866  
FXUS02 KWBC 260600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EDT FRI OCT 26 2018  
 
VALID 12Z MON OCT 29 2018 - 12Z FRI NOV 02 2018  
   
..PATTERN OVERVIEW
 
 
A MODERATELY PROGRESSIVE FLOW PATTERN ACROSS THE U.S. EARLY IN THE  
MEDIUM RANGE WILL GRADUALLY BECOME QUITE A BIT MORE AMPLIFIED BY  
THE MIDDLE OF NEXT WEEK. THE UPPER RIDGE WHICH AS BEEN PREVALENT  
OFF THE WEST COAST IS EXPECTED TO RETURN, WITH A DOWNSTREAM LARGE  
SCALE TROUGH EXPECTED TO SET UP ACROSS THE CENTRAL U.S. THIS FLOW  
PATTERN WILL SET THE STAGE FOR TRANSPORT OF COLD, POLAR AIR  
SOUTHWARD ACROSS THE NORTH CENTRAL U.S., WITH WET CONDITIONS ON  
THE EASTERN SIDE OF THE DEVELOPING TROUGH, FROM THE LOWER  
MISSISSIPPI VALLEY TO THE OHIO VALLEY.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS SHOWED SUFFICIENT CONSENSUS DURING THE FIRST HALF OF THE  
MEDIUM RANGE TO SUPPORT USE OF A MULTI-MODEL DETERMINISTIC BLEND  
(INCLUDING THE ECMWF/GFS/UKMET) DURING DAYS 3-4 (MON-TUE). ONE  
UPPER TROUGH/SURFACE LOW PRESSURE SYSTEM IS EXPECTED TO BE LIFT  
OUT OF THE EASTERN U.S. DURING THIS TIME PERIOD, WHILE THE UPPER  
RIDGE BUILDS WELL OFF THE WEST COAST, AND THE NEXT SIGNIFICANT  
SHORTWAVE CROSSES THE NORTHERN ROCKIES AND THEN BEGINS TO AMPLIFY  
ACROSS THE CENTRAL U.S. THE 18Z AND 00Z RUNS OF THE GFS WERE  
QUICKER THAN THE ECMWF AND THE MODEL CONSENSUS WITH BRINGING  
SHORTWAVE ENERGY EAST FROM THE NORTHERN ROCKIES INTO THE PLAINS  
SUN-MON, AND THE SLOWER 12Z GFS WAS PREFERRED AS PART OF THE  
MULTI-MODEL BLEND. AFTER DAY 5, MODELS SHOW GENERALLY GOOD  
AGREEMENT THAT THE FLOW WILL BECOME INCREASINGLY AMPLIFIED WITH  
RIDGING EXPANDING OFF THE WEST COAST AND A BROAD/DEEP UPPER TROUGH  
AMPLIFYING ACROSS THE CENTRAL U.S. SOLUTIONS DIFFER, HOWEVER, WITH  
RESPECT TO INDIVIDUAL SHORTWAVE COMPONENTS TRAVERSING THE LONG  
WAVE TROUGH. AS A RESULT OF DECREASED CONFIDENCE IN THE SPECIFICS,  
BOOSTED ECENS/GEFS ENSEMBLE MEANS TO COMPRISE A MAJORITY OF THE  
FORECAST BLEND DURING DAYS 6-7 (THU-FRI).  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
INCREASINGLY WET CONDITIONS ARE EXPECTED FROM THE LOWER  
MISSISSIPPI VALLEY TO THE OHIO VALLEY, ESPECIALLY BY THE MIDDLE TO  
END OF NEXT WEEK AS THE LARGE CENTRAL U.S. UPPER TROUGH DEVELOPS,  
FAVORING NORTHWARD TRANSPORT OF GULF OF MEXICO MOISTURE AND  
INSTABILITY WHERE IT WILL INTERACT WITH A SURFACE FRONTAL  
BOUNDARY. MODELS SHOW A DECENT SIGNAL THAT MULTI-INCH RAINFALL  
TOTALS WILL BE POSSIBLE. THE PACIFIC NORTHWEST AND THE NORTHERN  
ROCKIES WILL ALSO SEE MULTIPLE ROUNDS OF PRECIPITATION AS  
WEAKENING SHORTWAVES/FRONTAL SYSTEMS TRAVERSE THE NORTHERN  
PERIPHERY OF THE PACIFIC RIDGE. INITIALLY ABOVE AVERAGE  
TEMPERATURES ACROSS ROCKIES AND CENTRAL U.S. WILL QUICKLY DROP BY  
THE MIDDLE OF NEXT WEEK AS THE UPPER TROUGH AMPLIFIES AND A  
SURFACE COLD FRONT SPREADS POLAR AIR SOUTHWARD, WITH HIGH  
TEMPERATURES 5 TO 15 DEGREES BELOW AVERAGE ACROSS MUCH OF THE  
ROCKIES AND CENTRAL U.S. THROUGH THE MIDDLE/END OF NEXT WEEK.  
 
RYAN  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page