Prognostic Meteorological Discussion
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000
FXUS02 KWBC 061527
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1126 AM EDT MON JUL 06 2015

VALID 12Z THU JUL 09 2015 - 12Z MON JUL 13 2015

...OVERVIEW...

THIS APPEARS TO BE ONE OF THOSE PATTERN THAT WHILE LO0KING A BIT
MESSY/DISORGANIZED INITIALLY...A FAIRLY DISTINCT PATTERN ARISES
LATER IN THE FORECASTS AS SMALLER SCALE FEATURES TRANSITION TO A
LARGER SCALE PATTERN.  THE MAIN MESSAGE FROM THE MEDIUM RANGE
FORECAST IS THAT ENHANCED UPPER LEVEL RIDGING AND EAST COAST
TROUGHING IS A FAIRLY RELIABLE SIGNAL DESPITE BEING TOWARD THE END
OF THE FORECAST OR 6 TO 7 DAYS OUT IN THE FUTURE. WHILE AN UPPER
LOW MOVES OVER THE WEST COAST EARLY IN THE FORECAST...IT LIFTS
NORTHEASTWARD AS A SERIES OF SHORTER WAVELENGTH DISTURBANCES REACH
THE NORTHERN ROCKIES BY SATURDAY/DAY 3.  AT THE SAME TIME... A
MEAN CLOSED UPPER HIGH FORMS OVER THE SOUTHEAST US AND THEN
RETROGRADES STEADILY WESTWARD.  AS THE SHORTWAVES OVER THE
NORTHERN ROCKIES CROSS THE NORTHERN PLAINS ON SUNDAY/DAY 6...THEY
BEGIN TO DROP SOUTHEASTWARD TOWARD THE GREAT LAKES BY THE END OF
THE FORECAST AS THE CLOSED UPPER HIGH DEVELOPS INTO A FULL
LATITUDE RIDGE EXTENDING NORTH FROM THE SOUTHWEST ACROSS THE
ROCKIES INTO WEST CENTRAL CANADA.

...GUIDANCE EVALUATION/PREFERENCES...

THE MOST RECENT VERSIONS OF THE EUROPEAN/GEFS AND NAEFS ENSEMBLE
MEANS PAINT A PRETTY CONSISTENT PICTURE AS THE PERIOD STARTS WITH
THE UPPER LOW OVER THE WEST COAST AND A BROAD SOUTHWESTERLY UPPER
FLOW CUTS ACROSS THE SOUTHERN AND EASTERN PORTION OF THE NATION
WITH A MEAN RIDGE OVER THE SOUTHEAST AND A MEAN TROUGH OVER HUDSON
BAY.  THESE THREE ENSEMBLE SYSTEMS CONTINUE TO RESEMBLE EACH OTHER
AS THE UPPER LOW LIFTS NORTHEASTWARD ACROSS NEVADA ON DAY
4/FRIDAY. BY DAY 5/SATURDAY...THE TROUGH LOSES ANY IDENTIFIABLE
CHARACTERISTICS SINCE THIS THESE ARE THE MEANS FLOWS BUT CLEARLY
BY DAY 6/SUNDAY IT BECOMES CLEAR THAT A SIGNIFICANT SHIFT IS
SHOWING UP IN ALL ENSEMBLE SYSTEMS...WITH A BUILDING UPPER HIGH
DRIFTING WESTWARD ACROSS THE SOUTHERN US...A DEVELOPING RIDGE FROM
THE GREAT BASIN/ROCKIES NORTHWARD INTO WESTERN CANADA AND MEAN
TROUGHING OVER THE NORTHERN PLAINS/MISSISSIPPI VALLEY...WITH THE
EUROPEAN ENSEMBLE MEAN SHOWING THE MOST EXTENSIVE TROUGHING.  BY
DAY 7/MONDAY...THE ENSEMBLE MEANS ARE STILL IN LOCK STEP WITH
DEEPENING TROUGH OVER EASTERN CANADA INTO THE NORTHEAST THIRD OF
THE COUNTRY WHILE A HIGH AMPLITUDE UPPER RIDGE EXTENDS FROM THE
SOUTHWEST NORTHWARD INTO WEST CENTRAL CANADA.

