Prognostic Meteorological Discussion
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FXUS02 KWBC 261558
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EDT SUN MAR 26 2017

VALID 12Z WED MAR 29 2017 - 12Z SUN APR 02 2017

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

THE PATTERN ACROSS NORTH AMERICA THROUGH THE MEDIUM RANGE WILL
PERSIST WITH A RELATIVELY ACTIVE FLOW REGIME FROM THE NORTH
PACIFIC INTO BRITISH COLUMBIA AND THE U.S. NORTHWEST. THE FLOW
THROUGHOUT THE PERIOD WILL SPLIT AS IT MOVE EAST, WITH A NUMBER OF
RELATIVELY LOW AMPLITUDE WAVES PROPAGATING THROUGH THE NORTHERN
STREAM ACROSS CANADA, AND A HIGHLY AMPLIFIED, LOW WAVENUMBER
SOUTHERN STREAM FLOW ACROSS THE CONUS. PARTIAL PHASING OF THE TWO
STREAMS WILL OCCUR PERIODICALLY ACROSS SOUTHEASTERN CANADA AND THE
GREAT LAKES/NORTHEASTERN U.S, WITH THE POTENTIAL THE DEVELOPMENT
OF A COUPLE LOW PRESSURE SYSTEMS ACROSS THE NORTH ATLANTIC WELL
EAST OF NEW ENGLAND.

THIS AREA OF PHASING RESULTS IN A MODERATE LEVEL OF SPREAD
INITIALLY ON DAYS 3-4 (THU-FRI) AS A LOW DEVELOPS EAST OF NEW
ENGLAND AND QUICKLY DEEPENS SOUTH OF THE CANADIAN MARITIMES. THE
06Z GFS AND 00Z ECMWF/UKMET AS WELL AS THE 00Z ECMWF ENS MEAN/06Z
GEFS MEAN HAVE COME INTO SOMEWHAT BETTER AGREEMENT, HOWEVER, WITH
A TREND TOWARD A QUICKER EASTWARD PROGRESSION RELATIVE TO WHAT WAS
SHOWN BY THE 00Z GFS. ALSO ON DAYS 3-4, THE FIRST OF TWO DEEP
UPPER LOWS DURING THE MEDIUM RANGE IS FORECAST TO MOVE FROM THE
SOUTHERN ROCKIES INTO THE SOUTHERN/CENTRAL PLAINS. MODEL AGREEMENT
WITH RESPECT TO THIS SYSTEM IS RELATIVELY GOOD INITIALLY, BUT
SPREAD BEGINS TO INCREASE AS THE SYSTEM MOVES INTO THE MID-MS/OH
VALLEYS ON DAY 5 (FRI), WITH THE LOW/TROUGH DEAMPLIFYING AS IT
MOVES INTO A MID/UPPER RIDGE AXIS ACROSS THE EASTERN U.S. SPREAD
HAS DECREASED COMPARED TO THIS TIME YESTERDAY, HOWEVER, WITH THE
GFS AND ECMWF SOLUTIONS APPEARING TO MOVE TOWARD ONE ANOTHER. BY
DAY 6 (SAT), A COASTAL LOW IS FORECAST TO DEVELOP AND QUICKLY MOVE
EAST OFF THE MID-ATLANTIC COAST IN THE AFOREMENTIONED REGION OF
POLAR/SUBTROPICAL STREAM PARTIAL PHASING. FOR DAY 6, SPREAD IS
RELATIVELY LOW WITH RESPECT TO THIS COASTAL LOW, WITH THE 00Z
EC/EC MEAN/06Z GFS/GEFS MEAN ALL WITHIN 100-200 MILES OF EACH
OTHER WITH THEIR RESPECTIVE LOW POSITION AT 12Z SAT.

