147
FXUS02 KWBC 161909
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EST THU JAN 16 2025
VALID 12Z SUN JAN 19 2025 - 12Z THU JAN 23 2025
...STRONG ARCTIC SURGE WILL PUSH INTO THE CENTRAL U.S. THIS
WEEKEND AND REACH THE EAST BY EARLY NEXT WEEK...
..OVERVIEW
MODELS AND ENSEMBLES CONTINUE TO SHOW A VERY AMPLIFIED MEAN PATTERN
CONSISTING OF A DEEP TROUGH FROM NORTHEASTERN CANADA THROUGH THE
LOWER 48 AND AN EASTERN PACIFIC RIDGE EXTENDING WELL NORTHWARD.
THUS CONFIDENCE REMAINS HIGH IN THE FORECAST OF ARCTIC AIR DROPPING
SOUTHWARD OVER THE CENTRAL U.S. THIS WEEKEND AND EXPANDING TO
INCLUDE MUCH OF THE EAST BY EARLY NEXT WEEK. BY MIDWEEK MOST OF THE
PLAINS SHOULD SEE MODERATING TEMPERATURES WHILE THE COLD WILL
LIKELY LINGER OVER THE SOUTH AND EAST. IN CONTRAST, GUIDANCE IS
HAVING A LOT OF DIFFICULTY IN RESOLVING IMPORTANT EMBEDDED
SHORTWAVES THAT WILL PLAY AN IMPORTANT ROLE IN DETERMINING THE
COVERAGE AND AMOUNTS OF POTENTIAL WINTRY PRECIPITATION ACROSS THE
EAST ON SUNDAY AND THEN THE SOUTH INTO NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE IS STILL A FRUSTRATING AMOUNT OF MODEL SPREAD WITH A
SHORTWAVE AND SURFACE LOW/FRONTAL WAVE IMPACTING THE EAST ON SUNDAY
THAT AFFECTS SNOW CHANCES AND AMOUNTS. CMC RUNS HAVE BEEN FARTHER
INLAND WITH THE LOW TRACK WHICH IN TURN TRACKS QPF (SNOW) FARTHER
WEST INTO THE MID-ATLANTIC AND NORTHEAST AND EVEN KEEPS THE COASTAL
MID-ATLANTIC WITH RAIN AS THE PRECIPITATION TYPE. ECMWF RUNS HAVE
GENERALLY BEEN MORE SUPPRESSED WITH THE LOW TRACK TO KEEP SNOW IN
THE SOUTHERN MID-ATLANTIC AND OFFSHORE OF NEW ENGLAND FARTHER
NORTH, WITH THE EXCEPTION OF THE 06Z RUN, AND THE 12Z RUN TRENDED A
LITTLE FAVORABLY. THE EC-BASED AIFS ON THE OTHER HAND HAS BEEN
FAIRLY PERSISTENT IN ITS PRECIPITATION AXIS ACROSS THE MID-ATLANTIC
AND COASTAL NORTHEAST, AND THE UKMET IS SIMILAR. GFS RUNS HAD BEEN
SUPPRESSED BUT HAVE GRADUALLY BEEN TRENDING NORTHWARD. THUS THE
GENERAL TREND IS FOR INCREASING PRECIPITATION AND SNOW
PROBABILITIES ACROSS THE URBAN CORRIDOR FROM DC TO NYC TO BOSTON
WITH A LOW TRACK THAT IS IN THE MIDDLE OF THE MODEL SPREAD. BUT
SMALL SHIFTS IN THE LOW TRACK WILL CAUSE DRAMATIC DIFFERENCES IN
IMPACTFUL SNOW, SO CONTINUE TO MONITOR FORECASTS AS THIS SYSTEM
MOVES INTO THE SHORT RANGE.
ENERGY DIGGING SOUTH THROUGH THE WESTERN SIDE OF THE BROAD TROUGH
EARLY NEXT WEEK WILL ALSO BE A FACTOR IN MODEL UNCERTAINTY ON THE
PERIPHERY OF THE BROAD TROUGH. MODELS AS OF ABOUT A DAY AGO TENDED
TO HOLD MORE ENERGY BACK IN THE SOUTHWEST TO PRODUCE POSITIVELY
TILTED TROUGHING AROUND TUESDAY. TODAY'S MODEL GUIDANCE (WITH THE
EXCEPTION OF THE CMC) IS TRENDING AWAY FROM THAT PATTERN IN FAVOR
OF A SMALL CLOSED UPPER LOW TO THE WEST OF THE MAIN TROUGH IN THE
EASTERN PACIFIC TO SOUTHWEST OR GREAT BASIN. THERE ARE, OF COURSE,
SOME MODEL DIFFERENCES IN WHEN/HOW THAT FEATURE GETS ABSORBED BACK
INTO THE MEAN FLOW. THESE MODEL DIFFERENCES HAVE RAMIFICATIONS FOR
HOW MUCH PRECIPITATION (WINTRY IN MOST AREAS) AFFECTS THE SOUTH-
CENTRAL U.S. TO SOUTHEAST. IN A GENERAL SENSE, CMC ENSEMBLE MEMBERS
HAVE MORE WINTRY PRECIPITATION ACROSS THE SOUTH COMPARED TO THE
MORE SUPPRESSED GEFS AND ECMWF MEMBERS. THEN BY WEDNESDAY-
THURSDAY, THE BROAD TROUGH AXIS SHOULD FINALLY LIFT AND PUSH
EASTWARD, WHILE THERE IS GENERAL MODEL AGREEMENT FOR MORE TROUGHING
TO DROP INTO THE NORTHERN ROCKIES OR SO.
