480
FXUS02 KWBC 290703
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EST SUN DEC 29 2024
VALID 12Z WED JAN 01 2025 - 12Z SUN JAN 05 2025
..OVERVIEW
A BROAD UPPER TROUGH IS FORECAST TO SET UP ATOP THE CENTRAL AND
EASTERN U.S. FOR THE LATTER HALF OF THIS WEEK, COOLING TEMPERATURES
AND ALLOWING FOR LAKE EFFECT SNOW TO FORM BEHIND AN EXITING LOW
PRESSURE SYSTEM ACCOMPANIED BY PRECIPITATION IN THE NORTHEAST ON
WEDNESDAY. UPSTREAM, AN UPPER RIDGE WILL BUILD OVER THE WEST
WEDNESDAY-FRIDAY, THOUGH MOIST INFLOW INTO THE NORTHWEST COULD
MAINTAIN PRECIPITATION CHANCES THERE. EASTERN PACIFIC
ENERGY/TROUGHING LOOKS TO MOVE INLAND FRIDAY AND QUICKLY EAST
ACROSS THE WEST, WHICH BY NEXT WEEKEND COULD SUPPORT A DEVELOPING
LOW PRESSURE SYSTEM OVER THE PLAINS WITH POSSIBLE NORTH-CENTRAL
U.S. SNOW AND SOUTH-CENTRAL U.S. RAIN.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS AGREEABLE THAT UPPER TROUGHING WILL BE IN
PLACE ACROSS THE CENTRAL AND EASTERN U.S. FOR THE LATTER HALF OF
NEXT WEEK. A SURFACE LOW IN/NEAR THE NORTHEAST ON WEDNESDAY
CONTINUES TO SHOW MINOR SPREAD. THE 12Z ECMWF SWITCHED TO A
SOLUTION WHERE THE MAIN LOW WAS FARTHER OUT TO SEA COMPARED TO
CONSENSUS OF GFS RUNS AND THE ENSEMBLE MEANS ATOP CONNECTICUT OR SO
AT 12Z WEDNESDAY, AND THE NEWER 00Z RUN HAS JUMPED EVEN FARTHER
INLAND THAN THAT. REGARDLESS THE LOW SHOULD TRACK NORTH INTO
SOUTHEASTERN CANADA THURSDAY-FRIDAY WITH GOOD CONFIDENCE FOR MEAN
CYCLONIC FLOW IN ITS WAKE. BEHIND THIS SYSTEM, OVER THE PAST DAY OR
SO GUIDANCE HAS BEEN GRADUALLY IMPROVING ITS SIGNAL FOR A WEAK
WAVE PROGRESSING FROM THE PLAINS THROUGH OR NEAR THE TENNESSEE
VALLEY AND INTO THE WESTERN ATLANTIC THURSDAY INTO SATURDAY. MOST
DYNAMICAL SUPPORT FOR THIS FEATURE COMES FROM SHEARING PACIFIC
ENERGY WHICH LOOKS TO HAVE LOW PREDICTABILITY BY 5-7 DAYS OUT IN
TIME, SO CHANGES IN SPECIFICS ARE CERTAINLY POSSIBLE IN FUTURE
RUNS.
IN THE WEST, THE UPPER RIDGE AXIS SEEMS WELL REPRESENTED IN THE
GUIDANCE WEDNESDAY-FRIDAY BEFORE APPROACHING EASTERN PACIFIC
TROUGHING. BUT THE SURFACE DETAILS AND SMALL IMPULSES REMAIN QUITE
UNCERTAIN, AFFECTING FRONTAL POSITIONS AND THE AXIS OF THE
ATMOSPHERIC RIVER AND QPF. THEN THE EASTERN PACIFIC TROUGH
CONTINUES TO SHOW SPREAD IN ITS TIMING AND DEPTH, AFFECTING THE
WEST DOWNSTREAM. THE 12Z CMC WAS SLOWER THAN CONSENSUS WITH THE
TROUGH EVEN BY FRIDAY AND SHALLOW WITH THE TROUGHING AND WAS NOT
FAVORED. ECMWF RUNS ON THE OTHER HAND CONTINUE TO SHOW THE DEEPEST
AMPLITUDE WITH THE TROUGH. GFS RUNS FROM 12/18Z WERE SHALLOWER THAN
THE EC WITH THE TROUGH AND THE 00Z GFS HAS BECOME EVEN SHALLOWER
(AND FASTER AS A RESULT). THESE DIFFERENCES NATURALLY AFFECT ANY
SURFACE LOW AND FRONTAL DEVELOPMENT AND QPF IN THE CENTRAL U.S.
NEXT WEEKEND. A BLENDED APPROACH FAVORING THE ENSEMBLE MEANS SEEMED
BEST AT THIS POINT AWAITING FURTHER CLUSTERING.
