988
FXUS02 KWBC 301825
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
125 PM EST MON DEC 30 2024
VALID 12Z THU JAN 02 2025 - 12Z MON JAN 06 2025
...COLDER WEATHER IN THE CENTRAL AND EASTERN U.S. ALLOWS FOR
BROADENING WINTRY PRECIPITATION CHANCES OVER THE WEEKEND INTO EARLY
NEXT WEEK...
..OVERVIEW
QUASI-ZONAL FLOW OVER THE CONUS TO START THE PERIOD WILL
TRANSITION TOWARD INCREASED TROUGHING OVER THE EASTERN 1/2 OF THE
LOWER 48, DUE IN PART TO STRONG RIDGING OVER THE DAVIS
STRAIT/SOUTHERN GREENLAND AS WELL AS OVER THE EASTERN NORTH
PACIFIC/WESTERN CANADA. TROUGH ENTERING THE PAC NW THIS WEEKEND IS
POISED TO MOVE ACROSS THE SOUTHERN TIER WITH A POTENTIAL MESS OF
WINTRY WEATHER (SNOW/SLEET/FREEZING RAIN) ON THE NORTH SIDE OF ITS
PRECIPITATION SHIELD AND HEAVIER RAIN IN THE WARM SECTOR ACROSS
PORTIONS OF THE MID-SOUTH. TEMPERATURES ARE EXPECTED TO BE BELOW
NORMAL FROM THE NORTHERN PLAINS INTO THE NORTHEAST WITH ABOVE
NORMAL TEMPERATURES LIKELY FOR THE SOUTHWEST EARLY IN THE PERIOD
THAT MAY TREND BACK TOWARD MORE TYPICAL VALUES BY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS/ENSEMBLES REMAIN IN GOOD AGREEMENT THROUGH THE
PERIOD WITH THE OVERALL LONGWAVE PATTERN AND PATTERN TRANSITION,
BUT VARY ON SOME SYSTEM DETAILS. THE 00Z CANADIAN WAS SLOWER WITH
THE INCOMING WESTERN SHORTWAVE THAN THE CONSENSUS AND WAS NOT
PREFERRED HENCEFORTH. THE 00Z/06Z GFS DIFFERED IN THEIR HANDLING OF
THE SAME SHORTWAVE AFTER PASSING THROUGH THE ROCKIES AND NEITHER
WAS A GOOD FIT CONUS-WIDE TO THE BETTER CLUSTERING OF THE ECMWF
EPS/CONTROL (EX-HRES), GEFS MEAN (MOSTLY), AND THE EXCELLENT
CONTINUITY FROM THE PRIOR OVERNIGHT SHIFT. THIS MAINTAINED A
DEVELOPING CYCLONE OVER THE SOUTHERN PLAINS LATER THIS WEEKEND WITH
A TRACK INTO/THROUGH THE OHIO VALLEY. THE GUIDANCE DOES SHOW A
FAIR AMOUNT OF ALONG AND CROSS-TRACK SPREAD, WITH THE ECMWF-AIFS
NOTABLY QUICKER. FOR NOW, ENSEMBLE MEAN CONSENSUS NEAR THE 00Z
ECMWF CONTROL SEEMED PRUDENT.
..WEATHER/HAZARDS HIGHLIGHTS
NO EXCESSIVE RAINFALL AREAS ARE DEPICTED DURING DAYS 4-5, BUT BY
DAY 6-7 THERE MAY BE A NEED FOR ONE OVER THE MID-SOUTH. PLEASE SEE
OUR LATEST DAY 3-7 HAZARDS CHART FOR A GRAPHICAL DEPICTION.
LAKE EFFECT SNOW IS LIKELY LATER THIS WEEK INTO THE FIRST PART OF
THE WEEKEND WITH COLD AND BRISK FLOW ACROSS THE GREAT LAKES, LIKELY
PEAKING THURSDAY-FRIDAY. MEANWHILE SHORTWAVE ENERGY AND A WEAK
FRONTAL WAVE MAY PRODUCE A BAND OF LIGHT SNOW LATE THIS WEEK
SOMEWHERE WITHIN AN AREA ENCOMPASSING THE MIDWEST/OHIO VALLEY TO
CENTRAL APPALACHIANS. FARTHER SOUTH, PARTS OF THE WESTERN/CENTRAL
GULF COAST COULD SEE ONE OR MORE PERIODS OF LIGHT RAIN NEAR A
LINGERING FRONTAL BOUNDARY.
