483  
FXUS02 KWBC 060700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT WED JUN 06 2018  
 
VALID 12Z SAT JUN 09 2018 - 12Z WED JUN 13 2018  
   
..PATTERN OVERVIEW
 
 
A NORTHERN STREAM OMEGA BLOCK SIGNATURE IS NOTED IN THE GUIDANCE  
WITH THE KEY PLAYER BEING A POWERFUL UPPER TROUGH APPROACHING THE  
PACIFIC NORTHWEST EARLY IN THE WEEKEND. CHARACTERIZED BY 500-MB  
HEIGHT ANOMALIES AROUND 2 SIGMA, AN EMBEDDED CLOSED LOW/STRONG  
BAND OF HEIGHT FALLS WILL SLIDE EASTWARD REACHING THE NORTHERN  
ROCKIES BY 11/1200Z. ULTIMATELY THIS SHOULD SUPPRESS A MEAN UPPER  
RIDGE WHICH WILL SPRAWLED ACROSS THE DESERT SOUTHWEST EASTWARD TO  
THE SOUTHERN PLAINS. GRADUALLY THIS POSITIVE HEIGHT ANOMALY WILL  
REBOUND BY EARLY NEXT WEEK WITH REAL ESTATE GENERALLY COVERING THE  
SOUTHWESTERN QUARTER OF THE COUNTRY. TO THE NORTH, THE MENTIONED  
UPPER TROUGH PUSHING THROUGH THE NORTHERN ROCKIES ON MONDAY IS  
EXPECTED TO SLOW CONSIDERABLY AND MAY EVEN CLOSE OFF AT SOME POINT  
NEAR THE DAKOTAS/SOUTH-CENTRAL CANADA BORDER. ALL THE WHILE, THIS  
OMEGA BLOCK SET UP WILL SHIFT THE PATTERN DOWNSTREAM WITH BROAD  
UPPER TROUGHING ACROSS THE NORTHEASTERN U.S. GRADUALLY SLIDING  
OFFSHORE BY THE MIDDLE OF NEXT WEEK.  
 
   
..MODEL GUIDANCE/PREDICTABILITY EVALUATION/PREFERENCES
 
 
INITIALLY FOCUSING ON THE UPPER TROUGH BARRELING THROUGH THE  
PACIFIC NORTHWEST, MULTI-DAY ENSEMBLE SPAGHETTI PLOTS HAVE SHOWN A  
FASTER TREND. ON MONDAY MORNING, THE MEAN TROUGH AXIS IS ROUGHLY  
LOCATED OVER CENTRAL MONTANA WHILE THREE MODEL CYCLES AGO IT WAS  
BACK TOWARD THE PACIFIC NORTHWEST. PREVIOUS DAYS OFFERED RANDOM  
OPERATIONAL SOLUTIONS WHICH APPEARED MORE OUTLANDISH. HOWEVER,  
THROUGH DAY 5/JUNE 11, THE GUIDANCE HAS BEEN FAIRLY CONSISTENT  
WHICH BOLSTERS CONFIDENCE ACROSS THIS REGION. THE ATTENDANT HEIGHT  
FALLS HELP ERODE THE NORTHERN EXTENT OF THE MEAN RIDGE OVER THE  
SOUTHWESTERN TO SOUTH-CENTRAL U.S. WITH THE 12Z CMC AND 00Z/12Z  
UKMET SOLUTIONS HOLDING ON TO THE RIDGE A BIT LONGER. AS THE  
HEIGHTS RELAX ONCE THE PARENT UPPER LOW MOVES TOWARD THE  
SASKATCHEWAN/MANITOBA BORDER, A RETURN OF THE SEMI-PERMANENT RIDGE  
IS LIKELY DURING THE DAY 5-7, JUNE 11-13, TIMEFRAME. IT SHOULD  
GENERALLY RE-ASSUME A SIMILAR POSITION WITH A 588-DM HEIGHT  
CONTOUR STRETCHING FROM THE DESERT SOUTHWEST TOWARD THE  
SOUTHERN/CENTRAL PLAINS. CONSIDERING THE STRONG FEATURE  
ACCELERATING THROUGH THE NORTHERN ROCKIES ON MONDAY, A GREAT DEAL  
OF UNCERTAINTY LOOMS THEREAFTER AS SOLUTIONS WAVER ABOUT MULTIPLE  
SCENARIOS. THE 00Z GFS HAS MADE A SHIFT TOWARD A MORE PROGRESSIVE  
SOLUTION AFTER MOST GUIDANCE FAVOR CLOSING OFF THE UPPER LOW  
SOMEWHERE ACROSS SOUTH-CENTRAL CANADA WHERE A QUASI-STATIONARY  
MOTION IS ATTAINED. ENSEMBLE SPAGHETTI PLOTS VARY CONSIDERABLY  
WHICH PROMOTES MORE EMPHASIS ON THE GLOBAL ENSEMBLE MEANS. FARTHER  
DOWNSTREAM, THE EASTERN EXTENT OF THE OMEGA BLOCK WILL DRIFT  
EASTWARD WITH THE LEVEL OF AMPLIFICATION UP FOR DEBATE. SOME  
FAIRLY AMPLIFIED SOLUTIONS ARE IN THE CARDS ALTHOUGH TRUSTING ANY  
ONE OPERATIONAL MODEL WOULD NOT BE WISE HERE. AS AN EXAMPLE, AT  
13/0000Z, THE 00Z GFS KEEPS HEIGHT FALLS RESTRICTED TO NEW ENGLAND  
WHILE THE PRECEDING RUN SHIFTS DOWN TO THE LOWER MID-ATLANTIC  
REGION. HOWEVER, AT THE VERY LEAST, THE ULTIMATE SYNOPTIC  
CONFIGURATION APPEARS REASONABLE ACROSS THE BOARD.  
 
