075  
FXUS02 KWBC 170659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EST WED JAN 17 2018  
 
VALID 12Z SAT JAN 20 2018 - 12Z WED JAN 24 2018  
 
***PATTERN OVERVIEW***  
 
THE MEDIUM RANGE PERIOD WILL BEGIN ON SATURDAY WITH BROAD ZONAL  
FLOW ALOFT OVER THE NORTH CENTRAL U.S. AND A LARGE TROUGH OVER THE  
WESTERN THIRD OF THE NATION AND A SMALLER SCALE TROUGH NEAR THE  
GULF OF MEXICO. THIS WESTERN U.S. TROUGH WILL INDUCE SURFACE  
CYCLOGENESIS OVER THE PLAINS AND BECOME THE DOMINANT WEATHER STORY  
DURING THIS FORECAST PERIOD, ESPECIALLY SUNDAY AND INTO MONDAY.  
AFTER BRIEF RIDGING ALOFT OVER THE WEST, UNSETTLED CONDITIONS ARE  
EXPECTED TO RETURN TO THE WEST COAST AS TWO SEPARATE STORM SYSTEMS  
AFFECT THE REGION.  
 
***GUIDANCE ASSESSMENT AND PREFERENCES***  
 
MODELS AND ENSEMBLES ARE IN RELATIVELY GOOD AGREEMENT ON SATURDAY  
WITH THE OVERALL SYNOPTIC SCALE PATTERN. THE 12Z ECMWF BECOMES  
SLOWER THAN THE OTHER SOLUTIONS BY SUNDAY WITH THE MAJOR STORM  
SYSTEM EXITING THE ROCKIES ON SUNDAY AND THIS TREND BECOMES MORE  
NOTEWORTHY GOING INTO MONDAY. IT IS ALSO WELL TO THE SOUTHWEST OF  
ITS 12Z ENSEMBLE MEAN BY THIS TIME, DECREASING CONFIDENCE IN ITS  
SOLUTION. THE ECMWF IS ALSO NOTABLY DIFFERENT BY DEPICTING A  
STRONG NORTHERN STREAM SYSTEM OVER SOUTH CENTRAL CANADA TUESDAY  
MORNING WHERE THE MODEL CONSENSUS IS FAVORING A SURFACE HIGH.  
THERE WAS BETTER CLUSTERING WITH THE CMC, GFS, GEFS MEAN, AND EC  
MEAN, SO THESE SOLUTIONS WERE GIVEN THE GREATEST WEIGHTING IN THE  
FORECAST PROCESS. THE UKMET INDICATED MORE UPPER LEVEL RIDGING  
OVER THE WESTERN U.S. BY MONDAY IN CONTRAST TO THE MODEL  
CONSENSUS, WHICH INDICATES MORE OF A LOW AMPLITUDE TROUGH AT THAT  
TIME.  
 
WITH THE DEPARTURE OF THE CENTRAL-EASTERN U.S. STORM SYSTEM, MODEL  
SPREAD BECOME MORE SIGNIFICANT OVER THE CENTRAL AND WESTERN PARTS  
OF THE NATION AND DECREASING CONFIDENCE IN ANY ONE PARTICULAR  
DETERMINISTIC SOLUTION. THEREFORE A GREATER PERCENTAGE OF THE  
GEFS AND EC MEANS WAS INCORPORATED BY DAYS 6 AND 7 FOR PLACEMENT  
OF THE MAIN SYNOPTIC FEATURES.  
 
***SENSIBLE WEATHER***  
 
AN ACTIVE WEATHER PATTERN CAN BE EXPECTED FOR THE NATION'S  
MIDSECTION BEGINNING ON SUNDAY AS A STRONG SURFACE LOW DEVELOPS  
OVER THE CENTRAL AND NORTHERN PLAINS. THERE WILL BE TWO MAIN  
FACETS TO THIS STORM SYSTEM, WITH THE FIRST BEING SCATTERED TO  
NUMEROUS SHOWERS AND THUNDERSTORMS FROM EASTERN TEXAS TO THE OHIO  
VALLEY AS DEEP GULF OF MEXICO MOISTURE SURGES NORTHBOUND AHEAD OF  
THE COLD FRONT. THE SECOND WILL BE THE LIKELIHOOD OF A  
SIGNIFICANT WINTER STORM WITH POSSIBLE BLIZZARD CONDITIONS OVER  
PARTS OF THE DAKOTAS, MINNESOTA, AND WISCONSIN WHICH WOULD BE  
UNDER THE DEFORMATION ZONE OF THE MATURING CYCLONE. IN ADDITION  
TO THIS, HEAVY RAIN AND COPIOUS MOUNTAIN SNOW WILL REMAIN IN THE  
WEATHER HEADLINES FOR THE WESTERN U.S. AS A COUPLE OF PACIFIC  
SYSTEMS MAKE THEIR WAY INLAND, WITH A POSSIBLE ATMOSPHERIC RIVER  
EVENT ON SUNDAY FOR NORTHERN CALIFORNIA.  
 
THE MOST PRONOUNCED ANOMALIES FOR TEMPERATURES WILL BE IN THE WARM  
SECTOR OF THE CENTRAL U.S. STORM SYSTEM. OVERNIGHT LOWS IN  
PARTICULAR MAY BE 15 TO 25 DEGREES ABOVE NORMAL OVER MUCH OF THE  
PLAINS AND MIDWEST THIS WEEKEND, AND THEN REACHING THE EAST COAST  
STATES BY NEXT MONDAY. HIGH TEMPERATURES SHOULD NOT BE AS  
ANOMALOUS BUT STILL 10 TO 20 DEGREES ABOVE NORMAL OVER SOME AREAS.  
COLDER WEATHER RETURNS TO THE PLAINS AFTER THE COLD FRONT MOVES  
THROUGH.  
 
HAMRICK  
 

 
 
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