146  
FXUS02 KWBC 262048  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
347 PM EST TUE FEB 26 2019  
 
VALID 12Z FRI MAR 01 2019 - 12Z TUE MAR 05 2019  
 
1530 UTC UPDATE...  
 
MODELS SHOWED GOOD AGREEMENT AT THE LARGE SCALES THROUGHOUT THE  
MEDIUM RANGE, BUT CONTINUED TO SHOW SOME SIGNIFICANT DIFFERENCES  
WITH RESPECT TO INDIVIDUAL SYSTEMS, ESPECIALLY BY LATER IN THE  
FORECAST PERIOD. CONSENSUS WAS SUFFICIENT DURING DAYS 3-5  
(FRI-SUN) TO BASE THE FORECAST ON A MULTI-MODEL DETERMINISTIC  
BLEND (ECMWF/GFS/CMC/UKMET). THE ECMWF PLACED MORE EMPHASIS ON  
ENERGY TRANSFER TO A COASTAL LOW OFF THE MID-ATLANTIC/NORTHEAST  
SAT-SUN THAN MOST OTHER SOLUTIONS, AND THE PREFERENCE WAS TO SHOW  
A SLOWER TRANSFER MORE LIKE THE 06Z GFS AND 00Z UKMET/CMC. MORE  
SIGNIFICANT DIFFERENCES EMERGE FROM LATE DAY 5 ONWARD WITH THE  
NEXT WAVE OF LOW PRESSURE EXPECTED TO DEVELOP ALONG THE WAVY GULF  
COAST SURFACE FRONT. THE ECMWF WAS MUCH STRONGER/FARTHER NORTH  
WITH THIS LOW TRACK THAN THE CONSENSUS, AND WAS ON THE FRINGE OF  
ITS OWN ENSEMBLE MEMBERS. THUS, PREFERRED A SOMEWHAT MORE  
SUPPRESSED SOLUTION, GENERALLY SIMILAR TO A BLEND OF THE GFS AND  
GEFS/ECENS ENSEMBLE MEANS. BY MON-TUE MODELS BEGIN TO STRUGGLE  
WITH HOW TO HANDLE SHORTWAVE ENERGY ACROSS THE PACIFIC NORTHWEST  
ATTEMPTING TO UNDERCUT THE BLOCKING ALASKA RIDGE. GIVEN A RANGE OF  
SOLUTIONS AS WELL AS RUN-TO-RUN VARIABILITY, PREFERRED MUCH  
HEAVIER ENSEMBLE MEAN WEIGHTING BY DAYS 6-7. OVERALL, CHANGES TO  
CONTINUITY IN THIS UPDATE WERE RELATIVELY MINIMAL. THE FORECAST  
DISCUSSION FROM OVERNIGHT FOLLOWS BELOW.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 0659 UTC)...  
   
