964  
FXUS02 KWBC 220729 AAC  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION...UPDATED  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
329 AM EDT FRI MAR 22 2024  
 
VALID 12Z MON MAR 25 2024 - 12Z FRI MAR 29 2024  
 
...HEAVY SNOW LIKELY TO CONTINUE INTO MONDAY FOR PARTS OF THE  
NORTH-CENTRAL PLAINS AND UPPER MIDWEST...  
 
...HEAVY RAIN THREAT ACROSS THE LOWER MISSISSIPPI VALLEY TO  
SOUTHEAST EARLY TO MIDWEEK...  
   
..OVERVIEW
 
 
A STRONG LOW PRESSURE SYSTEM IS FORECAST TO INTENSIFY AND TRACK  
ACROSS THE CENTRAL PLAINS TO THE UPPER MIDWEST MONDAY-TUESDAY,  
BRINGING HEAVY SNOW TO THE NORTH-CENTRAL U.S. TO THE LOW'S NORTH  
AND WEST. STRONG WINDS AND VERY COLD TEMPERATURES ARE ALSO  
FORECAST. ON THE WARM SIDE OF THE SYSTEM, HEAVY RAIN ASSOCIATED  
WITH STRONG THUNDERSTORMS AHEAD OF A RELATIVELY POTENT COLD FRONT  
WILL LIKELY LEAD TO FLOODING ISSUES ACROSS THE LOWER MISSISSIPPI  
VALLEY AND SOUTHEAST MONDAY-TUESDAY, WITH SOME UNCERTAINTY BEYOND  
THAT IN HOW MUCH RAIN MAY FALL FOR THE EAST COAST. MEANWHILE, A LOW  
PRESSURE SYSTEM FROM THE PACIFIC IS FORECAST TO MOVE INTO THE  
NORTHWESTERN U.S., BRINGING RAIN AND MOUNTAIN SNOW TO THE REGION.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
12/18Z MODEL GUIDANCE WAS REASONABLY CONSISTENT WITH THE SURFACE  
LOW POSITION IN THE NORTH-CENTRAL U.S. MONDAY-TUESDAY, WITH GOOD  
AGREEMENT ACROSS MODEL SUITES AND RUN-TO-RUN CONSISTENCY. THE  
INCOMING 00Z SUITE ACTUALLY SHOWS A LITTLE MORE SPREAD WITH THE  
TIMING OF THE LOW, WITH THE GFS TRENDING FASTER WHILE THE ECMWF  
TRENDED SLOWER. FORTUNATELY THE 12/18Z AVERAGE POSITION WAS IN  
BETWEEN. THERE IS HIGH CONFIDENCE IN THE IMPACTFUL WINTER STORM  
OCCURRING, THOUGH WITH TYPICAL UNCERTAINTY IN MESOSCALE BANDING OF  
PLACEMENT OF HEAVIEST AMOUNTS AS WELL AS THE TIMING. BY WEDNESDAY,  
SPREAD INCREASES WITH THE LOW PLACEMENT. THE 12Z/18Z GFS RUNS WERE  
AGGRESSIVE IN SHOWING A LOW ALONG THE FRONT DOWN IN THE LOWER  
MISSISSIPPI VALLEY THAT ZOOMS NORTH TOWARD THE UPPER GREAT LAKES  
AND INTERACTS WITH THE MAIN LOW. A SECONDARY LOW THAT POTENT SEEMS  
LESS LIKELY AND FORTUNATELY THE 00Z GFS HAS BACKED OFF, WITH STILL  
SOME VARIATIONS BY WEDNESDAY AMONG GUIDANCE IN THE LOW BUT WITHIN  
TYPICAL SPREAD.  
 
