649
FXUS02 KWBC 040711
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
210 AM EST SAT FEB 04 2023
VALID 12Z TUE FEB 07 2023 - 12Z SAT FEB 11 2023
..GUIDANCE/PREDICTABILITY ASSESSMENT
DESPITE REASONABLY SIMILAR LARGER SCALE PATTERN TRANSITION FROM
SPLIT FLOW TO AMPLIFIED FLOW NEXT WEEK OVER THE COUNTRY, RECENT
MODELS AND ENSEMBLES HAVE BEEN OFFERING LESS THAN STELLAR FORECAST
SPREAD WITH THE WEATHER FOCUSING EMBEDDED SYSTEMS. THIS IS EVIDENT
STARTING EARLY IN THE WEEK WITH NORTHERN STREAM TIMING DIFFERENCES
AND THE EXTENT OF PHASING WITH A MAIN WEATHER FOCUSING SOUTHERN
STREAM CLOSED LOW ONCE SLATED TO EJECT OUT FROM THE SOUTHWEST
THROUGH THE EAST-CENTRAL U.S. WITH SOME FANFARE, BUT THERE IS A
GROWING SIGNAL FOR LATER NEXT WEEK FLOW AMPLIFICATION AND SLOWING
WITH DEVELOPMENT OF POTENT UPPER TROUGHS OFF THE WEST COAST AND
THE EAST-CENTRAL U.S., AND AMPLIFIED UPPER RIDGES OVER THE
WEST-CENTRAL U.S. AND WESTERN ATLANTIC.
TWO MAIN FORECAST SCENARIOS CONTINUE TO EXIST IN GUIDANCE
ASSOCIATED WITH THE EMERGENCE OF A SEPARATED SOUTHERN STREAM
WITHIN EMERGING SPLIT FLOW OVER THE NATION. IN THIS FLOW, A CLOSED
UPPER LOW DEVELOPS IN THE SOUTHWEST/NORTHERN MEXICO
TUESDAY-WEDNESDAY. RECENT GFS/CANADIAN RUNS AND TO A LESSER EXTENT
THE GEFS MEAN HAVE BEEN SLOWER TO EJECT THIS FEATURE DOWNSTREAM
THROUGH THE EAST-CENTRAL U.S. NEXT WEEK THAN RECENT ECMWF/UKMET
RUNS AND TO A LESSER EXTENT THE ECMWF ENSEMBLE MEAN. ENSEMBLE
MEMBERS BY AND LARGE SHOWED SIMILAR PROGRESSION TRENDS AS THEIR
PARENT MODELS WITH THE GEFS/CANADIAN/NAEFS ENSEMBLE MEANS LESS
PROGRESSIVE THAN THE ECMWF ENSEMBLE MEAN, BUT THE PROGRESSION
DIFFERENCES ARE LESS THAN AS IN THE MODELS. THIS REMAINS A
DIFFICULT EMERGING SPLIT FLOW FORECAST WITH LOW PREDICTABILITY,
BUT STILL SUSPECT THAT A SOLUTION ON THE LESS PROGRESSIVE SIDE OF
THE FULL ENVELOPE OF GUIDANCE MAKES MORE SENSE GIVEN MUCH GUIDANCE
DOES DEVELOP A SEPARATED SOUTHERN STREAM SYSTEM OF WHICH OFTEN ARE
ON THE SLOW SIDE TO EJECT. MODELS AND ENSEMBLES ARE SLOWLY
CONVERGING ON MORE COMMON PROGRESSION MORE IN LINE WITH ENSEMBLE
MEANS WITH THE 00 UTC GFS/CMC TRENDING SLIGHTLY FASTER AND THE 00
UTC ECMWF/UKMET TRENDING SLIGHTLY SLOWER, BUT THEY STILL HAVE SOME
WAY TO GO TO FINALLY REACH A COMMON SOLUTION.
ACCORDINGLY AND OVERALL, THE WPC MEDIUM RANGE PRODUCT SUITE
THROUGH MEDIUM RANGE TIME SCALES WAS PRIMARILY DERIVED FROM A
COMPOSITE BLEND OF THE 18 UTC GEFS MEAN AND 12 UTC ECMWF ENSEMBLE
MEAN GIVEN UNCERTAINTY OF MODEL DETAILS ALONG WITH WPC CONTINUITY
AND THE 01 UTC NATIONAL BLEND OF MODELS.
