684  
FXUS02 KWBC 070701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT THU APR 07 2022  
 
VALID 12Z SUN APR 10 2022 - 12Z THU APR 14 2022  
 
...ACTIVE WEATHER LIKELY ACROSS A LARGE PART OF THE COUNTRY NEXT  
WEEK...  
   
..OVERVIEW
 
 
LATEST GUIDANCE CONTINUES TO SHOW AN AMPLIFIED PATTERN IN WHICH  
ONE UPPER TROUGH DEPARTS FROM THE EAST AFTER SUNDAY WHILE ENERGY  
DIGGING IN FROM THE NORTHEASTERN PACIFIC REINFORCES WESTERN U.S.  
MEAN TROUGHING THAT SHOULD FINALLY EMERGE INTO THE PLAINS BY  
AROUND MIDWEEK. THERE IS A DECENT SIGNAL IN THE GUIDANCE THAT THIS  
PATTERN SHOULD PRODUCE ACTIVE WEATHER OVER A SIGNIFICANT PORTION  
OF THE LOWER 48 NEXT WEEK--INCLUDING RAIN/SNOW OVER THE WEST,  
EVENTUALLY A VIGOROUS STORM SYSTEM OVER THE PLAINS/UPPER MIDWEST  
WITH SOME SNOW TO THE NORTHWEST OF ITS TRACK, AND A THREAT FOR  
AREAS OF HEAVY RAINFALL PLUS STRONG TO SEVERE CONVECTION OVER SOME  
SOUTHERN AREAS OF THE CENTRAL U.S. HOWEVER WITHIN THIS BROAD THEME  
THERE ARE A NUMBER OF UNCERTAINTIES FOR DETAILS THAT TEMPER  
CONFIDENCE IN SPECIFICS OF THE FORECAST, NOT ONLY FOR THE MAIN  
AREA OF FOCUS OVER THE WESTERN-CENTRAL U.S. BUT ALSO FRONTAL  
POSITION OVER THE EAST DUE TO DIFFERENCES IN HOW LEADING SHORTWAVE  
ENERGY INITIALLY EJECTING ACROSS THE PLAINS ULTIMATELY EVOLVES.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
ASIDE FROM THE FAIRLY STABLE HANDLING OF THE UPPER TROUGH  
DEPARTING FROM THE EAST EARLY IN THE PERIOD, LATEST MODELS AND  
ENSEMBLES ARE GENERALLY STILL FINDING IT CHALLENGING TO RESOLVE  
SOME IMPORTANT ASPECTS OF THE FORECAST. DEPICTION OF LEADING  
SHORTWAVE ENERGY CROSSING THE NORTHERN TIER U.S. AND SOUTHERN  
CANADA HAS RECENTLY BECOME AN INCREASINGLY PROBLEMATIC PART OF THE  
FORECAST, LEADING TO SOME WIDE DIFFERENCES IN THE SOUTHERN EXTENT  
OF A FRONT OVER THE EAST. 12Z AND NEW 00Z UKMET RUNS ARE ON THE  
EXTREMELY AMPLIFIED SIDE OF THE SPREAD WITH THE SHORTWAVE ENERGY  
AND THUS PUSH THE FRONT QUITE FAR SOUTH. ON THE OTHER HAND THE 12Z  
ECMWF DEFLECTED THE ENERGY AROUND THE EASTERN NORTH AMERICA RIDGE,  
KEEPING THE FRONT FARTHEST NORTH. GIVEN THE CURRENT SPREAD,  
PREFERENCE WAS TO EMPHASIZE THE 12Z ECMWF AND THE 18Z GEFS/12Z  
ECMWF MEANS WHICH LEAN TOWARD THE NORTHERN SIDE OF THE SPREAD FOR  
THE FRONT BUT REPRESENT A MODEST SOUTHWARD ADJUSTMENT FROM  
CONTINUITY. FURTHER CHANGES CAN BE MADE IF NEWER GUIDANCE IMPROVES  
CONFIDENCE.  
 
