109
FXUS02 KWBC 080657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 AM EST FRI DEC 08 2023
VALID 12Z MON DEC 11 2023 - 12Z FRI DEC 15 2023
..OVERVIEW
SURFACE LOW PRESSURE WILL BE IN PLACE IN THE NORTHEAST AS THE
MEDIUM RANGE PERIOD BEGINS MONDAY, BRINGING POSSIBLY HEAVY RAIN
AND SNOW TO THE REGION BEFORE THE SYSTEM EXITS BY TUESDAY. AFTER A
BOUT OF LIGHT TO MODERATE PRECIPITATION IN THE NORTHWEST ON MONDAY
AS WELL, MUCH OF THE LOWER 48 WILL TREND DRIER BY TUESDAY. BY
MIDWEEK AND BEYOND THOUGH, RETURN FLOW FROM THE GULF OF MEXICO
STREAMING INTO THE SOUTHERN HIGH PLAINS AHEAD OF A FOUR CORNERS
UPPER LOW SHOULD LEAD TO INCREASING PRECIPITATION CHANCES THERE,
WHILE MOIST EASTERLY FLOW COULD SPREAD CONVECTION INTO THE FLORIDA
PENINSULA.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO BE AGREEABLE FOR THE EARLY PART OF THE
FORECAST PERIOD, INCLUDING INITIAL TROUGHING IN THE EASTERN U.S.
SUPPORTING SURFACE LOW PRESSURE IN THE NORTHEAST. MODELS INDICATE
THIS TROUGH SHOULD EXIT QUICKLY WHILE ANOTHER TROUGH THAT IS NOT
AS DEEP PUSHES THROUGH THE GREAT LAKES REGION TUESDAY-WEDNESDAY.
GUIDANCE ALSO SHOWS NOTABLE AGREEMENT REGARDING ENERGY DROPPING
INTO THE SOUTHWEST AND FORMING A CLOSED LOW BY WEDNESDAY, JUST
WITH SOME MINOR PLACEMENT DIFFERENCES IN THE MODELS AND ENSEMBLE
MEMBERS. OVERALL A MULTI-MODEL DETERMINISTIC BLEND WAS USED FOR
THE FIRST PART OF THE MEDIUM RANGE FORECAST PERIOD.
BY THURSDAY-FRIDAY, THE 12Z AND THE PREVIOUS 00Z RUN (BOTH FROM
DEC 7) OF THE ECMWF WERE QUITE AGGRESSIVE WITH ANOTHER SHORTWAVE
COMING IN BEHIND THE SOUTHWEST UPPER LOW, WHICH THEN TAKES OVER IN
COMING THROUGH CALIFORNIA AND THE CENTRAL GREAT BASIN AND MERGES
WITH THE PREEXISTING LOW. THOUGH THE DETERMINISTIC RUN IS
SUPPORTED BY SOME OF ITS ENSEMBLE MEMBERS, OTHER GUIDANCE DOES NOT
FAVOR THIS SOLUTION, AND NEITHER DO THE AI/MACHINE LEARNING ECMWF
VERSIONS. THUS REMOVED THE ECMWF FROM THE FORECAST BLEND BUT KEPT
SOME EC ENSEMBLE MEAN AS A NOD TO THIS POSSIBILITY. THE NEWER 00Z
ECMWF IS SORT OF IN BETWEEN, WITH A WEAKER SHORTWAVE THAN ITS
PREVIOUS RUN BUT STRONGER THAN OTHER GUIDANCE, BUT ENDING UP WITH
AN UPPER LOW IN THE GREAT BASIN WHERE GFS RUNS HAVE A RIDGE ON
FRIDAY. THE 00Z CMC TRENDED TOWARD AN EC-LIKE SOLUTION AFTER ITS
12Z RUN WAS MORE LIKE THE GFS RUNS. SO THERE IS STILL SOME
UNCERTAINTY HERE. THERE IS AT LEAST SOME AGREEMENT WITH RIDGING
DOWNSTREAM ACROSS THE CENTRAL U.S. PUSHING TOWARD THE EASTERN U.S.
