Prognostic Meteorological Discussion
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000
FXUS10 KWNH 270602
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 AM EDT WED JUL 27 2016

VALID JUL 27/0000 UTC THRU JUL 30/1200 UTC

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

00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS


...MULTIPLE SHORTWAVES MOVING EAST OVER THE SOUTHWEST
RIDGE...DROPPING SOUTHEAST INTO A DEVELOPING EAST COAST TROUGH...
...SHORTWAVE ENERGY MOVING NORTH THROUGH THE LOWER MS
VALLEY...BECOMING ABSORBED INTO THE EAST COAST TROUGH...

PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

A COMPLEX PATTERN OVER THE CONUS FOR THE SHORT TERM PERIOD...WITH
THE FORECAST AGAIN EXPECTED TO BE INFLUENCED BY SMALL SCALE
CONVECTIVE FEATURES/VORTS...WHICH WILL BE DIFFICULT TO TRACK. ON
THE LARGE SCALE THERE IS PRETTY GOOD AGREEMENT AMONGST THE
MODELS...WITH A SOUTHWESTERN U.S. UPPER RIDGE...AND A DEVELOPING
BROAD TROUGH OVER THE EASTERN HALF OF THE NATION. HELPING TO
DEVELOP THIS TROUGHING WILL BE MULTIPLE SHORTWAVES RIDING UP AND
OVER THE RIDGE AND DIGGING SOUTHEAST ACROSS THE MS VALLEY AND INTO
THE EAST. THERE IS REASONABLY GOOD AGREEMENT AS WELL THAT THE MID
LEVEL TROUGH/CLOSED LOW OVER THE LOWER MS VALLEY WILL BE PULLED
NORTH AND GRADUALLY ABSORBED INTO THE TROUGH.

THE DISAGREEMENT COMES FROM THE TIMING/STRENGTH OF TWO SHORTWAVES
MOVING OVER THE RIDGE ACROSS THE PLAINS AND ALSO THE LOWER MS
VALLEY ENERGY...AND HOW THESE SYSTEMS INTERACT WITH EACH OTHER.
DIFFERENCES WITH THE FIRST SHORTWAVE DROPPING SOUTHEAST ACROSS THE
NORTHERN PLAINS AND MIDWEST WED AND THURS ARE FAIRLY
MINOR...ALTHOUGH THE 00Z NAM DOES HAVE SLIGHTLY MORE AMPLIFICATION
THAN THE GLOBAL MODELS. THIS ENERGY IS EXPECTED TO ABSORB THE MID
LEVEL LOW/TROUGH OVER THE LOWER MS VALLEY AND PULL THE REMNANT
ENERGY NORTHEAST INTO THE OH VALLEY AND MID-ATLANTIC REGION
THROUGH FRI AND THIS IS WHEN MORE SUBSTANTIAL MODEL DIFFERENCES
ARE NOTED. GRADUALLY THE 12Z UKMET AND 12Z CMC LAG THE 00Z NAM/00Z
GFS AND TO A LESSER EXTENT THE 12Z ECMWF. A WAVE OF LOW PRESSURE
WILL DEVELOP ALONG A FRONT AND WILL TRAVERSE THE OH
VALLEY/MID-ATLANTIC REGION THURS AND FRI..AND THE SAME
CORRESPONDING TIMING DIFFERENCES ARE NOTED HERE TOO WITH THE
NAM/GFS SOLUTIONS FASTER AND THE UKMET/CMC AND ECMWF ALL SLOWER.

UPSTREAM A SECOND SHORTWAVE WILL BE DIGGING DOWN FROM THE PLAINS
AND ACROSS THE MIDWEST FRI AND SAT. THE 12Z CMC AND 00Z NAM ARE
BOTH APPEARING TO BE TOO DEEP AND A LITTLE TOO SLOW. IN FACT...THE
00Z NAM DEVELOPS A SECOND AND WELL-DEFINED SURFACE WAVE OVER THE
MIDWEST BY SAT WHICH IS NOT SUPPORTED BY ANY MODEL. THE 00Z
GFS/12Z UKMET AND 12Z ECMWF ARE ALL A LITTLE MORE PROGRESSIVE WITH
THE ENERGY AND HAVE MUCH WEAKER SURFACE REFLECTIONS. ALONG THE
EAST COAST BY SAT...THE 00Z GFS AND 12Z ECMWF TEND TO COME INTO
BETTER AGREEMENT WITH THEIR SURFACE WAVE DETAILS. BY THEN...THE
12Z UKMET AND 00Z NAM BOTH APPEAR TO BE TOO STRONG WITH THEIR
SURFACE WAVES. BASED ON THE LATEST TRENDS AND CLUSTERING SEEN WITH
THE GFS AND ECMWF...ALONG WITH RELATIVELY GOOD ENSEMBLE
SUPPORT...A BLEND OF THE 00Z GFS AND 12Z ECMWF WILL BE PREFERRED.


...SHORTWAVE TROUGH AIMING FOR THE NORTHWEST BY SAT...

PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE GUIDANCE HAS A SHORTWAVE TROUGH CROSSING THE GULF OF AK AND
DROPPING SOUTHEAST ACROSS BRITISH COLUMBIA BY FRI..WITH THE ENERGY
CLIPPING THE NORTHWEST U.S. ON SAT. THE 12Z UKMET APPEARS TO BE A
LITTLE TOO PROGRESSIVE WITH THIS SYSTEM. THE REMAINING MODELS ARE
CLUSTERED A LITTLE SLOWER...WITH THE BEST OVERALL CLUSTERING
RESIDING MORE WITH THE 00Z GFS AND 12Z ECMWF. A BLEND OF THE TWO
LATTER SOLUTIONS WILL BE PREFERRED.

ORRISON

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

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

$$





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