FARTHER SOUTH, THERE REMAINS NOTABLE MODEL SPREAD REGARDING THE  
HEAVY RAIN AREA IN THE SOUTH-CENTRAL TO SOUTHEASTERN U.S., WITH THE  
GFS/GEFS KEEPING THE HEAVIEST RAINFALL FARTHER NORTH THAN THE  
ECMWF CLUSTER BY TUESDAY. THIS IS PROBABLY PARTLY DUE TO THAT  
SECONDARY FRONTAL LOW THAT THE GFS WAS SHOWING. AT LEAST THERE IS  
SOME OVERLAP IN THE HEAVY RAINFALL POTENTIAL TO INDICATE A SLIGHT  
RISK. THE DIFFERENCES ALOFT AND AT THE SURFACE AND WITH RAINFALL  
PLACEMENT ONLY GROW FROM MID- TO LATE WEEK. THE 12Z ECMWF IS SLOW  
WITH MOVING SOUTHERN STREAM ENERGY DEVELOPING INTO A CLOSED LOW  
OVER THE SOUTHEAST COMPARED TO OTHER GUIDANCE AND EVEN THE EC-BASED  
AI/ML MODELS. THE EC ENSEMBLE MEAN WAS SLOWER TOO BUT NOT TO THE  
SAME EXTENT OF SHOWING A SLOW CLOSED LOW. THUS FAVORED A GFS/GEFS  
MEAN/EC MEAN BLEND FOR THE EAST BY DAYS 6-7. THE 00Z GFS HAS SLOWED  
A BIT WHILE THE 00Z ECMWF IS FASTER, SO HOPEFULLY THERE WILL BE  
SOME CONTINUED MODEL CONVERGENCE THERE.  
 
IN THE WEST, THE FIRST MODEL THAT LOOKS TO DIVERGE FROM CONSENSUS  
WAS THE 12Z CMC BY WEDNESDAY, WHICH SHOWED UPPER AND SURFACE LOWS  
MUCH FARTHER WEST IN THE EASTERN PACIFIC THAN OTHER GUIDANCE. THEN  
THE GFS ENDED UP BRINGING THE POTENT ENERGY QUICKLY EAST INTO THE  
INTERMOUNTAIN WEST THURSDAY-FRIDAY. THE ECMWF SEEMED LIKE A GOOD  
MIDDLE GROUND IN TRACKING THE TROUGH EASTWARD AND GENERALLY MATCHED  
WELL WITH THE AI/ML MODELS. WITH THIS AND CONSIDERING THE GFS'S  
FAST BIAS, FAVORED THE EC MORE.  
 
THE WPC FORECAST USED A BLEND OF THE DETERMINISTIC GUIDANCE EARLY  
IN THE FORECAST PERIOD. GIVEN THE AFOREMENTIONED ISSUES WITH THE  
ECMWF IN THE EAST, THE GFS IN THE WEST, AND THE CMC EVERYWHERE,  
GRADUALLY INCREASED THE PROPORTION OF GEFS/EC ENSEMBLE MEANS TO THE  
ENTIRE BLEND BY DAY 7.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE DEEP SURFACE LOW TRACKING FROM THE CENTRAL PLAINS TO UPPER  
MIDWEST WILL BE THE DRIVER (ALONG WITH UPPER-LEVEL SUPPORT) FOR  
MULTI-HAZARD IMPACTFUL WEATHER FOR EARLY-MID NEXT WEEK. A  
WIDESPREAD LATE SEASON WINTER STORM SHOULD BE ONGOING MONDAY WITH  
HEAVY SNOW ACCUMULATION (8+") LIKELY FROM NORTHEASTERN NEBRASKA  
INTO EASTERN PARTS OF THE DAKOTAS, MUCH OF MINNESOTA, AND FAR  
NORTHWESTERN WISCONSIN, AS THIS REGION WILL BE ON THE COLDER SIDE  
OF THE LOW WITH A DEFORMATION ZONE DEVELOPING. HIGH WINDS DUE TO  
THE DEEP SURFACE LOW COULD LEAD TO BLIZZARD CONDITIONS IN SOME  
AREAS. TIMING/TRACK UNCERTAINTY MAY CHANGE THE EVENTUAL LOCATION  
OF THE IMPACTFUL WINTER WEATHER, BUT THE RISK FOR DISRUPTIONS TO  
DAILY LIFE AND HAZARDOUS TRAVEL IS LIKELY. HIGH WINDS ARE ALSO  
POSSIBLE SOUTHWARD ACROSS THE PLAINS ON MONDAY BEHIND THE COLD  
FRONT, THOUGH WITH DRIER WEATHER.  
 
