430
FXUS02 KWBC 121900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM 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
LATEST GUIDANCE MAINTAINS 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,
POSSIBLY DRIFTING INLAND BY NEXT FRIDAY. 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 NORTHERN HALF OR SO OF 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 HAVE BEEN ARE TWO PROMINENT UNCERTAINTIES IN THE
FORECAST DURING TUESDAY-WEDNESDAY: DETAILS OF A POTENTIALLY
IMPACTFUL STORM SYSTEM NEAR THE EAST COAST, AND NORTHEASTERN
PACIFIC/WESTERN CANADA EVOLUTION ALOFT THAT WILL AFFECT UPPER FLOW
AND PRECIPITATION SPECIFICS OVER THE WEST. THEN AS THE UPPER RIDGE
REBUILDS NEAR THE WEST COAST LATE IN THE WEEK, QUESTION MARKS
ARISE REGARDING DETAILS OF CENTRAL-EASTERN U.S. TROUGHING AND HOW
IT WILL AFFECT THE SURFACE PATTERN OVER THE EAST.
THE MODELS STILL AGREE IN SHOWING SHORTWAVE ENERGY PIVOTING
THROUGH THE SOUTHERN SIDE OF THE BROAD MEAN TROUGH SERVING TO FORM
A SURFACE LOW NEAR THE EAST COAST TUESDAY INTO WEDNESDAY.
CONSENSUS MAINTAINS AN ELONGATED AREA OF LOW PRESSURE ALONG OR
JUST OFFSHORE THE SOUTHEAST COAST BY EARLY TUESDAY BUT THEN
DISPLAYS INCREASING EAST-WEST SPREAD IN THE TRACK GOING INTO
WEDNESDAY. THESE TRACK DIFFERENCES REFLECT SENSITIVITY TO LOWER
PREDICTABILITY DETAIL ISSUES WITH THE UPPER SHORTWAVE. AMONG THE
00Z/06Z CYCLE OF GUIDANCE VALID INTO WEDNESDAY, THE
GEFS/ECENS/CMCENS MEANS WERE ALL FAIRLY CLOSE IN TRACK AND TIMING
NEAR THE MIDDLE OF RECENT MODEL SPREAD AND JUST OFFSHORE NEW
ENGLAND. THE 06Z GFS WAS CLOSEST TO THE MEANS AND THE NEW 12Z CMC
HAS ADJUSTED THAT WAY AS WELL AFTER BEING ON THE WESTERN SIDE OF
THE SPREAD IN THE 00Z RUN. LATEST UKMET RUNS HAVE ALSO REPRESENTED
THE WESTERN SIDE OF THE SPREAD. ON THE OTHER HAND, RECENT ECMWF
RUNS HAVE STRAYED FARTHER EAST WITH THE SURFACE LOW TRACK DUE TO
FASTER TIMING FOR THE NORTHERN PART OF THE SUPPORTING SHORTWAVE.
THE 00Z ECMWF-INITIALIZED MACHINE LEARNING MODELS GENERALLY
FOLLOWED A TRACK FAVORED BY THE ENSEMBLE MEANS, THOUGH WITH MOST
HINTING AT SOMEWHAT FASTER NORTHWARD PROGRESSION BY EARLY
WEDNESDAY. THE NEW 12Z GFS/GEFS MEAN TRENDED A LITTLE FARTHER
OFFSHORE. MOST OF THE OBSERVED RUN-TO-RUN VARIABILITY IS FAIRLY
TYPICAL FOR FORECASTS SEVERAL DAYS OUT IN TIME BUT STILL LEADS TO
SIGNIFICANT DIFFERENCES FOR PRECIPITATION AMOUNTS (AND IN SOME
CASES, TYPE) ALONG THE EAST COAST. PREFERENCES REMAINS WITH AN
INTERMEDIATE SOLUTION CLOSEST TO THE ENSEMBLE MEANS.
MEANWHILE THE QUESTION MARK FARTHER WEST INVOLVES WHAT COULD BE A
FAIRLY BRIEF BUT COMPLEX EVOLUTION OVER THE NORTHEASTERN
PACIFIC/WESTERN NORTH AMERICA TUESDAY-WEDNESDAY. THROUGH THE
00Z/06Z CYCLES, THE GFS/GEFS HAD BEEN STEADFAST IN MAINTAINING A
STRONG UPPER RIDGE OVER THE EAST PACIFIC/WEST COAST. IN CONTRAST
MOST OTHER MODELS/ENSEMBLE MEANS SHOW A SHORTWAVE DROPPING SOUTH
OVER THE ALASKA PANHANDLE/BRITISH COLUMBIA INTO THE PACIFIC, ALONG
WITH A SEPARATE PIECE OF ENERGY BREAKING OFF FROM A PACIFIC UPPER
LOW AND TRACKING UNDERNEATH THE NORTHERN SHORTWAVE. EVEN AMONG THE
ECMWF CLUSTER THERE IS CONSIDERABLE SPREAD FOR THE ASSOCIATED
SURFACE SYSTEM'S TRACK AND DEPTH. ECMWF-INITIALIZED MACHINE
LEARNING MODELS HAVE SHIFTED TO A GREATER MAJORITY IN FAVOR OF THE
ECMWF CLUSTER COMPARED TO 24 HOURS AGO, SO THE LATEST FORECAST
TILTED TOWARD A WEAKER VERSION OF THAT GROUPING. THE NEW 12Z GFS
HAS FINALLY SWITCHED TO THE MAJORITY SCENARIO BUT WITH SLOWER
SOUTHWARD PROGRESSION OF THE NORTHERN SHORTWAVE, THUS YIELDING A
FARTHER NORTH SURFACE WAVE. AT LEAST THE SPREAD IS NARROWING BUT
DIFFERENCES CONTINUE TO BE SIGNIFICANT FOR REFINING EXPECTED
PRECIPITATION COVERAGE AND TOTALS OVER THE WEST.
