Prognostic Meteorological Discussion
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387
FXUS10 KWNH 260503
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
103 AM EDT WED JUL 26 2017

VALID JUL 26/0000 UTC THRU JUL 29/1200 UTC

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

00Z NAM/GFS EVALUATION...WITH PRELIMINARY PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


...LOW/MID-LEVEL TROUGHING ACROSS THE GULF COAST...
...ENERGY ADVANCING EAST ACROSS GA/SC THROUGH WED/THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THERE ARE SOME MINOR TIMING DIFFERENCES WITH A LOW LEVEL WAVE
WITHIN THE TROUGH AXIS ACROSS THE SRN U.S. BY THU INTO FRI. THE
00Z NAM...12Z ECMWF...12Z CMC ARE A BIT FASTER WHILE THE 00Z
GFS/12Z UKMET A LITTLE SLOWER. THE ENSEMBLE MEANS SPLIT THE
DIFFERENCE...AND GIVEN THE RELATIVELY MINOR PLACEMENT
DIFFERENCE...A GENERAL MODEL COMPROMISE IS PREFERRED WITH THIS
SYSTEM.


...UPPER LOW TRACKING FROM ONTARIO TODAY...TO QUEBEC/NORTHEAST
U.S. THU...
...RENEWED CLOSED MID-LEVEL LOW NORTH OF MAINE BY SAT MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM...00Z GFS...12Z ECMWF BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THE UPPER LOW AS IT MOVES EAST AND
WEAKENS...BUT THERE ARE SOME DIFFERENCES WITH RENEWED ENERGY
DIGGING SOUTH AND DEVELOPING ANOTHER CLOSED LOW CENTER BY SAT
MORNING TO THE NORTH OF MAINE. THE 12Z UKMET/CMC ARE NORTH OF THE
BETTER MODEL CLUSTERING WITH THIS RENEWED CLOSED LOW AND SO THE
GOOD AGREEMENT OF THE 00Z NAM/GFS AND 12Z ECMWF ARE PREFERRED HERE.


...AMPLIFYING TROUGH OVER THE GREAT LAKES/NORTHEAST/MID-ATLANTIC
ON FRI/SAT...
...SURFACE LOW CROSSING THE CENTRAL PLAINS TODAY...REACHING THE
MID-ATLANTIC FOR FRI...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 30% 00Z GFS/70% 12Z ECMWF BLEND
CONFIDENCE: BELOW AVERAGE

REGARDING A 700-500 MB SHORTWAVE...CURRENTLY EJECTING EAST FROM WY
AND FORECAST TO REACH THE MID-MS RIVER VALLEY TONIGHT...THERE ARE
SOME DIFFERENCES WORTH NOTING. THE 00Z NAM REMAINS TOWARD THE
DEEPER SIDE OF THE DETERMINISTIC SPREAD AND THE 12Z UKMET SLOWER
SIDE...BUT THIS IS LIKELY DUE TO CONVECTIVE ENHANCEMENT OVER THE
CNTRL-NRN PLAINS EARLY WED MORNING. CONVECTIVELY GENERATED
PRECIPITATION DETAILS CAN BE FOUND IN THE QPFPFD.

