502
FXUS02 KWBC 110721
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 AM EST THU JAN 11 2024
VALID 12Z SUN JAN 14 2024 - 12Z THU JAN 18 2024
...AN ARCTIC AIRMASS BLANKETS MUCH OF THE NORTHERN AND CENTRAL
U.S. THROUGH EARLY NEXT WEEK...
..OVERVIEW
AN UPPER-LEVEL LOW WILL GET PRETTY WOUND UP NEAR JAMES BAY, CANADA
WHILE WAVES OF SHORTWAVE ENERGY ROTATE THROUGH ITS SOUTHERN
PERIPHERY (THE MIDWEST AND NORTHEAST U.S.). MEANWHILE, AN UPPER
RIDGE WILL DEVELOP AND AMPLIFY OVER THE EASTERN PACIFIC AND WEST.
THIS UPPER PATTERN WILL RESULT IN ARCTIC HIGH PRESSURE AT THE
SURFACE FLOWING THROUGH THE NORTHERN ROCKIES/PLAINS AND INTO MUCH
OF THE CENTRAL U.S..
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE ENSEMBLE MEANS CAPTURE THE SYNOPTIC EVOLUTION OF THE UPPER
LEVEL PATTERN REASONABLY WELL IN THE MEDIUM RANGE. THE
DETERMINISTIC GUIDANCE STRUGGLES TO CONSISTENTLY CLUSTER AROUND
ANY ONE SOLUTION. A BLEND OF THE 12Z AND 18Z GFS AS WELL AS THE
00Z AND 12Z EC WERE USED ON DAY 3 SINCE THE 12Z UKMET/CMC
STRUGGLED TO PRESENT ANYTHING SIMILAR TO WHAT THE ENSEMBLE MEANS
AND EC/GFS HAVE. ON DAY 4 THE 18Z GEFS AND 12Z ECE WERE INTRODUCED
TO THE BLEND TO MITIGATE SOME OF THE OVER AMPLIFICATION OF A
POSITIVELY TILTED TROUGH IN THE WEST BY THE 12Z EC. THE CANADIAN
IS INTRODUCED ON DAY 5 SINCE IT SORT OF CATCHES UP TO THE GENERAL
EC/GFS/ENSEMBLE MEAN SOLUTION WITH RESPECT TO THE SHORTWAVE
PROPAGATING THROUGH THE MISSISSIPPI VALLEY. THE PREVIOUS EC/GFS
RUNS WERE REMOVED. THE CANADIAN ENSEMBLE MEAN IS INTRODUCED ON DAY
6 AND REPLACES THE DETERMINISTIC 12Z CMC. ONLY THE THREE ENSEMBLE
MEANS REMAIN IN THE BLEND BY DAY 7.
THE GFS CONSISTENTLY HAS A STRONGER MEAN LOW OVER JAMES BAY
THROUGHOUT THE MEDIUM RANGE PERIOD. IT IS ALSO MORE PROGRESSIVE
WITH ITS EMBEDDED SHORTWAVE ENERGY COMPARED TO THE EC ON DAY 5,
BUT THE CANADIAN IS THE DEEPEST AND MOST PROGRESSIVE OF THE
OPERATIONAL MODELS. THE UKMET HAS IT'S SHORTWAVE STILL MOVING
THROUGH THE INTERMOUNTAIN WEST ON DAY 5. THE OPERATIONAL EURO AND
GFS HAVE BOTH SLOWED DOWN CONSIDERABLY OVER THEIR LAST FEW RUNS
AND NOW HAS THE SHORTWAVE MOVING THROUGH THE EASTERN THIRD OF THE
COUNTRY ON DAY 6, WHILE THE 12Z CANADIAN HAS THAT SAME ENERGY OUT
INTO THE WESTERN ATLANTIC. THE ENSEMBLE MEANS, ESPECIALLY THE GEFS
AND ECE, HAVE RELATIVELY LOW SPREAD ACROSS THE LOWER 48 THROUGHOUT
THE MEDIUM RANGE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAIN SENSIBLE WEATHER HIGHLIGHT DURING THE MEDIUM RANGE WILL
BE THE ARCTIC BLAST LIKELY TO IMPACT THE NORTHERN ROCKIES,
NORTHERN GREAT BASIN, GREAT PLAINS, MISSISSIPPI VALLEY AND
MIDWEST. THE SYNOPTIC SETUP, INCLUDING A STRENGTHENING UPPER RIDGE
IN THE WEST AND AN MASSIVE UPPER LOW IN THE EAST, WILL SUPPORT THE
DESCENT OF SURFACE HIGH PRESSURE THROUGH THE CENTRAL U.S. THIS
WEEKEND THROUGH EARLY NEXT WEEK. THE COLDEST PARTS OF THIS AIRMASS
WILL BE OVER PORTIONS OF NORTHERN MONTANA WHERE LOW TEMPERATURES
COULD BOTTOM OUT AROUND 40 DEGREES BELOW ZERO SUNDAY MORNING.
