EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1157 AM EDT SAT APR 19 2014 VALID 12Z TUE APR 22 2014 - 12Z SAT APR 26 2014 ...OVERVIEW... A RELATIVELY-STABLE WAVE PATTERN AT MID-LATITUDES WILL PRODUCE A SERIES OF MIGRATORY SYSTEMS FOR THE LOWER 48. ...MODEL PREFERENCES/UNCERTAINTY ASSESSMENTS/SENSIBLE WEATHER HIGHLIGHTS...... THE 19/00Z MODEL CYCLE...EXCLUDING THE DETERMINISTIC CANADIAN...SEEMED TO REASONABLY DEPICT THE SERIES OF MIGRATORY SYSTEMS TRAVERSING THE EASTERN PACIFIC...WEST COAST ...MIDWEST ...AND NORTHEAST THROUGH DAY 6. FOR THE PAST 2 to 3 DAYS...THE MODEL GUIDANCE HAS DONE A NICE JOB OF TIMING THE PATTERN AND ITS REPLACEMENT--EAST OF THE ROCKIES. IE...FROM A MULTI-WAVE...SPLIT-FLOW TYPE PATTERN EXITING THE EASTERN CONUS (DAY 3-4)...TO ONE THAT GIVES THE APPEARANCE OF A SERIES OF HIGHER-AMPLITUDE TROUGHS ACCOMPANIED BY BROAD SHORTWAVE RIDGES. THE 19/00Z ENSEMBLE SPREAD IS A RATHER TIGHTLY-CLUSTERED SET OF SOLUTIONS. THE 19/00Z GEFS/ECENS MEANS AND THEIR DETERMINISTIC RUNS COULD EASILY BE BLENDED INTO DAY 6 (26/00Z) ACROSS THE GREAT LAKES...INVOF HAIDA GWAII (QUEEN CHARLOTTE ISLAND) AND SOUTH OF PRINCE EDWARD ISLAND. A NEGATIVE-TILT TROUGH AXIS SOLUTION INVOF 50N LAT 130W LONG...IS THE ACCEPTED SOURCE REGION AND ENTRY POINT FOR A STORM TRACK THAT WILL MAINTAIN A SPRING RAIN/HIGH ELEVATION SNOW PATTERN IN THE NORTHWEST AFTER DAY 5. ASIDE FROM THE EARLY DAY 3 SYSTEM TRACKING THROUGH THE NORTHERN ROCKIES...THE SOUTHERN EXTENSIONS OF THE PACIFIC COLD FRONTS...WILL BE ESSENTIALLY DRY--(EXCEPT AT HIGH ELEVATION)--AND BREEZY/WINDY EVENTS FOR THE I-80 CORRIDOR FROM THE BAY AREA TO THE GREAT BASIN AND THROUGH THE CENTRAL ROCKIES. DOWNSTREAM...ALONG AND EAST OF THE CONTINENTAL DIVIDE (ALONG THIS I-80 CORRIDOR)...THE HIGHER-AMPLITUDE FLOW ALLOWS SHORTWAVE RIDGES TO BROADEN WARM ADVECTION AND EXPAND BREEZY CONDITIONS NORTHWARD FROM THE SOUTHERN PLAINS TO THE MIDWEST/OHIO VALLEY. AND ALTHOUGH THIS PATTERN DOES NOT FAVOR AN OPEN-GULF LOW-LEVEL MOISTURE FEED INTO THE MISSOURI VALLEY BASIN...A DRYLINE-TYPE CONVECTIVE PATTERN DOES BODE WELL FOR WEST TEXAS...EASTERN NEW MEXICO...WESTERN OKLAHOMA...EASTERN COLORADO AND WESTERN KANSAS. HIT-N-MISS CONVECTION AND ISOLATED HEAVY RAINFALL POTENTIAL...INCLUDING NOCTURNAL SHOWERS...ARE ANTICIPATED AHEAD OF THE DRY LINE. DAYS 3-4...AND ALONG THE DRYLINE...THE CHALLENGE APPEARS TO BE HOW EXPANSIVE THE DRY-ADIABATIC WARMING WILL BE...FOR THE SOUTHERN AND CENTRAL HIGH PLAINS. THE DRY AIR INTRUSION AND RAPIDLY-SOARING TEMPERATURES COULD EASILY BEGIN TO TRANSLATE NORTHEASTWARD INTO THE LOWER MISSOURI VALLEY...OZARKS AND WESTERN OHIO VALLEY INTO DAY 5...AS A SLOWLY-AMPLIFYING SURFACE WAVE TAKES SHAPE OVER THE NORTHERN PLAINS AND GREAT LAKES. THE DETERMINISTIC 19/00Z GFS/ECMWF GENERALLY DEPICT A SUB 994MB SURFACE LOW INVOF SOUTHEAST/SOUTH CENTRAL SOUTH DAKOTA AROUND 24/12Z. THERE ARE SOME SLIGHT DIFFERENCES BEYOND DAY 5 WITH THE CYCLONE TRACK AND DEPTH THROUGH THE NORTHEAST...BUT A BLEND OF THE ECENS/GEFS MEANS APPEARED A GOOD MIDDLE GROUND FOR NOW. VOJTESAK