618  
FXUS02 KWBC 111505  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1005 AM EST SUN FEB 11 2018  
 
VALID 12Z WED FEB 14 2018 - 12Z SUN FEB 18 2018  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
CLOSED UPPER LOW OFF THE SOUTHERN CA COAST EARLY IN THE PERIOD  
WILL MOVE EASTWARD THROUGH THE SOUTHWEST, BRINGING WIDESPREAD RAIN  
AND HIGH ELEVATION SNOW. BROAD CYCLONIC FLOW OVER MOST OF THE  
REMAINDER OF THE CONTIGUOUS U.S. WILL BRING COLDER AIR TO MUCH OF  
THE CENTRAL U.S. IN GENERAL, GUIDANCE SHOWS GOOD LARGE SCALE  
AGREEMENT, BUT NUMEROUS DIFFERENCES REMAIN AT SMALLER SCALES.  
LATEST MODELS HAVE TRENDED TOWARD A QUICKER EASTWARD PROGRESSION  
OF THE UPPER LOW, BECOMING ABSORBED INTO AN AMPLIFYING TROUGH  
ACROSS THE WESTERN U.S. BY THU (WITH THE 00Z UKMET BEING THE LONE  
HOLDOUT). FURTHER, ENSEMBLE MEMBERS IN BOTH THE ECENS AND GEFS HAS  
SHOWN A SUBSTANTIAL SHIFT IN THIS DIRECTION AS WELL. THUS, THE  
LATEST RUNS OF THE ECMWF/GFS WERE INCORPORATED, TRENDING THE  
FORECAST IN THIS DIRECTION. BY FRI, THE ECMWF IS ONCE AGAIN SLOWER  
THAN THE GFS WITH RESPECT TO UPPER ENERGY CROSSING THE CENTRAL  
U.S. AND GREAT LAKES, WHICH RESULTS IN A DIFFERENCE WITH RESPECT  
TO TIMING OF THE SURFACE FRONTAL WAVE AS IT CROSSES THE GREAT  
LAKES/NORTHEAST. THE 00Z ECENS MEAN SHOWED A QUICKER TIMING THAN  
THE DETERMINISTIC ECMWF, AND WAS VERY SIMILAR TO THE 06Z GFS.  
THUS, THE FORECAST LEANS TOWARD THE 06Z GFS ON DAY 5 ACROSS THE  
NORTHEASTERN U.S. NEXT ROUND OF SHORTWAVE ENERGY REACHES THE PAC  
NW BY FRI NIGHT/SAT, WITH AN UPPER TROUGH AMPLIFYING ACROSS THE  
WEST ONCE AGAIN BY SAT NIGHT/SUN. MODEL/ENSEMBLE AGREEMENT IS A  
BIT BETTER SURROUNDING THIS SYSTEM, BUT DIFFERENCES IN SURFACE  
PATTERN EVOLUTION APPEAR AS THE SYSTEM REACHES THE CENTRAL U.S. BY  
DAY 7. BROAD AGREEMENT AMONG MODELS/ENSEMBLES ON STRONG RIDGING  
BUILDING ONCE AGAIN IN THE NORTH PACIFIC BY EARLY NEXT WEEK ALONG  
WITH THE PERSISTENT HUDSON BAY UPPER LOW SHOULD CONTINUE TO  
SUPPORT OCCASIONAL SOUTHWARD MOVEMENT OF ARCTIC AIR MASSES INTO  
THE NORTHERN HIGH PLAINS. SUBTROPICAL RIDGING ATTEMPTING TO PRESS  
NORTHWARD ALONG THE EASTERN SEABOARD SHOULD PREVENT THE COLDEST OF  
AIR FROM PROGRESSING TO THE EAST COAST IN THIS SETUP.  
 
THE WPC FORECAST WAS INITIALLY BASED HEAVILY ON A DETERMINISTIC  
BLEND INCLUDING THE 00Z ECMWF/06Z GFS, WITH A GRADUAL TREND TOWARD  
INCREASED ENSEMBLE MEAN (00Z ECENS/NAEFS) WEIGHTING THROUGH THE  
PERIOD.  
 
RYAN  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
PRECIPITATION WILL EXPAND INTO AND THROUGH THE SOUTHWEST AS THE  
UPPER LOW NUDGES EASTWARD WED-FRI. CONTINUED SOUTHWESTERLY FLOW  
ALOFT WILL HELP RAISE PW VALUES TO +2 TO +4 STANDARD DEVIATIONS  
WHICH SUGGESTS SOME LOCALLY HEAVY RAINFALL, DEPENDING ON OTHER  
FACTORS OF COURSE. AMOUNTS MAY VARY FROM A TENTH OR TWO IN THE  
LOWER DESERTS AROUND THE COLORADO RIVER TO ABOUT A HALF INCH NEAR  
OR JUST N/NE OF PHOENIX/TUCSON TO PERHAPS AN INCH OR MORE IN THE  
MOUNTAINS. TEMPERATURES WILL GENERALLY BE ABOVE AVERAGE OVERNIGHT  
BUT NEAR TO BELOW AVERAGE DURING THE DAY GIVEN CLOUD COVER AND  
PRECIPITATION.  
 
TO THE NORTH, GENERALLY BELOW AVERAGE TEMPERATURES ARE EXPECTED  
FROM MONTANA AND THE HIGH PLAINS INTO THE UPPER MIDWEST AS A  
COUPLE WEAKER SHORTWAVES GET SWEPT ALONG THE QUASI-ZONAL  
UPPER-LEVEL FLOW FORECAST TO PERSIST OVER THE CENTRAL/EASTERN US.  
ABOVE AVERAGE TEMPERATURES ARE EXPECTED ACROSS MUCH OF THE EASTERN  
THIRD OF THE CONUS AS UPPER RIDGING MEANDERS ACROSS FLORIDA. 70S  
MAY REACH AS FAR NORTH AS CENTRAL VIRGINIA ON THURSDAY WITH 60S  
PAST THE MASON-DIXON LINE. A COLD FRONT WILL KNOCK DOWN  
TEMPERATURES LATER IN THE WEEK, ESPECIALLY UP NORTH ALONG THE  
US/CANADIAN BORDER, BUT THE SOUTHEAST WILL REMAIN MILD FOR  
MID-FEBRUARY. PRECIPITATION BY NEXT WEEKEND WILL EXPAND ACROSS THE  
LOWER MISSISSIPPI VALLEY INTO THE OHIO/TENNESSEE VALLEYS WITH SOME  
WINTRY PRECIPITATION ON ITS NORTH SIDE.  
 
FRACASSO  
 

 
 
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