..PATTERN OVERVIEW
 
 
GUIDANCE HAS BEEN CONSISTENT WITH THE FORECAST MEAN FLOW FROM THE  
MULTI-DAY MEAN PERSPECTIVE, SHOWING BROADLY CYCLONIC FLOW OVER THE  
LOWER 48--JUST TO THE SOUTH OF A GENERAL EAST-WEST AXIS OF  
RELATIVELY LOW HEIGHTS ACROSS SOUTHERN CANADA. THIS AXIS OF LOW  
HEIGHTS WILL CONTAIN ONE OR MORE UPPER LOWS THAT WOULD HELP TO  
PUSH VERY COLD AIR INTO THE CENTRAL U.S. WITH THE NORTHERN HIGH  
PLAINS POSSIBLY SEEING A COUPLE DAYS OF EXCEPTIONALLY LOW  
ANOMALIES OF AT LEAST 30-40F BELOW NORMAL. AT THE SAME TIME FLOW  
FROM THE PACIFIC WILL BRING MOISTURE INTO PARTS OF THE WEST  
(ESPECIALLY CALIFORNIA INTO THE CENTRAL ROCKIES). EVEN WITH THE  
AGREEABLE MEAN FLOW, SOME EMBEDDED DETAILS HAVE BEEN DIFFICULT TO  
RESOLVE. IN PARTICULAR EASTERN U.S. DETAILS HAVE VARIED WITH  
TRENDS OVER THE PAST DAY SHOWING A WEAKER POTENTIAL STORM OVER THE  
GREAT LAKES/NORTHEAST THIS WEEKEND BUT INCREASED THREAT FOR AREAS  
OF LOCALLY HEAVY RAINFALL OVER THE GULF COAST/SOUTHEAST DURING THE  
PERIOD.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE COMBINATION OF THE SHORT RANGE PACIFIC NORTHWEST UPPER LOW AND  
INITIAL SOUTHERN CANADA ELONGATED UPPER LOW CONTINUE TO PROVIDE  
FORECAST DIFFICULTIES. THE PAST TWO RUNS OF THE ECMWF/ECMWF MEAN  
(00Z/25 AND 12Z/25) SHIFTED MORE OFFSHORE WITH THE WESTERN LOW AND  
EASTWARD WITH THE CANADA LOW. THE RESULT IS MINIMAL GREAT  
LAKES/OHIO VALLEY INTO NEW ENGLAND SURFACE DEVELOPMENT DURING THE  
WEEKEND WITH LOWEST PRESSURES TENDING TO STAY OFFSHORE. OTHER  
SOLUTIONS SHOW VARYING DEGREES OF FASTER EJECTION OF THE WESTERN  
LOW ENERGY AND FARTHER WEST SOUTHERN CANADA LOW--LEADING TO  
SOMEWHAT BETTER DEFINED LOW PRESSURE THAN THE ECMWF/ECMWF MEAN  
ALBEIT WITH WEAKER DEPTH THAN SEEN IN SOME PREVIOUS GUIDANCE  
(ESPECIALLY THE GFS). GUIDANCE BEHAVIOR OVER THE NORTHERN  
U.S./SOUTHERN CANADA OVER RECENT DAYS DOES NOT LEND A LOT OF  
CONFIDENCE TO ANY PARTICULAR MODEL SYSTEM ON ITS OWN. THE ONE  
COMMON THEME IN LATEST SOLUTIONS IS A LESS AMPLIFIED OVERALL  
TROUGH ALOFT, LEADING TO SLOWER SOUTHWARD PROGRESSION OF THE  
STRONG COLD FRONT DROPPING THROUGH THE PLAINS.  
 
MEANWHILE FOR THE SOUTHERN STREAM SYSTEM HEADING INTO CALIFORNIA  
THIS WEEKEND, MODELS/ENSEMBLE MEANS HAVE SETTLED INTO THE EXPECTED  
TRACK FAIRLY WELL BUT ARE REMARKABLY PERSISTENT IN THEIR AMOUNT OF  
TIMING SPREAD AND IN SOME CASES RUN-TO-RUN VARIABILITY. THIS  
FAVORS MAINTAINING A GENERAL COMPROMISE TO HELP MAINTAIN STABILITY  
IN THE FORECAST. INTO THE WEEKEND A BLEND OF THE 18Z GFS AND 12Z  
ECMWF/UKMET/CMC PROVIDES A REASONABLE INTERMEDIATE STARTING POINT  
FOR THIS SYSTEM WHILE REPRESENTING ONLY 30 PERCENT INCLUSION OF  
THE ECMWF FOR AFOREMENTIONED ISSUES TO THE NORTH AND EAST. NEW  
00Z GUIDANCE THUS FAR STILL SUPPORTS LEANING AWAY FROM 12Z ECMWF  
SPECIFICS FOR THE NORTHERN LATITUDES DURING THE FIRST HALF OF THE  
PERIOD.  
 
