123
FXUS02 KWBC 101918
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
217 PM EST SAT DEC 10 2022
VALID 12Z TUE DEC 13 2022 - 12Z SAT DEC 17 2022
...MAJOR STORM SYSTEM TO BRING HEAVY SNOW/BLIZZARD CONDITIONS TO
NORTHERN-CENTRAL PLAINS WITH A HEAVY RAIN/SEVERE WEATHER THREAT
FOR SOUTHERN AREAS NEXT WEEK...
..OVERVIEW
A MAJOR STORM SYSTEM WILL BE EXITING THE ROCKIES BY THE START OF
THE PERIOD ON TUESDAY, WITH HIGH CONFIDENCE FOR A DEEP LOW
PRESSURE SYSTEM TO EMERGE INTO THE PLAINS. THIS SYSTEM SHOULD
BRING A WIDE ARRAY OF HAZARDS INCLUDING HEAVY RAIN/SEVERE WEATHER
TO THE SOUTH AND HEAVY SNOW/BLIZZARD CONDITIONS ACROSS PARTS OF
THE NORTH-CENTRAL PLAINS AND INTO THE UPPER MIDWEST AROUND MIDWEEK
WITH SOME CHANCE OF FREEZING RAIN FOR SOME AS WELL. THIS STORM
SYSTEM SHOULD TRACK STEADILY EASTWARD BRINGING A HEAVY RAIN THREAT
TO PARTS OF THE SOUTHEAST AND MID-ATLANTIC (WITH SOME MORE
UNCERTAIN SNOW POTENTIAL FARTHER NORTH) LATER NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THROUGH AROUND MIDWEEK, MODEL GUIDANCE HAS BEEN AND CONTINUES TO
BE WELL CLUSTERED FOR THE OVERALL PATTERN SETUP INVOLVING A
VIGOROUS SURFACE LOW CONSOLIDATING IN THE CENTRAL PLAINS AND
SHIFTING TOWARD THE MIDWEST. WHILE THERE REMAIN SOME MINOR WIGGLES
IN THE TIMING OF THE SURFACE LOW TRACK AND ITS ASSOCIATED FRONTS,
WITH RECENT CMC RUNS ON THE FASTER SIDE AND UKMET RUNS A LITTLE
SLOWER THROUGH THE 00Z CYCLE, THEY SEEM TO BE CONVERGING A LITTLE
BETTER FOR THE 12Z CYCLE. BY DAY 4/WEDNESDAY AND BEYOND, THERE HAS
BEEN QUITE A BIT MORE MODEL WAFFLING WITH THE EVOLUTION OF THE
UPPER AND SURFACE LOWS PARTICULARLY IN THE DETERMINISTIC GFS AND
GEFS ENSEMBLES. YESTERDAY'S 12Z, 18Z, AND TODAY'S 00Z RUNS
INDICATED A FASTER WEAKENING AND PROGRESSION EASTWARD OF THE UPPER
LOW (AND SHUNTING OF A SURFACE LOW DIRECTLY EAST) LIKELY DUE AT
LEAST IN PART TO INTERACTION WITH AN UPSTREAM PACIFIC UPPER LOW
THAT OTHER MODELS KEPT SEPARATE. HOWEVER, THE 06Z GFS AND GEFS
TRENDED BACK TOWARD OTHER GUIDANCE WITH THESE FEATURES, AND THEIR
12Z RUNS APPEAR EVEN MORE IN LINE. SO HOPEFULLY THE EARLIER
GFS/GEFS RUNS WERE AN ANOMALY AND MODELS STICK WITH BETTER
AGREEMENT ON THE TYPE OF SOLUTION THAT HAS BEEN MOST CONSISTENT IN
THE ECMWF SUITE--NAMELY, THE UPPER LOW GRADUALLY TRACKING EASTWARD
LATE WEEK WHICH HELPS TO FORM A SURFACE LOW IN THE SOUTHEAST THAT
LOOKS TO TRACK AS A NOR'EASTER NEAR THE COAST. THE CMC HAD BEEN
FASTER WITH THAT SURFACE LOW FOR A FEW RUNS NOW, BUT THE 12Z CAME
IN SLOWER. THERE IS STILL UNCERTAINTY WITH THE DETAILS OF THE
EXACT TRACK OF THIS POTENTIAL NOR'EASTER, WHICH WILL HAVE NOTABLE
IMPLICATIONS FOR PRECIPITATION TYPES ACROSS THE EAST, BUT AT LEAST
CONFIDENCE IN THE PATTERN ON A BROAD SCALE IS RISING ESPECIALLY
GIVEN THE RECENT 12Z MODELS. THE WPC FORECAST LEANED TOWARD THE
MORE AGREEABLE 00Z ECMWF/EC ENSEMBLE MEAN AND 06Z GEFS MEAN BY THE
LATTER HALF OF THE FORECAST PERIOD, WHICH WAS SIMILAR TO THE
PREVIOUS WPC FORECAST AND NOW TO THE NEWER 12Z GUIDANCE.
