368  
FXUS02 KWNH 210700  
PREEPD  
 
PRELIMINARY EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EST TUE NOV 21 2017  
 
VALID 12Z FRI NOV 24 2017 - 12Z TUE NOV 28 2017  
 
...RECORDS TEMPS FOR THE SW/WRN US AND A PROLONGED HEAVY RAIN/SNOW  
PATTERN FOR THE NWRN US...  
 
   
..OVERVIEW
 
 
AN AMPLIFIED FLOW PATTERN WILL BE IN PLACE FOR THE NEXT WEEK AS  
HIGHLIGHTED ALOFT BY A TROUGH OVER THE GULF OF AK/ERN PACIFIC...A  
RIDGE OVER THE W-CENTRAL US...AND A TROUGH OVER THE ERN US. MUCH  
OF THE PACIFIC NORTHWEST WILL REMAIN IN AN ACTIVE AND PROLONGED  
WET PERIOD WITH COOLER TEMPS...AS WILL THE GREAT LAKES REGION AND  
THE NORTHEAST. A VAST MAJORITY OF SRN CA...THE DESERT  
SOUTHWEST...SRN ROCKIES AND SRN PLAINS WILL BE DRY WITH ABOVE  
NORMAL TEMPS. SOME LOCATIONS WILL REACH OR EXCEED RECORD  
TEMPS...PRIMARILY FOR LOCATIONS IN THE SOUTHWEST. THE CENTRAL U.S.  
WILL BEGIN WITH ABOVE AVERAGE TEMPS PRIOR TO A WEEKEND COOLING  
TREND. ADDITIONAL WET WEATHER IS LIKELY OVER FL ASTRIDE A SLOWLY  
MOVING AND WAVY FRONTAL BOUNDARY.  
 
   
..GUIDANCE/UNCERTAINTY PREFERENCES...
 
 
MODELS AND ENSEMBLES ARE IN GOOD AGREEMENT WITH THE LARGER SCALE  
FLOW...BUT SIGNIFICANT DIFFERENCES REMAIN WITH THE TIMING AND  
AMPLITUDE OF MUCH LESS PREDICTABLE EMBEDDED SMALLER SCALE SYSTEMS  
THAT FOCUS YOUR LOCAL WEATHER. BLENDED REASONABLY CLUSTERED 12 UTC  
GFS/ECMWF AND GEFS/ECMWF ENSEMBLES TO MITIGATE EMBEDDED SYSTEM  
ERROR...LEANING A BIT MORE ON THE GEFS MEAN. THE 12 UTC GEFS MEAN  
AND 12 UTC GUIDANCE OVERALL OFFERS SLIGHTLY MORE AMPLIFIED/LESS  
PROGRESSIVE FLOW VS 18 UTC/00 UTC GUIDANCE. WATER VAPOR IMAGERY  
SHOWS HIGHLY AMPLIFIED PACIFIC TO NOAM FLOW. WHILE SMALLER  
WAVELENGTH SPACING WITH EMBEDDED IMPUSLES CAN KICK SYSTEMS  
ALONG...GUIDANCE HISTORICALLY TENDS TO DE-AMPLIFY HIGHLY AMPLIFIED  
FLOW TOO QUICKLY.  
 
   
..WEATHER HIGHLIGHTS
 
 
IT REMAINS THE CASE THAT HEAVY DAILY RAINS AND LOCALLY HEAVY  
ELEVATION SNOWS WILL PERSIST OVER THE NWRN US FOR THE NEXT WEEK.  
UPPER RIDGING SUPPORTS WELL ABOVE AVERAGE TEMPERATURES FROM THE  
SOUTHWEST/SRN CA TO THE INTERMOUNTAIN WEST/ROCKY STATES. SOME  
RECORD HIGHS/LOWS ARE LIKELY. MILD TEMPS WILL EXTEND EASTWARD  
THROUGH THE PLAINS AHEAD OF A COLD FRONT THU AND FRI. COOLER TEMPS  
WILL FILTER IN THIS WEEKEND AFTER THE FRONTAL PASSAGE. THERE IS A  
GOOD CHANCE FOR APPRECIABLE PRECIPITATION ALONG THE GULF/SOUTHEAST  
US COAST...ESPECIALLY FL...AS LOW PRESSURE CENTERS MEANDER ALONG A  
SLOW MOVING FRONT. RAIN AND SNOW IS ALSO EXPECTED FOR THE GREAT  
LAKES REGION WITH POTENT NRN STREAM CLIPPER PASSAGES AND  
POST-SYSTEM LAKE EFFECT.  
 
SCHICHTEL  
 

 
 
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