660
FXUS02 KWBC 141900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST THU DEC 14 2023
VALID 12Z SUN DEC 17 2023 - 12Z THU DEC 21 2023
..A WET PATTERN IS LIKELY FOR THE EAST COAST NEXT WEEK
..OVERVIEW
A STRONG SURFACE LOW IS FORECAST TO TRACK ALONG THE EAST COAST
EARLY NEXT WEEK WITH WIDESPREAD HEAVY RAINFALL AND HIGH WINDS NEAR
THE COASTLINE. SOME UNCERTAINTY REMAINS IN THE AMOUNTS AND
PLACEMENT OF THE HEAVY RAIN DUE TO MODEL DIFFERENCES IN THE UPPER
LEVELS AND THE SURFACE LOW TRACK. AFTER THIS SYSTEM PUSHES
OFFSHORE, A DRIER PATTERN WILL DEVELOP OVER THE EASTERN TWO-THIRDS
OF THE NATION WHILE AN UPPER LOW MOVES SOUTH ALONG THE WEST COAST,
PRODUCING PERIODS OF PRECIPITATION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW A WESTWARD TREND IN THE TRACK OF
THE EAST COAST SURFACE LOW, AND THERE ARE STILL SIGNIFICANT
DIFFERENCES BETWEEN THE MODELS WITH HOW THEY HANDLE THE
INTERACTIONS BETWEEN UPPER LEVEL LOWS. THE MODELS ALL AGREE THAT
THERE WILL BE A LEADING SOUTHERN STREAM LOW SWINGING UP THE EAST
COAST AND A SECOND NORTHERN STREAM LOW DIVING SOUTH FROM THE UPPER
MIDWEST TOWARDS THE MID-ATLANTIC THAT WILL INTERACT ALONG THE EAST
COAST. THE 00Z GUIDANCE SUITE (WITH THE EXCEPTION OF THE ECMWF)
WAS SHOWING MORE OF A CONSENSUS TOWARDS A FASTER PROGRESSION OF
THE LOWS, BUT THE 12Z GUIDANCE SUITE (WITH THE EXCEPTION OF THE
GFS) IS STARTING TO TREND TOWARDS A SLOWER SOLUTION WHERE THE
SECOND LOW LINGERS LONGER NEAR THE NORTHEAST UNITED STATES. THERE
IS LOWER THAN AVERAGE CONFIDENCE IN THE SENSIBLE WEATHER FORECAST
DETAILS LIKE QPF DUE TO THE UNCERTAINTIES IN THE UPPER LEVELS.
AGREEMENT AMONG MODELS IS MUCH HIGHER IN THE WEST WITH RIDGING
OVER THE INTERIOR WEST EARLY NEXT WEEK AND AN UPPER LEVEL LOW
MOVING SOUTH ALONG THE WEST COAST MID-NEXT WEEK. THERE ARE
EXPECTED DIFFERENCES IN THE POSITION AND TIMING OF THE SOUTHWARD
MOVING LOW, AND A GENERAL MIDDLE OF THE ROAD SOLUTION WAS USED FOR
THIS FORECAST.
THE WPC FORECAST WAS BASED ON THE 00/06Z GUIDANCE THAT WAS
AVAILABLE AT FORECAST PRODUCTION TIME. MORE SPECIFICALLY, A BLEND
OF THE 00Z ECMWF/UKMET/CMC AND 06Z GFS DETERMINISTIC GUIDANCE
ALONG WITH A BIT OF THE GEFS AND EC ENSEMBLE MEANS WAS USED EARLY
IN THE PERIOD. LATER IN THE PERIOD, THE WEIGHT ON ENSEMBLE MEANS
WAS INCREASED TO UP TO 50% BY DAYS 6 AND 7.
..WEATHER/HAZARDS HIGHLIGHTS
THE SURFACE LOW AND DEEP TROUGHING ALOFT WILL SUPPORT HEAVY
RAINFALL THAT COULD BE WIDESPREAD ON SUNDAY AND MONDAY. THERE ARE
SIGNIFICANT DIFFERENCES IN THE PLACEMENT AND AMOUNTS OF RAINFALL.
