707  
FXUS02 KWBC 061619  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1218 PM EDT SAT APR 06 2019  
 
VALID 12Z TUE APR 09 2019 - 12Z SAT APR 13 2019  
 
...CONFIDENCE INCREASING THAT A SIGNIFICANT LATE-SEASON STORM WILL  
IMPACT PORTIONS OF THE NORTHERN PLAINS AND MIDWEST WITH HEAVY RAIN  
AND SNOW MID TO LATE NEXT WEEK...  
 
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
A MODERATELY PROGRESSIVE NORTHERN STREAM EARLY IN THE MEDIUM RANGE  
WILL BECOME MORE AMPLIFIED OVER TIME, WITH SPLIT FLOW BECOMING  
INCREASINGLY PROMINENT THROUGH THE EXTENDED PERIOD. ONE SOUTHERN  
STREAM SHORTWAVE IS EXPECTED TO CROSS THE SOUTHEAST U.S. TUE-WED,  
WITH ANOTHER CROSSING FROM THE WEST COAST TO THE FOUR  
CORNERS/ROCKIES DURING THE SAME TIME FRAME. THE SECOND OF THESE  
WAVES IS FORECAST TO QUICKLY AMPLIFY AS IT APPROACHES THE CENTRAL  
U.S. LATE TUE INTO WED, WITH SUPPORT INCREASING FOR A SIGNIFICANT  
LATE-SEASON CYCLONE ACROSS THE CENTRAL U.S. BY WED-FRI. ADDITIONAL  
SHORTWAVE ENERGY IS EXPECTED TO DROP SOUTHWARD ALONG THE WEST  
COAST WED-SAT, EVENTUALLY CONSOLIDATING INTO AN ANOMALOUS UPPER  
TROUGH (500 HPA HEIGHT ANOMALIES OF -2 TO -3 STANDARD DEVIATIONS)  
ACROSS THE SOUTHWESTERN STATES.  
 
A MULTI-MODEL DETERMINISTIC BLEND WAS USED AS A FORECAST STARTING  
POINT DURING DAYS 3-5 (TUE-THU), INCLUDING THE 06Z GFS AND 00Z  
ECMWF/UKMET/CMC. GUIDANCE HAS SHOWN A TREND TOWARD MORE SEPARATION  
OF STREAMS ACROSS THE EASTERN U.S. TUE-WED, KEEPING A SOMEWHAT  
LESS AMPLIFIED AND MORE DISTINCT SOUTHERN STREAM SYSTEM THAT  
CROSSES THE SOUTHEAST AND MOVES EAST INTO THE ATLANTIC. THIS TREND  
WAS REFLECTED ACROSS A RANGE OF MODEL/ENSEMBLE SOLUTIONS AND IS  
WELL-REPRESENTED BY A GENERAL MODEL BLEND. FARTHER WEST, MODELS  
HANDLE THE SHORTWAVE CROSSING THE WESTERN U.S. TUE-THU SIMILARLY,  
WITH ONLY MINOR DIFFERENCES IN TIMING AND/OR AMPLITUDE. MODELS  
HAVE SHOWN SIGNIFICANT DIFFICULTY OVER THE PAST COUPLE DAYS  
HANDLING THIS SYSTEM AS THE SURFACE LOW DEEPENS RAPIDLY ACROSS THE  
CENTRAL PLAINS WED AND THEN LIFTS NORTHEASTWARD. SOLUTIONS HAVE  
VARIED BETWEEN KEEPING A MORE OPEN UPPER WAVE AND QUICKLY MOVING  
THE SURFACE LOW EASTWARD, AND A MORE CLOSED UPPER LOW WITH A  
DEEPER SURFACE LOW THAT PROGRESSES EAST MUCH MORE SLOWLY. THERE  
WAS A LARGE REDUCTION IN SPREAD DURING THE LAST ENSEMBLE CYCLE,  
WITH SOLUTIONS OVERWHELMINGLY TRENDING TOWARD THE IDEA OF A  
DEEPER/SLOWER SYSTEM. INTERESTINGLY, THE UKMET HAS BEEN THE MOST  
CONSISTENT DETERMINISTIC SOLUTION, SHOWING A SOLUTION SIMILAR TO  
THE CURRENT CONSENSUS FOR AT LEAST THE PAST THREE RUNS. GIVEN  
THESE CONSIDERATIONS, AND SOLUTIONS WHICH WERE BETTER CENTERED  
WITHIN THE ENSEMBLE CONSENSUS, THE 00Z ECMWF/UKMET SOLUTIONS WERE  
WEIGHTED A BIT MORE RELATIVE TO THE GFS/CMC, ESPECIALLY BY  
WED-THU.  
 
