815  
FXUS10 KWNH 281633  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1133 AM EST SUN JAN 28 2018  
 
VALID JAN 28/1200 UTC THRU FEB 1/0000 UTC  
   
.SEE NOUS42 KWNO (ADMNFD) FOR UPPER AIR INGEST STATUS
 
 
12Z INITIAL MODEL EVALUATION WITH PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
MODEL INITIALIZATION ERRORS APPEAR NEGLIGIBLE  
 
***EVOLVING LONG WAVE TROUGH OVER THE EASTERN U.S. BY TUESDAY***  
***SURFACE LOW EVOLUTION OFFSHORE THE MID-ATLANTIC/NEW ENGLAND***  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF/ENSEMBLE MEANS  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
A RELATIVELY WEAK SOUTHERN STREAM SHORTWAVE CURRENTLY CROSSING THE  
NORTHERN GULF OF MEXICO IS SUPPORTING A DEVELOPING SURFACE LOW  
SOUTH OF THE FLORIDA PANHANDLE, ALONG WITH AN INVERTED SURFACE  
TROUGH EXTENDING NORTHWARD ACROSS THE SOUTHEAST STATES. FARTHER  
TO THE NORTH, THERE WILL BE AN INTRUSION OF NORTHERN STREAM  
SHORTWAVE ENERGY CROSSING THE MIDWEST THAT WILL BE DIGGING  
SOUTHEAST ACROSS THE OHIO AND TENNESSEE VALLEYS THROUGH MONDAY.  
THESE TWO FEATURES WILL ATTEMPT TO PHASE ALONG THE EAST COAST ON  
MONDAY AND WILL LIKELY LEAD TO THE DEVELOPMENT OF A LONG WAVE  
TROUGH OVER THE EASTERN U.S. THAT WILL TAKE ON A NEUTRAL TO  
SLIGHTLY NEGATIVE TILT. THE SURFACE LOW OVER THE GULF OF MEXICO  
IS FORECAST TO LIFT NORTHEAST AND UNDERGO INTENSIFICATION NEAR THE  
SOUTHEAST U.S. COAST SUNDAY NIGHT AND THEN MOVE OFFSHORE THE  
DELMARVA BEFORE THEN INTENSIFYING SOUTHEAST OF NEW ENGLAND MONDAY  
NIGHT.  
 
THIS IS THE FEATURE WITH THE GREATEST AMOUNT OF MODEL SPREAD  
DURING THE SHORT TERM FORECAST PERIOD. PART OF THIS IS OWING TO  
DIFFERENCES IN THE AMOUNT OF PHASING THAT WILL TAKE PLACE WITH  
SHORTWAVE ENERGY ALOFT. THESE DIFFERENCES BECOME APPARENT AS  
EARLY AS MONDAY EVENING EAST OF THE MID-ATLANTIC COAST, WITH THE  
00Z UKMET BEING MUCH SLOWER THAN THE MODEL CONSENSUS AND LACKING  
ENSEMBLE SUPPORT. THE CMC AND ECMWF ARE ALSO A LITTLE SLOWER,  
WITH THE ECMWF DEPICTING A SECOND WAVE OF LOW PRESSURE ALONG THE  
FRONT. THE GFS AND THE MAIN SURFACE LOW FROM THE ECMWF ARE IN  
BEST AGREEMENT WITH THE ENSEMBLE MEANS, SO A BLEND OF THESE ALONG  
WITH SOME OF THE MEANS SEEMS PRUDENT.  
 
***CENTRAL U.S. STORM SYSTEM TUESDAY AND WEDNESDAY***  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF  
CONFIDENCE: ABOVE AVERAGE  
 
SHORTWAVE ENERGY CROSSING SOUTHWEST CANADA ON TUESDAY IS FORECAST  
TO RESULT IN THE DEVELOPMENT OF A PARTIALLY CLOSED UPPER LOW OVER  
SOUTH-CENTRAL CANADA BY MIDWEEK WITH A SHEARED SHORTWAVE AXIS TO  
THE SOUTH. A STRONG SURFACE LOW IS EXPECTED JUST TO THE EAST OF  
THE UPPER LEVEL TROUGH AND NORTH OF THE CANADIAN BORDER WITH A  
STRONG COLD FRONT EXTENDING SOUTHWARD ACROSS THE CENTRAL AND  
NORTHERN PLAINS, ALONG WITH A SECONDARY SURFACE LOW NEAR WESTERN  
KANSAS.  
 
THE 00Z UKMET APPEARS TO BE SLIGHTLY PROGRESSIVE WITH THE TRACK OF  
THE MAIN SURFACE LOW OVER MANITOBA BUT OTHERWISE AGREES WELL WITH  
COLD FRONT TIMING, AND THE ECMWF SLIGHTLY SLOWER. THE 12Z NAM AND  
GFS APPEAR TO TAKE THE LEAD ON THE ARRIVAL OF THE FRONT, WITH THE  
NAM SHOWING A FASTER PROGRESSION THAN YESTERDAY. A COMPROMISE OF  
THE 12Z GFS AND 00Z ECMWF BEST APPROXIMATE THE MODEL CONSENSUS AND  
A BLEND OF THESE TWO SOLUTIONS SHOULD SUFFICE.  
 
***SHORTWAVE APPROACHING THE PACIFIC NORTHWEST LATE TUESDAY***  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
A LARGE LOW PRESSURE GYRE NEAR 50 DEGREES NORTH BEGINS TO APPROACH  
THE COASTAL WATERS OF NORTHERN BRITISH COLUMBIA BY MONDAY NIGHT  
ALONG WITH A DEEPLY OCCLUDED SURFACE LOW THAT IS EXPECTED TO  
SLOWLY FILL AS IT GETS CLOSER TO LAND. A LOBE OF SHORTWAVE ENERGY  
ALOFT ACCOMPANIED BY A SURFACE COLD FRONT IS EXPECTED TO PIVOT  
AROUND THE SOUTHERN PERIPHERY OF THE LARGE UPPER LOW AND AFFECT  
THE PACIFIC NORTHWEST BY MONDAY NIGHT AND INTO EARLY TUESDAY,  
ALONG WITH FALLING HEIGHTS ALOFT. A SHEARED AXIS OF UPPER LEVEL  
ENERGY IS LIKELY TO REMAIN OVER WASHINGTON STATE GOING INTO THE  
MIDDLE OF THE WEEK.  
 
IN TERMS OF MODEL SOLUTIONS, THERE IS GOOD OVERALL AGREEMENT WITH  
THE PLACEMENT OF THE MAIN UPPER LOW APPROACHING THE BC COAST, WITH  
THE 00Z CMC SLIGHTLY TO THE NORTH OF THE MODEL CONSENSUS.  
REGARDING THE SHORTWAVE IMPULSE TRACKING TOWARDS WASHINGTON STATE,  
THE NAM IS NOW IN BETTER AGREEMENT WITH THE MODEL CONSENSUS  
COMPARED TO YESTERDAY, AND THE MODELS ARE CLOSE ENOUGH TO MERIT A  
GENERAL MODEL COMPROMISE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
D. HAMRICK  
 

 
 
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