABLE UPPER RIDGE NEAR THE WEST COAST BY NEXT THURSDAY. OVER
THE PAST COUPLE DAYS GUIDANCE HAS FORMED TWO PRONOUNCED CLUSTERS
IN PRINCIPLE, WITH THE GFS/GEFS HOLDING ONTO A PERSISTENT RIDGE
VERSUS REMAINING GUIDANCE SHOWING VARYING DEGREES OF HEIGHT FALLS.
THIS MAKES FOR A SIGNIFICANT DIFFERENCE IN HOW STRONG OF A SURFACE
SYSTEM MAY REACH THE PACIFIC NORTHWEST AND FOR PRECIPITATION AND
COVERAGE AMOUNTS OVER THE WEST, WITH THE GFS/GEFS SCENARIO MUCH
LIGHTER AND CONFINED WITH WHAT PRECIPITATION OCCURS. THE BEST
COURSE OF ACTION STILL SEEMS TO BE A COMPROMISE ALONG THE WEST
COAST WITH MODEST DENTING OF THE UPPER RIDGE AND ASSOCIATED WEAK
LOW PRESSURE.
THE WPC FORECAST BEGAN WITH A MODEL BLEND OF THE 18Z GFS AND 12Z
ECMWF AND CMC WITH A BIT OF GEFS AND EC MEAN AS WELL TO SMOOTH OUT
SOME DIFFERENCES. BY DAY 5/WEDNESDAY THE ENSEMBLE MEANS MADE UP 40
PERCENT OF THE BLEND BUT WAS ACTUALLY ABLE TO HOLD THIS PROPORTION
STEADY THROUGH DAYS 6-7 GIVEN THAT THE LARGE SCALE PATTERN
STABILIZES DURING THE LATTER PART OF NEXT WEEK, AS UPPER RIDGING
EDGES INTO THE WEST AND TROUGHING REMAINS FARTHER EAST.
..WEATHER/HAZARDS HIGHLIGHTS
VERY COLD AIR ORIGINALLY STEMMING FROM THE ARCTIC WILL BE ATOP THE
NORTHERN GREAT BASIN AND ROCKIES AND SOUTHEASTWARD THROUGH THE
CENTRAL U.S. AS THE MEDIUM RANGE PERIOD BEGINS MONDAY, SUPPORTED
BY COLD SURFACE HIGH PRESSURE AND AMPLIFIED TROUGHING ALOFT. LOW
TEMPERATURES IN THE -10 TO -20 RANGE AND HIGHS STAYING NEAR OR
BELOW 0F WILL BE COMMON ACROSS THE NORTHERN HALF OF THE PLAINS AND
INTO THE UPPER MIDWEST, WHILE FARTHER WEST THE COLDEST AIR SHOULD
AFFECT MONTANA WITH LOWS IN THE -20S AND EVEN -30S. ANY WIND
CHILLS WOULD BE EVEN COLDER AND THUS MORE DANGEROUS. THE COLD AIR
DIVING FARTHER SOUTH INTO THE SOUTHERN HALF OF THE PLAINS AND
MISSISSIPPI VALLEY WILL NOT BE AS COLD IN TERMS OF ABSOLUTE
TEMPERATURES, BUT TEMPERATURE ANOMALIES OF 20 TO 40 DEGREES BELOW
AVERAGE ARE LIKELY TO SET WIDESPREAD RECORDS ACROSS THE SOUTH
MONDAY-TUESDAY. BY WEDNESDAY, TEMPERATURES FINALLY LOOK TO
MODERATE IN THE CENTRAL U.S., THOUGH CHILLY TEMPERATURES (ALBEIT
IN MODERATED FORM) WILL SHIFT INTO THE EASTERN THIRD OF THE
COUNTRY BEFORE WARMING CLOSER TO NORMAL ON THURSDAY. SOME
REINFORCING COLD MAY REACH THE NORTHERN PLAINS BY THURSDAY AND THE
CENTRAL PLAINS BY FRIDAY, BUT IT SHOULD BE LESS EXTREME THAN WHAT
IS FORECAST EARLIER IN THE PERIOD, WITH ANOMALIES MORE LIKE 10-20F
BELOW NORMAL.
ALONG THE SOUTHERN FRINGE OF THE ARCTIC HIGH, SOME LIMITED
MOISTURE LOOKS TO OVERRUN A GULF COAST TO FLORIDA FRONTAL BOUNDARY
AND COULD PRODUCE ACCUMULATING SNOW FROM PORTIONS OF THE LOWER
MISSISSIPPI VALLEY STRETCHING INTO THE TENNESSEE VALLEY AND THE
SOUTHERN/CENTRAL APPALACHIANS ON MONDAY. THOUGH THERE IS STILL
MODEL SPREAD, SOME CONVERGENCE IN RECENT GUIDANCE REGARDING THE
TIMING AND PLACEMENT OF A SURFACE LOW FORMING ALONG THIS FRONT
SUGGESTS THAT SNOW POTENTIAL FARTHER NORTHEAST OF THOSE REGIONS
COULD HOLD OFF UNTIL TUESDAY. MEANWHILE FARTHER SOUTH, CONVECTION
IS FORECAST THAT COULD FOCUS NEAR THE STALLED FRONT IN NORTHERN
FLORIDA WITH INCREASING DEEP MOISTURE, WHICH COULD PRODUCE HEAVY
RAINFALL POTENTIAL, AND A MARGINAL RISK REMAINS IN PLACE THERE IN
THE ERO FOR MONDAY. THEN AS GULF TO WESTERN ATLANTIC LOW PRESSURE
DEVELOPS ALONG THE FRONT AND PIVOTS NORTHEAST, SNOW COULD SPREAD
ACROSS THE MID-ATLANTIC TO NORTHEAST TO THE WEST OF THE LOW TRACK.
THE MOST RECENT WPC FORECAST CONTINUES TO SHOW A BAND OF 30
PERCENT OR GREATER POTENTIAL FOR 0.25 INCH LIQUID IN THE FORM OF
SNOW FROM NEAR THE NORTHERN MID-ATLANTIC COAST THROUGH NEW ENGLAND
IN THE SNOW PROBABILITIES. THOUGH THIS FORECAST STAYED PRETTY
CONSISTENT WITH THE PREVIOUS ONE, SNOW COVERAGE/AMOUNTS WILL BE
VERY SENSITIVE TO STORM TRACK AND STRENGTH, SO ADDITIONAL CHANGES
IN THE MOST LIKELY SCENARIO ARE LIKELY. FARTHER NORTH, EXPECT
CONTINUED PERIODS OF LAKE EFFECT SNOW WITH PERSISTENCE OF COLD AIR
AND BREEZY CONDITIONS.
BY TUESDAY-THURSDAY, MOISTURE SHOULD INCREASE OVER THE NORTHWEST
AROUND TUESDAY-WEDNESDAY, BUT WITH LOW CONFIDENCE IN SPECIFICS OF
PRECIPITATION TOTALS AND SOUTHWARD EXTENT. THIS EVENT WILL LIKELY
SEE SNOW CONFINED TO HIGHER ELEVATIONS THAN IN THE SHORTER TERM,
BUT AREAS WHERE EARLIER COLD AIR PERSISTS LONGER THAN FORECAST
COULD STILL PRESENT SOME LOWER ELEVATION WINTER WEATHER ISSUES.
TATE/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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