396  
FXUS02 KWBC 121903  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
202 PM EST WED JAN 12 2022  
 
VALID 12Z SAT JAN 15 2022 - 12Z WED JAN 19 2022  
 
...WINTRY WEATHER IS BECOMING INCREASINGLY LIKELY FROM PARTS OF  
THE TENNESSEE VALLEY INTO THE EAST THIS WEEKEND INTO EARLY NEXT  
WEEK, BUT WITH PLENTY OF UNCERTAINTY...  
 
   
..OVERVIEW
 
 
THE MOST NOTABLE WEATHER FEATURE DURING THE MEDIUM RANGE PERIOD,  
AND ONE OF THE MOST UNCERTAIN, IS A DEVELOPING SURFACE LOW  
PRESSURE SYSTEM THAT SLIDES ACROSS THE SOUTHEAST AND THEN PIVOTS  
NORTHWARD NEAR THE EAST COAST AHEAD OF A POTENT MID-UPPER  
SHORTWAVE TROUGH. UNCERTAINTY IN SPECIFIC IMPACTS AND WEATHER TYPE  
REMAIN HIGH, BUT OVERALL GUIDANCE CONTINUES TO TREND TOWARD A LOW  
PRESSURE SYSTEM POSSIBLY INLAND OR AT LEAST NEAR ENOUGH TO THE  
EAST COAST TO CAUSE IMPACTFUL WINTRY WEATHER. 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
 
 
THE LATEST 00Z/06Z (AND INCOMING 12Z GUIDANCE) CONTINUES TO SHOW  
FAIRLY GOOD AGREEMENT ON THE LARGE SCALE PATTERN ACROSS THE CONUS,  
WITH PLENTY OF LINGERING UNCERTAINTY IN SOME IMPACTFUL DETAILS.  
THE MAIN SYSTEM TO NOTE IS A STRONG SHORTWAVE TRACKING ACROSS THE  
CENTRAL PLAINS AND INTO THE SOUTHEAST THIS WEEKEND BEFORE IT  
PIVOTS NEAR THE EAST COAST BY MONDAY. THIS WILL INDUCE  
CYCLOGENESIS AT THE SURFACE WITH BETTER AGREEMENT, COMPARED TO  
PREVIOUS DAYS, IN A SURFACE LOW MOVING THROUGH THE SOUTHEAST AND  
DEEPENING AS IT LIFTS UP NEAR THE EAST COAST. THERE REMAINS SOME  
PLACEMENT DIFFERENCES IN THE SURFACE LOW, ESPECIALLY IN THE EAST  
AROUND DAY 5, BUT OVERALL, MUCH OF THE GUIDANCE CONTINUES TO TREND  
FARTHER WEST, NOW BRINGING THE LOW OVER OR EVEN INLAND FROM THE  
EAST COAST BY EARLY MONDAY. THE GFS (INCLUDING TODAYS 12Z RUN) HAS  
CONSISTENTLY BEEN THE FARTHEST WEST WITH THE LOW AMONGST THE  
DETERMINISTIC SOLUTIONS, ALTHOUGH ITS HARD TO CALL IT AN OUTLIER  
JUST YET GIVEN THE LATEST TRENDS WITH THE NEW INCOMING 12Z  
GUIDANCE. ON THE OTHER SIDE, THE UKMET IS MORE SUPPRESSED TO THE  
SOUTH AND A LOOK AT THE ENSEMBLE GUIDANCE FROM THE GEFS AND ECENS  
SHOWS PLENTY OF UNCERTAINTY IN EXACT LOW PLACEMENT BUT MEMBERS ARE  
TENDING TO CLUSTER AT THIS POINT SOMEWHERE IN BETWEEN THE GFS AND  
UKMET. BOTH THE 00Z ECMWF AND CMC (AND THE NEW 12Z RUNS) ARE A  
LITTLE CLOSER TO THE ENSEMBLES AND THUS A PREFERRED STARTING POINT  
FOR THE WPC FORECAST AT THIS TIME. THIS LED TO A SURFACE LOW OVER  
SOUTHERN NEW JERSEY WHICH IS PRETTY CLOSE TO PREVIOUS WPC  
CONTINUITY. IT SHOULD, HOWEVER, BE STRESSED THAT THE ENERGY  
LEADING TO THIS POTENT SHORTWAVE IS STILL OUT IN THE PACIFIC OCEAN  
AT THIS TIME THUS, DATA SAMPLING IS POOR. AS THE ENERGY REACHES  
THE NORTHWEST U.S. AND ENCOUNTERS MORE OBSERVATIONS, ADDITIONAL  
SHIFTS (POTENTIALLY LARGE) IN THE MODELS ARE LIKELY.  
 
