Prognostic Meteorological Discussion
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FXUS02 KWBC 251559
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EST SUN JAN 25 2015

VALID 12Z WED JAN 28 2015 - 12Z SUN FEB 01 2015

...AN ACTIVE SPLIT-FLOW PATTERN FOR THE LOWER 48...

...OVERVIEW...
THE CURRENT WAVE PATTERN CONFIGURATION---ACROSS NORTH
AMERICA---ALLOWS FOR A HIGH DEGREE OF PREDICTABILITY THIS MEDIUM
RANGE FORECAST PERIOD. THIS INCLUDES...A SPLIT-FLOW REGIME---AN
ACTIVE SOUTHERN STREAM FOR THE WEST COAST AND RIO GRANDE VALLEY
WITH PACIFIC INFLUENCE...PLUS A WINTER-LIKE STORM TRACK---FAVORING
THE NORTHEAST QUARTER OF THE COUNTRY---WITH CONTINENTAL
INFLUENCES.

...UNCERTAINTY ASSESSMENT...
THE DETAILS OF THE FLOW PATTERN ARE IN GOOD AGREEMENT UNTIL DAY
5...WHEN THE MODEL DIFFERENCES `CROP UP` AND CONCERN THE
DEPTH/BREATH OF THE LEADING EDGE OF A CANADIAN AIRMASS INTRUSION
INTO THE LOWER 48.

THE SOUTHERN STREAM ENTITY MIGRATING ACROSS THE CENTRAL PLAINS AND
MID-MS VALLEY---WHICH PULLS THE LEADING EDGE OF A CANADIAN AIRMASS
SOUTHWARD INTO THE LOWER 48---IS NOT THE POINT OF CONTENTION. ITS
THE DEPTH OF THE SHALLOW AIRMASS AND THE COLD ADVECTION
TRAJECTORIES ACROSS THE MID-MS VALLEY INTO THE SOUTHERN
PLAINS---THAT WILL BE THE CHALLENGE. THE CONSEQUENCES
THEREAFTER...ARE TIED TO THE SPLIT-FLOW PATTERN IN THE WEST AND
THE SOUTHERN STREAM ENERGY AND MOISTURE THAT IS `REPLACED` BY
ANOTHER UPPER-LEVEL CIRCULATION TRAPPED BENEATH THE UPPER-LEVEL
RIDGE ALONG THE SOUTHWESTERN COAST OF NORTH AMERICA.

AS MUCH AS THE FOCUS IS---FOR MID-LEVEL ENERGY ENTRAINMENT INTO
THE EASTERN NORTH AMERICAN TROUGH AND POTENTIAL FOR EMBEDDED
WINTER WEATHER ACROSS THE GREAT LAKES AND ALONG THE EASTERN
SEABOARD---THE SPLIT-FLOW PATTERN IN THE SOUTHWEST WILL BE PRESENT
AT/BEYOND DAY 5...SETTING UP AN OVER-RUNNING FLOW REGIME FOR THE
RIO GRANDE...SOUTHERN PLAINS AND LOWER MS VALLEY---WITH THE
EMBEDDED SOUTHERN STREAM INFUSING DOWNSTREAM INTO THE BASE OF THE
EASTERN TROUGH.

THIS SOUTHERN STREAM HAS NUMEROUS IMPLICATIONS DOWNSTREAM---ON
SEVERAL LEVELS---NAMELY...DEPTH OF THE CANADIAN AIRMASS ON
TEMPERATURES ALONG THE SOUTHERN TIER STATES AND MISSOURI
VALLEY---AND OVER-RUNNING LIGHT PRECIPITATION P-TYPE CHALLENGES.


