Prognostic Meteorological Discussion
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FXUS02 KWBC 251548
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1147 AM EDT WED MAY 25 2016

VALID 12Z SAT MAY 28 2016 - 12Z WED JUN 01 2016

FROM THE MACRO-SCALE (WEST-TO-EAST)---THE MEDIUM RANGE FORECAST
USED A BLEND OF THE 25/00Z DETERMINISTIC UKMET/ECMWF TO
31/00Z---THEN TAPERED AWAY FROM THE ECMWF (WITH NO UKMET AVAILABLE
AFTER 31/00Z) TO AN ALL ECENS/NAEFS MEAN-BASED FORECAST AFTER
1/00Z. THE FLOW PATTERN HAS A `SUMMER` LOOK TO IT...WITH LIGHT
WINDS ALOFT AND A PREVAILING RIDGE IN PLACE ACROSS THE NORTHEAST
QUARTER OF THE NATION. THE RIDGE CREATING A RATHER SLUGGISH
SOUTH-TO-NORTH `DRIFT` OF THE FLOW AND ALL THE FEATURES EMBEDDED
WITHIN IT. THIS`LL PRODUCE A PATTERN OF DIURNALLY-ACTIVE
CONVECTIVE CLUSTERS FOR THE PLAINS...AND A SERIES OF
WESTWARD-MOVING MID-LEVEL SHORTWAVES FOR THE SOUTHEAST COAST.

STILL GOOD AGREEMENT OVER THE CENTRAL AND NORTHERN PLAINS--- WITH
THE TRACK AND INTENSITY OF A SSW-TO-NNE MIGRATING CENTRAL ROCKIES
SHORTWAVE DAYS 3-4. THE NON-BLEND PREFERENCES (GFS/CANADIAN) WERE
ACCEPTABLE OVER THIS PORTION OF THE CONTINENT---JUST COULD NOT USE
THEM ELSEWHERE TODAY FOR DAYS 5-7. AS A SIDE NOTE...THE DAY3-4
CYCLONE AND ADDITIONAL CONVECTIVE ELEMENTS THAT `FIRE OFF`
DOWNSTREAM SHOULD BE SUFFICIENT TO PULL A SLIGHTLY COOLER AIRMASS
SOUTHEAST FROM SOUTHERN CANADA---INTO THE MIDWEST. BUT WITH THE
DOWNSTREAM RIDGE IN PLACE AND A SYSTEM WITH TROPICAL
CHARACTERISTICS STALLED DOWNSTREAM OF THE RIDGE...THE FRONTAL
PROGRESSION WILL SPREAD OUT ON A MORE OR LESS A `WEST TO EAST AND
SOUTHWEST TO NORTHEAST` PATH BEYOND DAY 4...HEADING INTO DAY 5.

HEADING INTO DAY 5 (30/00Z-30/12Z)...THE 25/00Z FORECAST CYCLE
YIELDED A PAIR OF `CUTOFF` LOWS (OR DISTURBANCES) ALONG/NEAR 30N.
ONE INVOF 80W AND THE OTHER NEAR 120W AND BOTH WERE REASONABLY
DEPICTED WITH RESPECT THEIR SENSIBLE WEATHER IMPACTS UPON THE
LOWER 48.

THEY (THE CUTOFFS) BEING SO SEPARATED FROM THE JET-LEVEL FLOW
(WELL NORTH ACROSS CANADA)---AND ANY MID-CONTINENTAL FRONTAL
PROGRESSION---THAT THEIR MIGRATORY TRACK FORECASTS BECOME VERY
SENSITIVE. TO SMALLER SCALE FACTORS SUCH AS ORGANIZED LOW-LEVEL
CONVERGENCE AND/OR CONVECTIVE PROCESSES---IN PARTICULAR---THE EAST
COAST DISTURBANCE. THE LACK OF AN UPSTREAM `KICKER` PLAYS A MORE
SIGNIFICANT ROLE IN THE RATHER SLOW MOVEMENT OF THE FEATURE. TIME
WILL TELL IF MID-CONTINENTAL FLOW WILL SPREAD SUFFICIENTLY SOUTH
AND EAST OF THE OHIO VALLEY TO PRODUCE SOME INFLUENCE ON THE
SOUTHEAST DISTURBANCE.

FOR THIS PARTICULAR MEDIUM RANGE PERIOD...THE SOUTHEAST COAST WILL
BE DOMINATED BY A DIFFUSE AND OCCASIONALLY `PULSING` DISTURBANCE
WITH TROPICAL CHARACTERISTICS--- THAT APPEARS TO OSCILLATE IN
INTENSITY AS IT WOBBLES SLOWLY NORTHWESTWARD THROUGH TIME. THE ONE
INTRIGUING ASPECT OF THIS PARTICULAR `DISTURBANCE` IS ITS SURFACE
REFLECTION---AN OSCILLATING ONSHORE/OFFSHORE FEATURE---THAT WILL
BE NEARLY IMPOSSIBLE TO DEPICT ON THE DAILY SURFACE CHARTS (A 12Z
SNAPSHOT)---GIVEN THE CONVECTIVE ELEMENTS THAT WILL DEVELOP AND
ROTATE EVER-SO SLOWLY WESTWARD AROUND A VERY BROAD CYCLONIC
MID-LEVEL FLOW CENTERED NEAR 30-31N 77W-78W FOR A GOOD PORTION OF
THE PERIOD. NHC HAS THIS FEATURE HIGHLIGHTED IN THEIR TROPICAL
WEATHER OUTLOOK---SO PLEASE REFER TO THEIR INFORMATION IN THE
SHORTER TERM --- AS THE FEATURE EVOLVES OFFSHORE---BENEATH THE
UPPER-LEVEL TROUGH (AND EMBEDDED CYCLONIC FLOW).

VOJTESAK











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