Prognostic Meteorological Discussion
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000
FXUS10 KWNH 291845
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EST THU JAN 29 2015

VALID JAN 29/1200 UTC THRU FEB 02/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/GEM AND THE
ECMWF


...PAIR OF SHORTWAVES CROSSING THE OH VALLEY...
...NEGATIVELY TILTING TROUGH IMPACTING THE NORTHEAST...
...SURFACE LOWS PHASING OVER NEW ENGLAND...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE LATEST WATER VAPOR IMAGERY CONTINUES TO SHOW A PAIR OF
DISTINCT SHORTWAVE IMPULSES TRACKING THROUGH THE MID MS VALLEY AND
TOWARD THE OH VALLEY. THE CORRESPONDING SURFACE WAVES WILL BOTH
MIGRATE EASTWARD THROUGH THE OH VALLEY AND LOWER GREAT LAKES
REGION THROUGH TONIGHT. MEANWHILE...WITH THE INTRUSION OF
ADDITIONAL NORTHERN STREAM ENERGY FROM THE GREAT LAKES
REGION...THE GUIDANCE DEPICTS A LARGER SCALE TROUGH AMPLIFYING AND
GOING NEGATIVE TILT OVER NEW ENGLAND FRI...WITH A CLOSED LOW THEN
DEVELOPING JUST OFFSHORE SOUTHERN NEW ENGLAND BY FRI NIGHT. THE
STRONG HEIGHT FALLS/DYNAMICS WILL ALLOW SURFACE LOW PRESSURE TO
REDEVELOP NEAR LONG ISLAND BY FRI MORNING AND THEN INTENSIFY INTO
THE GULF OF MAINE BY EARLY SAT.

THE 12Z NAM IS RELATIVELY STRONGER COMPARED TO THE 12Z GFS/12Z
ECMWF AND 12Z GEM. THE NAM TUCKS LOW PRESSURE IN JUST A LITTLE
CLOSER TO THE COAST OF MAINE LATER FRI NIGHT AND EARLY SAT AS A
RESULT VERSUS THE GFS/ECMWF AND GEM. THE 12Z UKMET ALSO TENDS TO
TUCK ITS SURFACE LOW IN CLOSER TO THE COAST. THE NEW GFS IS IN
BETTER AGREEMENT WITH THE 00Z ECENS AND 00Z GEM ENSEMBLE LOW
CLUSTERS VERSUS THE 00Z GEFS MEMBERS. THEREFORE...THERE IS A
STRONGER SIGNAL FOR THE LOW CENTER DEVELOPING OFFSHORE NEW ENGLAND
TO BE JUST A TAD FARTHER OFFSHORE VERSUS THE NAM/UKMET OUTPUT.
WILL FAVOR A BLEND OF THE 12Z GFS AND 12Z ECMWF AS A RESULT WHICH
HAVE THE STRONGER ENSEMBLE CLUSTERING SUPPORT.


...BROAD TROUGH/CLOSED LOW IMPACTING THE SOUTHWEST/FOUR CORNERS
REGION...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: ABOVE AVERAGE

ALL OF THE MODELS SHOW AN ELONGATED N/S TROUGH AXIS OFFSHORE
CALIFORNIA WHICH STRETCHES DOWN INTO THE SUBTROPICS WEST OF THE
BAJA PENINSULA. THIS ENERGY IS FORECAST TO LIFT EAST-NORTHEAST AND
DEEPEN INTO A FAIRLY BROAD CLOSED UPPER LOW BY MIDDAY FRI OVER
SOUTHERN CA. ON SAT AND SUN...THE ENERGY THEN GETS SUPPRESSED
SOUTHWARD INTO NORTHWEST MEXICO AND THE ADJACENT BAJA PENINSULA IN
RESPONSE TO STRONG NORTHWESTERLY NORTHERN STREAM FLOW OVER THE
CENTRAL AND NORTHERN ROCKIES. THE GLOBAL MODELS ARE IN GOOD
AGREEMENT ON THE LARGER SCALE WITH THE EVOLUTION OF THESE HEIGHT
FALLS...HOWEVER BY THE END OF THE PERIOD THE 12Z ECMWF AND 12Z GEM
PLACE THEIR CLOSED LOW A BIT EAST OF THE 12Z GFS AND 12Z UKMET.
INTERESTINGLY THE 12Z GEFS MEAN FAVORS THE EASTWARD CAMP OF THE
ECMWF/GEM...WHEREAS THE 00Z ECENS MEAN FAVORS THE FARTHER WEST
GFS/UKMET CAMP. WILL SUGGEST MAINTAINING A COMPROMISE BETWEEN THE
GFS AND ECMWF.


...HEIGHT FALLS DIGGING INTO THE CENTRAL U.S. SAT AND SUN...
...FRONTAL ZONE SINKING SOUTHWARD...
...LOW PRESSURE DEVELOPING OVER THE LOWER TO MID MS VALLEY...

PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF
CONFIDENCE: AVERAGE

THE MODELS SHOW AN AREA OF HEIGHT FALLS DIGGING THROUGH THE
NORTHERN HIGH PLAINS BY MIDDAY SAT WHICH BEGINS TO AMPLIFY A BIT
MORE THROUGH SUN INTO THE MIDWEST. THIS WILL SEND A COLD FRONT
SOUTHEAST ACROSS THE REGION AS WELL. LOW PRESSURE MEANWHILE IS
EXPECTED TO DEVELOP ALONG THE SOUTHERN PORTION OF THIS BOUNDARY
EITHER OVER THE LOWER OR MID MS VALLEY.

THE 12Z UKMET CONTINUES ITS THEME OF PREVIOUS RUNS IN BEING MORE
AMPLIFIED...BUT IT HAS TRENDED A BIT FLATTER...AND TOWARD THE
FLATTER GLOBAL MODEL CONSENSUS. THE 12Z GFS AND 12Z ECMWF ARE VERY
WELL CLUSTERED AROUND A FLATTER SHORTWAVE THAT DIGS SOUTHEAST
TOWARD THE MID MS AND LOWER OH VALLEYS ON SUN. THE 12Z NAM AND
ESPECIALLY THE 12Z GEM ARE A BIT SHARPER AND SLOWER...BUT NO WHERE
AS STRONG AS THE UKMET. THE WELL CLUSTERED GFS/ECMWF CAMP DEVELOP
LOW PRESSURE OVER THE LOWER MS VALLEY BY EARLY SUN WHICH MOVES TO
THE TN VALLEY LATE IN THE DAY. THE NAM HAS THE SAME IDEA...EXCEPT
IT IS STRONGER/SLOWER LOW AND A BIT NORTH OF THE GFS/ECMWF LOW
TRACKS. THE UKMET FOCUSES A DEEPER LOW MUCH FARTHER NORTH FROM THE
MID MS VALLEY TOT HE UPPER OH VALLEY. THE GEM IS SO SLOW WITH THE
ENERGY ALOFT...THAT IT ONLY HAS A WEAK SURFACE REFLECTION BY LATE
SUN OVER THE LOWER MS VALLEY. THE 12Z GEFS MEAN FAVORS A SLIGHTLY
FASTER VERSION OF THE GFS. BASED ON SUCH STRONG AGREEMENT AND WITH
SUPPORTING TRENDS TOWARD A RELATIVELY FLATTER EVOLUTION...A BLEND
OF THE GFS AND ECMWF WILL BE PREFERRED.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

ORRISON

$$





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