369  
FXUS02 KWBC 200542  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
142 AM EDT SAT APR 20 2019  
 
VALID 12Z TUE APR 23 2019 - 12Z SAT APR 27 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
UPPER-LEVEL FLOW DURING THE EXTENDED PERIOD WILL BE LARGELY  
SEPARATED INTO A PROGRESSIVE NORTHERN STREAM ACROSS CANADA AND THE  
U.S. NORTHERN TIER, AND A MUCH LESS PROGRESSIVE SOUTHERN STREAM,  
WITH THE POTENTIAL/TENDENCY FOR SYSTEMS TO CLOSE OFF ALOFT. MODELS  
CONTINUE TO STRUGGLE WITH THIS FLOW PATTERN, WITH PREDICTABILITY  
REDUCTIONS RESULTING FROM TIMING/AMPLITUDE DIFFERENCES WITHIN EACH  
STREAM FURTHER AMPLIFIED BY POTENTIAL INTERACTION (OR LACK  
THEREOF) BETWEEN THE STREAMS. AS A RESULT, FORECAST  
CONFIDENCE/PREDICTABILITY QUICKLY DECREASES TO BELOW AVERAGE BY  
THE LATTER PORTION OF THE FORECAST PERIOD.  
 
MODELS HAVE SETTLED ON A SLOWER PROGRESSION OF A COMPACT UPPER  
LOW/SURFACE LOW PRESSURE SYSTEM AWAY FROM THE NORTHEASTERN U.S.  
TUE-WED, AND SOLUTIONS NOW HANDLE THIS FEATURE COMPARABLY. THE  
EVOLUTION/PROGRESSION OF AN UPPER LOW INITIALLY ACROSS THE FOUR  
CORNERS REGION ON DAY 3 (TUE) REMAINS THE MOST SIGNIFICANT PROBLEM  
FOR THIS FORECAST PERIOD. DETERMINISTIC SOLUTIONS HANDLE THIS  
FEATURE SIMILARLY THROUGH EARLY WED AS THE FEATURE ELONGATES AND  
MOVES INTO THE SOUTHERN PLAINS. GUIDANCE HAS OVERALL TRENDED  
SLIGHTLY QUICKER WITH THE PROGRESSION OF THIS SYSTEM THAN THE  
ECMWF SHOWED AT THIS TIME LAST NIGHT, BUT REMAINS SLOWER THAN SOME  
OF THE MUCH MORE PROGRESSIVE SOLUTIONS SHOWN PREVIOUSLY BY THE  
GFS. DIFFERENCES CONTINUE TO GROW BY THU-SAT, WITH THE GFS  
CONTINUING TO FAVOR A MORE DOMINANT/AMPLIFIED NORTHERN STREAM AND  
A MUCH MORE PROGRESSIVE SOUTHERN STREAM WAVE, QUICKLY CROSSING THE  
SOUTHEAST BY THU NIGHT. THE ECMWF CONTINUES TO FAVOR MORE  
SEPARATION BETWEEN STREAMS, KEEPING A CLOSED UPPER LOW ACROSS THE  
LOWER MISSISSIPPI VALLEY/SOUTHEAST THROUGH FRI-SAT. GIVEN  
OBSERVATION OF PREVIOUS SIMILAR SYSTEMS OVER RECENT WEEKS,  
CONTINUE TO FAVOR MORE SEPARATION BETWEEN STREAMS, AND A SOLUTION  
MORE ALONG THE LINES OF THE ECMWF AND ECENS ENSEMBLE MEAN. FARTHER  
WEST, THERE IS GENERAL AGREEMENT AMONG THE GUIDANCE THAT NORTHERN  
STREAM HEIGHT FALLS SHOULD APPROACH THE PACIFIC NORTHWEST BY  
FRI-SAT, WITH TIMING/STRUCTURAL DIFFERENCES AMONG DETERMINISTIC  
SOLUTIONS BY THAT TIME FAVORING AN ENSEMBLE APPROACH. THE SAME  
HOLDS TRUE FOR ANOTHER ROUND OF SOUTHERN STREAM ENERGY POTENTIALLY  
NEARING CALIFORNIA BY SAT.  
 
GIVEN THESE CONSIDERATIONS, THE FORECAST DURING DAYS 3-5 (TUE-THU)  
WAS BASED ON A MULTI-MODEL (ECMWF/GFS/CMC) DETERMINISTIC BLEND,  
WITH A SHIFT TO MAJORITY WEIGHTING OF ECENS/NAEFS ENSEMBLE MEANS  
DURING DAYS 6-7 (FRI-SAT).  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE SYSTEM CROSSING THE SOUTHERN PLAINS TUE-WED IS EXPECTED TO  
PRODUCE WIDESPREAD SHOWERS AND THUNDERSTORMS, WITH MODELS  
INDICATING THE POTENTIAL FOR HEAVY RAINFALL FROM CENTRAL TEXAS  
NORTH INTO OKLAHOMA. SCATTERED TO NUMEROUS SHOWERS AND  
THUNDERSTORMS ARE EXPECTED TO ACCOMPANY THE SYSTEM EASTWARD INTO  
THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST THU-FRI, BUT ANY SIGNAL  
FOR HEAVY RAINFALL IS MUCH LESS CLEAR IN THE GUIDANCE GIVEN  
INCREASED SPREAD ON THE SPECIFIC EVOLUTION OF THE SYSTEM. ASSUMING  
THE SLOWER/MORE AMPLIFIED SOLUTIONS CURRENTLY FAVORED VERIFY,  
WOULD EXPECT THE CONTINUED POTENTIAL FOR AT LEAST AREAS OF LOCALLY  
HEAVY RAINFALL ACROSS PORTIONS OF THE GULF COAST AND SOUTHEAST.  
 
ABOVE AVERAGE TEMPERATURES ARE EXPECTED THROUGH MUCH OF THE PERIOD  
ACROSS PORTIONS OF THE WESTERN U.S. AS UPPER RIDGING BUILDS IN  
BEHIND THE SOUTHERN STREAM TROUGH. HIGH TEMPERATURES ARE FORECAST  
TO BE 10 TO 20 DEG F ABOVE AVERAGE FROM CALIFORNIA TO THE GREAT  
BASIN ON TUE, WITH WARM TEMPERATURES PROGRESSING EAST INTO THE  
ROCKIES AND PORTIONS OF THE CENTRAL PLAINS WED-THU. THE ARRIVAL OF  
A COLD FRONT BY LATER IN THE WEEK SHOULD BRING A RETURN TO NEAR OR  
SLIGHTLY BELOW NORMAL TEMPERATURES TO THE PACIFIC NORTHWEST AND  
NORTHERN GREAT BASIN.  
 
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  
 

 
 
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