935  
FXUS02 KWBC 291601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST SAT DEC 29 2018  
 
VALID 12Z TUE JAN 01 2019 - 12Z SAT JAN 05 2019  
   
..OVERVIEW
 
 
THE MEDIUM RANGE PERIOD FEATURES A POSSIBLY CLOSED LOW PROGESSING  
EASTWARD FROM THE FOUR CORNERS REGION ON DAY 3 (TUE) TO THE  
SOUTHEAST/TENNESSEE VALLEY BY DAY 6 (FRI) BEFORE BECOMING ABSORBED  
INTO THE LARGER SCALE TROUGHING. TO THE NORTH, ADDITIONAL ENERGY  
SLIDES ALONG THE U.S./CANADIAN BORDER UNDERNEATH OF DEEP LOW  
ROTATING OVER HUDSON BAY. OUT WEST, UPPER RIDGING ACROSS THE EAST  
PACIFIC SHIFTS INLAND AS AN UPSTREAM SHORTWAVE TROUGH MOVES  
TOWARDS THE PACIFIC NORTHWEST. THE OVERALL PATTERN WOULD BRING  
WIDESPREAD RAIN TO THE EASTERN HALF OF THE NATION WHILE  
PRECIPITATION AGAIN INCREASES IN THE PACIFIC NORTHWEST.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A TREND IN BOTH GLOBAL MODELS AND ENSEMBLES IS EMERGING TOWARDS A  
SLOWER AND SLIGHTLY STRONGER UPPER LOW PROGRESSING FROM THE FOUR  
CORNERS TO THE EAST NEXT WEEK. THE LATEST RUN OF THE CMC FAVORS A  
MORE ELONGATED TROUGH TYPE FEATURE ACROSS THE CENTRAL U.S. AND AS  
A RESULT IS NOTICEABLY FASTER THAN THE REST OF THE GUIDANCE AND  
THUS WAS NOT INCLUDED IN THE BLEND. THERE IS SOME QUESTION AS TO  
THE LOCATION OF THE SURFACE LOW ON DAY 5 WITH THE ECMWF BEING  
NOTICEABLY FARTHER NORTH THAN THE GFS (NORTHERN MS/AL VS CENTRAL  
GULF COAST) BUT BASED ON THE ENSEMBLE LOW PLOTS, SOMEWHERE IN THE  
MIDDLE OF THE TWO IS PROBABLY A GOOD PLACE TO BE AT THIS POINT.  
OUT IN THE WEST, BEYOND DAY 5, TIMING OF THE RIDGE-TROUGH-RIDGE  
PATTERN IN THE EASTERN PACIFIC AND NORTHWEST U.S. BECOMES AN  
ISSUE, ESPECIALLY IN THE OPERATIONAL MODELS. THE ENSEMBLE MEANS  
APPEARED TO PRESENT A MORE AGREEABLE (WITH OBVIOUS SUPRESSION)  
SOLUTION THIS LATE IN THE PERIOD.  
 
THE BLEND FOR THIS CYCLE OF THE WPC MEDIUM RANGE PROGS FEATURES A  
MAJORITY DETERMINISTIC MODEL BLEND (BETWEEN THE 06Z GFS/00Z  
ECMWF/00Z FV3-GFS) DAYS 3-5, WITH INCREASING WEIGHTING OF THE  
ENSEMBLE MEANS (GEFS/ECENS) FROM DAY 5 AND BEYOND. CONTINUES TO  
INCLUDE A SMALL BIT OF THE 00Z DETERMINISTIC ECMWF THROUGH DAY 7  
BECAUSE IT SEEMED TO FIT BEST WITH THE ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
CLOSED LOW IN THE SOUTHWEST SHOULD BRING A SECOND ROUND OF  
PRECIPITATION TO PARTS OF EASTERN ARIZONA AND NEW MEXICO, WITH THE  
HIGHEST POTENTIAL FOR ACCUMULATING SNOWS CONFINED TO THE HIGHER  
MOUNTAINS. AS THIS LOW PROGRESSES ACROSS THE SOUTHERN TIER, THIS  
WILL PROMOTE HEAVY RAINFALL POTENTIAL FROM THE DEEP SOUTH INTO THE  
EASTERN U.S. NEXT WEEK. A SURFACE LOW LIFTING THROUGH THE  
SOUTHEAST INTO THE MID-ATLANTIC IS LIKELY TO PROVIDE A FOCUS FOR  
ENHANCED RAINFALL WITH THE BEST CHANCE FOR 3+ INCH 5-DAY RAINFALL  
TOTALS CURRENTLY EXTENDING FROM THE CENTRAL GULF COAST INTO  
GEORGIA.MOISTURE REACHING THE GREAT LAKES/NEW ENGLAND MAY BE IN  
THE FORM OF SNOW, ESPECIALLY WITH LAKE EFFECT ACTIVITY BEHIND LOW  
PRESSURE EXITING NEW ENGLAND MID-WEEK. THE PACIFIC NORTHWEST CAN  
EXPECT AN INCREASE IN RAIN/HIGH ELEVATION SNOW BY THURSDAY AND  
CONTINUING INTO FRIDAY--WITH SOME MEANINGFUL TOTALS LIKELY IN THE  
OLYMPICS/WASHINGTON CASCADES AND THE NORTHERN PORTIONS OF THE  
NORTHERN ROCKIES.  
 
IN REGARDS TO TEMPERATURES, THE NORTHERN PLAINS CAN EXPECT VERY  
COLD TEMPERATURES ON TUESDAY--WITH HIGH TEMPERATURES REACHING  
15-25F BELOW NORMAL. BY WEDNESDAY, TEMPERATURES WILL REBOUND IN  
THIS REGION AND ARE EXPECTED TO BE UPWARDS OF 10-15F ABOVE NORMAL.  
THE CENTRAL AND SOUTHERN PLAINS WILL ALSO BE MUCH BELOW NORMAL ON  
TUESDAY AND WEDNESDAY--BECOMING NEAR NORMAL BY THURSDAY. THE  
EXCEPTION WILL BE ALONG THE WESTERN GULF COAST AS AN ACTIVE PERIOD  
FOR PRECIPITATION IS EXPECTED. MEANWHILE, THE EAST COAST WILL BE  
ANOMALOUSLY WARM ON TUESDAY--RETURNING TO NEAR NORMAL BY  
WEDNESDAY. LATER IN THE MEDIUM RANGE PERIOD (FRI-SAT), THE CENTRAL  
U.S. WILL BE ABOVE AVERAGE--WITH HIGH TEMPERATURES 15-20F ABOVE  
NORMAL. THE WEST COAST SHOULD BE NEAR NORMAL THROUGH THE MEDIUM  
RANGE PERIOD.  
 
SANTORELLI/REINHART  
 
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  
 

 
 
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