THE WPC FORECAST WAS BASED ON A BLEND OF THE 12Z ECMWF, 12/18Z
GFS, AND 12Z CMC EARLY IN THE PERIOD. ELIMINATED THE CMC FROM THE
BLEND AND DECREASED THE EC AND GFS PROPORTIONS GRADUALLY, IN FAVOR
OF THE ENSEMBLE MEANS. THE MEANS REACHED OVER HALF THE BLEND BY THE
END OF THE PERIOD. FUTURE CHANGES TO THE FORECAST ARE LIKELY
ESPECIALLY BY DAYS 6-7.
..WEATHER/HAZARDS HIGHLIGHTS
A SURFACE LOW PRESSURE SYSTEM IN THE NORTHEAST MIDWEEK WILL ALLOW
FOR PRECIPITATION THERE. EXPECT COASTAL/LOWER ELEVATION RAIN, WHILE
HIGHER ELEVATION AREAS OF THE INTERIOR NORTHEAST SUCH AS THE
ADIRONDACKS AND THE GREEN AND WHITE MOUNTAINS WILL SEE ACCUMULATING
SNOW. IN THE WAKE OF THIS SYSTEM, EXPECT MULTIPLE DAYS OF COLD AND
BRISK FLOW ACROSS THE GREAT LAKES AND NORTHEAST, WITH LAKE EFFECT
SNOW PERSISTING THROUGH THE LATTER HALF OF THE WEEK, PERHAPS
EXTENDING INTO SATURDAY OVER SOME LOCATIONS. 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/CENTRAL APPALACHIANS.
MOIST INFLOW INTO THE WEST SHOULD GET RENEWED BY WEDNESDAY AND
LEAD TO ADDITIONAL ROUNDS OF PRECIPITATION THROUGH LATE WEEK IN THE
PACIFIC NORTHWEST AND AT TIMES FARTHER EAST INTO THE NORTHERN
ROCKIES. PRECIPITATION AMOUNTS FROM DAY TO DAY AND IN TOTAL VARY
CONSIDERABLY IN MODELS AS THERE IS A FAIR AMOUNT OF SPREAD FOR
SYSTEM/FRONTAL SPECIFICS. MODEL GUIDANCE IS NOW SUGGESTING THAT
SOME HEAVY PRECIPITATION IS POSSIBLE ACROSS OREGON IN PARTICULAR ON
WEDNESDAY, BUT PLACEMENT HAS BEEN WAFFLING AND THE UNCERTAINTY
CONTINUES/INCREASES INTO THURSDAY. THE COMBINATION OF FORECAST
TOTALS AND GUIDANCE SPREAD DO NOT SEEM TO WARRANT RISK AREAS IN THE
DAYS 4-5 EROS YET. HOWEVER THIS REGION WILL BE SENSITIVE DUE TO
RECENT/ONGOING RAINFALL AND WILL MONITOR GUIDANCE IN FUTURE CYCLES
FOR ANY TRENDS TOWARD CLUSTERING IN THE WETTER END OF THE ENVELOPE.
EVEN WITH A BETTER DEFINED FEATURE ARRIVING AROUND FRIDAY AND
PUSHING INTO THE WEST ON SATURDAY, THERE ARE DIFFERENCES WITH THE
SOUTHWARD EXTENT OF MOISTURE FOCUS DUE TO SPREAD FOR SURFACE LOW
TRACK OVER THE PACIFIC ON FRIDAY AND THEN THE AMPLITUDE OF THE
SUPPORTING UPPER TROUGH BY SATURDAY.
AS UPPER TROUGHING PUSHES EAST, LOW PRESSURE WILL DEVELOP OVER THE
PLAINS IN RESPONSE. WHILE THE DETAILS REMAIN NEBULOUS,
PRECIPITATION CHANCES LOOK TO INCREASE GENERALLY ACROSS THE PLAINS
AND MISSISSIPPI VALLEY ON SATURDAY. THIS PRECIPITATION WOULD BE
SNOW IN THE NORTH-CENTRAL U.S. GIVEN THE COLD TEMPERATURES, WITH
RAIN IN THE SOUTH. THERE MAY BE A TRANSITION ZONE OF ICE IN BETWEEN
THE RAIN AND SNOW, AND SOME LOCATIONS COULD TRANSITION FROM SNOW
TO RAIN OR VICE VERSA; THE MIDDLE MISSISSIPPI VALLEY APPEARS MOST
LIKELY FOR TRANSITIONING PRECIPITATION TYPES AT THIS POINT. KEEP AN
EYE ON FUTURE FORECASTS AS DETAILS ARE LIKELY TO CHANGE.
GENERALLY, THE MEAN UPPER RIDGE OVER THE WEST WILL PROMOTE ABOVE
NORMAL TEMPERATURES FROM THE GREAT BASIN AND SOUTHWEST TO THE
SOUTHERN/CENTRAL PLAINS THROUGH THE PERIOD, AND 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 (AFTER ONE MORE WARMER THAN AVERAGE DAY IN THE
NORTHEAST ON WEDNESDAY). THE NORTHERN PLAINS IS 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
BARELY REACHING 0F AND LOWS BETWEEN -10F AND -15F IN SOME AREAS.
MEANWHILE 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.
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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