559  
FXUS02 KWBC 131909  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
309 PM EDT SAT APR 13 2024  
 
VALID 12Z TUE APR 16 2024 - 12Z SAT APR 20 2024  
 
...DEEPENING PLAINS SURFACE LOW LIKELY TO BRING SEVERE AND HEAVY  
RAINFALL THREATS AHEAD OF IT AND STRONG WINDS AND NOTABLE SNOW  
BEHIND...  
 
   
..OVERVIEW
 
 
A CLOSED UPPER LOW ENTERING THE CENTRAL HIGH PLAINS TO START THE  
PERIOD TUESDAY WILL SUPPORT A DEEPENING SURFACE LOW PRESSURE SYSTEM  
THAT TRACKS INTO THE UPPER MIDWEST/GREAT LAKES WEDNESDAY-THURSDAY.  
VARIOUS HAZARDS ARE LIKELY WITH THIS STORM SYSTEM, INCLUDING  
SEVERE WEATHER AND BANDS OF HEAVY RAINFALL ON THE WARM SIDE ALONG  
WITH A BROAD AREA OF GUSTY WINDS. BEHIND THIS STORM, ANOTHER UPPER  
TROUGH/LOW DIGGING INTO THE NORTHWEST TUESDAY SHOULD ULTIMATELY  
EVOLVE INTO A WELL-ORGANIZED UPPER LOW NEAR/OVER THE UPPER GREAT  
LAKES AND AMPLIFY TROUGHING IN THE EASTERN THIRD OF THE NATION BY  
LATE WEEK. BEHIND THIS, UPPER RIDGING LOOKS TO BUILD OVER THE  
NORTHWEST/WESTERN CANADA.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE REMAINS REASONABLY AGREEABLE ON THE LARGE  
SCALE/PRESENCE OF THESE FEATURES, BUT STILL WITH PLENTY OF  
DISAGREEMENT IN THE TIMING AND DETAILS. WITH THE INITIAL LOW OUT OF  
THE PLAINS EARLY-MID WEEK, THERE IS SOME MODEL RUN-TO-RUN TIMING  
VARIABILITY STILL, BUT ENOUGH AGREEMENT TO SUPPORT A PURELY  
DETERMINISTIC MODEL BLEND. THE NEXT SYSTEM TRACKING FROM THE  
NORTHWEST INTO THE UPPER GREAT LAKES SHOWS MORE UNCERTAINTY ON ITS  
EVOLUTION AND PLACEMENT, THOUGH WITH SOME MODEL CONVERGENCE IN  
RECENT CYCLES. AROUND MIDWEEK, MOST MODELS ARE MORE AGREEABLE THAN  
A DAY AGO REGARDING HOW MUCH TROUGHING WILL GET INTO THE NORTHERN  
ROCKIES/HIGH PLAINS, AFFECTING SNOW TOTALS THERE. THE 00Z CMC WAS  
THE MAIN OUTLIER IN SHOWING LESS TROUGHING, BUT THE 12Z CMC WAS IN  
BETTER AGREEMENT. THERE WERE ALSO SOME DIFFERENCES WEDNESDAY IN  
WHEN THIS ENERGY CONSOLIDATES INTO A CLOSED UPPER LOW, WITH GFS  
RUNS BEING SLOWER TO CLOSE IT OFF, BUT THE 12Z GFS HAS COME INTO  
BETTER ALIGNMENT WITH THAT TIMING.  
 
MODELS THEN SHOW THIS UPPER LOW TRACKING EASTWARD THROUGH SOUTH-  
CENTRAL TO SOUTHEASTERN CANADA THURSDAY-SATURDAY, THOUGH WITH  
VARIATIONS ON THE EXACT TIMING AS WELL AS THE SOUTHERN EXTENT OF  
THE TROUGH AMPLITUDE INTO THE U.S. AT LEAST RECENT MODEL CYCLES DO  
NOT SHOW TOO MANY AXIS DIFFERENCES WITH THE TROUGH/LOW COMPARED TO  
THE 12Z 4/12 RUN OF THE ECMWF FOR EXAMPLE. THE DETAILS OF NORTHWEST  
RIDGING AND SOUTHWEST SOUTHERN STREAM TROUGHING COULD ALSO USE  
MORE TIME TO DETERMINE. THUS THE WPC FORECAST GRADUALLY  
TRANSITIONED FROM A MULTI-MODEL DETERMINISTIC BLEND FAVORING THE  
GFS AND ECMWF EARLY IN THE PERIOD TO A HALF MODEL/HALF ENSEMBLE  
MEAN BLEND BY DAY 7.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
 
