712  
FXUS02 KWBC 260701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EST TUE DEC 26 2017  
 
VALID 12Z FRI DEC 29 2017 - 12Z TUE JAN 02 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT..
 
 
SYNOPTIC SCALE FLOW PATTERN OVER NORTH AMERICA WILL REMAIN LARGELY  
PERSISTENT INTO 2018...WITH WARMED UPPER RIDGING INTO THE WRN US  
AND COLD TROUGHING/BROAD CYCLONIC FLOW ENTRENCHED OVER THE CENTRAL  
AND ERN US. SHORTWAVE ENERGY/HEIGHT FALLS MOVING INLAND ACROSS THE  
NWRN US LATE FRI/SAT WILL BRIEFLY WEAKEN THE RIDGE AND FOCUS  
TERRAIN ENHANCED PRECIPITATION BEFORE THE RIDGE RECOVERS BY EARLY  
NEXT WEEK. THIS PATTERN WILL SUPPORT CONTINUED FRIGID TEMPERATURES  
FAR SOUTHWARD ACROSS MUCH OF THE CENTRAL AND ERN U.S. A SERIES OF  
HARD TO TIME IMPULSES ALOFT WOULD EACH HAVE THE POTENTIAL THERE TO  
PRODUCE SOME MODEST BUT LOCALLY IMPACTFUL QUICK SWATHS OF  
ICE/SNOW...WRINGING OUT LIMITED MOISTURE.  
 
MEANWHILE...A CLIPPER IS EXPECTED TO CROSS THE GREAT LAKES ON FRI  
AND THE EASTERN U.S. ON SAT. THE ENERGY ASSOCIATED WITH THIS  
SYSTEM STILL HAS SOME POTENTIAL TO BRING SOME WINTER WEATHER TO  
PORTIONS OF THE ERN/NERN STATES. BY EARLY NEXT WEEK THE ARCTIC  
FRONT IS EXPECTED TO BE IN THE GULF OF MEXICO AND THROUGH FLORIDA.  
GUIDANCE INDICATES WEAK FRONTAL WAVES WILL DEVELOP ALONG THIS  
FRONT BEFORE POTENTIALLY DEEPENING OVER THE WRN ATLANTIC TO SOME  
DEGREE.  
 
MODEL AND ENSEMBLE FORECAST SPREAD ALOFT HAS DECREASED OVER THE  
PAST COUPLE OF DAYS...BUT ENOUGH TIMING/EMPHASIS DIFFERENCES EXIST  
TO STILL FAVOR AN ENSEMBLE MEAN BASED COMPOSITE SOLUTION FOR  
DERIVATION OF THE WPC MEDIUM RANGE PRODUCT SUITE. THE SURFACE  
PATTERN AND PCPN PATTERN IS MORE COMPATABLE AND OFFER SIMILAR  
TYPES OF THREATS IN THE COLD AIRMASS.  
   
..WEATHER/THREATS HIGHLIGHTS
 
 
THE PATTERN WILL CONTINUE TO SUPPORT THE INCURSION OF ARCTIC AIR  
INTO MUCH OF THE CENTRAL AND EASTERN U.S., WITH HIGH TEMPERATURES  
15 TO 25 DEG F BELOW AVERAGE THROUGH MUCH OF THE PERIOD. WHILE A  
FEW RECORD LOWS ARE POSSIBLE, THE TYPE OF RECORD MOST IN JEOPARDY  
APPEARS TO BE RECORD LOW MAXIMUM TEMPERATURES. THE POTENTIAL FOR  
AT LEAST SOME WINTER WEATHER WILL EXIST ACROSS PORTIONS OF THE  
SOUTHEAST THU-THU NIGHT AS A WAVE OF LOW PRESSURE BEGINS TO  
DEVELOP ALONG THE FRONT IN THE GULF/WESTERN ATLANTIC. AS THIS  
SYSTEM MOVES NORTH AND EVENTUALLY PHASES/DEVELOPS INTO A MATURE  
CYCLONE ACROSS SOUTHEASTERN CANADA BY SUN MORNING, THE POTENTIAL  
FOR SNOW/WIND WILL INCREASE, ESPECIALLY ACROSS NORTHERN/EASTERN  
NEW ENGLAND. CONFIDENCE IS LOW IN ANY ADDITIONAL WINTER THREATS  
FOR THE EASTERN/SOUTHEASTERN U.S. BY EARLY NEXT WEEK, BUT ANY  
POTENTIAL WEAK WAVE OF LOW PRESSURE ALONG THE FRONT IN THE GULF  
COULD RESULT IN POTENTIAL AREAS OF WINTER WEATHER. MEANWHILE, THE  
PACIFIC NORTHWEST WILL SEE A COUPLE ROUNDS OF POTENTIAL  
PRECIPITATION. THE FIRST WITH SHORTWAVE/FRONT ARRIVING FRI  
NIGHT/SAT, AND ANOTHER BY SUN-MON. BOTH OF THESE WILL PRODUCE RAIN  
AND MOUNTAIN SNOWS FOR THE NORTHWEST AND THE NORTHERN ROCKIES.  
 
RYAN/SCHICHTEL  
 

 
 
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