SETTING THE STAGE AROUND DAY 5...FOR MEDIUM RANGE ADJUSTMENT
THEREAFTER---
THE ORGANIZED MID-LEVEL WAVE IN THE CENTRAL ROCKIES AND LOW-LEVEL
CIRCULATION MIGRATING ACROSS THE PLATTE VALLEY REMAINS A
`TRACK-ABLE` FEATURE INVOF NORTHEAST ILLINOIS (29/12Z-DAY 4)---AND
THE 25/00Z DETERMINISTIC GUIDANCE SUPPORTS/DEPICTS A 1006 MB
SURFACE LOW MOVING EASTWARD ALONG I-80 BETWEEN CHICAGO AND
CLEVELAND (HEADING INTO DAY 5). THE DEPTH OF THE CANADIAN AIRMASS
THAT SPREADS IN BEHIND THIS CIRCULATION IS NOT A CHALLENGE ACROSS
THE GREAT LAKES HEADING INTO DAY 6...IT THE SPREAD OF THE AIRMASS
ALONG...SOUTH AND WEST OF THE MS RIVER AND ENCOMPASSING THE ENTIRE
MISSOURI VALLEY---IS WHERE THE 25/00Z DETERMINISTIC GUIDANCE HAS
SOME FUNDAMENTAL DIFFERENCES. HERE...A BLEND OF THE MEANS APPEARS
TO BE IN ORDER...BASED ON THE ECMWF (IN PARTICULAR)...GFS AND
CANADIAN SOLUTIONS VARYING TO SUCH A DEGREE AS TO COMPLETELY
FLIP-FLOP THE THERMAL PROFILES IN THE NORTHERN PLAINS---FROM
EARLIER RUNS. THIS LEADING EDGE OF THE NEWLY-INTRODUCED CANADIAN
AIRMASS AND THE ARCTIC DRAPE THAT FOLLOWS---WILL BE SETTING THE
STAGE FOR SENSIBLE WEATHER CHANGES DURING THE LATTER HALF OF THE
FORECAST PERIOD.

...MODEL PREFERENCES...
THE DAY3-TO-DAY5 FORECAST MAINTAINS GOOD CONTINUITY---WITH THE
25/00Z ECENS-NAEFS AND SOME DETERMINISTIC ECMWF TO HOLD THE
PATTERN IN PLACE ALONG/EAST OF 100W LONGITUDE. THEN...`MASSAGE`
THE DAY 6-7 PERIOD AWAY FROM THE DETERMINISTIC RUNS...TO ACCOUNT
FOR THE AREA OF LOW PRESSURE IN THE SOUTHWEST...MAINTAIN THE
STATIONARY UPPER-LEVEL LOW AND TROUGH IN HUDSON BAY AND SOUTHWARD
EXTENSION OF THE 500MB TROUGH INTO THE SOUTHERN MID-ATLANTIC...AND
TEMPER THE TRAJECTORIES OF AN ARCTIC INTRUSION. WENT WITH A 70/30
ECENS-NAEFS APPROACH...LEAVING ROOM FOR A BROAD ZONE OF CONFLUENT
FLOW ALOFT FROM WEST TEXAS TO THE PIEDMONT.

...SENSIBLE WEATHER HIGHLIGHTS...
WIDE FLUCTUATIONS IN TEMPERATURES FOR THE ENTIRE LENGTH OF THE
MISSOURI RIVER VALLEY EASTWARD TO THE DIVIDE THIS
PERIOD---RESULTING FROM THE SUCCESSION OF CANADIAN AIRMASS SURGES
ENTERING THE BASE OF THE EASTERN NORTH AMERICAN TROUGH.

LOW PRESSURE ORIGINATING INVOF BAJA CALIFORNIA AND ITS EMBEDDED
MID-LEVEL ENERGY WILL GENERATE A SERIES OF OVER-RUNNING
PRECIPITATION EVENTS FOR THE SOUTHWESTERN US...INCLUDING THE RIO
GRANDE VALLEY AND SOUTHERN PLAINS.

COLD AND WINTRY FOR THE UPPER MIDWEST...GREAT LAKES AND THE EAST
WITH SHORTWAVE ENERGY ENHANCING THE PROSPECTS FOR SNOW IN THE
NORTHEAST.

VOJTESAK

$$




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