Prognostic Meteorological Discussion
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FXUS10 KWNH 221703
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
102 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 NAM/GFS ALONG WITH PRELIMINARY
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 MORNING 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: BLEND OF THE 12Z GFS WITH THE 00Z CMC/ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW 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 CYLONIC CIRCULATION
IS FORECAST TO THEN RETROGRADE WESTWARD CROSSING NORTHERN FL LATER
IN THE WEEKEND. THERE ARE SOME UNCERTAINTIES IN THE POSITION OF
THIS SYSTEM WITH THE 12Z NAM DISPLACED SOUTHWARD MOVING THROUGH
SOUTH FL/FL KEYS. ON THE OTHER SIDE OF THE SPECTRUM IS THE 00Z
UKMET WHICH FAVORS A TRACK TOWARD SAVANNAH GA. GIVEN THE
DEVELOPING SPREAD...FEEL MOST COMFORTABLE FOLLOWING THE CENTER OF
THE SPREAD WHICH CONSISTS OF THE 12Z GFS AND 00Z CMC/ECMWF.


...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/00Z 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. UNTIL THE MODELS
COME INTO BETTER AGREEMENT...WPC WILL 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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