198  
FXUS10 KWNH 240418  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1217 AM EDT FRI APR 24 2020  
 
VALID APR 24/0000 UTC THRU APR 27/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z EVALUATION WITH INITIAL MODEL PREFERENCES AND FORECAST  
CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
LOW PRESSURE CROSSING MID-ATLANTIC ON FRIDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/00Z NAM/00Z GFS  
CONFIDENCE: MODERATE-HIGH  
 
THE SOUTHERN STREAM STORM SYSTEM WITH SURFACE LOW INITIALLY OVER  
THE CENTRAL APPALACHIANS WILL CONTINUE TRACKING EAST ACROSS THE  
MID-ATLANTIC ON FRIDAY, WITH A SECONDARY LOW LIKELY DEVELOPING  
SOUTHEAST OF NEW ENGLAND BY FRIDAY EVENING THAT BECOMES THE MAIN  
LOW PASSING SOUTH OF NOVA SCOTIA. THE 12Z CMC IS A LITTLE BIT  
WEAKER WITH THE ACCOMPANYING 500MB SHORTWAVE, AND ONCE THE SYSTEM  
EMERGES OFFSHORE, THE UKMET BECOMES SLIGHTLY SLOWER WITH THE  
CONSOLIDATED SURFACE LOW.  
 
LOW PRESSURE TRACKING FROM TEXAS TO THE OHIO VALLEY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/12Z EC MEAN/00Z GFS  
CONFIDENCE: LIMITED-MODERATE  
 
A SOMEWHAT COMPLICATED UPPER LEVEL PATTERN EVOLUTION ACROSS THE  
NORTH-CENTRAL U.S. WITH BROAD NORTHWEST FLOW WILL BE IN PLACE TO  
END THE WEEK. A STRONGER LEAD TROUGH WILL BE FOLLOWED BY A MORE  
SUBTLE SECONDARY TROUGH, TRACKING FROM THE NORTHERN ROCKIES TO THE  
MIDWEST STATES, AND EVENTUALLY CONSOLIDATE INTO ONE MAIN UPPER  
LEVEL TROUGH AND THEN CLOSED LOW OVER THE NORTHEAST U.S. BY THE  
END OF THE FORECAST PERIOD MONDAY MORNING. A SURFACE LOW WILL  
BECOME BETTER ORGANIZED ACROSS THE SOUTHERN PLAINS AND THEN CROSS  
THE MID-SOUTH AND OHIO VALLEY BY SATURDAY NIGHT, FOLLOWED BY  
LIKELY SECONDARY CYCLOGENESIS NEAR NEW ENGLAND AS A POTENTIAL  
NOR'EASTER FOR EARLY NEXT WEEK.  
 
IN TERMS OF THE MODELS, THE 00Z NAM APPEARS SLIGHTLY SLOWER WITH  
THE TRACK OF THE LOW, THE 12Z UKMET A LITTLE WEAKER AND SOUTH OF  
THE MODEL CONSENSUS, AND THE CMC A BIT MORE AMPLIFIED WITH THE  
UPPER TROUGH CROSSING THE MID-SOUTH ON SATURDAY. MUCH OF THIS  
WILL DEPEND ON THE SHORTWAVE ENERGY ROUNDING THE APPARENT TROUGH  
AXIS AND THEREFORE INFLUENCE THE TIMING OF PRECIPITATION AS  
WELL. THE ENERGY DIVING SOUTH FROM CANADA INTO PORTIONS OF NORTH  
DAKOTA AND INTO MINNESOTA SEEM TO BE WEAKER AND SLOWER WITH THE  
ECMWF. FOR DAY 3, THE NAM SEEMS SLIGHTLY SLOWER WITH THE UPPER  
LEVEL LOW, AND THE UKMET A BIT MORE SUPPRESSED WITH THE SURFACE  
LOW. THE 00Z GFS IS REASONABLY WELL CLUSTERED WITH THE LOW NEAR  
THE NORTHEAST COAST ALBEIT A LITTLE FASTER, ALTHOUGH THE 18Z GEFS  
MEAN IS DISPLACED SOME TO THE NORTH.  
 
PAIR OF TROUGHS AFFECTING THE NORTHWESTERN U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL BLEND FOR FIRST TROUGH, AND 00Z GFS/00Z  
NAM/12Z EC MEAN FOR SECOND TROUGH  
CONFIDENCE: MODERATE  
 
THE UPPER LEVEL RIDGE THAT IS CURRENTLY IN PLACE ACROSS THE WEST  
COAST REGION WILL BEGIN TO BE ERODED BY A MODERATELY STRONG STORM  
SYSTEM APPROACHING BRITISH COLUMBIA ON SATURDAY WITH A COLD FRONT  
REACHING THE PACIFIC NORTHWEST COAST. THERE WILL BE A BRIEF BREAK  
BEFORE A SECOND AND POTENTIALLY STRONGER SYSTEM APPROACHES FROM  
THE NORTHEAST PACIFIC SUNDAY NIGHT INTO MONDAY MORNING WITH  
ANOTHER FRONTAL PASSAGE. FOR THE FIRST SYSTEM, THERE IS ENOUGH  
DETERMINISTIC MODEL AGREEMENT TO MERIT THE USE OF A GENERAL BLEND.  
FOR THE SECOND SYSTEM, THE 12Z UKMET IS A BIT FASTER WITH THE  
SURFACE LOW AND FRONT, AND THE ECMWF BECOMES SLIGHTLY STRONGER  
WITH THE SHORTWAVE BY MONDAY MORNING.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
HAMRICK  
 

 
 
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