REGARDING PREFERENCES, THROUGH DAY 4/SUNDAY, WAS ABLE TO UTILIZE A  
MULTI-OPERATIONAL MODEL BLEND LED BY THE 18Z/12Z GFS AND 12Z ECMWF  
WITH MINOR CONTRIBUTIONS FROM THE 12Z CMC/UKMET. THEREAFTER,  
GRADUALLY INCORPORATED HEAVIER WEIGHTING OF THE ENSEMBLE MEANS  
WITH ONLY A 20 PERCENT INFLUENCE FROM THE 18Z/12Z GFS AND 12Z  
ECMWF GIVEN SIGNIFICANT UNCERTAINTIES WITHIN THE NORTHERN STREAM  
OMEGA BLOCK. ONE REGION WHICH REMAINS STABLE IS THE  
RE-ESTABLISHMENT OF THE UPPER RIDGE ACROSS THE SOUTHWESTERN U.S.  
WITH ENSEMBLE MEANS IN GOOD AGREEMENT THERE.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
WHILE MUCH OF THE COUNTRY CAN EXPECT ABOVE AVERAGE TEMPERATURES  
DURING THE PERIOD, THERE WILL BE A FEW EXCEPTIONS TO THIS RULE. IN  
PARTICULAR, EXPECT NUMBERS AROUND 5 TO 15 DEGREES BELOW  
CLIMATOLOGY THIS WEEKEND FROM NORTHERN CALIFORNIA AND THE PACIFIC  
NORTHWEST EASTWARD INTO THE CENTRAL GREAT BASIN/UPPER  
INTERMOUNTAIN WEST. MANY HIGH TEMPERATURES WILL STRUGGLE TO GET  
OUT OF THE 50S WITH LOWS IN THE 30S ACROSS THE CENTRAL GREAT  
BASIN. FURTHER EAST, DEEP TROUGHING ACROSS THE NORTHEASTERN U.S.  
WILL FAVOR SLIGHTLY COOLER TEMPERATURES, WITH SIMILAR IMPACTS  
ACROSS FLORIDA EXCEPT DRIVEN MORE BY EXTENSIVE CLOUD COVER AND  
RAINFALL. OTHERWISE, THE REST OF THE COUNTRY WILL REMAIN RATHER  
WARM, ESPECIALLY OVER THE MIDDLE OF THE COUNTRY IN ADVANCE OF THE  
BARRELING UPPER LOW. PRIMARILY AN ISSUE THIS WEEKEND, DEPARTURES  
FROM CLIMATOLOGY WILL RANGE FROM 10 TO 15 DEGREES ACROSS THE  
NORTHERN/CENTRAL ROCKIES TO THE ADJACENT GREAT PLAINS.  
 
MULTIPLE MESOSCALE CONVECTIVE COMPLEXES ARE LIKELY TO DEVELOP  
NORTH OF THE PREVAILING RIDGE IN THE FORM OF "RIDGE ROLLERS".  
PREDICTABILITY OF ANY SUCH EPISODE OF COURSE REMAINS LOW BUT  
ENHANCED RAINFALL IS EXPECTED ANYWHERE FROM THE MIDDLE MISSISSIPPI  
VALLEY DOWNSTREAM TO THE OHIO VALLEY. THERE WILL ALSO BE ENHANCED  
RAINFALL ACROSS THE LOWER GREAT LAKES INTO THE NORTHEASTERN U.S.  
FOR MUCH OF THE WEEKEND, PARTICULARLY ALONG THE WEST-EAST ORIENTED  
FRONTAL ZONE. THE FOCUS FOR CONVECTION WILL SHIFT SOUTHWARD INTO  
EARLY NEXT WEEK AS THE FRONTAL ZONE MOVES SOUTH OF 40N LATITUDE.  
FARTHER WEST, ENHANCED ONSHORE FLOW AND SEASONABLY STRONG DYNAMICS  
WILL SUPPORT WIDESPREAD RAINFALL FROM THE PACIFIC NORTHWEST INTO  
THE UPPER INTERMOUNTAIN WEST. LOCAL OROGRAPHICS SHOULD HELP FOCUS  
HIGHER AMOUNTS WHERE UPSLOPE FLOW PREVAILS. AS THE FRONTAL ZONE  
SHIFTS TOWARD THE MIDDLE OF THE COUNTRY, EXPECT RENEWED CONVECTION  
ACROSS THE NORTH-CENTRAL STATES INTO NEXT WEEK.  
 
RUBIN-OSTER  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK 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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