547  
FXUS02 KWBC 260659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EST TUE JAN 26 2021  
 
VALID 12Z FRI JAN 29 2021 - 12Z TUE FEB 02 2021  
 
...CALIFORNIA HEAVY PRECIPITATION TO TAPER OFF LATE WEEK FOLLOWED  
BY ANOTHER SIGNIFICANT EVENT LIKELY TO FOCUS ALONG THE CENTRAL  
WEST COAST FROM THE WEEKEND INTO EARLY NEXT WEEK...  
 
...WEEKEND INTO EARLY NEXT WEEK SYSTEM TO SPREAD A BROAD AREA OF  
RAIN AND WINTRY WEATHER ACROSS THE EASTERN HALF OF THE LOWER 48...  
 
...WEATHER PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY  
ASSESSMENT...  
 
THE LATEST GUIDANCE CONTINUES TO SHOW A PATTERN INVOLVING  
AMPLIFYING UPPER TROUGHS OVER THE EASTERN PACIFIC FOLLOWED BY  
PROGRESSION ACROSS THE LOWER 48. FOR THE FRI-TUE PERIOD OF  
INTEREST, THIS EVOLUTION WILL LEAD TO AREAS OF ENHANCED  
PRECIPITATION ALONG THE WEST COAST WITH LESSER AMOUNTS FARTHER  
INLAND OVER THE WEST ALONG WITH A SYSTEM THAT WILL SPREAD A LARGE  
AREA OF MOISTURE WITH VARIOUS PRECIPITATION TYPES OVER THE EASTERN  
HALF OF THE COUNTRY. A DEEP AND COMPACT UPPER LOW CROSSING THE  
NORTHEAST LATE THIS WEEK AND LINGERING CYCLONIC FLOW ALOFT WILL  
HOLD CHILLY AIR OVER THE EAST INTO THE WEEKEND, SUPPORTING  
POTENTIAL FOR FAIRLY WIDE COVERAGE OF WINTRY WEATHER OVER THE  
NORTHERN HALF OF THE EAST.  
 
MODELS AND ENSEMBLES HAVE MAINTAINED REASONABLE CONTINUITY FOR  
FEATURES IN GENERAL BUT WITH SOME TYPICAL SPREAD AND TRENDS. FOR  
THE SYSTEM FORECAST TO REACH THE CENTRAL U.S. THIS WEEKEND,  
SOLUTIONS ARE SPLIT OVER THE RELATIVE EMPHASIS OF LEADING  
SHORTWAVE ENERGY CROSSING THE WEST LATE THIS WEEK AND A TRAILING  
WEAKER SHORTWAVE ENTERING THE WEST BY EARLY SAT. GFS/UKMET RUNS  
HAVE BEEN EMPHASIZING THE LEADING FEATURE WHILE THE ECMWF/CMC HAVE  
BEEN WEAKENING THE LEADING SHORTWAVE IN FAVOR OF THE TRAILING ONE  
(OR SOME INTERACTION OF THE TWO). THE TRAILING IMPULSE IS RATHER  
SMALL IN SCALE AND THUS HAS LOW PREDICTABILITY. PARTIALLY DUE TO  
THESE DIFFERENCES, ONCE THE SYSTEM REACHES THE EAST THE GFS/GEFS  
HAVE TENDED TO BE SOMEWHAT FASTER/NORTHWARD WITH THE PARENT LOW AS  
WELL AS THE SECONDARY DEVELOPMENT OFF THE MID-ATLANTIC/NEW ENGLAND  
COAST. ON THE POSITIVE SIDE, IN SPITE OF THESE DETAIL DIFFERENCES  
THERE IS GOOD CONSENSUS ON THE OVERALL UPPER TROUGH AND POTENTIAL  
EMBEDDED CLOSED LOW FORMATION. THE PAST COUPLE ECMWF/ECMWF MEAN  
RUNS HAVE EXTENDED PRIOR SOUTHWARD TRENDS FOR LOW PRESSURE OVER  
THE EAST IN RESPONSE TO THE NEW ENGLAND UPPER LOW/LINGERING  
CYCLONIC FLOW. MORE RECENTLY THE GFS/GEFS HAVE DISPLAYED LESS OF  
THIS TREND.  
 
