685  
FXUS02 KWBC 032004  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
403 PM EDT WED APR 03 2019  
 
VALID 12Z SAT APR 06 2019 - 12Z WED APR 10 2019  
 
15Z UPDATE: SIMILAR TO YESTERDAY, THERE REMAINS CONSIDERABLE  
MODEL SPREAD ACROSS THE EASTERN HALF OF THE U.S. REGARDING THE  
STRUCTURE AND EVOLUTION OF THE LOW PRESSURE SYSTEM CROSSING THE  
GREAT LAKES REGION AND ITS ASSOCIATED FRONTAL BOUNDARIES.  
TELECONNECTIONS WITH THE POSITIVE ANOMALY OVER GREENLAND IS  
SUPPORTIVE OF A TROUGH OVER THE WESTERN PACIFIC AND ALSO OVER  
QUEBEC, CANADA. THE FV3 GFS WAS SUBSTITUTED FOR THE OPERATIONAL  
GFS FOR THIS FORECAST AS PART OF THE OVERALL BLEND GIVEN LARGER  
RUN-TO-RUN DIFFERENCES WITH THE OPERATIONAL GFS. THE UKMET AND  
CMC BEGIN EXHIBITED DIFFERENCES FROM THE ENSEMBLE MEANS AS EARLY  
AS THIS WEEKEND REGARDING THE TROUGH OVER THE CENTRAL U.S. AND  
MIDWEST STATES. GIVEN LOWER THAN AVERAGE CONFIDENCE FOR THE  
LATTER HALF OF THE FORECAST PERIOD, THE WPC FORECAST REMAINED  
FAIRLY CLOSE TO PREVIOUS CONTINUITY WHILE ALSO TAKING INTO ACCOUNT  
THE EC MEAN, GEFS MEAN, FV3, AND ECMWF.  
 
HAMRICK  
 
   
..OVERVIEW
 
 
EXPECT THE CONTINUATION OF A MODERATELY PROGRESSIVE PATTERN  
DOMINATED BY PACIFIC FLOW FROM THE WEEKEND INTO THE MIDDLE OF NEXT  
WEEK. THERE TWO LARGEST SCALE FEATURES OF NOTE WILL BE WESTERN  
U.S./ROCKIES ENERGY THAT SHOULD LEAD TO A TROUGH REACHING THE EAST  
BY NEXT WEEK AND AN UPSTREAM TROUGH MOST LIKELY MOVING INTO THE  
WEST NEXT TUE-WED. BETWEEN THESE TWO FEATURES, FAST FLOW WILL  
BRING MULTIPLE IMPULSES ACROSS THE PACIFIC NORTHWEST. GUIDANCE  
HAS BEEN CONSISTENT IN HIGHLIGHTING AN AREA FROM THE  
NORTHERN/CENTRAL WEST COAST EASTWARD INTO THE ROCKIES FOR  
SIGNIFICANT PRECIPITATION. THE UPPER TROUGH PROGRESSING INTO THE  
EAST WILL SPREAD A BROAD SHIELD OF MOISTURE ACROSS THE EASTERN  
HALF OF THE COUNTRY BUT WITH A LOT OF UNCERTAINTY OVER INTENSITY  
AND DURATION OF PRECIPITATION AT ANY PARTICULAR LOCATION.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
THE DETAILS ARE AS UNCERTAIN AS EVER FOR EVOLUTION OF THE OVERALL  
TROUGH FORECAST TO PROGRESS EASTWARD FROM THE WESTERN U.S./ROCKIES  
SAT ONWARD. AT THE START OF THE PERIOD THIS TROUGH SHOULD CONSIST  
OF A COMBINATION OF SOUTHERN STREAM ENERGY REACHING THE SOUTHERN  
ROCKIES/NORTHERN MEXICO ALONG WITH STRONG NORTHERN STREAM  
SHORTWAVE ENERGY PUSHING THROUGH THE NORTHWEST. OPERATIONAL  
MODELS AS A WHOLE ARE SIGNALING A DECENT POTENTIAL FOR AN EMBEDDED  
CLOSED LOW TO FORM BY SUN-MON BUT WITH TREMENDOUS NORTH-SOUTH  
SPREAD FOR THE PATH OF SUCH A LOW. SOLUTIONS AMONG LATEST RUNS  
VALID 12Z MON RANGE BETWEEN THE CANADIAN BORDER (12Z ECMWF AND 00Z  
FV3 GFS) AND CENTRAL/SOUTH-CENTRAL PLAINS INTO MISSISSIPPI VALLEY  
(RECENT GFS RUNS AND 00Z UKMET). THE OLD 00Z/02 ECMWF RUN IN FACT  
HAD A COMPACT UPPER LOW TRACKING EVEN FARTHER SOUTH. THE WIDE  
SPREAD IN GUIDANCE REQUIRED EARLIER THAN USUAL INCLUSION OF A  
SIGNIFICANT PERCENTAGE OF THE ENSEMBLE MEANS TO PROVIDE STABILITY  
FOR THE DETERMINISTIC FORECAST--EVEN IF CONFIDENCE IN THE EXACT  
ENSEMBLE MEAN SCENARIO IS NOT PARTICULARLY HIGH EITHER. BASED ON  
THE ENSEMBLE MEAN FORECAST A COMPLEX AREA OF PLAINS LOW PRESSURE  
SHOULD CONSOLIDATE AS IT TRACKS INTO/ACROSS THE GREAT  
LAKES-NORTHEAST DURING THE FIRST HALF OF NEXT WEEK. LOW TRACK  
WOULD DIFFER SIGNIFICANTLY IF SOME OF THE OPERATIONAL RUNS WERE TO  
VERIFY.  
 