THIS FORECAST CONTINUES THE TREND TOWARD MORE RAINFALL FARTHER
WEST IN THE EASTERN U.S. ON SUNDAY. THERE IS A SLIGHT RISK OF
EXCESSIVE RAINFALL FOR MOST OF THE CAROLINAS AND VIRGINIA,
SOUTHERN MARYLAND, AND WASHINGTON DC WHERE MANY MODELS HAVE
MULTIPLE INCHES OF RAIN. INSTABILITY WILL LIKELY BE MAXIMIZED NEAR
THE COAST FOR SOME HIGHER RAIN RATES, BUT THERE IS ENOUGH
DYNAMICAL SUPPORT FOR LIFT THAT HEAVY RAINFALL CAUSING INSTANCES
OF FLOODING IS POSSIBLE INLAND AS WELL. BY MONDAY, THE LOW IS
FORECAST TO LIFT QUICKLY NORTHWARD AND RAIN (AND SOME SNOW ON THE
BACKSIDE OF THE SYSTEM) SHOULD SPREAD INTO THE NORTHEAST. A
MARGINAL RISK OF EXCESSIVE RAINFALL IS IN PLACE FOR THE
POTENTIALLY HEAVY RAINFALL. AN UPGRADE TO A SLIGHT RISK MAY
EVENTUALLY BE NEEDED FOR MAINE GIVEN THE WET ANTECEDENT CONDITIONS
AND SENSITIVITY TO HEAVY RAIN THERE. PRECIPITATION SHOULD PULL
AWAY ON TUESDAY BUT LINGERING COASTAL SHOWERS COULD CONTINUE.
PRECIPITATION CHANCES WILL BE INCREASING NEXT WEEK FOR CALIFORNIA
AS SHORTWAVE ENERGY SUPPORTING A POSSIBLE ATMOSPHERIC RIVER
APPROACHES. RAIN AMOUNTS AND RATES ON SUNDAY AND MONDAY COULD BE
SUFFICIENT TO CAUSE SOME FLOODING CONCERNS, ESPECIALLY GIVEN SOME
INSTABILITY COULD REACH COASTAL AREAS. MARGINAL RISKS OF EXCESSIVE
RAINFALL ARE IN PLACE FOR MONDAY AND TUESDAY WHERE FLOODING MAY BE
A CONCERN. PRECIPITATION IS FORECAST TO ALSO PICK UP IN THE
PACIFIC NORTHWEST MONDAY INTO TUESDAY AS A AN UPPER LOW MOVES DOWN
THE COAST. SOME HIGHER ELEVATION SNOW WILL ALSO BE POSSIBLE,
THOUGH CONFIDENCE IN THE DETAILS REMAINS SOMEWHAT LOW.
AWAY FROM THE COASTS, THE CENTRAL U.S. WILL SEE MAINLY DRY
CONDITIONS NEXT WEEK. AREAS FROM THE WEST INTO MUCH OF THE PLAINS
WILL SEE WARMER THAN NORMAL TEMPERATURES NEXT WEEK UNDERNEATH
UPPER RIDGING, WITH TEMPERATURES 10-20F ABOVE AVERAGE PERIODICALLY
AFFECTING THE NORTHERN/CENTRAL HIGH PLAINS INTO THE UPPER MIDWEST.
MEANWHILE, THE NORTHEASTERN U.S. SHOULD SEE ABOVE NORMAL
TEMPERATURES EARLY IN THE WEEK BUT MODERATING BACK TOWARD NORMAL
BY TUESDAY BEHIND THE LOW PRESSURE SYSTEM. THE SOUTHEAST INCLUDING
FLORIDA LOOKS TO BE COOLER THAN AVERAGE NEXT WEEK BEHIND MULTIPLE
FRONTAL PASSAGES.
DOLAN/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, 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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