Prognostic Meteorological Discussion
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FXUS10 KWNH 221839
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT FRI JUL 22 2016

VALID JUL 22/1200 UTC THRU JUL 26/0000 UTC

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

...AN EVALUATION OF THE 12Z MODEL GUIDANCE ALONG WITH FINAL
PREFERENCES/FORECAST CONFIDENCE...


...AMPLIFIED FLOW ACROSS NEW ENGLAND/ASSOCIATED FRONTAL PASSAGE ON
SATURDAY...

PRELIMINARY PREFERENCE: A NON-12Z NAM MODEL COMPROMISE
FORECAST CONFIDENCE: ABOVE AVERAGE

WATER VAPOR IMAGERY THIS AFTERNOON SHOWED AN ACTIVE NORTHERN
STREAM WITH A PAIR OF SHORTWAVES MOVING THROUGH SOUTHERN
QUEBEC/SOUTHERN ONTARIO...RESPECTIVELY. EACH OF THESE FEATURES
SHOULD SKIRT UPPER NEW ENGLAND DURING THE NEXT 12 TO 24 HOURS
BEFORE THE MORE PROMINENT SYSTEM CROSSES THE NORTHEASTERN U.S. ON
SATURDAY EVENING. RELATIVE TO OTHER AVAILABLE GUIDANCE...THE 12Z
NAM IS MUCH SLOWER TRACKING THIS FEATURE THROUGH NEW ENGLAND.
ADDITIONAL DIFFERENCES EMERGE BUT THEY SEEM TO OCCUR ONCE THE
LONGWAVE TROUGH EXISTS THE COAST. A NON-12Z NAM MODEL COMPROMISE
APPEARS TO BE THE BEST COURSE OF ACTION HERE.


...CLOSED UPPER LOW RETROGRADING TOWARD NORTHERN FL BY MIDDAY
SUNDAY...

PRELIMINARY PREFERENCE: A NON-12Z NAM MODEL COMPROMISE
FORECAST CONFIDENCE: AVERAGE

AN ELONGATED UPPER TROUGH LINGERING WELL OFF THE CAROLINA COAST
CONTINUES TO BE A FOCUS FOR SHOWERS/THUNDERSTORMS IN THE OFFSHORE
WATERS. THIS FEATURE WILL GRADUALLY NOSE SOUTHWARD AND CLOSE OFF
NORTH OF THE BAHAMAS BY SATURDAY MORNING. THE CYCLONIC CIRCULATION
IS FORECAST TO THEN RETROGRADE WESTWARD CROSSING NORTHERN FL LATER
IN THE WEEKEND. THERE ARE SOME UNCERTAINTIES IN THE POSITION OF
THIS SYSTEM ALTHOUGH THEY HAVE DECREASED AFTER EVALUATING ALL OF
THE 12Z MODELS. THE 12Z NAM CONTINUES TO BE DISPLACED SOUTHWARD
MOVING THE SYSTEM THROUGH SOUTH FL/FL KEYS. MEANWHILE...THE 12Z
UKMET ADJUSTED ITS FORECAST BETTER JOINING THE CLUSTER OVER THE FL
PANHANDLE. WILL SHIFT THE PREFERENCE TO ACCOMMODATE THESE CHANGES
FAVORING A NON-12Z NAM MODEL COMPROMISE AND RAISE THE CONFIDENCE
ACCORDINGLY.


...PROGRESSIVE HEIGHT FALLS MOVING FROM THE PACIFIC NORTHWEST TO
SOUTHERN MANITOBA...
...QUICK-MOVING COLD FRONT CROSSING THE NORTHERN TIER...

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

A WELL-DEFINED SHORTWAVE CURRENTLY PRODUCING NUMEROUS SHOWERS OVER
SECTIONS OF WA WILL QUICKLY RACE EASTWARD REACHING THE
SASKATCHEWAN/MANITOBA BORDER BY 24/0000Z. THE PATTERN IS WELL
AGREED UPON AS A PAIR OF SURFACE LOWS MOVE THROUGH THE
U.S./CANADIAN GREAT PLAINS THIS WEEKEND. DIFFERENCES GROW AS THE
UPPER TROUGH/ASSOCIATED SURFACE BOUNDARY ACCELERATE EASTWARD WITH
TIMING DISPARITIES BETWEEN THE GFS/ECMWF CAMPS. LITTLE CHANGE WAS
NOTED BETWEEN THESE TWO SOLUTIONS DURING THE 12Z MODEL CYCLE.
OVERALL...UNTIL THE MODELS COME INTO BETTER AGREEMENT...WPC WILL
CONTINUE TO SPLIT THE DIFFERENCE BETWEEN THESE TWO CAMPS.


...RESIDUAL TROUGHING OVER THE CENTRAL GREAT BASIN LATE IN THE
PERIOD...

PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

IN THE WAKE OF THE SYSTEM TRACKING ALONG SOUTHERN PORTIONS OF
SASKATCHEWAN/MANITOBA...A BROAD BUT WEAK LONGWAVE TROUGH LINGERS
ACROSS THE CENTRAL GREAT BASIN. THERE ARE SUBTLE DIFFERENCES AMONG
THE SOLUTIONS BUT SUCH UNCERTAINTIES HAVE DECREASED RELATIVE TO
YESTERDAY. WITH THAT SAID...A GENERAL MODEL COMPROMISE IS A
REASONABLE PATH.


RUBIN-OSTER


...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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