857  
FXUS02 KWBC 071925  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
324 PM EDT TUE MAY 07 2019  
 
VALID 12Z FRI MAY 10 2019 - 12Z TUE MAY 14 2019  
 
...HEAVY RAINFALL THREAT FOR EASTERN/SOUTHEASTERN TEXAS AND THE  
LOWER MISSISSIPPI VALLEY LATE THIS WEEK INTO THE WEEKEND...  
 
15 UTC UPDATE...  
 
A BLEND OF THE LATEST DETERMINISTIC GUIDANCE WAS USED AS A  
FORECAST STARTING POINT THROUGH DAYS 3-5 (FRI-SUN). THE 00Z  
ECMWF/CMC AND 06Z FV3 WERE PREFERRED FRI-SAT AS THE GFS DIFFERED  
WITH ITS HANDLING OF THE NORTHERN STREAM SHORTWAVE CROSSING THE  
GREAT LAKES DURING THAT TIME FRAME. BY SUN THE OPERATIONAL GFS WAS  
USED IN PLACE OF THE FV3 DUE TO PREFERRED SLOWER TIMING WITH THE  
CLOSED UPPER LOW CROSSING THE DESERT SOUTHWEST AND NORTHERN BAJA  
CALIFORNIA. LARGER DIFFERENCES EMERGED IN THE MODELS BY DAYS 6-7  
(MON-TUE) WITH ADDITIONAL NORTHERN STREAM ENERGY AMPLIFYING ACROSS  
THE GREAT LAKES/NORTHEAST, AND THE RESULTANT SURFACE LOW OFF/ALONG  
THE NORTHERN MID-ATLANTIC/NORTHEAST COASTLINE. GREATER RUN-TO-RUN  
INCONSISTENCY SURROUNDING THIS SYSTEM REDUCED FORECAST CONFIDENCE,  
AND GREATER WEIGHT WAS PLACED TOWARD ENSEMBLE MEANS (ECENS AND  
NAEFS) BY THIS TIME FRAME. OVERALL, THE FORECAST REMAINED  
RELATIVELY CLOSE TO CONTINUITY, WITH ONLY MINOR ADJUSTMENTS.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 0700 UTC)...  
   
..OVERVIEW
 
 
EXPECT A STALLED FRONT NEAR AND NORTHEAST FROM THE WESTERN GULF  
COAST (ANCHORED BY LOW PRESSURE OVER EASTERN CANADA AS OF EARLY  
FRI) TO PROVIDE A FOCUS FOR PERIODS OF HEAVY RAIN ALONG AND NORTH  
OF THE WESTERN-CENTRAL GULF COAST REGION INTO THE WEEKEND. WITH  
CONTINUED UNCERTAINTY IN THE DETAILS, UPPER TROUGHING FORECAST TO  
AMPLIFY INTO THE PLAINS/MISSISSIPPI VALLEY AND THEN MOVE INTO THE  
EASTERN U.S. MAY DRAW SOME OF THIS MOISTURE NORTHEASTWARD LATER IN  
THE WEEKEND/EARLY NEXT WEEK WHILE SUPPRESSING PART OF THE  
FRONT--REDUCING THE HEAVY RAIN THREAT SOMEWHAT. ACROSS THE WEST  
THE UPPER PATTERN WILL BEGIN TO LOOK MORE LIKE A REX BLOCK AS A  
WARM RIDGE BUILDS OVER THE NORTHWEST WHILE A CALIFORNIA UPPER LOW  
AS OF FRI EVENTUALLY DRIFTS ALONG THE WESTERN U.S.-MEXICO BORDER.  
THIS UPPER LOW AND AN IMPULSE TRACKING TO ITS SOUTH AND EAST WILL  
PROMOTE MULTIPLE DAYS OF PRECIPITATION OVER THE SOUTHERN HALF OF  
THE WEST. GUIDANCE SHOWS SIGNS OF AN AMPLIFYING TROUGH DEVELOPING  
OVER THE EASTERN PACIFIC TOWARD THE END OF THE PERIOD NEXT TUE.  
 