BY FRIDAY. THE LATEST WPC FORECAST FOR THE LATTER PART OF THE
PERIOD WAS BASED ON A BLEND OF THE 18Z GFS AND GEFS MEAN ALONG
WITH THE 12Z CMC AND SOME 12Z EC ENSEMBLE MEAN.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION WILL BE ONGOING ACROSS THE NORTHEAST ON MONDAY. MUCH
WARMER THAN AVERAGE TEMPERATURES ARE POSSIBLE ACROSS MAINE IN
PARTICULAR EARLY IN THE DAY, WHICH ALONG WITH A BOUT OF HEAVY RAIN
COULD CAUSE QUICKLY MELTING SNOW FOR POSSIBLE FLOODING THERE. A
MARGINAL RISK IS PLANNED FOR DAY 4/MONDAY IN THE EXCESSIVE
RAINFALL OUTLOOK FOR THIS POTENTIAL, AND RIVER FLOODING IS ALSO A
THREAT. ON THE BACKSIDE OF THE LOW, PROBABILITIES FOR NOTABLE SNOW
ARE INCREASING ESPECIALLY IN THE HIGHER ELEVATIONS OF THE INTERIOR
NORTHEAST ON MONDAY. SOME BRISK TO STRONG WINDS ARE ALSO POSSIBLE
FROM THE SOUTH AHEAD OF THE COLD FRONT AND FROM THE WEST BEHIND
IT. THE PRECIPITATION SHOULD CLEAR OUT BY MONDAY NIGHT.
SOME LIGHT TO MODERATE PRECIPITATION IS LIKELY ACROSS THE
NORTHWEST ON MONDAY, WITH SOME ENHANCED SNOW TOTALS LINGERING IN
THE NORTHERN ROCKIES. AFTER THAT, PRECIPITATION WILL BE AT A
MINIMUM ACROSS THE LOWER 48 ON TUESDAY, BUT CHANCES FOR
PRECIPITATION SHOULD INCREASE ON WEDNESDAY-THURSDAY ACROSS THE
SOUTHERN HIGH PLAINS AS AN UPPER LOW SETTLES OVER THE SOUTHWEST
AND MOISTURE INTERACTS WITH A FRONT. SOME OF THIS PRECIPITATION
MAY BE SNOW, WITH TYPICAL ELEVATION/COVERAGE UNCERTAINTY.
MEANWHILE EASTERLY FLOW SETTING UP TO THE SOUTH OF STRONG EASTERN
U.S. HIGH PRESSURE WILL PROMOTE PERIODS OF RAIN OVER FLORIDA.
FINALLY, LIGHT PRECIPITATION IS POSSIBLE AT TIMES IN THE PACIFIC
NORTHWEST FOR THE LATTER HALF OF NEXT WEEK.
AS NOTED ABOVE, TEMPERATURES WILL BE WELL ABOVE AVERAGE IN THE
NORTHEAST ON MONDAY, AND SEVERAL RECORD HIGH MINIMUM TEMPERATURES
COULD BE BROKEN. BEHIND THE COLD FRONT, TEMPERATURES WILL BE
AROUND 5-10F BELOW AVERAGE ACROSS THE GULF COAST TO CENTRAL
APPALACHIANS ON MONDAY AND PUSHING INTO THE SOUTHEAST ON TUESDAY,
WHILE THE NORTHEAST MODERATES TO NEAR AVERAGE. AFTER THAT THE EAST
SHOULD SEE GENERALLY NEAR NORMAL TEMPERATURES, PERHAPS REACHING
ABOVE NORMAL BY FRIDAY. FARTHER WEST, THE MOST PERSISTENT ABOVE
AVERAGE TEMPERATURES WILL BE ACROSS THE NORTH-CENTRAL U.S. (OTHER
THAN A BRIEF COOLER SPELL ON TUESDAY) AS UPPER RIDGING BUILDS. THE
GREATEST ANOMALIES LOOK TO BE ON THURSDAY-FRIDAY FOR THE DAKOTAS
INTO THE UPPER MIDWEST AS TEMPERATURES REACH 10-20F ABOVE NORMAL.
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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