688  
FXUS02 KWBC 130700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST THU JAN 13 2022  
 
VALID 12Z SUN JAN 16 2022 - 12Z THU JAN 20 2022  
 
...WINTRY WEATHER IS EXPECTED ACROSS THE APPALACHIANS AND PARTS OF  
THE EASTERN SEABOARD, BUT UNCERTAINTY REMAINS WITH PRECIPITATION  
TYPE IN SOME AREAS AND WITH THE LOCATION OF THE HEAVIEST SNOW...  
 
   
..OVERVIEW
 
 
THE MOST NOTABLE WEATHER FEATURE DURING THE MEDIUM RANGE PERIOD IS  
A DEVELOPING SURFACE LOW PRESSURE SYSTEM THAT SLIDES ACROSS THE  
SOUTHEAST ON SUNDAY AND THEN PIVOTS NORTHWARD NEAR/ALONG THE EAST  
COAST AHEAD OF A POTENT MID-UPPER SHORTWAVE TROUGH. THIS WILL  
CAUSE IMPACTFUL WINTRY WEATHER TO SPREAD ACROSS MUCH OF THE EAST  
EARLY NEXT WEEK. HOWEVER, UNCERTAINTY REMAINS WITH THE EXACT LOW  
TRACK, WHICH LEADS TO LOW CONFIDENCE IN PRECIPITATION TYPE (WHICH  
COULD CHANGE IN SOME LOCATIONS AS THE EVENT PROGRESSES), THE AXIS  
OF THE HEAVIEST SNOW, AND THE WESTWARD EXTENT OF THE SNOW.  
MEANWHILE IN THE WEST, MAINLY DRY CONDITIONS ARE EXPECTED  
UNDERNEATH SURFACE HIGH PRESSURE, WITH THE EXCEPTION OF LIGHT  
PRECIPITATION IN THE PACIFIC NORTHWEST AND NORTHERN ROCKIES AS  
WEAK FRONTS TRACK THROUGH.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL GUIDANCE FOR THE 12/18Z CYCLE (AND THE INCOMING 00Z CYCLE)  
SHOWS A SIMILAR IDEA TO THE PREVIOUS COUPLE OF CYCLES OF MODEL  
GUIDANCE WITH THE IMPACTFUL SURFACE LOW IN THE EAST--THAT IS, A  
LOW TRACK AS DESCRIBED ABOVE STAYING ONSHORE IN THE DETERMINISTIC  
GUIDANCE, BUT WITH THE GEFS AND EC ENSEMBLE MEANS SHOWING A TRACK  
OFFSHORE, WHILE INDIVIDUAL ENSEMBLE MEMBERS DEMONSTRATE  
CONSIDERABLE SPREAD IN LOW PLACEMENT, WITH CERTAINLY SOME ENSEMBLE  
MEMBERS ALONG THE COAST OR INLAND. AGAIN, WHILE MODEL GUIDANCE  
EXHIBITS GOOD AGREEMENT FOR A STRENGTHENING LOW, THE EXACT LOW  
TRACK WILL CREATE SIGNIFICANT DIFFERENCES IN WEATHER TYPE AT  
CERTAIN LOCATIONS, ESPECIALLY NEAR THE ATLANTIC COAST TO ABOUT THE  
I-95 CORRIDOR. THE 12/18/00Z GFS ALONG WITH THE 12/00Z CMC ALL  
SHOW A TRACK BASICALLY ON THE WESTERN SIDE OF THE GUIDANCE  
ENVELOPE (WELL INLAND OVER THE NORTHERN MID-ATLANTIC MONDAY  
MORNING), WITH THE 12Z ECMWF A BIT FARTHER EAST BUT STILL ONSHORE.  
FELT IT PRUDENT TO CONTINUE WITH A LOW TRACK IN BETWEEN THE  
WESTERN DETERMINISTIC GUIDANCE AND THE EASTERN EC AND GEFS  
ENSEMBLE MEAN GUIDANCE, BUT SOMEWHAT FAVORING THE FAIRLY WELL  
CLUSTERED DETERMINISTIC MODELS. THE BEST PROXY FOR THIS AT THE  
TIME OF FORECAST CREATION WAS CLOSE TO THE 12Z ECMWF AND THE 12Z  
CMC ENSEMBLE MEAN; THE 12Z CMC ENSEMBLE MEAN ALONG WITH THE  
INCOMING 00Z CMC MEAN ARE THE FIRST ENSEMBLE MEANS TO SHOW AN  
ONSHORE TRACK WITH THE LOW. THIS LED TO A SURFACE LOW BASICALLY  
OVER PHILADELPHIA ON MONDAY MORNING, WHICH WAS A VERY MINOR SHIFT  
FARTHER INLAND/WEST COMPARED TO CONTINUITY. HOPEFULLY MODELS WILL  
CONVERGE AND CONFIDENCE WILL INCREASE WITHIN THE NEXT DAY FOR THE  
EXACT LOW TRACK, AS THE SHORTWAVE ENERGY LEADING TO THIS SYSTEM  
WILL ENTER THE PACIFIC NORTHWEST/SOUTHWESTERN CANADA AND HAVE  
BETTER DATA SAMPLING FOR INPUT INTO THE MODEL GUIDANCE.  
 
