Prognostic Meteorological Discussion
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000 FXUS02 KWBC 261641 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1240 PM EDT WED APR 26 2017 VALID 12Z SAT APR 29 2017 - 12Z WED MAY 03 2017 ...LATE SEASON WINTER STORM EXPECTED TO BRING SNOW TO THE SOUTHERN/CENTRAL ROCKIES AND PORTIONS OF THE ADJACENT HIGH PLAINS THIS WEEKEND...WITH SNOW ALSO POSSIBLE ACROSS THE UPPER MISSISSIPPI VALLEY EARLY NEXT WEEK... ...THREAT FOR HEAVY AND EXCESSIVE RAINFALL OVER SOUTHERN PORTIONS OF THE PLAINS AND MISSISSIPPI VALLEY THIS WEEKEND...ESPECIALLY FROM OKLAHOMA INTO ARKANSAS AND MISSOURI... ...PATTERN OVERVIEW AND GUIDANCE EVALUATION... MODEL GUIDANCE REMAINED IN GOOD AGREEMENT WITH THE LARGE SCALE FLOW PATTERN OVER THE LOWER 48 THIS WEEKEND AND INTO THE EARLY HALF OF NEXT WEEK WHICH WILL FEATURE A MEAN CENTRAL U.S. TROUGH SANDWICHED BETWEEN UPPER RIDGING OVER THE EASTERN PACIFIC AND WESTERN ATLANTIC. WITHIN THE MEAN FLOW...A CLOSED UPPER LOW OVER THE FOUR CORNERS REGION ON SATURDAY WILL SLOWLY EDGE EAST/NORTHEASTWARD TOWARDS THE CENTRAL PLAINS THIS WEEKEND. ON MONDAY...THE DYNAMIC SYSTEM...INCLUDING A DEEPENING SURFACE LOW...WILL LIFT THROUGH THE UPPER MISSISSIPPI VALLEY WHILE UPSTREAM ENERGY STREAKS SOUTHEASTWARD INTO THE PACIFIC NORTHWEST AND POTENTIALLY AMPLIFIES OVER THE INTERMOUNTAIN WEST AND ROCKIES. MODELS HAVE REMAINED FAIRLY STABLE WITH THE LONG WAVE PATTERN AND EVEN ARE STARTING TO COME INTO GOOD AGREEMENT WITH THE SMALLER SCALE FEATURES OF THE UPPER LOW EXITING THE FOUR CORNERS REGION...SO THE WPC FORECAST WAS LARGELY BASED ON A BLEND BETWEEN THE 00Z ECMWF AND 00Z/06Z GFS. HOWEVER...THE GEFS/ECMWF ENSEMBLE MEAN WERE ALSO INCORPORATED INTO THE FORECAST BLEND...ESPECIALLY NEXT MONDAY-WEDNESDAY...IN ORDER TO ACCOUNT FOR SOME OF THE SPREAD THAT DEVELOPS WITH THE DEEP SURFACE LOW EXITING THE UPPER MISSISSIPPI VALLEY AS WELL AS SOME OF THE UNCERTAINTY WITH THE AMPLITUDE AND TIMING OF THE ENERGY STREAKING INTO THE PACIFIC NORTHWEST. ...WEATHER HIGHLIGHTS... MULTIPLE WEATHER HAZARDS ARE EXPECTED WITH A DYNAMIC CLOSED LOW WHILE IT EDGES OUT OF THE FOUR CORNERS REGION AND LIFTS NORTHEASTWARD THROUGH THE CENTRAL U.S. THIS WEEKEND. INCREASING MOISTURE ADVECTION AHEAD OF THE SYSTEM WILL HEIGHTEN THE RISK FOR HEAVY AND EXCESSIVE RAINFALL OVER PORTIONS OF THE PLAINS AND MISSISSIPPI VALLEY THIS WEEKEND...ESPECIALLY OVER EASTERN OKLAHOMA AND INTO ARKANSAS AND MISSOURI. LATE SEASON SNOWFALL WILL ALSO BE POSSIBLE WITH THIS SYSTEM...INITIALLY OVER THE CENTRAL/SOUTHERN ROCKIES AND INTO PORTIONS OF THE ADJACENT HIGH PLAINS WHILE THE UPPER LOW CLOSES OFF OVER THE FOUR CORNERS REGION EARLY SATURDAY...FOLLOWED BY LOCATIONS OVER THE UPPER MISSISSIPPI VALLEY AS A DEEPENING SURFACE LOW LIFTS THROUGH THE REGION SUNDAY NIGHT INTO MONDAY. PLEASE REFER TO THE STORM PREDICTION CENTER (WWW.SPC.NCEP.NOAA.GOV) FOR INFORMATION ON THE SEVERE WEATHER THREAT WITH THIS SYSTEM. IN TERMS OF TEMPERATURES ACROSS THE NATION...A HIGH AMPLITUDE UPPER RIDGE OVER THE SOUTHEASTERN U.S. COULD BRING WIDESPREAD RECORD HIGH OR NEAR RECORD HIGH TEMPERATURES TO THE SOUTHEAST AND MID-ATLANTIC STATES THIS WEEKEND...BUT THEN TEMPERATURES SHOULD DECLINE TO NEAR NORMAL AFTER A COLD FRONT CROSSES THE REGION EARLY NEXT WEEK. WELL ABOVE NORMAL TEMPERATURES ARE FORECAST ACROSS SOUTHERN CA INTO THE DESERT SOUTHWEST EARLY TO MIDDLE PORTIONS OF NEXT WEEK AS WARM AIR ALOFT PROGRESSES DOWNSTREAM FROM THE ANTICYCLONE IN THE EASTERN PACIFIC. GERHARDT $$

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