214  
FXUS02 KWBC 220617  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
116 AM EST THU FEB 22 2018  
 
VALID 12Z SUN FEB 25 2018 - 12Z THU MAR 01 2018  
 
DUE TO TECHNICAL DIFFICULTIES, SOME PRODUCTS MAY NOT BE AVAILABLE  
OR UPDATED. PLEASE CHECK ISSUANCE TIMES. WE APOLOGIZE FOR ANY  
INCONVENIENCE.  
 
   
..PATTERN OVERVIEW
 
 
THE MID-LATITUDE FLOW SHOULD BE IN SOME SORT OF TRANSITIONAL STATE  
AS THE PERSISTENT POSITIVE HEIGHT ANOMALY OVER THE WESTERN  
ATLANTIC FINALLY BUCKLES. HOWEVER...THE BLOCKING RIDGE EAST OF THE  
HAWAIIAN ISLANDS SHOULD CONTINUE WHICH FAVORS A SERIES OF TROUGHS  
PUSHING ACROSS THE WESTERN U.S. DURING THE PERIOD. WITHIN THIS  
TRAIN OF SHORTWAVES...MANY OF THEM HAVE THE POTENTIAL TO BRING  
VAST IMPACTS TO THE REGIONS OF INTEREST. THE LEAD SYSTEM WILL WIND  
UP OVER THE UPPER GREAT LAKES ON SUNDAY MORNING BEFORE LIFTING  
INTO NORTHERN QUEBEC EARLY NEXT WEEK. ON ITS HEELS...A WELL  
ADVERTISED UPPER LOW BARRELS DOWN THE WEST COAST ACCOMPANIED BY  
IMPRESSIVELY LOW 1000-500 MB THICKNESS VALUES. THIS PARENT TROUGH  
SHOULD OPEN UP WHILE MOVING THROUGH THE DESERT SOUTHWEST AND INTO  
THE FOUR CORNERS REGION BY MID-WEEK. THIS COULD LEAD TO THE  
FORMATION OF ANOTHER DEEP CYCLONE MOVING TOWARD THE OH VALLEY LATE  
IN THE PERIOD. MEANWHILE...ANOTHER SHORTWAVE TAKES SHAPE OVER THE  
WEST COAST WHICH MAINTAINS THE VERY REPEATABLE SYNOPTIC PATTERN IN  
PLACE.  
 
   
..MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES
 
 
AS MENTIONED IN THE HEADER...RESOURCES REMAIN SOMEWHAT SCANT SO  
WILL FOCUS ON SOME OF THE MORE MEANINGFUL ISSUES. FIRST OF ALL...A  
DEEP SURFACE LOW PRIMED TO PUSH INTO THE UPPER GREAT LAKES ON  
SUNDAY MORNING HAS THE POTENTIAL TO BE SUB 980-MB BY 25/1200Z.  
CONSIDERING THE PAST FEW RUNS OF THE GFS/ECMWF...THE FORMER HAS  
BEEN CONSISTENTLY DEEPER WHICH THE 12Z ECMWF APPEARS TO HAVE  
TRENDED TOWARD. DOWNSTREAM RIDGING SHOULD FORCE THIS SHORTWAVE  
INTO EASTERN CANADA WHILE MID-LEVEL HEIGHTS BRIEFLY BUILD ACROSS  
THE CENTRAL U.S. EARLY MONDAY. THE NEXT SYSTEM IN THE CHAIN WILL  
BE IN THE FORM OF A CLOSED LOW WHICH HAS BEEN ADVERTISED FOR A FEW  
DAYS NOW. POTENTIAL 1000-500 MB THICKNESSES MAY PUSH INTO THE  
530-535 DM RANGE WHICH COULD SPREAD WINTRY PRECIPITATION TO SOME  
RATHER LOW ELEVATIONS ALONG THE CA COAST. OVERALL...THE 12Z ECMWF  
AND PRECEDING RUNS HAVE BEEN THE MOST STABLE WHILE THE GFS FROM  
THE PREVIOUS DAY WAS PERHAPS 24-HOURS SLOWER. THE 00Z GFS SPED UP  
FROM ITS PRECEDING RUN WHICH TAKES IT OUT AHEAD OF THE CONSENSUS  
SOLUTION EARLY TUESDAY. SUCH DIFFERENCES PROJECT FORWARD WITH SOME  
VAST SPREAD WHILE THE SYSTEM ACCELERATES ACROSS THE CENTER OF THE  
COUNTRY. BY 01/1200Z...THE 00Z GFS DEPICTS A POTENT SHORTWAVE  
CROSSING INTO THE OH VALLEY WHILE THE 12Z ECMWF/CMC ARE BACK  
TOWARD THE SOUTHERN/CENTRAL HIGH PLAINS. GIVEN THE STAGNANT RIDGE  
OVER THE EASTERN PACIFIC...A THIRD SYSTEM TAKES SHAPE ALONG THE  
WEST COAST WITH POSITIONS QUITE VARIABLE AMONG THE OPERATIONAL  
GUIDANCE.  
 