ELSEWHERE, RIDGING IS LIKELY TO HAVE HOLD OF THE WEST EARLY THIS  
WEEK, OTHER THAN A MEANDERING SOUTHERN STREAM UPPER LOW CENTERED  
OFFSHORE OF CALIFORNIA. THE SOUTHERN STREAM LOW IS FORECAST TO  
TRACK EASTWARD AND JOIN WITH THE MAIN FLOW BY AROUND TUESDAY, WITH  
SOME POSSIBLE INTERACTION WITH NORTHERN STREAM ENERGY IN THE  
EASTERN PACIFIC, BUT MOST GUIDANCE OTHER THAN THE 12Z CMC NOW HAS  
MORE SEPARATION WITH THESE PIECES OF ENERGY. THEN THERE IS GOOD  
MODEL AGREEMENT FOR AN AMPLIFIED RIDGE OVER THE WEST COAST BY  
THURSDAY DRIFTING EASTWARD FROM THE PACIFIC, WITH SOME MODEL  
DIFFERENCES IN POSSIBLE EMBEDDED SHORTWAVES PARTICULARLY SHOWN BY  
THE GFS RUNS. MEANWHILE, ADDITIONAL SHORTWAVES REINFORCE TROUGHING  
CENTERED OVER THE GREAT LAKES WEDNESDAY-THURSDAY, FOR WHICH THERE  
IS REASONABLE MODEL AGREEMENT.  
 
THE WPC MEDIUM RANGE FORECAST WAS BASED ON AN INITIAL BLEND OF THE  
12/18Z DETERMINISTIC GUIDANCE FAVORING THE ECMWF SOMEWHAT, ADDING  
THE CMC ENSEMBLE MEAN BY DAY 4 WITH ITS FAVORABLE LOW POSITION IN  
THE EAST AND INCREASING THE PROPORTION OF THE EC ENSEMBLE MEAN FOR  
THE LATTER PART OF THE PERIOD AS WELL, TO HELP TEMPER MINOR  
VARIATIONS IN MODEL GUIDANCE.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE SURFACE LOW LIFTING FROM ACROSS THE SOUTHEAST AND UP THE EAST  
COAST WILL BRING WITH IT A FULL ARRAY OF WEATHER HAZARDS AND  
THREATS. CONCERNING CHANCES FOR HEAVY SNOW ARE LIKELY IN THE  
SOUTHERN APPALACHIANS BEGINNING SATURDAY, SPREADING NORTHWARD  
ALONG/ON THE BACKSIDE OF THE DEEPENING LOW AND GENERALLY WEST OF  
THE I-95 CORRIDOR IN THE MID-ATLANTIC AND THE NORTHEAST. CHANCES  
ARE ALSO INCREASING FOR A POTENTIALLY SIGNIFICANT ICING EVENT,  
ESPECIALLY FROM PARTS OF FAR NORTHERN GEORGIA, THROUGH THE WESTERN  
CAROLINAS, AND INTO SOUTH-CENTRAL VIRGINIA WHERE WARM AND MOIST  
GULF OF MEXICO INFLOW WILL OVERRUN INITIALLY COLD AIR AT THE  
SURFACE. WPC HAS BOTH THE SNOW AND ICE THREATS HIGHLIGHTED IN THE  
MOST RECENT HAZARD OUTLOOK. TO THE SOUTH, MODERATELY TO LOCALLY  
HEAVY RAIN COULD MOVE ACROSS THE SOUTHEAST THIS WEEKEND, AND  
POSSIBLY UP THE IMMEDIATE EAST COAST SUNDAY INTO MONDAY. GUSTY  
WINDS SURROUNDING THE SURFACE LOW MAY CREATE HIGH WAVES OFF THE  
COAST LEADING TO POSSIBLE COASTAL FLOOD CONCERNS ALONG THE  
NORTHEAST COASTLINE. OF COURSE, ALL OF THIS IS HIGHLY DEPENDENT ON  
THE EXACT TRACK OF THE SURFACE LOW AND EVEN SMALL ADJUSTMENTS BACK  
TO THE EAST COULD BRING HEAVY SNOW POTENTIAL INTO EVEN COASTAL  
PARTS OF THE EAST.  
 
ELSEWHERE, AFTER THE MAIN LOW EXITS NORTHEAST OF THE U.S. ON  
TUESDAY, ANOTHER (WEAKER) LOW PRESSURE SYSTEM IS FORECAST TO TRACK  
OVER THE NORTH-CENTRAL U.S. IN RESPONSE TO A MID-UPPER SHORTWAVE  
AND BRING SOME SNOW TO THE UPPER MIDWEST AND GREAT LAKES, WITH  
POSSIBLY HIGHER TOTALS NEAR TYPICAL LAKE ENHANCEMENT AREAS. THE  
WEST COULD SEE SOME LIGHT PRECIPITATION DURING THE PERIOD,  
PARTICULARLY OVER THE PACIFIC NORTHWEST AND INTO THE NORTHERN  
ROCKIES EARLY NEXT WEEK, WITH MAINLY DRY CONDITIONS ELSEWHERE.  
RAIN COULD DEVELOP AGAIN ACROSS THE LOWER MISSISSIPPI VALLEY AND  
SOUTHEAST BEGINNING TUESDAY AND INCREASING WEDNESDAY WITH RETURN  
FLOW FROM THE GULF OF MEXICO.  
 
COOLER THAN NORMAL TEMPERATURES ARE EXPECTED GENERALLY OVER THE  
EASTERN U.S. EARLY NEXT WEEK, WITH PARTICULARLY CHILLY LOWS BELOW  
0F IN THE INTERIOR NORTHEAST SUNDAY MORNING, ABOUT 15-25 DEGREES  
BELOW AVERAGE. THE WEST TO THE PLAINS CAN EXPECT GENERALLY ABOVE  
AVERAGE CONDITIONS THROUGH TUESDAY. THEN AS A COLD SURFACE HIGH  
DROPS INTO THE NORTH-CENTRAL U.S. WEDNESDAY AND THURSDAY,  
TEMPERATURES WILL FALL TO 10-20F BELOW NORMAL IN THE UPPER MIDWEST.  
 
TATE/SANTORELLI  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE 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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