932  
FXUS02 KWBC 261542  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1041 AM EST FRI JAN 26 2018  
 
VALID 12Z MON JAN 29 2018 - 12Z FRI FEB 02 2018  
   
..OVERVIEW
 
 
PROGRESSIVE FLOW WILL TREND TOWARD BUILDING A RIDGE OFF THE PAC NW  
AND BRITISH COLUMBIA COASTS WHICH SUPPORTS DIGGING TROUGHING  
THROUGH THE PLAINS INTO THE MISSISSIPPI RIVER VALLEY LATER NEXT  
WEEK. THIS WILL BRING IN COLDER AIR TO AREAS JUST EAST OF THE  
ROCKIES AS A COLD FRONT PUSHES FROM WEST TO EAST DURING THE WEEK.  
AN INITIAL SYSTEM JUST OFF THE EAST COAST ON MONDAY WILL LIFT  
NORTHEASTWARD TOWARD THE CANADIAN MARITIMES BUT MAY PASS CLOSE  
ENOUGH TO SPREAD SOME RAIN/SNOW TO THE NORTHEAST EARLY IN THE  
WEEK.  
 
   
..GUIDANCE AND PREDICTABILITY ASSESSMENT
 
 
FOR THE LEAD SYSTEM OFF THE EAST COAST MONDAY/TUESDAY, THE MODELS  
AND ENSEMBLES CONTINUE TO STRUGGLE TO RESOLVE THE  
EVOLUTION/DETAILS OF THE FRONT AND MULTIPLE LOW PRESSURE CENTERS  
PURSUANT TO THE STRENGTH OF UPSTREAM VORTICITY AND DOWNSTREAM  
RIDGE AMPLIFICATION. 00Z/06Z GFS RUNS WERE STRONGER WITH THIS  
TRAILING VORTICITY THAN THE OTHER MODELS AND DEVELOPED A SFC LOW  
AROUND 36N AND JUST EAST OF 70W WHILE THE OTHERS (MINUS THE UKMET  
WHICH WAS WEST OF THE CONSENSUS) WERE MORE PROGRESSIVE. AT THIS  
POINT, GIVEN THE CHANGES SEEN OVER THE PAST SEVERAL DAYS IN BOTH  
THE ENSEMBLES AND DETERMINISTIC SOLUTIONS, HARD TO REALLY RULE  
ANYTHING OUT. HOWEVER, KEYED ON THE 00Z ECMWF/CANADIAN WITH THE  
06Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN MORE THAN THE GFS RUNS,  
BUT A BLEND OF THOSE SERVED AS A GOOD STARTING POINT FOR THE FIRST  
FEW DAYS OF THE FORECAST (MON-WED). HOW FAR WEST THE PRECIPITATION  
SHIELD GETS (AND AVAILABILITY OF COLD AIR TO SUPPORT WINTRY  
WEATHER) REMAINS UNCERTAIN.  
 
FOR THE WEST AND CENTRAL STATES, GUIDANCE HAS BEEN RATHER  
CONSISTENT ON THE INCOMING SYSTEM TO WA/OR MONDAY AND PROGRESSING  
EASTWARD TUE-THU WITH THE MAIN LOW PRESSURE STAYING JUST NORTH OF  
THE US/CANADIAN BORDER. MAIN FRONT AND SECONDARY ARCTIC FRONT WILL  
STEADILY WORK SOUTHEASTWARD AND REACH THE EAST COAST FRIDAY. BY  
THEN, QUESTION BECOMES IF SOUTHERN PART OF THE FRONT WILL SUPPORT  
A DEFINED LOW PRESSURE THAT MAY RIDE NORTHEASTWARD FOR THE END OF  
THE MEDIUM RANGE (AS PER THE 00Z/06Z GFS) OR REMAIN MOSTLY  
PROGRESSIVE (ECMWF/CANADIAN). ENSEMBLES SHOW THE FULL RANGE OF  
SOLUTIONS WITH NO CLEAR TREND AT THIS LONG LEAD TIME. KEPT AN L  
STAMP FOR NOW IN THE SOUTHEAST AS THE UPPER PATTERN COULD SUPPORT  
DEVELOPMENT.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
TEMPERATURES...  
 
THE SOUTHWEST WILL SEE ABOVE AVERAGE TEMPERATURES CONTINUE THROUGH  
THE PERIOD WHILE THE REST OF THE COUNTRY WILL BE MUCH MORE  
VARIABLE. RECORD HIGHS ARE POSSIBLE ON MONDAY/TUESDAY IN SOUTHERN  
CALIFORNIA INTO ARIZONA. QUICK SHOT OF COLD AIR WILL FOLLOW THE  
LEAD EASTERN SYSTEM ON TUESDAY BUT THEN ABOVE AVERAGE TEMPERATURES  
AHEAD OF THE MAIN PACIFIC SYSTEM WILL PUSH OUT OF THE PLAINS ON  
TUESDAY AND INTO THE MIDWEST/OHIO VALLEY WEDNESDAY THEN INTO THE  
EAST THURSDAY AND EARLY FRIDAY. MUCH COLDER AIR (10-20 DEGREES  
BELOW AVERAGE) WILL FOLLOW BEHIND THIS FRONT (AND THE ARCTIC  
FRONT) FIRST IN MONTANA ON WEDNESDAY THEN THROUGH THE HIGH PLAINS  
THURSDAY AND INTO THE MS RIVER VALLEY FRIDAY.  
 
PRECIPITATION...  
 
PAC NW WILL SEE MULTIPLE PRECIP EVENTS, STARTING WITH THE FRONTAL  
PASSAGE ON MONDAY THEN ONSHORE FLOW AND UPPER TROUGH PASSAGE  
TUESDAY/WEDNESDAY AND ANOTHER SYSTEM LATER IN THE WEEK. TREND WILL  
BE FOR GENERALLY LESS RAIN/SNOW THROUGH THE WEEK BUT TOTAL AMOUNTS  
SHOULD BE SEVERAL INCHES (OR SEVERAL FEET OF SNOW) IN FAVORED  
LOCATIONS WITH LESSER AMOUNTS (MAYBE EVEN NOTHING) IN THE RAIN  
SHADOW AREAS AND TO THE LEE OF THE CASCADES.  
 
AS THE FRONT CONTINUES EASTWARD, GULF WILL EVENTUALLY SUPPLY MORE  
MOISTURE FOR AREAS ALONG AND EAST OF THE MISSISSIPPI AS THE UPPER  
TROUGH DIGS IN. A MORE ORGANIZED SOUTHERN LOW DEVELOPMENT WOULD  
SUPPORT MORE RAIN/SNOW TO THE CENTRAL APPALACHIANS EASTWARD  
(GFS/GEFS VS GENERALLY DRIER ECMWF/ECMWF ENSEMBLES). WINTER  
WEATHER THREAT REMAINS FOR MUCH OF THE MIDWEST/GREAT  
LAKES/NORTHEAST/MID-ATLANTIC AND PERHAPS PARTS OF THE SOUTHEAST  
DEPENDING ON HOW THE FRONT EVOLVES. LAKE EFFECT SNOWS SHOULD  
RESUME THU/FRI IN THE WAKE OF THE FRONT WITH NORTHERLY TO  
NORTHWESTERLY FLOW AND PLENTY OF COLD AIR (-20S AT 850MB).  
 
FRACASSO  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page