305
FXUS02 KWBC 151902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
202 PM EST WED JAN 15 2025
VALID 12Z SAT JAN 18 2025 - 12Z WED JAN 22 2025
...STRONG ARCTIC SURGE WILL PUSH INTO THE CENTRAL U.S. THIS
WEEKEND AND EXPAND EAST EARLY NEXT WEEK...
..OVERVIEW
A VERY AMPLIFIED PATTERN IS EXPECTED THROUGH THE MEDIUM RANGE
PERIOD, WITH AN EASTERN PACIFIC RIDGE AND A DEEP TROUGH EXTENDING
THROUGH THE LOWER 48. THIS PATTERN WILL ALLOW ARCTIC AIR TO SURGE
SOUTH INTO THE CENTRAL U.S. THIS WEEKEND, AND THE ANOMALOUSLY COLD
AIR MASS WILL EXPAND EAST AND SOUTHEAST EARLY NEXT WEEK. WITHIN THE
HIGHLY CONFIDENT OVERALL TROUGH, GUIDANCE IS COMING CLOSER TO
CONVERGING FOR DETAILS OF A COUPLE LOWER-PREDICTABILITY LEADING
SHORTWAVES--ONE AIDING IN POTENTIALLY HEAVY RAIN OVER PARTS OF THE
SOUTHEAST ON SATURDAY AND ANOTHER THAT MAY PRODUCE SOME SNOW OVER
THE ROCKIES ON SATURDAY AND THEN A PROGRESSIVE WAVE WITH MOSTLY
LIGHT PRECIPITATION OF VARIOUS TYPES NEAR THE EAST COAST ON SUNDAY.
GUIDANCE IS ALSO STARTING TO PICK UP ON A LATE PERIOD WAVE THAT
COULD CREATE WINTER WEATHER CONCERNS IN THE SOUTHERN U.S. MID-NEXT
WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE HAS COME INTO GOOD AGREEMENT ON THE OVERALL PATTERN
AND SHORTWAVE DETAILS THROUGH THE WEEKEND. ON SATURDAY, A SHEARED
SHORTWAVE WILL PUSH EAST-NORTHEAST ACROSS THE SOUTHERN TIER WHILE A
SECOND SHORTWAVE MOVES SOUTH ACROSS THE ROCKIES. THIS SECONDARY
SHORTWAVE WILL MOVE QUICKLY EAST ON SUNDAY, SWINGING ACROSS THE
SOUTH TO THE MID-ATLANTIC. THERE ARE STILL MINOR DIFFERENCES IN THE
TIMING OF THE SECOND SHORTWAVE, BUT OVERALL MODEL AGREEMENT ON
THESE FEATURES IS GOOD.
MODEL SPREAD INCREASES SIGNIFICANTLY NEXT WEEK AS THEY TRY TO
RESOLVE DETAILS OF SHORTWAVES IN THE WEST. ANOTHER SHORTWAVE WILL
LIKELY DROP SOUTH INTO THE WESTERN U.S. BY MONDAY, BUT THE
SUBSEQUENT EVOLUTION OF THIS FEATURE IS UNCERTAIN. THE EVOLUTIONS
WILL BE INFLUENCED BY TIMING AND STRENGTH OF ANOTHER SHORTWAVE THAT
WILL LIKELY MOVE INTO THE NORTHWEST MID-NEXT WEEK, AND THERE IS A
LOT OF SPREAD FOR HOW THIS FEATURE MAY PASS THROUGH THE MEAN RIDGE
TO THE WEST. HOWEVER THE PATTERN EVOLVES, THE CHARACTER OF THIS
ENERGY WILL PLAY AN IMPORTANT ROLE IN THE SURFACE PATTERN ACROSS
LOWER LATITUDES ALONG WITH THE COVERAGE AND AMOUNTS OF WHAT COULD
BE MEANINGFUL WINTRY PRECIPITATION OVER PARTS OF THE SOUTH.
FOR WPC'S AFTERNOON FORECAST, A BLEND OF THE GFS/ECMWF/CMC/UKMET
WERE USED THROUGH THE WEEKEND WITH HEAVIER WEIGHT PLACED IN THE GFS
AND ECMWF WHICH ARE THE BEST CLUSTERED AND ARE DEMONSTRATING THE
MOST SKILL WITH THIS WEATHER PATTERN. FOR MONDAY-WEDNESDAY,
INCREASING AMOUNTS OF THE GEFS AND ECENS ENSEMBLE MEANS WERE ADDED
TO THE BLEND WHILE THE UKMET AND CMC AMOUNTS WERE GRADUALLY
DECREASED.
..WEATHER/HAZARDS HIGHLIGHTS
THE WELL-ADVERTISED SURGE OF ARCTIC AIR WILL BRING HAZARDOUS COLD
TO MUCH OF THE LOWER 48 THIS WEEKEND INTO EARLY NEXT WEEK. COLD
WILL SPREAD FROM THE ROCKIES AND PLAINS ON SATURDAY TO THE SOUTH
AND MIDWEST ON SUNDAY AND TO THE EAST AND SOUTHEAST ON MONDAY.
