Prognostic Meteorological Discussion
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000
FXUS10 KWNH 260720
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
320 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 MODEL EVALUATION...WITH FINAL 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 IS TOWARD THE FASTER SIDE WITH AN 850 MB CIRCULATION NEAR
THE SOUTHEAST COAST WHILE THE 00Z GFS IS SLOWER WITH THIS FEATURE.
THE 00Z ECMWF/UKMET/CMC AND ENSEMBLE MEANS SPLIT THE DIFFERENCE
BETWEEN THE NAM AND GFS. 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: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW SIMILARLY WITH THE UPPER LOW AS IT MOVES EAST AND
WEAKENS...AND HAVE COME INTO BETTER AGREEMENT WITH RENEWED ENERGY
DIGGING SOUTH AND DEVELOPING ANOTHER CLOSED LOW CENTER BY SAT
MORNING TO THE NORTH OF MAINE. GIVEN THE FAIRLY GOOD MODEL
AGREEMENT...A GENERAL MODEL BLEND IS PREFERRED FOR THE FINAL
PREFERENCE 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: 00Z GFS/ECMWF/UKMET BLEND...LESS WEIGHT TO 00Z GFS BY
12Z/29
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 BUT THE 00Z UKMET SPED UP
FROM ITS PREVIOUSLY SLOWER 12Z RUN. HOWEVER...THIS FEATURE 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 00Z CMC REMAINS 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/ECMWF/UKMET GIVEN THE 00Z NAM APPEARS A BIT
SLOWER THAN THE BETTER ENSEMBLE CLUSTERING...AND THE 00Z 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. THE 00Z ECMWF NUDGED NORTH A BIT WITH THE SURFACE LOW BY
12Z/29 BUT THE 00Z UKMET IS FARTHER SOUTH. THEREFORE...A BLEND OF
THE GFS/ECMWF/UKMET IS PREFERRED BUT WITH MORE WEIGHT TOWARD THE
SOUTHERN 12Z ECMWF/00Z UKMET FOR SAT MORNING.


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

THE 00Z DETERMINISTIC MODELS HAVE COME INTO BETTER AGREEMENT WITH
THE UPPER TROUGH/VORTICITY MAX BY THU MORNING OVER THE WESTERN
U.S.  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. ONLY THE 00Z UKMET APPEARS DIFFERENT HERE BY
12Z/29 WITH A SLOWER PROGRESSION COMPARED TO THE OTHERWISE GOOD
MODEL 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/00Z 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 00Z UKMET IS FLATTEST FOLLOWED BY
THE 00Z CMC. THE ECMWF IS IN THE MIDDLE BUT GIVEN THE 12Z ECMWF
MEAN IS A BIT FLATTER THAN THE 12Z/00Z 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 OR 00Z ECMWF IS PREFERRED WITH THE 00Z ECMWF TRENDING
SLIGHTLY DEEPER COMPARED TO ITS 12Z RUN.


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

OTTO

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