PARTS OF THE NORTHERN ROCKIES DOWN THROUGH THE CENTRAL PLAINS AND
MIDDLE MISSISSIPPI VALLEY MAY DROP TO BELOW ZERO DEGREES SATURDAY,
SUNDAY AND MONDAY NIGHTS. THIS WILL MAKE FOR VERY DANGEROUS
OUTDOOR CONDITIONS. MINIMUM TEMPERATURE ANOMALIES ARE FORECAST TO
BE BETWEEN 20-40 DEGREES BELOW AVERAGE FOR THESE AREAS. FREEZING
TEMPERATURES WILL ALSO MAKE THEIR WAY TO THE GULF COAST MONDAY AND
TUESDAY NIGHT. TEMPERATURES WILL BEGIN TO REBOUND ON WEDNESDAY AS
ANOTHER DISTURBANCE ENTERS THE NORTHERN PLAINS/UPPER MIDWEST AND
SHIFTS SURFACE WINDS OUT OF THE SOUTH.
THE SHORTWAVE TROUGH RESPONSIBLE FOR ADVECTING TROPICAL MOISTURE
INTO THE NORTHWEST LEADING TO THE PRODUCTION OF HEAVY SNOW WILL
THEN SPREAD THAT SAME MOISTURE REGIME INTO PARTS OF THE
CENTRAL/SOUTHERN ROCKIES AND INTERMOUNTAIN WEST PRODUCING SNOW FOR
THOSE AREAS ON SUNDAY. SNOW PROBABILITIES REMAIN HIGH FOR THE
WASATCH, UINTA, COLORADO ROCKIES, SAN JUAN AND SANGRE DE CRISTO
MOUNTAINS. A SWATH OF SNOW SHOWERS MAY ALSO SPREAD INTO THE
CENTRAL/SOUTHERN PLAINS AND MIDDLE MISSISSIPPI VALLEY ON SUNDAY.
SNOW WILL CONTINUE OVER THE COLORADO ROCKIES INTO MONDAY WHILE
SOME MORE SNOW SHOWERS DEVELOP OVER THE TENNESSEE/OHIO VALLEYS. A
COASTAL LOW IS EXPECTED TO DEVELOP JUST OFF OF THE SOUTHEAST COAST
LATER ON MONDAY AND GENERATE SHOWERS AND THUNDERSTORMS ACROSS THE
CENTRAL GULF COAST AND MUCH OF FLORIDA THROUGH MIDWEEK. THE EXACT
TRACK OF THIS SYSTEM HAS YET TO BE IRONED OUT BUT THERE SEEMS TO
BE SOME AGREEMENT BETWEEN THE EURO AND GFS FOR SOME SNOW SHOWERS
EXTENDING FROM THE MID-ATLANTIC UP INTO THE NORTHEAST TUESDAY INTO
WEDNESDAY AFTERNOON. THE EUROPEAN ENSEMBLE MEAN HAS BEEN A BIT
MORE AGGRESSIVE WITH SNOW PROBABILITIES DOWN THE I-95 CORRIDOR
COMPARED TO THE GEFS AND CMCE, BUT THEY'VE ALL TRENDED HIGHER WITH
THEIR SNOW/SLEET PROBABILITIES.
A NEW SYSTEM ENTERS THE NORTHWEST NEXT WEDNESDAY, BRINGING WITH IT
MOUNTAIN SNOW AND COASTAL RAIN. WESTERLY WINDS WILL ADVECT THE
FRIGID ARCTIC AIRMASS OVER THE GREAT LAKES LEADING TO PERSISTENT
LAKE EFFECT SNOW THIS WEEKEND THROUGH THE MIDDLE OF NEXT WEEK.
KEBEDE
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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