MEANWHILE FARTHER WEST, GUIDANCE IS STILL WORKING ON HOW TO DEPICT  
GULF OF ALASKA ENERGY THAT SHOULD FLOW SOUTHEASTWARD INTO THE  
WESTERN U.S., WITH MODEST DIFFERENCES IN TIMING AND EXACTLY WHEN A  
CLOSED LOW FORMS HAVING SIGNIFICANT INFLUENCE ON THE CHARACTER OF  
LOW PRESSURE NEARING THE CENTRAL/NORTHERN WEST COAST BY EARLY  
MONDAY. THE MANUAL FORECAST SHOWS A BETTER DEFINED SYSTEM THAN THE  
WEAK AND SUPPRESSED 12Z (AND NEW 00Z) ECMWF BUT NOT AS STRONG AS  
THE GFS/UKMET/CMC GIVEN THE CURRENTLY LOW PREDICTABILITY OF THIS  
EVOLUTION. BY LATE IN THE PERIOD THE ENSEMBLE SPAGHETTI PLOTS ARE  
EXTREMELY MESSY OVER THE EASTERN PACIFIC AND WESTERN U.S. SO  
DETAIL CONFIDENCE REMAINS QUITE LOW. IN LIGHT OF THIS UNCERTAINTY,  
THERE IS A POSITIVE CONSIDERATION THAT THE 18Z/00Z GFS AND LATEST  
CMC/ECMWF RUNS ALL CLUSTER DECENTLY IN PRINCIPLE FOR HOW THE UPPER  
TROUGH/LOW EJECTS INTO THE PLAINS/MIDWEST TO PRODUCE WHAT WOULD BE  
A SIGNIFICANT STORM SYSTEM WITH GENERAL SUPPORT FROM THE ENSEMBLE  
MEANS.  
 
TRAILING FLOW COULD BRING ANOTHER SYSTEM TOWARD THE PACIFIC  
NORTHWEST BUT AGAIN WITH BELOW AVERAGE CONFIDENCE. THE NEW 00Z GFS  
HAS TRENDED FAVORABLY TOWARD THE ENSEMBLE MEANS FOR THE EASTERN  
PACIFIC/WESTERN U.S. UPPER PATTERN BY THE END OF THE PERIOD, IN  
CONTRAST TO THE STRONG RIDGE OR SOUTHERN/ELONGATED TROUGH OF THE  
12Z AND 18Z RUNS RESPECTIVELY.  
 