BY THE LATTER HALF OF THE PERIOD THE 18Z GEFS/12Z ECMWF MEANS  
PROVIDE A REASONABLE TEMPLATE FOR DEPICTING THE EXPECTED PATTERN  
THOUGH OPERATIONAL RUNS PROVIDE SOME DEGREE OF RELATIVE AGREEMENT,  
ARGUING FOR KEEPING AS MUCH AS 50 PERCENT OF THEIR IDEAS BY DAY 6  
MON AND 30 PERCENT BY DAY 7 TUE. IN PARTICULAR THE OPERATIONAL  
RUNS ARE SUGGESTING THAT ANOTHER DEEP UPPER LOW CENTER COULD TRACK  
TOWARD THE UPPER GREAT LAKES DURING THE DAY NEXT TUE. FARTHER  
WEST THERE IS FAIR AGREEMENT ON AN UPPER RIDGE BUILDING INTO THE  
WEST AHEAD OF ANOTHER PACIFIC SYSTEM. CURRENT MEANS ARE SIMILAR  
AFTER RECENT TRENDS IN THE GEFS MEAN TOWARD THE ECMWF MEAN. THE  
12Z GFS WAS THE ONE NOTABLY LESS PROBABLE SOLUTION BY THE END OF  
NEXT TUE AS IT WAS FASTER THAN OTHER SOLUTIONS TO BRING HEIGHT  
FALLS TO THE WEST COAST.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
AFTER A BRIEF PERIOD OF DRIER WEATHER OVER THE WEST, EXPECT THE  
ARRIVAL OF ANOTHER PACIFIC SYSTEM TO BRING MOISTURE INTO  
CALIFORNIA BY AROUND THE START OF THE WEEKEND WITH RAIN AND HIGHER  
ELEVATION SNOW THEN SPREADING EASTWARD INTO THE CENTRAL ROCKIES.  
MUCH OF THE PRECIPITATION WITH THIS SYSTEM SHOULD DEPART BY EARLY  
NEXT WEEK. THE SIERRA NEVADA RANGE SHOULD SEE HIGHEST TOTALS WITH  
OTHER RELATIVE MAXIMA OVER FAVORED LOCATIONS ALONG THE CENTRAL  
CALIFORNIA COAST AND THE GREAT BASIN/CENTRAL ROCKIES. MEANWHILE  
DURING THE FIRST HALF OF THE PERIOD LOW LEVEL UPSLOPE FLOW ON THE  
WESTERN SIDE OF COLD HIGH PRESSURE OVER THE PLAINS ALONG WITH  
SHEARING SHORTWAVE ENERGY SHOULD PROMOTE SOME SNOW ALONG PORTIONS  
OF THE NORTHERN ROCKIES.  
 
FROM LATE THIS WEEK INTO THE WEEKEND EXPECT SOME SNOW TO SPREAD  
ACROSS THE NORTHERN PLAINS AND EVENTUALLY INTO THE NORTHEAST,  
THOUGH RECENT WEAKER TRENDS WITH SURFACE LOW PRESSURE HAVE LOWERED  
POTENTIAL SNOWFALL AMOUNTS SOMEWHAT. BEHIND THE SYSTEM THERE  
SHOULD BE A PERIOD OF LAKE EFFECT SNOW DOWNWIND FROM PORTIONS OF  
THE GREAT LAKES WITHOUT ICE COVER. EXPECT SOME AREAS OF RAIN TO  
THE SOUTH. LESS AMPLIFIED TRENDS FOR FLOW ALOFT HAVE INCREASED  
THE POSSIBILITY THAT THE FRONT TRAILING FROM THE WEEKEND EASTERN  
U.S. SYSTEM MAY HANG UP OVER FLORIDA AND THE GULF OF MEXICO, WITH  
EMBEDDED SOUTHERN STREAM SHORTWAVES HELPING TO ENHANCE RAINFALL  
ALONG/NORTH OF THE FRONT. SOME HEAVY RAINFALL MAY BE POSSIBLE  
OVER THE CENTRAL/EASTERN GULF COAST REGION AND NORTHERN FLORIDA  
INTO THE SOUTHEAST. WITH COLD AIR PUSHING SOUTH/SOUTHEAST WITH  
TIME THERE WILL BE INCREASING POTENTIAL THAT THE NORTHERN FRINGE  
OF PRECIPITATION ACROSS SOUTH-CENTRAL LATITUDES COULD BE IN THE  
FORM OF SNOW BY EARLY NEXT WEEK.  
 