AFTER THE AFOREMENTIONED QUESTION MARKS ABOUT ENERGY REACHING THE  
WEST SAT, THERE IS ONGOING SPREAD FOR THE AMPLITUDE AND TIMING OF  
THE NEXT UPPER TROUGH APPROACHING THE WEST. GFS RUNS HAVE BEEN ON  
THE SLOWER/AMPLIFIED SIDE OF THE SPREAD BUT WITH RUNS THROUGH THE  
18Z CYCLE HEDGING A BIT TOWARD THE ECMWF CLUSTER FOR THE TROUGH  
ITSELF AND UPSTREAM FLOW. HOWEVER THE NEW 00Z GFS REVERSED THIS  
TREND A BIT AND THE 00Z UKMET IS FAIRLY CLOSE TO IT BY THE END OF  
ITS RUN LATE SUN. THE GEFS MEAN IS CLOSER TO GFS RUNS IN  
PRINCIPLE.  
 
A COMPOSITE OF OPERATIONAL 12Z/18Z MODELS REFLECTED A REASONABLE  
INTERMEDIATE SOLUTION FOR THE FIRST HALF OF THE PERIOD WITH CMC  
INPUT SUFFICIENTLY LOW TO DOWNPLAY SOME REGIONAL SPECIFICS THAT  
COMPARED A LITTLE LESS FAVORABLY TO CONSENSUS. FOR THE REST OF  
THE PERIOD, TRENDS THROUGH THE 18Z CYCLE RECOMMENDED A SLIGHT TILT  
TOWARD THE 12Z ECMWF/ECMWF MEAN RELATIVE TO THE 18Z GFS/GEFS MEAN  
WHILE MAINTAINING A SMALL CMC COMPONENT. THE OPERATIONAL MODELS  
WERE CLOSE ENOUGH FOR THE GENERAL PATTERN/SYSTEM EVOLUTION THROUGH  
THE END OF THE PERIOD TO ALLOW FOR MAJORITY INCLUSION OF THEIR  
SOLUTIONS AND YIELD SYSTEMS WITH SOMEWHAT BETTER DEFINITION THAN  
THE MEANS.  
 
   
..WEATHER/THREATS HIGHLIGHTS
 
 
THE RANGES OVER FAR SOUTHWESTERN CALIFORNIA MAY STILL SEE MODERATE  
TO HEAVY PRECIPITATION LATE THIS WEEK WHILE LIGHTER ACTIVITY  
LINGERS OVER THE REST OF THE STATE. EXPECT GENERALLY MODERATE  
AMOUNTS OF RAIN AND HIGHER ELEVATION SNOW TO SPREAD ACROSS THE  
REMAINDER OF THE WEST AS THE SUPPORTING SHORTWAVE ALOFT CROSSES  
THE REGION. THEN FROM THE WEEKEND INTO NEXT WEEK UPSTREAM ENERGY  
ALOFT AND A COUPLE FRONTAL SYSTEMS WILL BRING ADDITIONAL MOISTURE  
TO THE WEST COAST. MUCH OF THE PACIFIC NORTHWEST MAY SEE A PERIOD  
OF MODERATE TO HEAVY RAIN/MOUNTAIN SNOW EARLY IN THE EVENT  
FOLLOWED BY A MORE CONCENTRATED EMPHASIS OF HEAVY PRECIPITATION ON  
SOUTHWESTERN OREGON AND NORTHERN CALIFORNIA. SOME OF THIS  
MOISTURE SHOULD EXTEND INTO THE NORTHERN ROCKIES. SPECIFICS OF  
THE HEAVIEST PRECIPITATION WILL DEPEND ON THE EXACT AMPLITUDE AND  
TIMING OF THE APPROACHING UPPER TROUGH BUT THE GENERAL SIGNAL FOR  
SOUTHWESTERN OREGON/NORTHERN CALIFORNIA HAS BEEN FAIRLY STABLE  
OVER RECENT DAYS.  
 