OVER THE EASTERN PACIFIC/WESTERN U.S. DURING MON-WED, FASTER/MORE  
AMPLIFIED TRENDS IN THE GFS/GEFS MEAN OVER THE PAST DAY HAVE  
NARROWED THE GUIDANCE SPREAD FOR THE TROUGH EXPECTED TO MOVE INTO  
THE WEST. THROUGH THE 12-18Z CYCLES THE GFS/GEFS MEAN STILL  
SEEMED TO BE IN THE TRENDING PROCESS, WHILE TELECONNECTIONS  
RELATIVE TO PROMINENT HEIGHT ANOMALY CENTERS OVER THE WESTERN  
PACIFIC (NEGATIVE) AND NORTHEAST ATLANTIC/GREENLAND (POSITIVE)  
HAVE BEEN PROMOTING HEIGHT FALLS REACHING THE SOUTHERN HALF OF THE  
WEST. THUS THE FORECAST TILTED MORE TOWARD THE ECMWF  
MEAN/ECMWF/NAEFS MEAN. THE 12Z CMC WAS ON THE EXTREME SIDE OF THE  
ENVELOPE FOR TROUGH AMPLITUDE. THE NEW 00Z GFS/GEFS MEAN APPEAR  
CLOSER TO FORECAST PREFERENCE. ALSO WORTH NOTING, GUIDANCE  
RAPIDLY DIVERGES FOR DETAILS OF FAST NORTH PACIFIC FLOW BY NEXT  
MON AND THESE DIFFERENCES MIGRATE INTO THE NORTHEASTERN PACIFIC BY  
TUE-WED. ISSUES ACROSS THOSE AREAS MAY ALSO AFFECT THE FORECAST  
FOR THE WEST AT THAT TIME.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
WITHIN THE FAVORED AREA FOR SIGNIFICANT RAINFALL AND HIGHER  
ELEVATION SNOW FROM THE NORTHERN/CENTRAL WEST COAST INTO THE  
ROCKIES, HIGHEST TOTALS WILL LIKELY OCCUR OVER NORTHERN CALIFORNIA  
AND WESTERN OREGON/WASHINGTON WHERE THE SAT-MON PERIOD SHOULD  
FEATURE STRONG FLOW ALOFT WITH MULTIPLE EMBEDDED SHORTWAVES.  
PREDICTABILITY IN SMALL-SCALE DETAILS IS LOW BUT THERE IS  
POTENTIAL FOR ONE OR MORE NARROW BANDS OF VERY FOCUSED PRECIP. BY  
TUE-WED THE UPPER TROUGH MOVING INTO THE WEST WILL SHIFT THE FOCUS  
FOR RAIN/SNOW FARTHER INLAND--MOST LIKELY ACROSS THE NORTH-CENTRAL  
INTERMOUNTAIN WEST AND ROCKIES. SOME OF THIS MOISTURE MAY REACH  
THE CENTRAL PLAINS AS WELL. EASTERN SLOPES OF THE ROCKIES COULD  
SEE ACTIVITY ENHANCED BY LOW LEVEL UPSLOPE FLOW AROUND MIDWEEK.  
 
