Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11

000
FXUS10 KWNH 250431
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1130 PM EST MON NOV 24 2014

VALID NOV 25/0000 UTC THRU NOV 28/1200 UTC

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

00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES

SHORTWAVE TROUGH/LOW PRESSURE TRACKING FROM THE N. PLAINS TO THE
APPALACHIANS TODAY THROUGH WED...

PREFERENCE: 1/2 EACH NAM/GFS
CONFIDENCE: ABOVE AVERAGE

THE NAM AND GFS HAVE TRENDED FASTER AND STRONGER FROM PREVIOUS
RUNS...SHOW GOOD AGREEMENT WITH EACH OTHER...AND ARE FASTER AND
STRONGER THAN THE 12Z ECMWF.  GIVEN THE NAM AND GFS HAVE TRENDED
SIMILARLY AND CLOSE TO EACH OTHER...A BLEND OF THE NAM AND GFS IS
PREFERRED...WHICH ALSO ADDRESSES ANY LINGERING UNCERTAINTY.

LOW PRESSURE TRACKING UP THE EAST COAST TONIGHT THROUGH WED
NIGHT...

PREFERENCE: 1/3 EACH 12Z ECMWF ENSEMBLE MEAN/21Z SREF MEAN/00Z NAM
CONFIDENCE: AVERAGE

CHANGES IN THE LARGE-SCALE DEPICTIONS OF THE 00Z NAM AND GFS
COMPARED TO THEIR 18Z RUNS IS RELATIVELY SMALL.  THUS...THE
LARGE-SCALE PREFERENCES FROM THE DURING THE DAY ON MONDAY ARE
STILL RELEVANT.  THE ONLY CHANGE IS TO ADD THE NAM TO THE
PREFERENCES SINCE IT SETTLES NEAR THE MIDDLE OF THE SOLUTION
ENVELOPE FOR THE LOW TRACK AND DEPTH.  THE GFS LIES TOWARD THE
NORTHEAST SIDE OF THE GUIDANCE.

ONE NOTE ABOUT THE NAM WORTH FORWARDING IS THAT FROM 00-12Z
WED...THE NAM APPEARS TO SUFFER FROM GRID-SCALE FEEDBACK OVER THE
SOUTHERN APPALACHIANS...WHICH ULTIMATELY RESOLVES ITSELF.
HOWEVER...ITS RESULTING THERMAL PROFILES AND QPF OVER THE SOUTHERN
APPALACHIANS MAY BE UNRELIABLE.  THIS OBSERVATION IS SUPPORTED BY
THE NAM CONUSNEST WHICH SHOWS NO PRECIPITATION DEVELOPING.

REGARDING LOWER LEVEL THERMAL PROFILES WEST OF THE LOW...THE NAM
MAY BE MORE USABLE THAN THE GFS SINCE THE GFS LIES TOWARD THE
NORTHEASTERN SIDE OF THE GUIDANCE WITH ITS LOW TRACK AND MAY
PRODUCE DECOUPLED FLOW INLAND TOO SOON AND FOR TOO LONG.  ANOTHER
FACTOR WHICH INTRODUCES SOME UNCERTAINTY REGARDING TEMPERATURES IS
THE RECENT WARM PERIOD AND RESULTING WARM GROUND THAT COULD
RADIATE SUFFICIENTLY WARM AIR TO COUPLE WITH THE FLOW JUST ABOVE
THE SURFACE.  THE NAM AT TIMES FORECASTS 925 MB FLOW OF 30 TO 50
KNOTS....WHICH COULD EASILY COUPLE WITH THE WINDS NEAR THE SURFACE
AND PRODUCE A SUFFICIENTLY DEEP MIXED LAYER HELPING TO KEEP THE
AIR NEAR THE GROUND WARMER THAN DEPICTED BY GUIDANCE.  MODELS
USUALLY HAVE A VERY DIFFICULT TIME RESOLVING THE BOUNDARY LAYER
STRUCTURE.

SHORTWAVE TROUGH BEGINNING TO INFLUENCE THE PACIFIC NORTHWEST
THURSDAY...

PREFERENCE: GFS OR ECMWF
CONFIDENCE: HIGH

THE NAM IS NEARLY AN OUTLIER WITH ALLOWING A LARGE PORTION OF THIS
TROUGH TO BEGIN MOVING ASHORE BY EARLY THURSDAY.  THE PRIMARY
RESULT EARLY IN THE DAY IS TO BUILD THE SHORTWAVE RIDGE AND SHIFT
THE MOST FAVORABLE CONDITIONS FOR ASCENT FARTHER NORTH.  GIVEN A
LACK OF SUPPORT FOR THIS SOLUTION...THE RECOMMENDATION IS FOR THE
GFS OR ECMWF.

...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...
...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

JAMES

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.