TEMPERATURE ANOMALIES ARE FORECAST TO REACH 15-35 DEGREES BELOW
NORMAL, WITH THE MOST EXTREME ANOMALIES IN THE PLAINS. COLDEST
TEMPERATURES ON AN ABSOLUTE BASIS SHOULD BE OVER NORTHERN PLAINS
AND UPPER MIDWEST WHERE SUBZERO HIGHS AND LOWS IN THE -20S ARE
EXPECTED. WIND CHILLS SHOULD BE EVEN COLDER AND MORE DANGEROUS. WPC
HAS BEGUN POSTING KEY MESSAGES REGARDING THIS COLD OUTBREAK. THE
NORTHERN-CENTRAL ROCKIES/PLAINS SHOULD MODERATE CONSIDERABLY BY
TUESDAY-WEDNESDAY WHILE COLD WEATHER WILL PERSIST INTO WEDNESDAY
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 READINGS SLOWLY BEGINNING TO PUSH EASTWARD
FROM THE WEST COAST.
SHORTWAVE ENERGY MOVING OVER THE SOUTHERN U.S. WILL PUSH A LOW
PRESSURE SYSTEM ACROSS THE SOUTHEAST THIS WEEKEND. THE LEADING
FRONT MAY BECOME EAST-WEST ORIENTED, WHICH WOULD SUPPORT TRAINING
SHOWERS AND THUNDERSTORMS THAT COULD PRODUCE LOCALLY HEAVY
RAINFALL. THUS, THERE IS A MARGINAL RISK OF HEAVY RAINFALL FOR
PORTIONS OF THE SOUTHEAST ON SATURDAY (DAY 4 ERO). THIS SYSTEM
SHOULD QUICKLY MOVE NORTHEAST AHEAD OF AN APPROACHING COLD FRONT
LATER THIS WEEKEND, WHICH WILL LEAD TO A DECREASED RISK OF HEAVY
RAINFALL IN THE SOUTHEAST FOR SUNDAY (DAY 5 ERO). PRECIPITATION
WILL ALSO EXTEND WELL TO THE NORTH AHEAD OF THE APPROACHING COLD
FRONT THIS WEEKEND, WITH PRECIPITATION CHANCES FOR MOST AREAS EAST
OF THE MISSISSIPPI RIVER AND CHANCES FOR WINTRY PRECIPITATION FOR
MUCH OF THE NORTHEAST AND CENTRAL APPALACHIANS.
FARTHER WEST, EXPECT SNOW TO MOVE SOUTHWARD ACROSS THE
ROCKIES/HIGH PLAINS INTO SATURDAY IN ASSOCIATION WITH THE ARCTIC
SURGE AND DIGGING SHORTWAVE ENERGY. UPSLOPE FLOW SHOULD HELP TO
ENHANCE ACCUMULATIONS OVER SOME AREAS. ANOTHER SHORTWAVE MAY
PRODUCE SOME SNOW OVER PARTS OF THE ROCKIES EARLY NEXT WEEK. WHAT
THIS SHORTWAVE DOES 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.
HOWEVER, THE SOUTHERN EXTENT OF THE COLD AIR AT THE SURFACE MEANS
THAT IF THERE IS PRECIPITATION IT WOULD MAINLY BE IN THE FORM OF
WINTRY PRECIP, PERHAPS ALL THE WAY TO THE GULF COAST, AND FREEZING
RAIN/ICE IS AN INCREASING CONCERN FOR PARTS OF THE SOUTH GIVEN THE
POSSIBILITY OF A WARM NOSE ATOP ARCTIC COLD AIR. SOUTHERN TIER SNOW
POTENTIAL SHOWS UP IN THE WINTER WEATHER PROBABILITIES FOR 0.25
INCH LIQUID IN THE FORM OF SNOW, NOW 10-15 PERCENT OVER AN AREA
JUST NORTH OF THE WESTERN HALF OF THE GULF COAST FOR THE EARLY
MONDAY-EARLY TUESDAY PERIOD AND ABOUT 10-35 PERCENT ACROSS A MUCH
BROADER SWATH OF THE SOUTH INTO SOUTHERN MID-ATLANTIC EARLY TUESDAY
INTO EARLY WEDNESDAY.
UNCERTAINTIES IN THE SETUP ALOFT OVER THE SOUTHWEST INTO NEXT WEEK
MAKE THE PATTERN AT THE SURFACE SOMEWHAT UNCERTAIN AS WELL.
HOWEVER, THERE IS A GENERAL TREND FOR WEAKER WINDS OVER SOUTHERN
CALIFORNIA INTO THE WEEKEND, BUT OFFSHORE FLOW MAY STRENGTHEN AGAIN
BY MONDAY AS 850MB WINDS INCREASE (DRAMATICALLY IN SOME MODELS).
KEEP AN EYE ON SPC FIRE WEATHER FORECASTS FOR FURTHER INFORMATION.
DOLAN/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page