..WEATHER/HAZARD HIGHLIGHTS
EARLY NEXT WEEK ROUNDS OF LIGHT PRECIPITATION WILL PASS OVER
PORTIONS OF THE GREAT LAKES AND THE NORTHEAST REGION WITH
SHORTWAVE PASSAGES AND THE APPROACH OF A LEAD LOW/FRONTAL SYSTEM.
THERE MAY BE LAKE ENHANCEMENT OF THE SNOWFALL FOR THE FAVORED
AREAS DOWNWIND OF THE GREAT LAKES WHICH COULD RESULT IN HIGHER
AMOUNTS THAN SURROUNDING LOCATIONS. MODERATE PRECIPITATION IS
EXPECTED TO OVERSPREAD THE WEST COAST AND INLAND TO THE
INTERMOUNTAIN WEST AND ROCKIES REGION EARLY NEXT WEEK. FOR MOST OF
LOWER COASTAL AREAS THE PRECIPITATION WILL LIKELY FALL AS RAIN AND
THEN TRANSITION TO SNOW FOR THE MID-BASE TO HIGHEST ELEVATIONS;
WITH TYPICAL TERRAIN ENHANCEMENT ACROSS THE COASTAL RANGES AND THE
SIERRA NEVADA. AS THE LOW PRESSURE SYSTEM ADVANCES EASTWARD THE
PRECIPITATION AHEAD OF IT COULD OVERSPREAD THE CENTRAL U.S. THE
DETAILS OF THIS PRECIPITATION INCLUDING PLACEMENT AND
PRECIPITATION TYPE REMAIN UNCERTAIN GIVEN THE MODEL DIFFERENCES.
THE CURRENT FORECAST SHOWS ENHANCED RAINFALL AMOUNTS CENTERED
ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY AND
SURROUNDING AREAS BY TUESDAY-WEDNESDAY WITH ENHANCED LOW/FRONTAL
SYSTEM INDUCED RETURN GULF OF MEXICO MOISTURE INFLOW AND
INSTABILITY. WPC HAS IDENTIFIED AN AREA ACROSS THE EASTERN
SOUTHERN PLAINS AND PARTS OF THE LOWER MISSISSIPPI VALLEY INTO THE
TENNESSEE VALLEY AS HAVING THE POTENTIAL FOR EXCESSIVE RAINFALL
WITH BEST MOISTURE CONVERGENCE AND FAVORABLE RIGHT ENTRANCE REGION
UPPER JET DYNAMICS. WPC EXPERIMENTAL MARGINAL RISK AREAS ARE TO BE
ISSUED FOR THAT AREA TUESDAY INTO THURSDAY. THE NORTHERN EDGE OF
THE PRECIPITATION SHIELD HAS THE POTENTIAL FOR A SWATH OF SNOW/ICE
ACROSS PORTIONS OF THE SOUTHERN PLAINS TO MIDWEST AND INTERIOR
NORTHEAST NEXT WEEK. UPSTREAM EASTERN PACIFIC SYSTEM APPROACH
TUESDAY/WEDNESDAY SHOULD OFFER MODEST SYSTEM AMPLITUDE AND
ASSOCIATED MOISTURE/RAINFALL POTENTIAL ACROSS THE PACIFIC
NORTHWEST ALONG WITH TERRAIN/MOUNTAIN SNOWS INLAND FROM THE
NORTHWEST THROUGH THE NORTHERN GREAT BASIN/ROCKIES. THERE IS
THOUGH AN AFOREMENTIONED AND GROWING GUIDANCE SIGNAL THAT THIS
LEADS TO THE AMPLIFICATION OF THE OEVRALL FLOW SIGNIFICANTLY INTO
LATER NEXT WEEK ACROSS THE NATION AND ADJOINING OCEANS, BUT WITH
LIMITED PRECIPITATION RE-EMERGENCE LATER NEXT WEEK TO MONITOR.
SCHICHTEL
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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