STRENGTHENING LOW LEVEL FLOW OF MOISTURE FROM THE GULF OF MEXICO  
AHEAD OF THE UPPER TROUGH EMERGING FROM THE WEST/ROCKIES WILL  
SPREAD A BROAD AREA OF PRECIPITATION FROM PORTIONS OF THE PLAINS  
THROUGH THE EAST DURING THE PERIOD. THERE IS AT LEAST A MODERATE  
DEGREE OF CONSENSUS THAT AREAS FROM THE EASTERN HALF OF TEXAS  
THROUGH THE LOWER MISSISSIPPI VALLEY AND POSSIBLY INTO THE  
SOUTHERN APPALACHIANS WILL SEE A THREAT OF HEAVY RAINFALL. THERE  
ARE INDICATIONS THAT THE NORTHEAST MAY SEE SIGNIFICANT AMOUNTS AS  
WELL. OTHERWISE THE WIDE DISPARITY IN GUIDANCE FOR SPECIFICS OF  
UPPER LEVEL/SURFACE EVOLUTION WILL MAKE IT DIFFICULT TO HAVE MUCH  
CONFIDENCE IN DETERMINING AREAS THAT WILL SEE HIGHEST PRECIP  
TOTALS. PARTS OF NEW ENGLAND MAY SEE WINTRY WEATHER WITH THIS  
SYSTEM.  
 
OVER THE WEST EXPECT MODESTLY BELOW NORMAL DAYTIME HIGHS FROM THE  
WEST COAST INTO NORTHERN ROCKIES. THE SOUTHWEST/SOUTHERN ROCKIES  
INTO GREAT BASIN WILL SEE A BRIEF PERIOD OF WARMTH SUN-TUE (SOME  
PLUS 10F OR GREATER ANOMALIES) BEFORE UPPER TROUGHING EXPANDS THE  
COVERAGE OF BELOW NORMAL TEMPERATURES OVER THE WEST BY MIDWEEK.  
MOST OF THE WEST SHOULD SEE ABOVE NORMAL MINS DURING THE PERIOD.  
FARTHER EASTWARD EXPECT AN AREA OF MUCH ABOVE NORMAL MIN TEMPS TO  
PROGRESS FROM THE PLAINS THROUGH THE EAST SAT-TUE. PLUS 15-25F  
ANOMALIES MAY CHALLENGE DAILY RECORD WARM LOW VALUES AT SOME  
LOCATIONS. ANOMALIES SHOULD BE LESS EXTREME FOR HIGHS. COOL FLOW  
BEHIND THE SYSTEM CROSSING THE EAST SHOULD BRING SOME MODESTLY  
BELOW NORMAL HIGHS INTO THE NORTHERN HALF OF THE CENTRAL/EASTERN  
STATES BY NEXT WED.  
 
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 PRECIPITATION ACROSS PORTIONS OF CALIFORNIA, THE PACIFIC  
NORTHWEST, AND THE NORTHERN GREAT BASIN, SAT-MON, APR 6-APR 8.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE  
CENTRAL PLAINS, THE NORTHERN PLAINS, AND THE NORTHERN ROCKIES,  
TUE-WED, APR 9-APR 10.  
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC  
NORTHWEST, SAT-MON, APR 6-APR 8.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE MIDDLE  
MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI VALLEY, THE SOUTHERN  
PLAINS, AND THE TENNESSEE VALLEY, SAT-SUN, APR 6-APR 7.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE MID-ATLANTIC,  
AND THE SOUTHERN APPALACHIANS, MON, APR 8.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE CENTRAL  
PLAINS, THE LOWER MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE  
TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE UPPER  
MISSISSIPPI VALLEY, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY  
AND THE NORTHERN PLAINS.  
- HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF CALIFORNIA  
AND THE PACIFIC NORTHWEST, SAT-SUN, APR 6-APR 7.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF MAINLAND ALASKA AND THE  
ALEUTIANS, TUE-WED, APR 9-APR 10.  
- HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS,  
TUE-WED, APR 9-APR 10.  
 
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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