448  
FXUS02 KWBC 091615  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1114 AM EST TUE JAN 09 2018  
 
VALID 12Z FRI JAN 12 2018 - 12Z TUE JAN 16 2018  
 
...E-CENTRAL TO NERN US STORM THREAT WITH HEAVY ICE/SNOW POTENTIAL  
AND LEAD HEAVY RAINS...  
...WET FLOW DEVELOPING NEXT WEEK INTO THE NWRN US AND A  
MIDWEST/GREAT LAKES CLIPPER LOW...  
 
...EAST-CENTRAL TO ERN US GUIDANCE/PREDICTABILITY ASSESSMENT AND  
THREAT...  
 
A SLOWLY TRANSIENT WRN RIDGE AND ERN TROUGH PATTERN ALOFT WILL  
ESTABLISH ITSELF OVER THE LOWER 48 STATES BY THIS WEEKEND. POTENT  
SRN STREAM SHORTWAVE ENERGY LIFTING ON THE LEADING EDGE OF THE  
AMPLIFIED MEAN TROUGH POSITION IS EXPECTED TO DYNAMICALLY SUPPORT  
AN E-CENTRAL TO INTERIOR NERN US WINTER STORM HEAVY SNOW AND  
TRANSITIONAL ZONE HEAVY THREAT AS ARCTIC AIR CLASHES WITH MOIST  
WARM AIR TO WRAPBACK AND FOCUS AHEAD OF DEVELOPING FRONTAL LOW.  
THIS MOISTURE WILL MEANWHILE SUPPORT SOME HEAVIER RAINS IN THE  
WARM SECTOR UP THE ERN SEABOARD.  
 
WPC PROGS FOCUS FOCUS ON GUIDANCE FROM THE DETERMINISTIC ECMWF AND  
ECMWF ENSEMBLES DURING THE MAIN FRI-SUN WINTER STORM THREAT PERIOD  
WHOSE WELL CLUSTERED GUIDANCE OFFERS A SLIGHTLY MORE PROGRESSIVE  
SOLUTION THAN CONTINUITY THAT SEEMS TO FIT WELL ON THE ERN  
PERIPHERY OF THE AMPLIFIED SUPPORTING MID-UPPER LEVEL TROUGH. THE  
LATEST GFS OFFERS LESS LOW DEVELOPMENT AND THE GEFS LESS  
PROGRESSION...THAT WHILE PLAUSIBLE SEEM LESS LIKELY. ALL THESE  
SOLUTIONS THOUGH SUPPORT LESS THAN NORMAL UNCERTAINTY OVERALL FOR  
A SIGNIFICANT SYSTEM THREAT WITH REASONABLY SIMILAR QPF  
POTENTIAL...ALBEIT WITH VARIED LOCAL EMPHASIS.  
 
...NWRN US AND MIDWEST/GREAT LAKES GUIDANCE/PREDICTABILITY  
ASSESSMENT AND THREAT...  
 
FOR NEXT MON/TUE...MOST GUIDANCE HAS CONVERGED UPON A MORE COMMON  
SOLUTION OF BRINGING AMPLE ERN PACIFIC ENERGY AND AN ASSOCIATED  
MOIST FRONTAL PUSH INTO THE NWRN US NEXT MON/TUE. HAVE TRENDED  
TOWARD THIS SLIGHTLY FASTER SYSTEM PROGRESSION GIVEN THE THE BULK  
OF GUIDANCE TRENDS...BUT WAS HESITANT TO SHIFT AS FAR EAST THROUGH  
THE MEAN RIDGE POSITION ALOFT AS THE LATEST 06 UTC GFS. THIS  
SCENARIO WOULD USHER IN A WET AND UNSETTLED FLOW ACROSS THE NWRN  
US/NRN CA IN THIS TIME FRAME IN A CHANGING PATTERN WITH NEAR  
NORMAL PREDICTABILITY.  
 
THIS SOLUTION WILL MEANWHILE ALLOW FOR LEAD NRN STREAM SHORTWAVE  
ENERGY DIGGING DOWN TO THE LEE OF THE AFOREMENTIONED RIDGE TO  
SUPPORT A LEAD A CLIPPER SYSTEM THROUGH THE MIDWEST/GREAT LAKES  
THAT SHOULD SUPPORT MODEST WINTERY WEATHER AND ENHANCED LAKE  
EFFECT SNOWS DESPITE LIMITED MOISTURE AVAILABILITY ON THE HEELS OF  
THE LEAD STORM. IT IS ALSO EXPECTED THAT SEVERAL POTENT SHOTS OF  
COLD HIGH PRESSURE WILL DIG SOUTHWARD ACROSS THE CENTRAL US AND  
SPREAD ACROSS THE SRN AND ERN US BEHIND BOTH THE LEAD SYSTEM AND  
THE CLIPPER LOW.  
 
SCHICHTEL  
 

 
 
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