ELSEWHERE, RIDGING IS LIKELY TO HAVE HOLD OF THE WEST THIS  
WEEKEND, OTHER THAN A MEANDERING SOUTHERN STREAM UPPER LOW  
CENTERED OFFSHORE OF CALIFORNIA. THIS FEATURE IS FORECAST TO TRACK  
EASTWARD EARLY IN THE WORKWEEK AND JOIN WITH THE MAIN FLOW, AND  
POSSIBLY INTERACT WITH NORTHERN STREAM ENERGY ENTERING THE PACIFIC  
NORTHWEST AROUND MONDAY. MODEL AGREEMENT FOR THIS OVERALL PATTERN  
WAS FAIRLY GOOD, BUT WITH INCREASING DIFFERENCES ESPECIALLY WITH  
EMBEDDED SHORTWAVES AS THE PERIOD PROGRESSED. ENERGY PROGRESSES  
DOWNSTREAM EARLY NEXT WEEK WITH SOME UNCERTAINTY IN AMPLITUDE  
ACROSS THE GREAT LAKES NEXT TUESDAY INTO WEDNESDAY, AND POTENTIAL  
INTERACTION WITH LINGERING ENERGY FROM THE EAST COAST LOW.  
 
THE BLEND FOR THE UPDATED WPC MEDIUM RANGE FORECAST USED A GENERAL  
MODEL CONSENSUS (LEANING MORE TOWARDS THE ECMWF) FOR DAYS 3-4.  
AFTER THAT, BEGAN INCORPORATING SOME MODEST AMOUNTS OF THE  
ENSEMBLE MEANS TO HELP TEMPER THE LATE PERIOD UNCERTAINTIES.  
OVERALL, THIS LED TO A FAIRLY CONSISTENT FORECAST WITH THE  
OVERNIGHT WPC PACKAGE.  
 
   
..WEATHER HIGHLIGHTS
 
 
THE SURFACE LOW LIFTING FROM THE LOWER MISSISSIPPI VALLEY, ACROSS  
THE SOUTHEAST, AND UP THE EAST COAST WILL BRING WITH IT A FULL  
ARRAY OF WEATHER HAZARDS AND THREATS. ON THE NORTH SIDE OF THE  
INITIAL SYSTEM ON SATURDAY, THERE COULD BE SOME POTENTIAL FOR  
WINTRY WEATHER ACROSS PARTS OF THE MIDDLE/LOWER MISSISSIPPI VALLEY  
INTO TENNESSEE AND KENTUCKY ON SATURDAY, BUT CONFIDENCE IN AMOUNTS  
IS LOW GIVEN THE SURFACE LOW WILL NOT HAVE CONSOLIDATED BY THAT  
POINT. MORE 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 VA 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 TODAYS 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 LOW EXITS NORTHEAST OF THE U.S. ON TUESDAY,  
WESTERLY FLOW AND ANOTHER SHORTWAVE SHOULD MAY BRING FAVORABLE  
CONDITIONS FOR LAKE EFFECT/ENHANCED SNOW OVER THE GREAT LAKES. 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  
BEGINNING TUESDAY WITH RETURN FLOW FROM THE GULF OF MEXICO.  
 
TEMPERATURE-WISE, MUCH BELOW NORMAL TEMPERATURES (-15 TO -30F) IS  
FORECAST FOR THE NORTHEAST OVER THE WEEKEND, WITH SLIGHTLY COOLER  
THAN AVERAGE WEATHER THROUGH EARLY NEXT WEEK FOR THE SOUTHEASTERN  
QUADRANT OF THE COUNTRY. TEMPERATURES SHOULD GENERALLY BE ABOVE  
AVERAGE IN THE PLAINS PARTICULARLY FROM SUNDAY ONWARD AFTER A  
COOLER DAY SATURDAY. THE WEST SHOULD SEE TEMPERATURES WITHIN ABOUT  
5-10 DEGREES OF NORMAL, WITH A TENDENCY TOWARD SLIGHTLY WARMER  
THAN AVERAGE CONDITIONS ESPECIALLY FOR MORNING LOWS.  
 
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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