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
OVER AND NEAR THE WESTERN U.S. THE PREVAILING MULTI-DAY TREND IS  
FOR A STRONGER RIDGE TO BUILD INTO THE NORTHWEST AND SLOWER  
PROGRESSION OF THE UPPER LOW EXPECTED TO TRACK NEAR THE WESTERN  
U.S.-MEXICO BORDER. IN GENERAL RECENT GFS/GEFS RUNS HAVE BEEN  
SOMEWHAT AHEAD OF THE ECMWF/ECMWF MEAN WITH THESE TRENDS. THE 12Z  
ECMWF MADE A FAVORABLE ADJUSTMENT RELATIVE TO ITS FASTER PRIOR  
RUNS SO IT COULD BE INCLUDED IN THE FORECAST THROUGH THE PERIOD,  
WHILE AFOREMENTIONED TRENDS SEEM TO FAVOR SOMEWHAT MORE GEFS MEAN  
THAN ECMWF MEAN FOR THE ENSEMBLE INPUT BY THE LATTER HALF OF THE  
PERIOD. THE 12Z CMC MEAN LOOKS QUITE SUSPICIOUS WITH A RATHER  
FAST MOVING EASTERN PACIFIC TROUGH THAT REACHES THE WEST COAST BY  
DAY 7 TUE. SOME DETAILS REMAIN COMPLEX, IN PARTICULAR FOR AN  
IMPULSE THAT LIKELY TRACKS SOUTH OF THE CALIFORNIA UPPER LOW  
AROUND FRI AND MAY CONTINUE INTO THE SOUTHERN ROCKIES/PLAINS--BUT  
WITH THE POTENTIAL FOR A PORTION OF THE ENERGY TO CURL BACK TOWARD  
THE UPPER LOW.  
 
EVOLUTION OF UPPER TROUGHING EXPECTED TO AMPLIFY OVER THE  
PLAINS/MISSISSIPPI VALLEY DURING THE WEEKEND--AND THE ASSOCIATED  
SURFACE REFLECTION--CONTINUE TO BE A SIGNIFICANT FORECAST PROBLEM.  
AMONG GUIDANCE FROM THE 12-18Z CYCLES THERE WERE ESSENTIALLY TWO  
CLUSTERS. THE SLOWER/SHARPER/MORE SEPARATED GROUP OF THE  
ECMWF/UKMET/CMC ALOFT LED TO A WEAKER AND MORE SUPPRESSED SURFACE  
FEATURE WHILE THE MORE CONSOLIDATED GFS/GEFS MEAN/CMC MEAN HAD A  
STRONGER/NORTHWARD SURFACE SYSTEM. THE ONE THING IN COMMON IS A  
MULTI-DAY TREND TOWARD THE TRAILING COLD FRONT REACHING FARTHER  
SOUTHWARD. OPERATIONAL GFS RUNS WERE A LITTLE SUSPICIOUS IN HOW  
THEY PHASED NORTHERN ONTARIO ENERGY INTO THE ORIGINAL SHORTWAVE SO  
THEY MIGHT BE TOO STRONG. THE 18Z FV3 GFS DID NOT SHOW SUCH  
PHASING AND THE NEW 00Z GFS HAS TRENDED AWAY FROM THAT AS WELL.  
BEYOND THAT THE DETAILS APPEAR TOO FINE IN SCALE TO RESOLVE  
CONFIDENTLY AT THE EXTENDED TIME FRAME, THUS FAVORING A BLENDED  
APPROACH. BEHIND THIS SYSTEM ADDITIONAL SHORTWAVE ENERGY (AGAIN  
WITH LOW CONFIDENCE FOR SPECIFICS) WILL COMPLICATE THE FORECAST  
WITHIN THE OVERALL MEAN TROUGH.  
 