OF THE OVERNIGHT OPERATIONAL MODELS...THE UKMET SEEMS THE LARGEST
OUTLIER...THROUGH DAY 5...WITH A STRONG SHORTWAVE TROUGH HEADED
FOR NEW ENGLAND.  THE OOZ CANADIAN IS SOMEWHAT SIMILAR TO THE 06Z
GFS/00Z ECMWF BUT SLIGHTLY SLOWER.  BOTH THE 00Z/06Z AND 00Z ECMWF
APPEAR TO BE MORE SIMILAR TO EACH OTHER AND MORE CONSISTENT WITH
THE SMOOTHED AVERAGES OF THE ENSEMBLE MEANS SO A COMBINATION OF
OPERATIONAL RUNS AND MEANS WERE USED TO GENERATE THE MANUAL
GRAPHICS.  A COMBINATION OF THE 00Z ECMWF AND THE 00Z GFS WERE
HEAVILY WEIGHTED IN THE FIRST TWO DAYS OF THE FORECAST.  BUT EVEN
ON DAYS 5 AND 6...A 60/40 BLEND STILL FAVORED THE OPERATIONAL
GFS/ECMWF SLIGHTLY OVER THE MEANS...SINCE THEY WERE GENERALLY
SIMILAR.  ONLY ON DAY 7 DID THE BLEND REVERT TO 70/30
MEANS/OPERATIONALS DUE TO GREATER SPREAD IN THE OPERATIONAL RUNS
AND THE CONSISTENCY OF THE SIGNAL OBSERVED IN THE ENSEMBLE MEANS.

CONTINUITY HAS BEEN GOOD WITH THE IDEA OF PERSISTENT TROUGHING OFF
THE WEST COAST IN THE WAKE OF THE CALIFORNIA UPPER LOW.  HOWEVER
MODELS/ENSEMBLE MEANS HAVE BEEN SHOWING SOME DAY TO DAY
OSCILLATION IN DEPTH.  TRENDS OVER THE PAST 24 HRS HAVE BEEN
SOMEWHAT DEEPER IN CONTRAST TO THE OPPOSITE TREND SEEN OVER THE
DAY BEFORE.

...SENSIBLE WEATHER HIGHLIGHTS...

THE POTENTIAL EXISTS FOR ONE OR MORE EPISODES OF HEAVY
SHOWERS/THUNDERSTORMS AT SOME LOCATIONS WITHIN AN AREA FROM THE
NORTHERN PLAINS ACROSS THE MID-UPPER MISSISSIPPI VALLEY... GREAT
LAKES/OHIO VALLEY/TENNESSEE VALLEY... AND THE MID ATLANTIC STATES.
 INITIAL FOCUS SHOULD BE ALONG A WEAK FRONTAL SYSTEM SPANNING
KANSAS ACROSS THE MISSISSIPPI AND OHIO VALLEYS...WITH A POSSIBLE
SHORTWAVE ENHANCING RAINFALL AMOUNTS.

THE LIFTING OF THE CALIFORNIA LOW ACROSS THE NORTHWEST AND THEN
ITS PROGRESSION EASTWARD AND SOUTHEASTWARD WOULD ALSO BE ANOTHER
SOURCE FOR ENHANCED PRECIPITATION WITH DIURNAL ENHANCEMENT OF THE
CONVECTION.

THE INTERIOR NORTHWEST SHOULD FINALLY SEE A PERIOD OF COOLING
AFTER THURSDAY... STABILIZING WITHIN A FEW DEGREES OF NORMAL.
OTHERWISE BELOW NORMAL HIGHS SHOULD PREVAIL OVER THE WEST WITH
SOME MODERATION LATE WEEKEND/EARLY NEXT WEEK.  FARTHER EASTWARD
TEMPERATURES WILL DEPEND TO SOME EXTENT ON TIMING OF
CLOUDS/RAINFALL.  TENDENCY SHOULD BE TOWARD BELOW NORMAL READINGS
NRN-CNTRL AREAS THU AND THEN NEAR TO SLIGHTLY ABOVE NORMAL BEFORE
TRENDING DOWN AGAIN NEAR THE LATE PERIOD MIDWEST/GRTLKS SYSTEM.
RIDGING ALOFT SHOULD PROMOTE ABOVE NORMAL TEMPS ESPECIALLY OVER
THE SOUTHEAST BUT GRADUALLY SPREADING WESTWARD WITH TIME
CORRESPONDING TO LIKELY MOVEMENT AND DEVELOPMENT OF THE WESTERN
RIDGE LATE IN THE FORECAST.

KOCIN

$$





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