FOR TEMPERATURES THE EXTREMELY COLD ANOMALIES OVER THE CENTRAL  
U.S. WILL CONTINUE TO BE THE DOMINANT STORY WITH HIGHS POSSIBLY AT  
LEAST 30-40F BELOW NORMAL OVER THE NORTHERN-CENTRAL PLAINS FROM  
SAT ONWARD. ESPECIALLY BY SUN THERE MAY BE FAIRLY BROAD COVERAGE  
OF LOCATIONS NEARING OR REACHING DAILY RECORDS FOR COLD HIGHS WITH  
SOME SCATTERED DAILY RECORD LOWS ALSO POSSIBLE. SOME OF THIS COLD  
AIR WILL SPREAD INTO THE EAST BY SUN-TUE WITH TEMPERATURES 10-20F  
BELOW NORMAL EVEN REACHING THE EAST COAST. THE NORTHWEST WILL BE  
CHILLY AS WELL WITH SOME INTERIOR AREAS 10-20F BELOW NORMAL MOST  
DAYS. ABOVE NORMAL TEMPERATURES SHOULD BE CONFINED TO MOSTLY  
MORNING LOWS OVER THE SOUTHERN HALF OF THE WEST AND FOR SOME  
MIN/MAX READINGS OVER THE SOUTH/EAST AHEAD OF THE INITIAL PLAINS  
COLD FRONT.  
 
RAUSCH  
 
HAZARDS:  
HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA, THE PACIFIC NORTHWEST,  
AND THE SOUTHWEST, SAT-SUN, MAR  
2-MAR 3.  
AND TUE, MAR 5.  
HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST AND THE MID-ATLANTIC,  
SUN-MON, MAR 3-MAR 4.  
HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, THE  
NORTHERN GREAT BASIN, THE CENTRAL  
ROCKIES, CALIFORNIA, THE PACIFIC NORTHWEST, AND THE SOUTHWEST,  
SAT-MON, MAR 2-MAR 4.  
HEAVY SNOW ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE CENTRAL  
ROCKIES, THE CENTRAL GREAT BASIN,  
THE CENTRAL PLAINS, AND THE SOUTHWEST, FRI-TUE, MAR 1-MAR 5.  
HEAVY SNOW ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND THE  
NORTHERN PLAINS, FRI, MAR 1.  
HEAVY SNOW ACROSS PORTIONS OF THE SOUTHERN APPALACHIANS, THE  
MID-ATLANTIC, THE CENTRAL  
APPALACHIANS, THE OHIO VALLEY, AND THE TENNESSEE VALLEY, SUN-MON,  
MAR 3-MAR 4.  
HEAVY SNOW ACROSS PORTIONS OF THE MID-ATLANTIC, THE NORTHEAST, AND  
THE GREAT LAKES, SAT-SUN, MAR  
2-MAR 3.  
HEAVY SNOW ACROSS PORTIONS OF THE MID-ATLANTIC AND THE NORTHEAST,  
MON, MAR 4.  
FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHEAST.  
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY, THE TENNESSEE  
VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE MID-ATLANTIC, THE  
SOUTHERN APPALACHIANS, THE SOUTHEAST,  
THE PACIFIC NORTHWEST, AND THE OHIO VALLEY.  
FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHEAST.  
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL  
PLAINS, THE GREAT LAKES, THE LOWER  
MISSISSIPPI VALLEY, THE CENTRAL APPALACHIANS, THE NORTHERN PLAINS,  
THE TENNESSEE VALLEY, THE  
PACIFIC NORTHWEST, THE NORTHERN ROCKIES, THE CENTRAL ROCKIES, THE  
MIDDLE MISSISSIPPI VALLEY, THE  
NORTHEAST, THE SOUTHERN APPALACHIANS, THE NORTHERN GREAT BASIN,  
THE UPPER MISSISSIPPI VALLEY, THE  
MID-ATLANTIC, THE SOUTHERN PLAINS, AND THE OHIO VALLEY, FRI-TUE,  
MAR 1-MAR 5.  
HIGH WINDS ACROSS PORTIONS OF THE ALEUTIANS, SAT-MON, MAR 2-MAR 4.  
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF MAINLAND  
ALASKA, FRI, MAR 1.  
AND MON, MAR4.  
 
ADDITIONAL 3-7 DAY HAZARDS INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page