Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 230753
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION...CORRECTED PARAGRAPH 4
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
352 AM EDT TUE SEP 23 2014

VALID 12Z FRI SEP 26 2014 - 12Z TUE SEP 30 2014

...OVERVIEW...
A BROAD UPPER-LEVEL RIDGE WILL GRADUALLY SETTLE OVER THE OHIO
VALLEY...MIGRATING EAST-NORTHEASTWARD FROM THE WEST CENTRAL AND
SOUTHERN PLAINS DURING THIS MEDIUM RANGE PERIOD. AND A PACIFIC
TROUGH WILL PREVAIL ALONG THE WEST COAST EARLY IN THE
PERIOD...THEN MIGRATE ACROSS THE INTERMOUNTAIN WEST INCLUDING THE
SOUTHERN ROCKIES BY PERIOD`S END.

...UNCERTAINTY ASSESSMENT...
STILL A TROUBLESOME FORECAST FOR THE SOUTHEAST...LOWER MS VALLEY
AND OZARKS AFTER DAY 4. THE LINGERING MID-LEVEL DISTURBANCE INVOF
THE OZARKS ATTEMPTS TO DRAW UPON THE LOW-LEVEL MOISTURE TAP AND
CAPITALIZE ON A WEAKNESS IN THE SOUTHWESTERN PERIPHERY OF THE
SURFACE-TO-700 MB LAYER RIDGE PLANTED DOWNSTREAM OVER THE OHIO
VALLEY AND DELMARVA. COUPLED WITH A STATIONARY BOUNDARY IN THE
NORTHERN GULF OF MEXICO---THE PRESENCE AND PERSISTENT OF THIS
SURFACE RIDGE OVER THE EAST CENTRAL STATES AND WESTERN ATLANTIC
OCEAN WILL PROVIDE A RATHER CONSISTENT EASTERLY TO NORTHEASTERLY
FLOW ACROSS THE SOUTHEASTERN STATES AND INTO THE GULF OF MEXICO.

CONCERNING QPF...
THE DETERMINISTIC 22/12Z UKMET WOULD BE THE MOST AGGRESSIVE
SOLUTION---WITH ITS 1006MB SFC LOW INVOF NORTHEAST MS AT 28/12Z.
THE 22/12Z ECMWF AND 22/18Z GFS LIKE THE IDEA OF LOWER PRESSURE
DEVELOPMENT IN THE MS DELTA...BUT DELAY THE DEVELOPMENT OF AN
ORGANIZED AND `TRACK-ABLE` SURFACE WAVE A GOOD 24-36 HOURS LATER
(INTO THE DAY 6 PERIOD) BEFORE ACCOMPLISHING THE SAME TASK.

THIS SUGGESTS SEVERAL THINGS---NAMELY THE EASTERLY FLOW WILL HAVE
A PROPENSITY FOR GENERATING WEAK CYCLONIC FLOW ALONG THE NORTHERN
FRINGES OF THE STATIONARY FRONT AND TWO...THERE WILL BE SOME
INTERACTION AND POSSIBLE PHASING WITH RESIDUAL VORTICITY
MEANDERING OVER THE LOWER MISSOURI VALLEY DURING THIS CHALLENGING
DAY 5 FORECAST. THE SYNOPTIC-SCALE PATTERN ALLOWS FOR IT...AND
LEAVES THE WESTERN PORTION OF THE GULF WIDE OPEN FOR ANY SUBTLE
WAVE TO MAKE THE NORTHWARD TURN ALONG THE WESTERN PERIPHERY OF THE
SURFACE RIDGE.

THE PATTERN WILL BE A SLOWLY-EVOLVING ONE. A QUICK LOOK AT THE 00Z
CYCLE GUIDANCE AT PRESS TIME---THE GFS/UKMET AND CANADIAN---ALL
SUGGEST THE SURFACE RIDGE PATTERN ALONG THE EAST COAST REMAINS IN
PLACE.

...MODEL PREFERENCES...
FOR THE LOWER 48...CAN SEE WHERE A BLEND OF THE 22/12Z
ECENS-NAEFS-GEFS WILL WORK SINCE IT KEEPS THE UPPER-LEVEL TROUGH
INTACT DURING ITS MIGRATION ACROSS 35N-40N AND MORE
IMPORTANTLY---THE UPPER-LEVEL RIDGE PLANTED IN THE EASTERN US. IT
DOES NOT RESOLVE THE QPF DIFFERENCES.