PRECIPITATION WILL BE ONGOING ACROSS THE ROCKIES/CENTRAL U.S. WITH  
MULTIPLE WEATHER HAZARDS AS THE UPPER LOW HELPS TO DEEPEN A PLAINS  
SURFACE LOW INTO TUESDAY. THE STORM PREDICTION CENTER HAS BEEN  
HIGHLIGHTING EASTWARD PROGRESSING SEVERE THUNDERSTORM POTENTIAL  
REACHING THE LOWER TO MID-MISSISSIPPI VALLEY TO WESTERN OHIO VALLEY  
ON TUESDAY GIVEN THE ABUNDANT INSTABILITY AND MOISTURE PRESENT  
WITH THIS SYSTEM. THESE INGREDIENTS COULD ALSO PRODUCE HEAVY  
RAINFALL WITH INTENSE RATES CAPABLE OF FLASH FLOODING OVER PARTS OF  
THE PLAINS AND THE UPPER MIDWEST. EXCESSIVE RAINFALL OUTLOOKS  
CONTINUE TO SHOW MARGINAL RISKS STRETCHING FROM THE MID-LOWER  
MISSISSIPPI VALLEY TUESDAY INTO THE TENNESSEE AND LOWER OHIO  
VALLEYS WEDNESDAY ALONG WITH THE POTENTIALLY SEVERE STORMS, WHILE  
FARTHER NORTH ALONG THE LOW TRACK THE AMPLE LIFT SHOULD PROVIDE  
SUPPORT FOR POSSIBLY HEAVY RAINFALL. WATCHING A CORRIDOR FROM  
EASTERN NEBRASKA AND SOUTH DAKOTA INTO PARTS OF IOWA AND SOUTHERN  
MINNESOTA FOR AN EMBEDDED SLIGHT RISK ON TUESDAY, WHERE HEAVIER  
TOTALS ARE LIKELY TO MAXIMIZE. THIS AREA WILL LIKELY SEE EXCEEDANCE  
OF FLASH FLOOD GUIDANCE VALUES THERE, BUT IN THIS REGION OF THE  
COUNTRY THIS DOES NOT OFTEN RESULT IN NOTABLE FLOODING IMPACTS, SO  
HELD OFF. BEHIND THE LOW, THE STORM SHOULD PRODUCE A BROAD AREA OF  
GUSTY WINDS FOCUSING MAINLY ACROSS THE NORTH-CENTRAL HIGH PLAINS ON  
TUESDAY.  
 
THE NEXT UPPER TROUGH DIGGING INTO THE WESTERN U.S. AND EXTENDING  
INTO THE NORTHERN PLAINS EARLY-MID WEEK, ALONG WITH ANOTHER FRONTAL  
BOUNDARY, SHOULD TEND TO FOCUS PRECIPITATION OVER THE NORTHERN  
HALF OR SO OF THE ROCKIES AND HIGH PLAINS FOR A FEW DAYS. THUS  
NOTABLE SNOW WILL BE LIKELY OVER THE HIGHER ELEVATIONS. CHANCES FOR  
MEANINGFUL SNOW IN LOWER ELEVATIONS ARE DECREASING, BUT BLOWING  
SNOW IS A CONCERN. THEN AS SYSTEMS PROGRESS, RAIN AND CONVECTION  
ARE FORECAST TO MOVE INTO THE EASTERN U.S. INTO LATE WEEK, WHILE  
LINGERING ACROSS THE SOUTH-CENTRAL U.S. AS THE FRONTAL SYSTEM  
STALLS.  
 
EXPECT A BROAD AREA OF ABOVE NORMAL TEMPERATURES OVER THE EASTERN  
HALF OF THE COUNTRY INTO THE SOUTHERN PLAINS TUESDAY-THURSDAY, WITH  
ADVANCING FRONTAL SYSTEMS SLOWLY TRIMMING THE WESTERN SIDE OF THE  
WARMTH. EXPECT HIGHS IN THE EASTERN U.S. TO BE UP TO 10-15F OR SO  
ABOVE NORMAL WITH ANOMALIES FOR MORNING LOWS TENDING TO BE SEVERAL  
DEGREES HIGHER. THE UPPER TROUGH DIGGING INTO THE WEST AND THEN  
INCLUDING THE NORTHERN PLAINS WILL LIKELY START TO BRING BELOW  
NORMAL HIGHS INTO THE NORTHWEST BY TUESDAY, FOLLOWED BY READINGS  
10-15F BELOW AVERAGE OVER THE NORTHERN ROCKIES/HIGH PLAINS BY NEXT  
WEDNESDAY-THURSDAY WHILE GRADUALLY EXPANDING FARTHER SOUTH AND EAST  
BEHIND THE SECONDARY COLD FRONT LATE WEEK.  
 
TATE/SANTORELLI  
 
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 FORECAST (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 
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