Prognostic Meteorological Discussion
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000 FXUS02 KWBC 270640 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 239 AM EDT FRI APR 27 2018 VALID 12Z MON APR 30 2018 - 12Z FRI MAY 04 2018 ...OVERVIEW... ON MONDAY...A BROAD CYCLONIC CIRCULATION WILL BE IN THE PROCESS OF EXITING THE NORTHEASTERN U.S. WHILE AMPLIFIED FLOW LOOMS UPSTREAM OVER THE REMAINDER OF THE COUNTRY. MEAN UPPER RIDGING SHOULD CONTINUE ADVANCING FROM THE MS RIVER VALLEY TOWARD THE EASTERN SEABOARD DURING THE MONDAY-THURSDAY TIMEFRAME AS HEIGHTS LOWER OVER THE WESTERN/CENTRAL STATES. WITHIN THIS REGION OF TROUGHING...TWO SEPARATE SYSTEMS ARE FORECAST TO EJECT TOWARD THE CENTRAL U.S. DURING THE PERIOD. INITIALLY...A SHORTWAVE SHOULD LIFT TOWARD THE NORTH-CENTRAL STATES WITH THE POTENTIAL FOR A DEEP SURFACE LOW TO CROSS THE DAKOTAS ON TUESDAY MORNING BEFORE LIFTING INTO ONTARIO BY MID-WEEK. THE PARENT UPPER TROUGH SHOULD RE-LOAD AS HEIGHTS LOWER ACROSS THE SOUTHWESTERN U.S. WITH AN EVENTUAL EASTWARD PROGRESSION OF THIS MEAN TROUGH. THIS WILL ULTIMATELY USHER A COLD FRONT ACROSS THE MS RIVER VALLEY BY DAY 7/MAY 4. ...MODEL EVALUATION/UNCERTAINTIES/PREFERENCES... THE DEPARTING UPPER LOW OVER THE NORTHEASTERN STATES IS WELL RESOLVED WITH SOME UNCERTAINTIES REGARDING TIMING...PARTICULARLY AS THE 00Z GUIDANCE HAS COME IN SLOWER. HOWEVER...THE 12Z ECMWF STILL SITS ON THE WESTERN SIDE OF THE SPREAD ON TUESDAY AS SUGGESTED BY THE ENSEMBLE SPAGHETTI PLOTS. CONSIDERING THE EVOLVING WESTERN/CENTRAL U.S. TROUGH...MODELS STILL ARE UNCERTAIN REGARDING THE INTENSITY OF THE CYCLONE LIFTING TOWARD THE DAKOTAS/UPPER MIDWEST ON TUESDAY. THE PAST SEVERAL RUNS OF THE GFS HAVE BEEN MORE EMPHATIC WITH THE DEEPER SOLUTION WHILE THE CMC SOLUTION CONTINUES TO BOUNCE AROUND A BIT. MEANWHILE...THE 12Z/00Z ECMWF RUNS ARE DECIDEDLY WEAKER AS DICTATED BY THE FLATTER MID-LEVEL SHORTWAVE. SHIFTING FOCUS BACK TO THE SECONDARY HEIGHT FALLS...IT REMAINS WELL AGREED UPON OUTSIDE OF THE 12Z UKMET WHICH SHIFTED THE ENTIRE TROUGH DOWNSTREAM. FORTUNATELY...THE LATEST UKMET HAS MADE A WESTWARD ADJUSTMENT BRINGING ITS SOLUTION CLOSER TO THE UPSTREAM CONSENSUS. THE ENTIRE SYNOPTIC PATTERN SHOULD ULTIMATELY SHIFT EASTWARD ALLOWING THIS SYSTEM TO CROSS THE VICINITY OF THE MS RIVER VALLEY BY LATE NEXT WEEK. BY DAY 7/MAY 4...A MEAN RIDGE SHOULD SETTLE OVER THE WEST COAST WITH THE POTENTIAL FOR A WEAKNESS ACROSS THE FOUR CORNERS REGION. ENSEMBLE MEAN SOLUTIONS ARE WELL CLUSTERED AND SUPPORTIVE OF THIS ULTIMATE