AS MENTIONED ABOVE, THE FIRST HALF OF THE FORECAST EMPHASIZED THE  
12Z ECMWF AND 18Z GEFS/12Z ECMWF MEANS TO YIELD THE DESIRED  
FRONTAL ALIGNMENT OVER THE EAST, WITH ONLY 30 PERCENT TOTAL INPUT  
OF THE 18Z GFS AND 12Z CMC/UKMET. LATER IN THE PERIOD A MORE  
BALANCED MODEL/MEAN BLEND CAPTURED A GOOD INTERMEDIATE STARTING  
POINT FOR THE SYSTEM THAT MAY TRACK INTO THE PLAINS AND UPPER  
MIDWEST BY NEXT WEDNESDAY-THURSDAY.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
EARLY IN THE PERIOD EXPECT THE BEST RAIN/MOUNTAIN SNOW FOCUS TO BE  
OVER THE PACIFIC NORTHWEST AND CENTRAL WEST COAST. HOWEVER THE  
DETAILS OF LOCATION AND INTENSITY ARE UNUSUALLY UNCERTAIN FOR A  
FORECAST ONLY 3-4 DAYS OUT IN TIME AS GUIDANCE VARIES WIDELY FOR  
THE STRENGTH AND TRACK OF ARRIVING LOW PRESSURE. LIGHTER ACTIVITY  
SHOULD PREVAIL EASTWARD THROUGH THE NORTHERN ROCKIES. THEN SOME  
MOISTURE SHOULD EXTEND SOUTHWARD INTO THE SIERRA NEVADA, WITH RAIN  
AND MOUNTAIN SNOW EXTENDING ACROSS CENTRAL AND POSSIBLY SOME  
SOUTHERN PARTS OF THE WEST. BY TUESDAY THE SOUTHERN MONTANA INTO  
COLORADO ROCKIES AND NORTH-CENTRAL HIGH PLAINS SHOULD BEGIN TO SEE  
A FAVORABLE COMBINATION OF UPPER TROUGH DYNAMICS AND LOW LEVEL  
UPSLOPE FLOW THAT WOULD INCREASE PRECIPITATION OVER THOSE AREAS,  
WITH THE HIGH PLAINS POSSIBLY SEEING SOME SPRINGTIME SNOW IN  
ADDITION TO THE ROCKIES. POTENTIALLY STRONG LOW PRESSURE THAT MAY  
TRACK FROM THE PLAINS INTO THE UPPER MIDWEST WOULD EXTEND SNOW  
FARTHER NORTHEAST ACROSS THE NORTHERN TIER ALONG WITH STRONG  
WINDS. MEANWHILE IN THE WARM SECTOR, THERE WILL BE INCREASING  
COVERAGE AND INTENSITY OF RAINFALL OVER THE EASTERN  
PLAINS/MISSISSIPPI VALLEY WITH THE ESTABLISHMENT OF MOIST LOW  
LEVEL FLOW FROM THE GULF OF MEXICO. PERSISTENCE OF THE GULF INFLOW  
COULD LEAD TO A COUPLE DAYS OR SO WITH A HEAVY RAIN THREAT OVER OR  
NEAR THE LOWER MISSISSIPPI VALLEY. ALSO THE STORM PREDICTION  
CENTER IS MONITORING THE POTENTIAL FOR SEVERE WEATHER OVER SOME  
SOUTHERN AREAS IN THE CENTRAL U.S. CHECK THEIR LATEST OUTLOOKS FOR  
MORE INFORMATION. FARTHER NORTH, A FRONT DRAPED OVER THE MIDWEST  
COULD ALSO PROVIDE A FOCUS FOR RAINFALL THOUGH LIKELY WITH LOWER  
TOTALS GIVEN LESS MOISTURE/INSTABILITY. LACK OF CONFIDENCE IN SOME  
SPECIFICS OF EASTERN PACIFIC/WESTERN U.S. FLOW MAINTAINS THE  
POTENTIAL FOR SOME CHANGES IN THE ABOVE MOST LIKELY SCENARIO.  
 
COLDER AIR MOVING INTO THE WEST WILL INITIALLY BRING HIGHS DOWN TO  
AS MUCH AS 10-20F BELOW NORMAL OVER THE NORTHWEST/NORTHERN ROCKIES  
AS OF SUNDAY. AN AREA OF MINUS 10-25F ANOMALIES FOR HIGHS SHOULD  
THEN REACH INTO THE INTERMOUNTAIN WEST, ROCKIES, AND  
NORTHERN-CENTRAL PLAINS BY NEXT TUESDAY-WEDNESDAY. THE NORTHERN  
HALF OF THE PLAINS SHOULD STILL SEE HIGHS AROUND 15-20F BELOW  
NORMAL ON THURSDAY. SUNDAY SHOULD PROVIDE THE BEST POTENTIAL FOR  
SOME LOCATIONS IN THE NORTHWEST TO SEE MAX TEMPERATURES NEAR OR  
BELOW CURRENT RECORD COLD HIGHS BUT MONDAY COULD STILL PRODUCE A  
FEW LINGERING RECORDS. MEANWHILE MOST OF THE EASTERN HALF OF THE  
COUNTRY SHOULD TREND FROM MOSTLY BELOW NORMAL TEMPERATURES (MINUS  
5-15F ANOMALIES) ON SUNDAY, AND POTENTIAL FOR A LATE FROST ACROSS  
PARTS OF THE SOUTHEASTERN QUADRANT OF THE COUNTRY, TO MOSTLY ABOVE  
NORMAL READINGS (PLUS 5-15F ANOMALIES FOR HIGHS AND PERHAPS  
SLIGHTLY WARMER FOR MORNING LOWS) SPREADING FROM WEST TO EAST  
AFTER THE WEEKEND. HOWEVER CONFIDENCE IS LOWER FOR EXACT  
TEMPERATURES OVER THE NORTHERN HALF OF THE EAST DUE TO UNCERTAIN  
POSITION OF A FRONT DURING THE FIRST HALF OF NEXT WEEK.  
 
RAUSCH/TATE  
 
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, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, 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/#PAGE=ERO  
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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