WHILE GUIDANCE RETURNS TO BETTER AGREEMENT FOR THE WEST COAST
UPPER RIDGE BY NEXT THURSDAY-FRIDAY, DETAIL DIFFERENCES WITHIN THE
DOWNSTREAM TROUGH AFFECT THE PROGRESSION OF THE COLD FRONT
EXPECTED TO REACH THE CENTRAL-EASTERN STATES AS WELL AS LOCATION
AND DEPTH OF LOW PRESSURE. BY THE END OF THE PERIOD NEXT FRIDAY,
THERE APPEARS TO BE A GENERAL TREND OVER THE PAST 12-24 HOURS
TOWARD SOMEWHAT MORE POTENTIAL LOW PRESSURE DEVELOPMENT NEAR OR A
LITTLE INLAND FROM THE EAST COAST BUT WITH NO AGREEMENT FOR
SPECIFICS. A MODEL/ENSEMBLE MEAN BLEND NUDGED THE FORECAST TO
REFLECT LATEST TRENDS WHILE DOWNPLAYING SPECIFICS OF ANY
PARTICULAR SOLUTION.
AN AVERAGE OF LATEST OPERATIONAL GUIDANCE DURING THE FIRST HALF OF
THE PERIOD HELPED TO MAINTAIN CONTINUITY FOR THE SYSTEM NEAR THE
EAST COAST AND MODESTLY INCORPORATE TRENDS TOWARD THE MAJORITY
CLUSTER ALONG THE WEST COAST. THEN A MIX OF THE MODELS AND 06Z
GEFS/00Z ECENS MEANS (REACHING 40 PERCENT WEIGHT LATE) REPRESENTED
PREFERENCES WELL LATER IN THE FORECAST.
..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 AIR MAY REACH THE NORTHERN PLAINS BY THURSDAY AND
EXPAND TO INCLUDE MOST AREAS BETWEEN THE ROCKIES AND APPALACHIANS
THURSDAY. EXPECT LESS EXTREME TEMPERATURE ANOMALIES THAN THOSE
FORECAST EARLIER IN THE PERIOD, BUT FRIDAY MAY STILL SEE LOWS
10-20F BELOW NORMAL AND HIGHS 10-25F 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. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK FOR
MONDAY MAINTAINS A MARGINAL RISK AREA, WITH ONLY MINOR ADJUSTMENT
FROM PREVIOUS ISSUANCE. THE NORTHERN EDGE OF THE GUIDANCE SPREAD
FOR HIGHEST TOTALS HAS BEEN DRIFTING SOUTH OVER THE PAST DAY WHILE
LATEST ECMWF RUNS REMAIN ON THE SOUTHERN SIDE. AS GULF TO WESTERN
ATLANTIC LOW PRESSURE DEVELOPS ALONG THE FRONT AND PIVOTS
NORTHEAST, SNOW COULD SPREAD ACROSS THE MID-ATLANTIC AND 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.
LATEST SOLUTIONS BEFORE THE 12Z CYCLE LED TO A SLIGHT INCREASE IN
PROBABILITIES ALONG A SIMILAR AXIS. HOWEVER SNOW COVERAGE/AMOUNTS
WILL REMAIN 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. THEN A FRONT AND
POSSIBLE LOW PRESSURE REACHING THE EAST LATE IN THE WEEK MAY
PRODUCE SOME PRECIPITATION, BUT AT THIS POINT CONFIDENCE IS VERY
LOW REGARDING COVERAGE/AMOUNTS AS WELL AS FOR WHERE THE RAIN-SNOW
LINE WILL BE.
EXPECT MOISTURE TO INCREASE OVER THE NORTHWEST AROUND
TUESDAY-WEDNESDAY, BUT STILL WITH FAIRLY LOW CONFIDENCE IN
SPECIFICS OF PRECIPITATION TOTALS AND SOUTHWARD EXTENT. 12Z GFS
TRENDS AT LEAST SUPPORT LEANING AWAY FROM THE DRIER SIDE OF THE
PRIOR GUIDANCE SPREAD. 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. MIDWEEK WINDS NEAR THE
PACIFIC NORTHWEST COAST ARE ALSO VERY UNCERTAIN, GIVEN DIFFERENCES
FOR LOW PRESSURE THAT MAY AFFECT THE REGION.
RAUSCH/TATE
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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