AHEAD OF THE EASTERN PACIFIC UPPER TROUGH, MOISTURE IN THE FORM OF
A MODERATE ATMOSPHERIC RIVER WILL BE DIRECTED INTO THE PACIFIC
NORTHWEST TO NORTHERN CALIFORNIA, LIKELY PEAKING THURSDAY NIGHT
INTO FRIDAY MORNING. THERE ARE REMAINING TIMING AND PLACEMENT
DIFFERENCES FOR THE POSITIONING OF PEAK MOISTURE TRANSPORT AND
HEAVIEST RAINFALL, BUT INCREASED AMOUNTS A BIT INTO THE FAVORED
AREAS OF SOUTHWESTERN OR AND NORTHWESTERN NORCAL. STILL CONTINUED
TO HOLD OFF ON ANY EXCESSIVE RAINFALL AREAS IN THE DAYS
4-5/THURSDAY-FRIDAY EROS, BUT SOME AREAS WITHIN THIS REGION MAY BE
MORE SENSITIVE THAN NORMAL TO HEAVY RAINFALL WITH THE WET
ANTECEDENT CONDITIONS. MODEST PRECIPITATION INCLUDING HIGHER
ELEVATION SNOW IS LIKELY INTO THE INTERMOUNTAIN WEST AND
NORTHERN/CENTRAL ROCKIES. ADDITIONAL ROUNDS OF LIGHT TO MODERATE
PRECIPITATION ARE POSSIBLE IN THE NORTHWEST INTO THE WEEKEND.
AS THE UPPER TROUGH MOVES INTO THE CENTRAL U.S., SURFACE LOW
PRESSURE IS FORECAST TO DEVELOP OVER THE SOUTHERN PLAINS OVER THE
WEEKEND. WHILE THE DETAILS REMAIN NEBULOUS, PRECIPITATION CHANCES
LOOK TO INCREASE GENERALLY ACROSS THE PLAINS AND MISSISSIPPI VALLEY
SATURDAY AND STRETCHING FARTHER INTO THE EAST-CENTRAL U.S. SUNDAY-
MONDAY AS THE LOW MOVES EAST. AS CURRENTLY FORECAST, THIS
PRECIPITATION WOULD BE SNOW IN THE NORTHERN HALF OR SO OF THE U.S.
GIVEN THE COLD TEMPERATURES, WITH RAIN IN THE SOUTH. NBM WEATHER
TYPE PROBABILITIES SHOW AN OVERLAP OF WINTRY P-TYPES
(SNOW/SLEET/FREEZING RAIN) IN BETWEEN THE RAIN AND SNOW AREAS,
WITH SOME LOCATIONS TRANSITIONING BETWEEN EACH TYPE. THE CENTRAL
PLAINS INTO MIDDLE MISSISSIPPI VALLEY APPEARS MOST LIKELY FOR
TRANSITIONING PRECIPITATION TYPES AT THIS POINT. HEAVY RAIN AND
THUNDERSTORMS ARE POSSIBLE IN THE TENNESSEE VALLEY ON SUNDAY. KEEP
AN EYE ON FUTURE FORECASTS AS DETAILS ARE LIKELY TO CHANGE. THE
WINTER WEATHER OUTLOOK DEPICTS A LARGE AREA OF 10-40% PROBABILITIES
OF "PLOWABLE" SNOW/SLEET FROM THE PLAINS EASTWARD ACROSS THE
MIDWEST EARLY NEXT WEEK.
GENERALLY, THE MEAN UPPER RIDGE OVER THE WEST WILL PROMOTE ABOVE
NORMAL TEMPERATURES FROM THE GREAT BASIN AND SOUTHWEST TO THE
SOUTHERN/CENTRAL PLAINS LATE WEEK INTO THE WEEKEND. HIGHS WILL
REACH WELL INTO THE 70S IN THE DESERT SOUTHWEST, AND TEMPERATURES
COULD WARM INTO THE LOW 80S IN SOUTHERN TEXAS BY NEXT WEEKEND.
MEANWHILE THE MEAN TROUGH IN THE CENTRAL/EASTERN U.S. WILL LEAD TO
COOLER THAN NORMAL TEMPERATURES FROM THE NORTH-CENTRAL U.S. INTO
THE MIDWEST TO EASTERN SEABOARD. THE NORTHERN PLAINS ARE FORECAST
TO SEE THE MOST ANOMALOUS TEMPERATURES, AROUND 10-20F BELOW NORMAL
FOR HIGHS AND AROUND 5-15F BELOW NORMAL FOR LOWS. THIS TRANSLATES
TO HIGHS NOT REACHING OR BARELY REACHING 0F AND LOWS BETWEEN -10F
AND -20F IN SOME AREAS. DAILY RECORDS THERE FOR THIS TIME OF YEAR
ARE GENERALLY IN THE -30S AND COLDER (LOW MINS) AND AROUND -20F FOR
LOW MAXES. THE PROBABILITY OF REACHING RECORDS AT MOST LONG-TERM
STATIONS OVER THE NORTHERN PLAINS IS VERY LOW (THROUGH NEXT
MONDAY).
FRACASSO/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 (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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