FOR DAY 3-4 ACROSS THE WEST COAST...THE DETERMINISTIC 22/12Z
UKMET...CANADIAN AND 22/18Z GFS WERE TIGHTLY CLUSTERED WITH THE
MAJORITY OF THE EC ENSEMBLE MEMBERS--- SIGNALING THE PRESENCE OF A
CLOSED 500MB CIRCULATION WITHIN THE BASE OF THE UPPER-LEVEL
TROUGH. THE DETERMINISTIC 22/12Z ECMWF SUPPORTS THE DEVELOPMENT OF
A NEGATIVE-TILT TROUGH EVOLUTION IN THE SOUTHEASTERN GULF OF
ALASKA THROUGH TIME RATHER THAN FOLLOW THE CONSENSUS...STRAYING
AWAY FROM ITS OWN PREVIOUS CLOSED LOW SOLUTION THE PREVIOUS TWO
CYCLES. THE 22/12Z DETERMINISTIC ECMWF IS THE LEAST LIKELY
SOLUTION AND CAN`T IMAGINE IT BLASTING SUCH A STRONG SHORTWAVE
INTO AND THROUGH THE SURFACE RIDGE BETWEEN DAY 4-6...UNLESS ITS
SOURCE REGION IS THE BAY OF CAMPECHE. DO THINK THE PACIFIC TROUGH
HAS LITTLE OPTION BUT TO SLOWDOWN THROUGH TIME AND MY DAY 7
SURFACE GRAPHIC ANTICIPATES THIS TO SOME EXTENT WITH A GRADUAL
`SEEPAGE` OF COOLER CANADIAN AIR ALONG THE EAST SIDE OF THE
MONTANA AND WYOMING PORTION OF THE CONTINENTAL DIVIDE. ALONG WITH
THE SLOWER PROGRESSION OF THE UPPER-LEVEL TROUGH...A SUCCESSION OF
SHORTWAVES EJECTING NORTHEASTWARD OUT OF THE BASE OF THE 500MB
TROUGH. THE KEY THOUGH---IS SEPARATION---WITH THE UPPER-LEVEL
TROUGH REMAINING LOCKED IN ACROSS THE CENTRAL ROCKIES INTO DAY 7
AND NORTHWEST OF THE BETTER GULF MOISTURE. THE `OPEN` WESTERN GULF
OF MEXICO BEING MORE OF A SUB-SYNOPTIC SCALE MOISTURE SOURCE FOR
WEAK EASTERLY WAVE/INVERTED TROUGH MIGRATION ALONG THE SOUTHERN
FLANKS OF THE SURFACE RIDGE....ACROSS THE NORTHERN GULF OF MEXICO
AND BENDING NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE
SURFACE RIDGE.

THIS IS ESSENTIALLY WHY I CAN`T PUT MUCH STOCK IN A BLEND OF THE
THREE 22/12Z MEANS WITH RESPECT TO DETERMINISTIC QPF ALONG THE
SOUTHERN PERIPHERY OF THE SURFACE RIDGE.

...SENSIBLE WEATHER HIGHLIGHTS...
THE HIGHEST PROBABILITIES FOR PRECIPITATION WILL CONTINUE TO BE IN
THE SOUTHEASTERN QUARTER OF THE NATION AND ALONG THE STATIONARY
BOUNDARY. IN THE WEST...HIGHER PROBABILITIES OF PRECIPITATION WILL
BE LOCATED ALONG THE NORTHEAST QUADRANT OF THE UPPER-LEVEL TROUGH
AND INVOF THE EMBEDDED 500MB CIRCULATION MIGRATING ACROSS THE
GREAT BASIN...INTERMOUNTAIN WEST AND CONTINENTAL DIVIDE.

THE INFLUENCE OF THE UPPER-LEVEL RIDGE OVER THE OHIO VALLEY AND
WESTWARD PROGRESSION OF THE SURFACE RIDGE WILL KEEP THE NORTHERN
PLAINS...GREAT LAKES...OHIO VALLEY AND NEW ENGLAND GENERALLY
CLEAR/DRY WITH VERY MILD AND/OR PLEASANT DAYTIME HIGHS.

VOJTESAK

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