THE NORTHEAST WILL SEE BREEZY TO WINDY CONDITIONS LATE THIS WEEK  
IN THE GRADIENT BETWEEN STRONG ATLANTIC LOW PRESSURE AND GREAT  
LAKES HIGH PRESSURE. THE SYSTEM FORECAST TO EMERGE OVER THE  
PLAINS TO START THE WEEKEND SHOULD TRACK EASTWARD AND ULTIMATELY  
LEAD TO SECONDARY LOW PRESSURE OFF THE MID-ATLANTIC/NEW ENGLAND  
COAST BY AROUND LATE SUNDAY OR EARLY MONDAY. THIS SYSTEM WILL  
SPREAD A BROAD AREA OF PRECIPITATION ACROSS THE EASTERN HALF OF  
THE COUNTRY WITH SOME WINTRY WEATHER POSSIBLE FROM THE NORTHERN  
PLAINS/MIDWEST THROUGH THE GREAT LAKES/OHIO VALLEY AND  
MID-ATLANTIC/NORTHEAST. SNOWFALL TOTALS WITHIN PORTIONS OF THIS  
AREA MAY BE SIGNIFICANT DEPENDING ON EXACT SYSTEM EVOLUTION.  
CHECK THE WINTER WEATHER OUTLOOK FORECASTS FOR A PROBABILISTIC  
DEPICTION OF LOCATIONS EXPECTED TO SEE THE BEST POTENTIAL FOR  
MEANINGFUL SNOW. RAIN WILL PREVAIL TO THE SOUTH WITH SOME LOCALLY  
MODERATE TO HEAVY ACTIVITY POSSIBLE BUT SYSTEM PROGRESSION MAY BE  
A LIMITING FACTOR FOR RAINFALL TOTALS.  
 
AREAS NEAR THE EAST COAST WILL TEND TO SEE BELOW NORMAL  
TEMPERATURES IN THE LATE WEEK/EARLY WEEKEND TIME FRAME. THE UPPER  
LOW CROSSING THE NORTHEAST WILL BRING AT LEAST ONE DAY OF HIGHS  
10-20F BELOW NORMAL TO LOCATIONS NEAR ITS PATH. AS THE SYSTEM  
INITIALLY NEAR THE WEST COAST PROGRESSES EASTWARD LATE THIS WEEK  
INTO THE WEEKEND, TEMPERATURES OVER THE PLAINS AND THEN  
EAST-CENTRAL U.S. WILL RISE TO ABOVE OR WELL ABOVE NORMAL  
VALUES--ESPECIALLY FOR MORNING LOWS WHICH WILL SEE BROAD COVERAGE  
OF 10-20F ANOMALIES. THEN CLOSER TO THE EAST COAST  
CLOUDS/PRECIPITATION WILL KEEP LOWS ABOVE NORMAL BUT HIGHS SHOULD  
BE WITHIN A FEW DEGREES ON EITHER SIDE OF NORMAL. MEANWHILE SOME  
AREAS OVER THE PLAINS MAY SEE READINGS 10F OR MORE ABOVE NORMAL  
INTO NEXT WEEK. THE SOUTHWESTERN STATES WILL BE MODERATELY BELOW  
NORMAL THROUGH THE PERIOD WITH MOSTLY SINGLE-DIGIT NEGATIVE  
ANOMALIES AND PERHAPS A FEW POCKETS THAT ARE SLIGHTLY COOLER.  
 
RAUSCH  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK 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  
 

 
 
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