FARTHER SOUTH AHEAD OF THE COLD FRONT, AMPLE MOISTURE STREAMING IN  
AND A STRONG JET ALOFT WILL SUPPORT HEAVY RAIN AND POTENTIALLY  
SEVERE THUNDERSTORMS FOR THE LOWER MISSISSIPPI VALLEY MONDAY,  
SHIFTING INTO THE SOUTHEAST ON TUESDAY. SLIGHT RISKS ARE IN PLACE  
IN THE DAY 4-5 EXCESSIVE RAINFALL OUTLOOKS DUE TO THE POTENTIAL OF  
A LIKELY SQUALL LINE CAUSING RAIN RATES OF 2+" PER HOUR. THE AREAL  
COVERAGE OF HEAVY QPF IS SOMEWHAT LESS ON TUESDAY COMPARED TO  
MONDAY, BUT STILL HAVE A SLIGHT RISK CONSIDERING THAT THE  
ECMWF/GFS ARE AGREEABLE IN INDICATING THE SQUALL LINE LASTING INTO  
THE EARLY PART OF THE DAY ON TUESDAY INTO MS/AL. BY MIDWEEK, THE  
STORMY WEATHER THEN REACHES THE FLORIDA PANHANDLE NORTH INTO THE  
CAROLINAS UP THE EASTERN SEABOARD, BUT WITH CONSIDERABLE SPREAD IN  
RAINFALL AMOUNTS BY WEDNESDAY-THURSDAY DUE TO THE MODEL  
DIFFERENCES.  
 
SOME LINGERING MODERATE SNOW IS POSSIBLE ACROSS PARTS OF THE  
SOUTH-CENTRAL ROCKIES ON MONDAY, WITH LIGHT AMOUNTS ELSEWHERE  
ACROSS THE INTERMOUNTAIN WEST. THE PACIFIC NORTHWEST COULD SEE SOME  
MODERATE LOWER ELEVATION RAIN AND HIGHER ELEVATION SNOW AMOUNTS  
MONDAY, WITH INCREASING TOTALS BY TUESDAY-WEDNESDAY AND EXPANDING  
INTO CALIFORNIA AS TROUGHING AND LOW PRESSURE APPROACH. SOME  
MODERATE TO HEAVY PRECIPITATION SHOULD EXPAND INTO THE  
INTERMOUNTAIN WEST MIDWEEK, AND WILL CONTINUE TO MONITOR THE  
POTENTIAL FOR FURTHER EXPANSION OF THE PRECIPITATION POSSIBLY IN  
THE FORM OF SNOW TO AFFECT THE NORTH-CENTRAL PLAINS ONCE AGAIN BY  
THURSDAY.  
 
MUCH COLDER THAN AVERAGE TEMPERATURES (MORE COMPARABLE TO JANUARY)  
ARE LIKELY FOR THE NORTHERN AND CENTRAL HIGH PLAINS IN THE WAKE OF  
THE STRONG COLD FRONT. HIGHS WILL ONLY BE IN THE 20S AND 30S FOR  
THESE AREAS ON MONDAY, BUT A MODERATING TREND WILL COMMENCE GOING  
INTO THE MIDDLE OF THE WEEK, EVEN THOUGH MONTANA AND NORTH DAKOTA  
WILL STILL REMAIN CHILLY BY LATE MARCH STANDARDS. THE WEST SHOULD  
SEE GENERALLY COOLER THAN AVERAGE HIGHS AND NEAR AVERAGE LOWS NEXT  
WEEK, WHILE THE EAST CAN EXPECT BOUTS OF ABOVE AND BELOW NORMAL  
TEMPERATURES AVERAGING OUT TO NEAR NORMAL.  
 
TATE  
 
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 FORECAST (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page