SPECIFICS OF THE AMPLIFYING TROUGH WILL HAVE A SIGNIFICANT  
INFLUENCE ON THE DURATION OF THE POTENTIAL HEAVY RAIN EVENT OVER  
THE SOUTH AND HOW MUCH MOISTURE MAY STREAM FARTHER NORTHEASTWARD.  
THE ECMWF CLUSTER DESCRIBED ABOVE WOULD LEAD TO MORE  
MOISTURE/FRONTAL WAVINESS REACHING NORTHEASTWARD AND A SHORTER  
DURATION OF RAINFALL OVER THE GULF COAST STATES. AGAIN PREFERRED  
AN INTERMEDIATE APPROACH GIVEN LACK OF CONFIDENCE IN NORTHERN  
STREAM TROUGH SPECIFICS. NOTE THAT THE IMPULSE TRACKING SOUTH OF  
THE CALIFORNIA UPPER LOW ON FRI MAY ALSO PLAY A ROLE IN PROMOTING  
A FRONTAL WAVE OVER THE EAST. IN SPITE OF THE DIFFERENCES OVER  
THE SOUTH AND EAST DURING THE WEEKEND, THERE IS ACTUALLY SOME  
CONVERGENCE OF SOLUTIONS TOWARD A WAVE OFF THE MID-ATLANTIC/NEW  
ENGLAND COAST EARLY NEXT WEEK. TRENDS IN THE 00Z GFS AND OTHER  
INCOMING 00Z MODELS SUGGEST THE 12-18Z GFS SOLUTIONS ARE LESS  
LIKELY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE BEST CONFIDENCE IN HEAVY RAINFALL POTENTIAL OVER  
EASTERN/SOUTHEASTERN TEXAS THROUGH THE LOWER MISSISSIPPI VALLEY  
WILL BE IN THE FRI-SAT TIME FRAME. THEN LATEST TRENDS SHOW AN  
INCREASING POSSIBILITY THAT ONE OR MORE FRONTAL WAVES LIFTING  
THROUGH THE EASTERN STATES MAY PULL AREAS OF SIGNIFICANT RAINFALL  
INTO THE TENNESSEE VALLEY AND MID-ATLANTIC WHILE REDUCING  
PRECIPITATION OVER PARTS OF THE GULF COAST REGION. HOWEVER THE  
FRONT EXTENDING INTO THE WESTERN GULF AND NORTHERN MEXICO WILL  
STILL BE CLOSE ENOUGH TO MAINTAIN POTENTIAL FOR RAINFALL OF  
VARYING INTENSITY THROUGH THE FIRST HALF OF NEXT WEEK. ELSEWHERE  
OVER THE EASTERN HALF OF THE COUNTRY, THE STORM OVER EASTERN  
CANADA EARLY FRI WILL BRING A BRIEF PERIOD OF ENHANCED RAINFALL TO  
THE NORTHEAST WHILE THE SYSTEM DROPPING INTO THE  
PLAINS/MIDWEST/GREAT LAKES DURING THE WEEKEND SHOULD BE  
ACCOMPANIED BY MOSTLY LIGHT-MODERATE PRECIPITATION.  
 
OVER THE WEST, CONTINUE TO EXPECT TERRAIN-ENHANCED PRECIPITATION  
FROM PORTIONS OF CALIFORNIA INTO THE SOUTHERN HALF OF THE ROCKIES.  
HIGHEST 5-DAY TOTALS SHOULD BE OVER THE ROCKIES. ISOLATED  
HIGHEST ELEVATIONS OF THE ROCKIES COULD SEE A LITTLE SNOW BUT WITH  
MUCH LOWER POTENTIAL THAN WILL BE THE CASE BEFORE FRI. WESTERN  
AREAS SHOULD GRADUALLY TREND DRIER BUT OVERALL EXPECT A LONGER  
DURATION OF PRECIPITATION GIVEN SLOWER TRENDS FOR THE UPPER LOW  
TRACKING NEAR THE U.S.-MEXICO BORDER. EVENTUALLY THE UPPER LOW  
SHOULD INCREASE ACTIVITY OVER THE SOUTHERN HIGH PLAINS.  
 
EXPECT VERY WARM TEMPERATURES OVER THE NORTHWEST FOR MULTIPLE DAYS  
AS THE UPPER RIDGE BUILDS OVER THE REGION. THERE SHOULD BE DECENT  
COVERAGE OF PLUS 10-20F ANOMALIES WITH LOCALLY HIGHER DEPARTURES  
FROM NORMAL. DAILY RECORDS FOR HIGHS/WARM LOWS WILL BE POSSIBLE  
AND SOME AREAS MAY APPROACH 90F. MEANWHILE THE FORECAST PATTERN  
WILL KEEP THE SOUTHERN PLAINS THROUGH SOUTHWEST WELL BELOW NORMAL  
FOR HIGHS. THE SOUTHERN HIGH PLAINS SHOULD SEE THE MOST EXTREME  
ANOMALIES OF MINUS 15-25F FOR HIGHS ON FRI. AREAS FROM THE  
MIDWEST TO NORTHEAST WILL BE MODERATELY COOL DURING THE PERIOD,  
5-10F BELOW NORMAL AND LOCALLY A BIT COOLER.  
 
RAUSCH  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE  
TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE  
SOUTHEAST, AND THE SOUTHERN PLAINS, FRI-SUN, MAY 10-MAY 12.  
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND  
THE SOUTHERN PLAINS, TUE, MAY 14.  
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC, SAT-SUN, MAY  
11-MAY 12.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE  
LOWER MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE GREAT LAKES,  
THE MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI VALLEY, THE  
SOUTHERN PLAINS, AND THE OHIO VALLEY.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE CENTRAL  
PLAINS, THE LOWER MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE  
GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI  
VALLEY, THE SOUTHERN PLAINS, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL PLAINS.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN  
ROCKIES, THE CENTRAL PLAINS, AND THE SOUTHERN PLAINS, FRI-SAT, MAY  
10-MAY 11.  
 
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