333  
FXUS02 KWBC 051552  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1051 AM EST FRI JAN 05 2018  
 
VALID 12Z MON JAN 08 2018 - 12Z FRI JAN 12 2018  
   
..RAIN FINALLY RETURNS TO SOUTHERN CALIFORNIA
 
 
   
..OVERVIEW
 
 
A PACIFIC SYSTEM WILL PUSH THROUGH CALIFORNIA ON TUESDAY WITH RAIN  
AND HIGH MOUNTAIN SNOW FOR MUCH OF THE GOLDEN STATE (INCLUDING  
DOWN TO SAN DIEGO) AS ANOTHER IN THE EAST SLOWLY EXITS OFF THE  
SOUTHEAST/FLORIDA COASTS. ANOTHER ARCTIC AIRMASS WILL DIVE INTO  
THE HIGH PLAINS BY MIDWEEK AND MERGE WITH THE FORMER CALIFORNIA  
SYSTEM TO SPREAD MORE RAIN AND NORTHERN SNOW TO THE  
CENTRAL/EASTERN STATES THU/FRI.  
 
   
..GUIDANCE ASSESSMENT AND PREFERENCES
 
 
FOR THE WESTERN SYSTEM, THE 06Z GFS AND 00Z ECMWF CONTINUED TO  
SHOW GOOD CLUSTERING WITH THEIR ENSEMBLE MEANS WHILE THE LATEST  
RUNS OF THE UKMET/CANADIAN PRESENTS A SLOWER SOLUTION. A BLEND OF  
THE NON-UKMET/CANADIAN MODELS SERVED AS A GOOD STARTING POINT AS  
THE COLD FRONT WILL PUSH INTO CALIFORNIA AND THE SOUTHWEST BY  
TUESDAY AND THEN INTO THE SOUTHERN PLAINS ON WEDNESDAY/THURSDAY.  
THE NORTHERN PORTION OF THIS SYSTEM APPEARS TO HAVE COME INTO  
BETTER AGREEMENT WITH RECENT MODEL RUNS AS A SURFACE LOW HEADS  
INTO SOUTHWEST CANADA AND DRAGS A WEAKENING COLD FRONT THROUGH THE  
PACIFIC NORTHWEST EARLY TUESDAY. AGAIN...A BLEND OF THE GFS/ECMWF  
PRESENTED A GOOD SOLUTION FOR THE WPC PROGS.  
 
IN THE SOUTHEAST, THERE IS PRETTY GOOD AGREEMENT AMONGST MOST OF  
THE MODELS ON A POSSIBLY CLOSED LOW SLIDING ACROSS THE CENTRAL  
GULF COAST ON MONDAY AND EVENTUALLY OFF THE FLORIDA OR SOUTHEAST  
COAST BY MID-WEEK AS IT BECOMES ABSORBED INTO BROADER FLOW. THE  
EXCEPTION TO THIS IS THE 00Z ECMWF WHICH SHOWS A CLOSED LOW  
DROPPING SOUTHWARD INTO THE EASTERN GULF AND LINGERING OFF THE  
WESTERN FLORIDA COAST UNTIL LATE IN THE WEEK. AT THIS TIME...THIS  
APPEARS TO BE A CLEAR OUTLIER SO THE WPC FORECAST HERE WAS BASED  
ON A BLEND OF THE ENSEMBLE MEANS AND THE 06Z GFS.  
 
FOR THE END OF THE WEEK, AN ARCTIC AIRMASS SPILLING SOUTHEASTWARD  
EAST OF THE DIVIDE WILL LIKELY CATCH UP TO THE OLD PACIFIC FRONT  
MOVING THROUGH THE SOUTHERN PLAINS ON THURSDAY. THE 06Z AND 00Z  
GFS CONTINUE TO BE A BIT TOO QUICK (PERHAPS ITS TYPICAL FAST BIAS  
AFTER ~5 DAYS) WITH THE OLD PACIFIC UPPER LOW BUT MANAGES TO  
BECOME SLOWER AS IT INFUSES TRAILING VORTICITY INTO THE TROUGH.  
TRENDED TOWARD THE ECMWF ENSEMBLE MEAN AND GEFS MEAN BY NEXT  
FRIDAY AS THE DETAILS OF THE GFS/ECMWF REMAIN UNRESOLVED.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
AFTER MANY MONTHS WITHOUT APPRECIABLE RAIN, SOUTHERN CALIFORNIA  
AND THE SAN JOAQUIN VALLEY SHOULD SEE AT LEAST MODEST TO LOCALLY  
HEAVY AMOUNTS OF RAIN AND HIGH ELEVATION SNOW (RATHER WARM SYSTEM)  
ESPECIALLY TUESDAY. THE SOUTHERN AND SOUTHWESTERN SLOPES WILL BE  
FAVORED AND SEVERAL FEET OF SNOW ARE EXPECTED IN THE SIERRAS.  
ELSEWHERE, THE POSSIBLE CLOSED LOW AND SFC LOW WITH ATTENDANT COLD  
FRONT SHOULD YIELD MODEST RAINS TO PORTIONS OF FLORIDA EARLY IN  
THE WEEK WHILE ANOTHER ROUND OF RAIN AND MOUNTAIN SNOWS RETURNS TO  
THE PACIFIC NORTHWEST AT THE END OF THE WEEK. MORE RAIN AND  
NORTHERN SNOW WILL BE ALSO BE LIKELY LATER IN THE WEEK ALONG/AHEAD  
OF THE PACIFIC AND ARCTIC COLD FRONTS IN THE CENTRAL AND EASTERN  
US.  
 
TEMPERATURES WILL BE A BIT VARIABLE OVER THE CONUS, WITH A  
MODERATING TREND IN THE EAST BUT A COOLING TREND OVER MONTANA INTO  
THE PLAINS STARTING WEDNESDAY BEHIND THE ARCTIC FRONT.  
 
FRACASSO/SANTORELLI  
 

 
 
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