101  
FXUS02 KWBC 260653  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
153 AM EST MON NOV 26 2018  
 
VALID 12Z THU NOV 29 2018 - 12Z MON DEC 3 2018  
 
GENERAL WEATHER PATTERN  
-----------------------  
QUASI-ZONAL FLOW ALOFT ENCOMPASSES MUCH OF THE CONTINENTAL U.S.  
AFTER THE DEPARTURE OF THE LARGE STORM SYSTEM FROM THE NORTHEAST  
STATES ON THURSDAY, WITH A LOW AMPLITUDE PERTURBATION CROSSING THE  
PLAINS. THIS QUICKLY CHANGES GOING INTO FRIDAY AS A POTENT  
PACIFIC DISTURBANCE CROSSES THE INTERMOUNTAIN WEST AND THEN  
REACHES THE CENTRAL PLAINS BY SATURDAY. AFTER A BRIEF RESPITE, A  
SECOND STORM SYSTEM WILL LIKELY AFFECT THE PACIFIC NORTHWEST AND  
ALLOW FOR THE TROUGH TO REBUILD ACROSS MUCH OF THE WEST BY SUNDAY,  
WHICH MAY EVENTUALLY AFFECT THE CENTRAL U.S. BY THE END OF THE  
FORECAST PERIOD NEXT MONDAY.  
 
MODEL GUIDANCE EVALUATION  
-------------------------  
THE EVOLUTION AND TRACK OF THE PACIFIC LOW PRESSURE SYSTEM  
REACHING CALIFORNIA LATE THURSDAY AND THEN THE CENTRAL U.S. IS  
BECOMING BETTER REFINED BY THE DETERMINISTIC GUIDANCE COMPARED TO  
24 HOURS AGO. ALTHOUGH THE 00Z GFS REMAINS MORE PROGRESSIVE WITH  
THE TROUGH AXIS COMPARED TO THE 00Z ECMWF WITH SIMILAR AMPLITUDE  
BY SATURDAY, THE DIFFERENCES ARE NOT AS PRONOUNCED COMPARED TO  
YESTERDAY'S MODEL RUNS, AND BOTH OF THESE MODELS APPEAR TO DEPICT  
A REASONABLE EVOLUTION AND THE 12Z/18Z VERSIONS WERE INCORPORATED  
INTO THE WPC FORECAST. THIS ALSO HAS SOME SUPPORT FROM THE 00Z  
CMC.  
 
THERE IS ALSO GROWING CONSENSUS FOR A SECOND PACIFIC STORM SYSTEM  
TO AFFECT THE NORTHWESTERN U.S. BY SATURDAY, DESPITE SOME  
PLACEMENT AND TIMING DIFFERENCES. THE CMC IS MORE AMPLIFIED THAN  
THE GFS AND ECMWF REGARDING THE UPPER LEVEL TROUGH BY SUNDAY  
MORNING OVER THE INTERMOUNTAIN WEST. THE ENSEMBLE MEANS PROVIDED  
A REASONABLE PLACEMENT FOR THIS FEATURE FOR THE SUNDAY AND MONDAY  
TIME FRAME.  
 
SENSIBLE WEATHER  
----------------  
ACROSS THE WESTERN U.S., THE FIRST ROUND OF HEAVY PRECIPITATION IS  
EXPECTED THURSDAY NIGHT AND INTO FRIDAY AS THE STRONG PACIFIC LOW  
MOVES ONSHORE, WITH A POTENTIAL ATMOSPHERIC RIVER EVENT FOR  
CENTRAL AND NORTHERN CALIFORNIA. ENHANCED RAINFALL IS BECOMING  
MORE PROBABLE FOR THE TOPOGRAPHICALLY FAVORED AREAS OF CALIFORNIA,  
ESPECIALLY FOR THE LOWER ELEVATIONS OF THE SIERRA NEVADA WHERE A  
FEW INCHES OF RAINFALL WILL BE POSSIBLE, AND HEAVY SNOW FOR THE  
HIGHER RIDGES. INLAND HEAVY SNOW IS LIKELY FOR THE MOUNTAIN  
RANGES OF THE INTERMOUNTAIN WEST AS THE MOISTURE SURGE ADVECTS  
EASTWARD. THE SECOND STORM SYSTEM THAT WILL LIKELY AFFECT THE  
PACIFIC NORTHWEST THIS WEEKEND SHOULD ALSO BRING PERIOD OF HEAVY  
RAIN AND HIGH ELEVATION SNOW.  
 
ACTIVE WEATHER IS ALSO ANTICIPATED FROM THE SOUTHERN PLAINS TO THE  
OHIO VALLEY FRIDAY NIGHT INTO SUNDAY AS A SURFACE LOW IS FORECAST  
TO DEVELOP AND INTENSIFY AS IT TRACKS NORTHEASTWARD, AND THIS  
FEATURE WOULD BE RELATED TO THE LARGE SCALE TROUGH FROM THE FIRST  
PACIFIC LOW PREVIOUSLY MENTIONED. THERE IS AN INCREASING SIGNAL  
IN THE MODEL GUIDANCE FOR A BAND OF MODERATE TO HEAVY RAIN IN THE  
WARM SECTOR OF THIS LOW, AND SPC IS MONITORING THE POTENTIAL FOR  
SEVERE WEATHER GIVEN THE STRONG DYNAMICS ALOFT THAT ARE EXPECTED  
IN COMBINATION WITH ENHANCED MOISTURE ADVECTION. SNOW IS BECOMING  
MORE LIKELY TO THE NORTHWEST OF THE LOW TRACK ACROSS THE CENTRAL  
PLAINS AND UPPER MIDWEST, HOWEVER PLACEMENT DIFFERENCES LIMIT  
CONFIDENCE AS TO WHERE THE BAND OF HEAVIEST SNOW WOULD BECOME  
ESTABLISHED. WINDY CONDITIONS IN THE WAKE OF THE DEPARTING STORM  
SYSTEM ALSO APPEAR LIKELY FOR PARTS OF THE PLAINS BY SUNDAY.  
 
D. HAMRICK  
 
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