UPSTREAM FARTHER WEST, DIFFERENCES REMAIN REGARDING AN UPPER LOW
CLOSING OFF IN THE PACIFIC, BUT MODELS (ESPECIALLY THE 12Z SUITE)
SEEM TO BE CONVERGING ON A SOLUTION THAT KEEPS THE UPPER LOW
FARTHER OUT INTO THE PACIFIC. ADDITIONALLY, PERIODS OF ENERGY MAY
DIP SOUTH FROM THE FAR NORTHERN STREAM AND COULD INTERACT WITH THE
CENTRAL U.S. UPPER LOW. UNCERTAINTY REMAINS GIVEN THE BLOCKY
PATTERN OVER THE PACIFIC/WESTERN NORTH AMERICA. THE MODEL BLEND
FAVORING THE 00Z ECMWF AND EC MEAN AND 06Z GEFS MEAN ALSO WORKED
REASONABLY WELL FOR THIS AREA.
..WEATHER/HAZARD HIGHLIGHTS
AS THE UPPER TROUGH EMERGES INTO THE PLAINS AND A SURFACE LOW
CONSOLIDATES AND DEEPENS, DEEP AMPLE MOISTURE WILL SPREAD AHEAD OF
A COLD FRONT TO PRODUCE SIGNIFICANT RAINFALL ACROSS THE
LOWER/MIDDLE MISSISSIPPI VALLEY INTO THE TENNESSEE
VALLEY/APPALACHIANS AND VICINITY, STEADILY SHIFTING EAST WITH
TIME. THE LATEST WPC EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOKS SHOW
SLIGHT RISKS ACROSS EASTERN ARKANSAS, SOUTHEASTERN MISSOURI, FAR
WEST TENNESSEE/KENTUCKY, AND NORTHERN MISSISSIPPI ON TUESDAY, WITH
THE SLIGHT SHIFTING EAST INTO THE TENNESSEE VALLEY/SOUTHERN
APPALACHIANS AND NORTHERN PARTS OF THE SOUTHEAST ON WEDNESDAY
WHERE STREAMFLOWS AND SOIL MOISTURE ARE ABOVE NORMAL, WHICH COULD
ENHANCE FLOODING POTENTIAL. THE STORM PREDICTION CENTER CONTINUES
TO MONITOR AND HIGHLIGHT THE POTENTIAL FOR STRONG TO SEVERE
CONVECTION ACROSS THE LOWER MISSISSIPPI VALLEY TUESDAY AND THE
CENTRAL GULF COAST ON WEDNESDAY AS WELL. ON THE BACKSIDE OF THE
LOW, COLD TEMPERATURES AND WRAP-BACK MOISTURE WILL SUPPORT
SIGNIFICANT SNOW/WINDS IN THE NORTHERN PLAINS/UPPER MIDWEST AS
SHOWN BY MAXED OUT WPC WINTER WEATHER OUTLOOK PROBABILITIES, WITH
SOME MIXED PRECIPITATION/FREEZING RAIN POTENTIAL IN THE TRANSITION
ZONE AS WELL AS ALONG THE EASTERN EDGE OF THE PRECIP SHIELD
NEAR/NORTH OF THE WARM FRONT. BY THE LATTER HALF OF THE WEEK,
CURRENT FORECASTS SHOW PRECIPITATION IS LIKELY TO SPREAD ACROSS
THE EAST COAST ALONG AND AHEAD OF THE FRONTAL SYSTEM, WITH
POTENTIAL FOR WINTRY WEATHER SPREADING ACROSS THE GREAT LAKES
REGION AND NORTHEAST. BUT PRECIPITATION TYPES AND AREAS OF
HEAVIEST PRECIPITATION HAVE A GREAT DEAL OF UNCERTAINTY ESPECIALLY
CONSIDERING POSSIBLE COASTAL LOW DEVELOPMENT OFF THE MID-ATLANTIC
COAST LATE WEEK.
THE WEST TO HIGH PLAINS SHOULD SEE BELOW NORMAL CONDITIONS THROUGH
THE PERIOD, WITH THE MOST WIDESPREAD READINGS OF GENERALLY 10-20F
BELOW NORMAL FOR HIGH TEMPERATURES BEHIND AND UNDERNEATH THE UPPER
LOW. ON THE OTHER HAND, TEMPERATURES WILL INITIALLY BE ABOVE
NORMAL CENTERED ACROSS EASTERN PARTS OF THE PLAINS AND THE
MISSISSIPPI VALLEY TUESDAY AND SHIFTING EAST. ANOMALIES WILL BE
GREATEST FOR MORNING LOWS, WITH SOME PLUS 15-25F ANOMALIES ACROSS
THE SOUTHERN TIER THROUGH THURSDAY. HIGHS ARE FORECAST TO BE
AROUND 10-15F ABOVE NORMAL FOR THE CENTRAL AND THEN EAST-CENTRAL
U.S., LOCALLY HIGHER AHEAD OF THE STORM SYSTEM. MUCH OF THE
COUNTRY LOOKS TO BE NEAR OR BELOW NORMAL BY NEXT FRIDAY AND
SATURDAY AFTER THE COLD FRONTAL PASSAGE AS HIGH PRESSURE
OVERSPREADS MUCH OF THE COUNTRY.
TATE/SANTORELLI
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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