SET UP. THROUGH MID-WEEK...FAVORED A COMBINATION OF THE 18Z/12Z GFS WITH THE 12Z ECMWF/CMC GIVEN DECENT MODEL AGREEMENT. INCLUSION OF THE 12Z ECMWF DID INCREASE PRESSURES A BIT WITH THE NORTH-CENTRAL U.S. CYCLONE. GRADUALLY INCORPORATED THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS INTO THE MIX THROUGH THE REMAINDER OF THE PERIOD GIVEN GROWING UNCERTAINTIES. WAS ABLE TO MAINTAIN AT LEAST 30 PERCENT OF AN OPERATIONAL COMPONENT IN THE BLEND THROUGH LATE NEXT WEEK GIVEN A DECENT HANDLE ON THE OVERALL PATTERN. ...THREATS/WEATHER HIGHLIGHTS... UNDERNEATH THE UPPER LOW ACROSS NEW ENGLAND...CHILLY TEMPERATURES ACCOMPANIED BY WRAP AROUND RAIN SHOWERS WILL BE LIKELY EARLY NEXT WEEK. FARTHER UPSTREAM...MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED IN ADVANCE OF THE SLOW MOVING UPPER TROUGH. THE INITIAL THREAT AREA WILL EXIST OVER THE NORTHERN ROCKIES/GREAT PLAINS AND INTO THE UPPER MIDWEST THROUGH MID-WEEK WITH A SOUTHERN SHIFT EXPECTED AS THE TROUGH RELOADS OVER THE WEST. AN ELONGATED AXIS OF MODERATE TO HEAVY RAINFALL WILL LIKELY EXTEND FROM THE SOUTHERN PLAINS UP TOWARD THE GREAT LAKES AS THE COLD FRONT EDGES EASTWARD. SOME AREAS OF SEVERE WEATHER MAY BE POSSIBLE AS SUGGESTED IN THE PREVIOUS STORM PREDICTION CENTER OUTLOOK. THERE COULD ALSO BE SOME THREAT FOR RATHER IMPRESSIVE RAINFALL AMOUNTS AS SHOWN BY SOME OF THE MORE RELIABLE OPERATIONAL GUIDANCE. THIS WOULD PARTICULARLY BE THE CASE OVER THE ARKLATEX INTO THE OZARKS. WITH A PROGRESSIVE PATTERN IN PLACE...EXPECT RELATED TEMPERATURE ANOMALIES TO NUDGE DOWNSTREAM IN TIME. AS MENTIONED...COOLER TEMPERATURES WILL INITIALLY PREVAIL OVER THE EASTERN U.S. WHILE WELL ABOVE AVERAGE READINGS OCCUPY THE CENTER OF THE COUNTRY. SUCH DEPARTURES ON THE ORDER OF 10 TO 15 DEGREES ABOVE CLIMATOLOGY WILL ADVANCE EASTWARD IN TIME WITH LOW TO POSSIBLY MID 80S LIKELY TO REACH THE CENTRAL APPALACHIANS AND MID-ATLANTIC ON WEDNESDAY/THURSDAY. THE COOLEST CONDITIONS SHOULD GENERALLY BE FOUND UNDERNEATH THE EXTENSIVE PRECIPITATION SHIELD AND IN THE WAKE OF THE UPPER TROUGH GIVEN A COLD ADVECTION PATTERN. EXPECTED TEMPERATURES SHOULD BE AROUND 5 TO 10 DEGREES BELOW AVERAGE IN SUCH LOCATIONS. RUBIN-OSTER ASSOCIATED WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS...SURFACE SYSTEMS...WEATHER GRIDS...QUANTITATIVE PRECIPITATION FORECASTS (QPF)...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITIES CAN BE FOUND AT... http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 $$

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