A SECOND SIGNIFICANT SHORTWAVE IS FORECAST TO MOVE INTO THE
PACIFIC NORTHWEST WED NIGHT/EARLY THU BEFORE QUICKLY DIVING
SOUTHEAST AND AMPLIFYING IN THE SOUTHERN STREAM, WITH AN UPPER LOW
FORECAST BY ALL GUIDANCE IN THE VICINITY OF THE FOUR CORNERS
REGION BY 12Z FRI. THERE ARE SOME TIMING DIFFERENCES WITH RESPECT
TO THE ARRIVAL OF THE SHORTWAVE IN THE NORTHWEST THU MORNING, WITH
THE 06Z GFS SLIGHTLY ON THE FAST SIDE, BUT THESE DIFFERENCES DO
NOT SEEM TO TRANSFER ONCE THE FEATURE CLOSES OFF ACROSS THE
SOUTHWEST. THE 00Z ECMWF HAS TRENDED TOWARD THE GFS ON DAY 6,
SHOWING THE UPPER LOW PERSISTING DEEPER AND FOR LONGER THAN ITS
PREVIOUS RUNS. HOWEVER, THE EC CONTINUES TO WEAKEN THE FEATURE AND
MOVE IT QUICKLY NORTHEAST INTO THE CENTRAL U.S. ON DAY 7 (SUN).
THE GFS/GEFS HAVE BEEN HIGHLY CONSISTENT FROM RUN-TO-RUN IN
KEEPING THE UPPER LOW STRONGER AND FARTHER WEST/SOUTH FOR LONGER.
ADDITIONAL NORTHERN STREAM SHORTWAVE ENERGY IS FORECAST TO
APPROACH THE NORTHWEST BY DAY 7, BUT SPREAD IS VERY HIGH WITH
RESPECT TO THE TIMING OF THIS FEATURE DUE TO THE LOWER AMPLITUDE
AND LOWER PREDICTABILITY OF THE MORE ACTIVE NORTHERN STREAM FLOW.
AGAIN WITH THIS FEATURE, THE GFS/GEFS ARE SLOWER THAN THE EC/EC
MEAN, BUT THE GFS/GEFS HAVE BEEN MORE CONSISTENT FROM RUN-TO-RUN.
THE 00Z NAEFS ALSO SUPPORTS A SOLUTION SIMILAR TO THE GFS/GEFS.

THE WPC FORECAST WAS HEAVILY WEIGHTED ON THE DETERMINISTIC
SOLUTIONS, PRIMARILY THE 00Z ECMWF/06Z GFS ON DAYS 3-5, WITH
MINORITY COMPONENTS OF THE 00Z EC MEAN/06Z GEFS MEAN INCLUDED. A
SIGNIFICANT INCREASE IN ENSEMBLE MEANS WERE INCLUDED BY DAYS 6-7,
WITH MORE WEIGHT PLACED TOWARD THE GEFS AND NAEFS, GIVEN THE
BETTER RUN-TO-RUN CONSISTENCY DEMONSTRATED BY THE GFS/GEFS. A
MINORITY COMPONENT OF THE 00Z ECMWF ENSEMBLE MEAN WERE ALSO
INCLUDED IN DAYS 6-7.


...SENSIBLE WEATHER HIGHLIGHTS/POTENTIAL HAZARDS...

GIVEN THE ANOMALOUS AND ENERGETIC NATURE OF THE SYSTEM ACROSS THE
CENTRAL U.S. ON DAYS 3-5, MODELS SHOW THE POTENTIAL FOR
SUBSTANTIAL LOW/MID-LEVEL MOISTURE FLUX ACROSS THE
SOUTHERN/CENTRAL PLAINS AND LOWER/MID-MS VALLEY, AND THE POTENTIAL
FOR DEEP CONVECTION ALONG WITH HEAVY/EXCESSIVE RAINFALL. THE STORM
PREDICTION CENTER IS ALSO INDICATING THE POTENTIAL FOR SEVERE
THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE LOWER MS VALLEY
DURING THIS TIME. FARTHER WEST, THE SHORTWAVE ENTERING THE
NORTHWEST WED/THU WILL BE ACCOMPANIED BY A POTENTIAL ATMOSPHERIC
RIVER WITH CONNECTIONS TO THE TROPICAL PACIFIC, THUS WOULD EXPECT
THE POTENTIAL FOR HEAVY RAIN AND HIGH ELEVATION SNOWS ACROSS THE
PAC NW. STANDARDIZED ANOMALIES SHOW THE POTENTIAL FOR ANOMALOUS
PWATS ASSOCIATED WITH THIS SYSTEM TO PENETRATE AS FAR INLAND AS
THE GREAT BASIN/INTERMOUNTAIN WEST, THUS THE POTENTIAL IS THERE
FOR SOME HEAVIER PRECIPITATION AMOUNTS IN THOSE REGIONS AS WELL,
PARTICULARLY IN FAVORED TERRAIN. AS THE SECOND UPPER LOW BEGINS TO
MOVE EAST TOWARD THE SOUTHERN PLAINS BY DAY 6-7, EXPECT ANOTHER
ROUND OF POTENTIAL CONVECTION FOR AREAS FROM THE SOUTHERN PLAINS
AND PERHAPS THE LOWER MS VALLEY.

WITH RESPECT TO TEMPERATURES, THE SPLIT FLOW PATTERN AT THE
MID/UPPER-LEVELS WILL KEEP MUCH OF THE CONUS GENERALLY MILD WITH
NEAR OR ABOVE AVERAGE TEMPERATURES. THE NORTHEAST AND PORTIONS OF
THE MID-ATLANTIC WILL SEE THE POTENTIAL FOR THE INCURSION OF
COOLER MARITIME AIR BY LATE IN THE WEEK INTO NEXT WEEKEND AS HIGH
PRESSURE BUILDS IN TO THE NORTH AND LOW PRESSURE POTENTIALLY
DEVELOPS OFF THE COAST.

RYAN

$$





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