A SURFACE LOW IS FORECAST TO TRACK THE CNTRL PLAINS TODAY AND
REACH THE MID-ATLANTIC REGION FOR FRI...PARTIALLY INFLUENCED BY AN
UPSTREAM MID-LEVEL SHORTWAVE EXPECTED TO CROSS THE UPPER GREAT
LAKES AND DIVE INTO THE NRN MID-ATLANTIC REGION BY SAT MORNING.
THE 12Z CMC IS QUICK TO PULL OUT AHEAD OF THE
DETERMINISTIC/ENSEMBLE GUIDANCE WITH THE 500 MB SHORTWAVE TRACKING
ACROSS THE N-CNTRL U.S. ON THU...LINGERING INTO FRI.  AT THE
SURFACE...THE LATEST ENSEMBLE SCATTER LOW PLOTS SHOW BETTER
AGREEMENT TODAY COMPARED TO YESTERDAY BUT SPREAD REMAINS FAIRLY
LARGE...REDUCING CONFIDENCE. THE PAST 4 CYCLES HAVE SHOWN A STEADY
TREND TO THE SOUTH THOUGH AND THERE IS BETTER CLUSTERING FOR A LOW
TRACK NEAR THE 00Z GFS AND 12Z ECMWF GIVEN THE 00Z NAM AND 12Z
UKMET APPEAR A BIT SLOWER THAN THE BETTER ENSEMBLE
CLUSTERING...AND THE 12Z CMC IS MUCH DEEPER WITH ITS FASTER AND
MORE WRAPPED UP 500 MB LOW OVER OHIO/LOWER MICHIGAN BY FRI
MORNING. THIS CHANGES A BIT BY SAT MORNING...12Z/29...WHEN THE 00Z
GFS ENDS UP TOWARD THE NRN SIDE OF THE LARGE ENSEMBLE SPREAD AND
THE 12Z ECMWF APPEARS CLOSER TO THE MIDDLE. THEREFORE...A BLEND OF
THE GFS/ECMWF IS PREFERRED BUT WITH MORE WEIGHT TOWARD THE 12Z
ECMWF...ESPECIALLY BY SAT MORNING.


...UPPER LOW/TROUGH CURRENTLY OVER NRN CA...SHEARING DOWNSTREAM
OVER THE NORTHERN INTERMOUNTAIN REGION ON THU...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z NAM...00Z GFS...12Z UKMET BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE 12Z ECMWF BEGINS TO OUTPACE THE DETERMINISTIC GUIDANCE WITH
THE UPPER TROUGH/VORTICITY MAX BY THU MORNING OVER THE WESTERN
U.S. AND THIS IS REFLECTED WITH THE 12Z ECMWF MEAN SLOWER THAN THE
DETERMINISTIC RUN. THE WAVE DAMPENS ACROSS THE NRN ROCKIES AND
BECOMES MORE DIFFICULT TO FIND BEYOND 12Z/28 BUT A DEFINED 700 MB
WAVE REMAINS INTO THE NRN PLAINS. THE 12Z CMC DEVELOPS AN
AGGRESSIVE MID-LEVEL VORTICITY MAX OUT AHEAD OF THE DAMPENING CA
WAVE WHICH IS UNSUPPORTED. THEREFORE...THE SIMILAR AND REMAINING
MODELS...00Z NAM...00Z GFS AND 12Z UKMET ARE PREFERRED HERE GIVEN
THEIR AGREEMENT.


...SHORTWAVE ARRIVING ACROSS THE PACIFIC NORTHWEST ON THURS...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.


...MID-LEVEL SHORTWAVE REACHING NEAR THE NRN CALIFORNIA COAST SAT
MORNING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF
CONFIDENCE: AVERAGE

ENSEMBLE SPAGHETTI HEIGHTS SHOW A FAIR AMOUNT OF SPREAD BY 12Z/29
ALONG THE NRN-CA COASTLINE. THE 00Z GFS/NAM SHOW TOWARD THE DEEPER
SIDE OF THE ENSEMBLES WHILE THE 12Z CMC/UKMET ARE FLATTEST. THE
ECMWF IS IN THE MIDDLE BUT GIVEN THE 12Z ECMWF MEAN IS A BIT
FLATTER THAN THE 12Z ECMWF...DO NOT WANT TO GO TOWARD THE DEEPER
SIDE OF THE DETERMINISTIC MODELS LIKE THE 00Z NAM/GFS.
THEREFORE...A COMPROMISE IN THE MIDDLE SIMILAR TO THE 12Z ECMWF IS
PREFERRED.


www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

OTTO

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