SPREAD STILL INCREASES WITH RESPECT TO THE EVOLUTION OF THIS  
SYSTEM DURING DAYS 6-7 (FRI-SAT), AND ITS POTENTIAL INTERACTION  
WITH THE NORTHERN STREAM AS IT MOVES INTO CANADA. GIVEN  
SIGNIFICANT CONTINUED RUN-TO-RUN VARIABILITY FROM FRI ONWARD,  
OPTED TO LEAN MUCH MORE HEAVILY ON ECENS/GEFS ENSEMBLE MEANS  
DURING THAT TIME FRAME. THIS PREFERENCE HOLDS ALONG THE WEST COAST  
AS WELL, WHERE MODELS HAVE STRUGGLED TO DEAL WITH THE SPECIFICS OF  
A SERIES OF SHORTWAVES DROPPING SOUTHWARD ACROSS THE WEST  
COAST/GREAT BASIN. THERE IS SOME CONSENSUS, HOWEVER, THAT ENERGY  
SHOULD EVENTUALLY CONSOLIDATE INTO A BROAD AND ANOMALOUS  
UPPER-LEVEL TROUGH ACROSS THE SOUTHWEST BY FRI-SAT.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
CONFIDENCE HAS INCREASED THAT A DEEP LATE-SEASON STORM SYSTEM  
SHOULD TRACK FROM THE CENTRAL PLAINS TO THE MIDWEST/GREAT LAKES  
DURING THE WED-FRI TIME PERIOD. THE UPPER-LEVEL SHORTWAVE WILL  
INITIALLY BRING RAINS AND POTENTIALLY HEAVY MOUNTAIN SNOWS TO MUCH  
OF THE ROCKIES TUE INTO WED. AFTER THE SYSTEM EMERGES INTO THE  
PLAINS, MODELS SHOW IMPROVED CONSENSUS THAT SIGNIFICANT BAND OF  
DYNAMICALLY FORCED PRECIPITATION IS LIKELY TO THE NORTH OF THE LOW  
TRACK, FROM PORTIONS OF EASTERN WYOMING AND THE DAKOTAS EAST TO  
THE UPPER MIDWEST. A VARIETY OF PRECIPITATION TYPES ARE LIKELY,  
BUT SUFFICIENT COLD AIR SHOULD BE IN PLACE TO SUPPORT A BAND OF  
MODERATE TO HEAVY SNOW. SOME AREAS NEAR THE PRECIPITATION  
TRANSITION ZONE WILL LIKELY SEE THE POTENTIAL FOR BOTH HEAVY RAIN  
AND SNOW. ADDITIONALLY, THE DEEP NATURE OF THE LOW (CENTRAL  
PRESSURES LIKELY IN THE MID 980-MB RANGE), WILL LIKELY RESULT IN  
THE POTENTIAL FOR STRONG AND GUSTY WINDS ACROSS A LARGE AREA OF  
THE CENTRAL U.S. FARTHER SOUTH, LIMITED MOISTURE RETURN AND  
POTENTIAL FOR A CAPPING INVERSION WILL LIMIT PRECIPITATION  
COVERAGE AHEAD OF THE SYSTEM FROM THE SOUTHERN PLAINS TO THE LOWER  
MISSISSIPPI VALLEY, ALTHOUGH GIVEN THE STRONG AND DYNAMIC NATURE  
OF THE LOW PRESSURE SYSTEM, ANY ISOLATED TO SCATTERED CONVECTION  
THAT DEVELOPS COULD BE STRONG. AS THE LOW MOVES INTO CANADA BY  
FRI-SAT AND THE COLD FRONT SWEEPS INTO THE EASTERN U.S.,  
WIDESPREAD RAINS ARE LIKELY FROM THE OHIO VALLEY TO THE  
MID-ATLANTIC AND NORTHEAST. FARTHER WEST, THE SERIES OF SHORTWAVES  
DIVING SOUTH ALONG THE WEST COAST WED-SAT WILL SUPPORT CONTINUED  
SCATTERED AND PERIODIC ROUNDS OF RAIN AND MOUNTAIN SNOW FOR MUCH  
OF THE WEST.  
 
WARM TEMPERATURES ARE EXPECTED AHEAD OF THE DEEP LOW PRESSURE  
SYSTEM TUE-WED FROM THE PLAINS TO THE LOWER/MID-MISSISSIPPI  
VALLEY, WHERE HIGH TEMPERATURES OF 5 TO 15 DEG F ABOVE AVERAGE ARE  
LIKELY. IN THE WAKE OF THIS LOW PRESSURE SYSTEM, A COLDER POLAR  
AIR MASS WILL OVERSPREAD AREAS FROM THE NORTHERN ROCKIES TO THE  
UPPER MIDWEST, WITH HIGH TEMPERATURES AS COLD AS 15 TO 25 DEG  
BELOW AVERAGE EXPECTED. A BROAD AREA OF COOL TEMPERATURES IS  
EXPECTED ACROSS THE INTERIOR WESTERN U.S. BY LATE NEXT WEEK AS  
UPPER TROUGHING AMPLIFIES OVERHEAD.  
 
RYAN  
 
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