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Model Diagnostics Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1658Z Apr 21, 2015)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1258 PM EDT TUE APR 21 2015

VALID APR 21/1200 UTC THRU APR 25/0000 UTC

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

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...

THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z
NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS.


...DEEP CYCLONIC FLOW AFFECTING THE GREAT LAKES/NORTHEASTERN U.S...
...ASSOCIATED SURFACE CYCLONES/SECONDARY COLD FRONT...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

WATER VAPOR IMAGERY THIS MORNING SHOWED AN EXPANSIVE UPPER LOW
SPINNING OVER THE UPPER GREAT LAKES WITH THE CYCLONIC CIRCULATION
EXTENDING FROM THE GREAT PLAINS TO THE EAST COAST. OVER THE COURSE
OF THE NEXT COUPLE OF DAYS...THIS VORTEX SHOULD SLOWLY LIFT TO THE
NORTH AND EAST BECOMING CENTERED OVER THE ONTARIO/QUEBEC BORDER BY
23/1200Z. A SERIES OF SHORTWAVES WILL CONTINUE TO SPIRAL AROUND IN
A COUNTERCLOCKWISE FASHION CARRYING ADDITIONAL THREATS FOR
PRECIPITATION ACROSS THE REGION. CONSIDERING SOME OF THE AVAILABLE
GUIDANCE...THE 12Z/06Z GFS CONTINUE TO BE DISPLACED TO THE
NORTHWEST LEADING TO A DIFFERENT IN THE POSITION OF ITS SURFACE
LOW AND MID-LEVEL CYCLONE CENTER. THE 12Z NAM/00Z ECMWF FORM A
SOLUTION CLOSER TO WHAT THE ENSEMBLE MEANS ARE SHOWING SO THE
RECOMMENDATION IS A BLEND OF THE 12Z NAM/00Z ECMWF.


...INITIAL UPPER LOW SPINNING ACROSS SOUTHERN CA...
...BROAD UPPER TROF SLIDING FROM THE SOUTHWESTERN U.S. TOWARD THE
SOUTHERN HIGH PLAINS...

PRELIMINARY PREFERENCE: MODEL COMPROMISE BETWEEN THE 12Z NAM/GFS
WITH THE 00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

THE TYPICAL SPRING BLOCKY PATTERN CONTINUES AS A PAIR OF CLOSED
LOWS AFFECT THE SOUTHWESTERN U.S. THE INITIAL COMPACT CIRCULATION
AFFECTING SOUTHERN CA SHOULD SLOWLY DRIFT NORTHWARD TOWARD
SOUTHERN NV BEFORE GIVING WAY TO A BROADER TROF MOVING IN FROM THE
EASTERN PACIFIC. AT FIRST THERE IS QUITE A BIT OF VARIABILITY IN
THE HEIGHT FIELDS AMONG THE MODELS BUT THIS DIMINISHES ONCE THE
TROF BEGINS TO ACCELERATE EASTWARD. RELATIVE TO YESTERDAY THE
GUIDANCE AS A WHOLE SEEMS TO HAVE A BETTER HANDLE ON THIS
EVOLUTION. MUCH OF THE UNCERTAINTY SEEMS TO DO WITH THE WEST-EAST
PLACEMENT OF A FRONTAL ZONE STRETCHING FROM SOUTHERN PLAINS ALONG
THE GULF COAST TO FL. THE 12Z GFS RECENTLY JOINED THE 00Z CMC IN
DEVELOPING A SURFACE LOW ACROSS THE FL PANHANDLE BY 24/0000Z WITH
VERY LITTLE SUPPORT NOTED IN THE ENSEMBLE LOW PLOTS. HOWEVER...THE
12Z GFS DOES APPEAR REASONABLE WITH THE PATTERN UPSTREAM IN TERMS
OF THE TROF PLACEMENT AND LOW DEVELOPMENT OFF THE HIGH PLAINS BY
FRIDAY EVENING. AT THIS TIME PREFER TO UTILIZE SOME FORM OF
COMPROMISE BETWEEN THE 12Z NAM/GFS WITH THE 00Z ECMWF.


...SECONDARY SHORTWAVE TRACKING THROUGH SOUTHERN CA BY FRIDAY...

PRELIMINARY PREFERENCE: MODEL COMPROMISE BETWEEN THE 12Z NAM/GFS
WITH THE 00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

IN THE WAKE OF THE INITIAL HEIGHT FALLS MOVING FROM THE DESERT
SOUTHWEST TO THE GREAT PLAINS WILL BE SECONDARY SHORTWAVE MOVING
TOWARD SOUTHERN CA BY 25/0000Z. THE 00Z UKMET APPEARS TO BE TOO
QUICK HERE SO WILL LEAN ON A SIMILAR PREFERENCE TO WHAT WAS
RECOMMENDED DOWNSTREAM. THAT IS A MODEL COMPROMISE BETWEEN THE 12Z
NAM/GFS AND 00Z ECMWF.


...MID-LEVEL HEIGHT FALLS MOVING ACROSS THE PACIFIC NORTHWEST
TONIGHT...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: AVERAGE

A STRETCHED OUT BAND OF VORTICITY CURRENTLY EXTENDING ACROSS THE
NORTHEAST PACIFIC WILL REACH THE WA COAST BY LATER TONIGHT. SOME
OF THE MODELS CARRY THIS SYSTEM AS A COMPACT UPPER LOW WHICH MAY
BE SLOW MOVING AT TIMES. THE 06Z GFS HAD BEEN ONE OF THE SLOWER
SOLUTIONS AS IT CLOSED OFF THE UPPER CENTER. HOWEVER...THE 12Z
CYCLE HAS TRENDED QUICKER LIKE OTHER MODELS FEATURING MORE OF AN
OPEN WAVE SOLUTION. BY 23/1200Z...THE 12Z NAM/GFS AND 00Z CMC
CLUSTER BUT ARE A BIT SLOWER THAN THE QUICKER 00Z ECMWF. AS THE
GAP BETWEEN THE MODELS HAS DECREASED...WILL JUST SPLIT THE
DIFFERENCE AND RECOMMEND A BLEND OF THE 12Z GFS/00Z ECMWF.


...STRONG CLOSED LOW DESCENDING FROM THE NORTHEAST PACIFIC ON
THURSDAY/FRIDAY...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

A BROAD UPPER LOW WILL SLOWLY WORK ITS WAY DOWN FROM THE NORTHEAST
PACIFIC. THERE ARE A NUMBER OF SOLUTIONS PRESENTED HERE WITH THE
ENSEMBLE SPAGHETTI PLOTS DEPICTING QUITE A BIT OF SCATTER. THE 00Z
ECMWF ENSEMBLES ON THE 540-DM PLOT CONTINUE TO SUGGEST A MORE
SOUTHWARD DISPLACED SOLUTION RELATIVE TO THE 00Z GEFS/CMC ENSEMBLE
MEMBERS. MOST RECENTLY THE 12Z GFS HAS TAKEN A SOUTHWARD TREND
TOWARD THIS ECMWF CAMP. GIVEN THE UNCERTAINTY AT HAND AND THE FACT
THE 12Z GFS HAS MADE THIS MOVE...WILL TAKE A BLEND OF THESE TWO
AND REASSESS AS NEWER GUIDANCE ARRIVES. THE OFFICIAL
RECOMMENDATION IS A 12Z GFS/00Z ECMWF BLEND BUT WITH SLIGHTLY
BELOW AVERAGE CONFIDENCE.



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