THE WPC FORECAST WAS BASED ON A MULTI-MODEL AND ENSEMBLE MEAN
BLEND EARLY IN THE FORECAST PERIOD GIVEN THE MODEL VARIATIONS EVEN
AT THE BEGINNING. INCREASED THE PROPORTION OF THE ENSEMBLE MEANS TO
WELL OVER HALF BY DAYS 6-7 DUE TO THE DETAIL DIFFERENCES AMONG THE
RELATIVELY PREDICTABLE LARGE SCALE PATTERN.
..WEATHER/HAZARDS HIGHLIGHTS
BY SUNDAY A BROAD AREA OF HAZARDOUSLY COLD ARCTIC AIR WILL ALREADY
COVER THE CENTRAL U.S. AND SHOULD EXPAND TO COVER MUCH OF THE EAST
BY MONDAY. EXPECT MANY AREAS TO SEE HIGHS AT LEAST 20F BELOW
NORMAL, WITH THE COLDEST ANOMALIES LIKELY TO BE OVER THE HIGH
PLAINS AND VICINITY WHERE HIGHS COULD BE 30-40F BELOW NORMAL.
COLDEST TEMPERATURES ON AN ABSOLUTE BASIS SHOULD BE OVER NORTHERN
PLAINS AND UPPER MIDWEST WHERE SUBZERO HIGHS AND LOWS IN THE -20S
ARE LIKELY. WIND CHILLS SHOULD BE EVEN COLDER AND MORE DANGEROUS.
WPC IS POSTING KEY MESSAGES REGARDING THIS COLD OUTBREAK. THE
NORTHERN-CENTRAL ROCKIES/PLAINS SHOULD MODERATE CONSIDERABLY BY
TUESDAY-WEDNESDAY (THOUGH WITH A POTENTIAL FOR HIGH WINDS) WHILE
COLD WEATHER MAY PERSIST INTO WEDNESDAY AND POSSIBLY TO SOME EXTENT
THURSDAY ACROSS THE SOUTH AND EAST. THE WEST WILL SEE A PERIOD OF
COOL BUT NOT EXTREME TEMPERATURES FROM THE WEEKEND INTO THE START
OF NEXT WEEK, WITH NEAR NORMAL AND THEN SLIGHTLY ABOVE NORMAL
READINGS SLOWLY BEGINNING TO PUSH EASTWARD FROM THE WEST COAST.
THE WAVE FORECAST TO TRACK QUICKLY OFF THE EAST COAST ON SUNDAY IS
LIKELY TO PRODUCE SOME POSSIBLY IMPACTFUL PRECIPITATION BEFORE ITS
DEPARTURE. AS DISCUSSED IN THE ABOVE SECTION, CHANCES FOR PLOWABLE
SNOW ARE TRENDING UP IN THE URBAN CORRIDOR WITH A
COMPROMISE/MIDDLE GROUND FORECAST TRACK FOR THE LOW, BUT
UNCERTAINTY REMAINS. AFTER THIS SYSTEM EXITS, THE PATTERN WILL BE
FAVORABLE FOR LAKE EFFECT SNOW THROUGH MIDWEEK. FARTHER SOUTH,
FRONTS PUSHING THROUGH FLORIDA COULD PROVIDE SOME FOCUS FOR RAIN.
FARTHER WEST, A SHORTWAVE DIGGING INTO THE WEST EARLY NEXT WEEK
MAY PRODUCE SOME SCATTERED SNOW DEPENDING ON ITS EVOLUTION. WHAT
THIS SHORTWAVE DOES AFTER MONDAY WILL DETERMINE HOW MUCH
PRECIPITATION EMERGES OVER THE SOUTHERN TIER FROM TEXAS EASTWARD ON
THE SOUTHERN PERIPHERY OF THE OVERALL UPPER TROUGH AND SURFACE
HIGH PRESSURE. THE SOUTHERN EXTENT OF THE COLD AIR AT THE SURFACE
MEANS THAT A MAJORITY OF PRECIPITATION COULD BE OF A WINTRY
VARIETY, PERHAPS ALL THE WAY TO THE GULF COAST. FREEZING RAIN/ICE
IS ALSO AN INCREASING CONCERN FOR PARTS OF THE SOUTH GIVEN THE
POSSIBILITY OF A WARM NOSE ATOP ARCTIC COLD AIR. SOUTHERN TIER SNOW
POTENTIAL CONTINUES TO SHOW UP IN THE WINTER WEATHER PROBABILITIES
FOR 0.25 INCH LIQUID IN THE FORM OF SNOW, 10-20 PERCENT OVER AN
AREA JUST NORTH OF THE WESTERN GULF COAST FOR THE EARLY MONDAY-
EARLY TUESDAY PERIOD AND 10-40 PERCENT ACROSS A MUCH BROADER SWATH
OF THE SOUTH INTO SOUTHERN MID-ATLANTIC EARLY TUESDAY INTO EARLY
WEDNESDAY. SOME PRECIPITATION POTENTIAL LINGERS THEREAFTER, BUT
THROUGH THIS WHOLE PERIOD CONFIDENCE IN DETAILS IS BELOW AVERAGE
DUE TO CONSIDERABLE MODEL DIFFERENCES AND VARIABILITY.
UNCERTAINTIES IN DETAILS ALOFT OVER THE SOUTHWEST INTO NEXT WEEK
MAKE THE SURFACE PATTERN UNCERTAIN AS WELL. HOWEVER, THERE IS SOME
POTENTIAL FOR A PERIOD OF RELATIVELY STRONGER WINDS OVER PARTS OF
CALIFORNIA AND VICINITY AROUND MONDAY-TUESDAY. CONTINUE TO MONITOR
STORM PREDICTION CENTER FIRE WEATHER FORECASTS FOR FURTHER
INFORMATION.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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