WITH THE NON-NCEP GUIDANCE UNAVAILABLE FOR USE IN THE MODEL  
BLENDER...HAD TO INCORPORATE THE GFS/GEFS SOLUTIONS AS FIT.  
UTILIZED A COMBINATION OF THE 18Z/12Z GFS WITH THE 18Z GEFS MEAN  
THROUGHOUT THE PERIOD WITH A GRADUAL DEDUCTION OF OPERATIONAL  
INFLUENCES TOWARD THE DAY 5-7...FEBRUARY 27-MARCH 1...REALM.  
UNFORTUNATELY...WITH THE ECMWF SOLUTIONS BEING AROUND 12 TO 18  
HOURS SLOWER BY DAY 7...THE MANUAL FORECAST MAY BE TOO QUICK SO  
CONFIDENCE IN IT IS VERY LOW.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
CONDITIONS WILL GENERALLY REMAIN QUITE MILD FROM THE MS RIVER  
EASTWARD...PARTICULARLY ON SUNDAY AND INTO MONDAY MORNING.  
RELATIVE TO CURRENT RECORDS...THERE MAY BE SOME OVERNIGHT MINIMA  
WHICH BREAK DAILY RECORDS FROM THE MID-SOUTH INTO THE MID-ATLANTIC  
ON SUNDAY. EXPECTED LOWS WILL BE ANYWHERE FROM THE MID/UPPER 50S  
INTO THE LOWER 60S. SUCH TEMPERATURES WILL RESIDE ANYWHERE FROM 20  
TO POSSIBLY 30 DEGREES ABOVE CLIMATOLOGY FOR LATE FEBRUARY.  
ANOMALIES SHOULD COME DOWN A BIT AS THE UPPER RIDGE WEAKENS WHILE  
UPSTREAM HEIGHTS SEMI-REGULARLY LOWER. OVER THE WESTERN U.S...THE  
PERSISTENCE OF UPPER TROUGHING WILL KEEP BELOW AVERAGE  
TEMPERATURES IN THE PICTURE ALL THE WAY INTO THE FIRST DAY OF  
MARCH. THE SHARPEST DEPARTURES FROM CLIMATOLOGY WILL BE OVER THE  
NORTHERN ROCKIES WITH ANOMALIES IN THE 15 TO 20 DEGREE RANGE. THE  
WEST COAST IS FORECAST TO ALSO REMAIN CHILLY AS OVERNIGHT LOWS  
PUSH BELOW FREEZING IN MANY LOCATIONS.  
 
GIVEN THE INTENSE WAVE OF LOW PRESSURE MOVING INTO THE UPPER GREAT  
LAKES ON SUNDAY MORNING...WOULD ANTICIPATE A DEFORMATION ZONE OF  
WINTRY PRECIPITATION OVER THE REGION. THIS SHOULD BE IN THE  
PROCESS OF EXITING THE REGION WHILE THE TRAILING COLD FRONT WILL  
SPREAD RAINFALL ALONG THE ENTIRE EASTERN SEABOARD AS WELL AS ALONG  
THE GULF COAST. ACROSS THE WEST COAST...THE UPPER LOW WILL FOCUS  
MODERATE/HEAVY RAIN/SNOW OVER WESTERN OR/WA WITH GREATER AMOUNTS  
ATTACHED TO THE HIGHER PEAKS OF THE CASCADES. PRECIPITATION SHOULD  
SPREAD DOWN THE COAST WITH APPRECIABLY LOW SNOW LEVELS GIVEN THE  
MAGNITUDE OF COLD AIR TO WORK WITH. AS THIS SYSTEM BARRELS TOWARD  
THE DESERT SOUTHWEST...AMPLE RETURN FLOW IN ADVANCE OF THESE  
HEIGHT FALLS WILL BRING WARM ADVECTION RAINFALL TO SECTIONS OF THE  
ARKLATEX AND POINTS EASTWARD. THIS COULD BE ACCOMPANIED BY  
HYDROLOGIC ISSUES DEPENDING ON THE DEGREE OF RECOVERY OF LOCAL  
RIVERS...STREAMS...AND CREEKS FROM THE ONGOING ACTIVITY.  
MEANWHILE...UNSETTLED CONDITIONS RETURN TO THE PACIFIC NORTHWEST  
WITH THE NEXT SYSTEM PRIMED TO MOVE THROUGH.  
 
RUBIN-OSTER  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page