080  
FXUS02 KWBC 240712  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
312 AM EDT SUN MAR 24 2024  
 
VALID 12Z WED MAR 27 2024 - 12Z SUN MAR 31 2024  
 
...HEAVY RAIN THREAT ACROSS THE SOUTHEAST MAY CONTINUE INTO MIDWEEK...  
 
...ROUNDS OF HEAVY RAIN AND SNOW POSSIBLE ACROSS MUCH OF THE WEST  
THROUGH THE PERIOD...  
   
..OVERVIEW
 
 
A COLD FRONT OR TWO PUSHING AHEAD OF A BROAD UPPER TROUGH IN THE  
CENTRAL-EASTERN U.S. AND EVENTUAL ATLANTIC SURFACE LOW DEVELOPMENT  
WILL HELP FOCUS RAINFALL FOR PORTIONS OF THE EASTERN SEABOARD FOR  
THE LATTER HALF OF THE WORKWEEK. THIS ACTIVITY COULD BE  
PARTICULARLY HEAVY FOR PORTIONS OF FLORIDA AND GEORGIA INTO THE  
CAROLINAS. MEANWHILE, ONE OR MORE PACIFIC SYSTEMS SHOULD BRING  
INCREASING TOTALS OF RAIN AND MOUNTAIN SNOW TO THE WEST COAST  
STATES AND THEN INTO THE ROCKIES MID-LATE WEEK INTO NEXT WEEKEND.  
INCREASING MOISTURE MAY COMBINE WITH SHORTWAVES IN THE NORTH-  
CENTRAL TO EAST-CENTRAL U.S. FRIDAY-SUNDAY, THOUGH WITH AMPLE  
UNCERTAINTY IN THE DETAILS OF PRECIPITATION PLACEMENT AND TYPE.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MOST GUIDANCE AGREES IN PRINCIPLE FOR THE LARGE SCALE UPPER  
PATTERN EVOLUTION, WITH CENTRAL-EASTERN U.S. UPPER TROUGHING TAKING  
ON A MORE NEGATIVE TILT BY FRIDAY-SATURDAY AS IT REACHES THE EAST  
COAST/WESTERN ATLANTIC WHILE DEEPENING MEAN TROUGHING BECOMES  
ESTABLISHED NEAR THE WEST COAST. THE MOST PROMINENT FORECAST ISSUES  
INVOLVE THE EAST COAST/WESTERN ATLANTIC EVOLUTION LATE THIS WEEK,  
ALONG WITH INDIVIDUAL FEATURES WITHIN THE WEST COAST TROUGH PLUS  
EJECTING ENERGY AND ITS INFLUENCE ON CENTRAL U.S. SURFACE WAVINESS.  
 
FOR THE LATE WEEK EAST COAST EVOLUTION, GUIDANCE CONTINUES TO VARY  
WITH THE DETAILS OF ENERGY ALOFT. HOWEVER, THE PAST COUPLE OF  
MODEL CYCLES HAVE AT LEAST SHOWN SOME CONVERGENCE AWAY FROM  
SOLUTIONS SHOWING SEPARATE CLOSED LOW DEVELOPMENT ALOFT. IN TERMS  
OF THE SURFACE LOW, THE GFS RUNS SEEM TO ALIGN THE BEST WITH THE  
ENSEMBLE MEANS WHILE THE ECMWF (BOTH 12Z AND NEW 00Z RUNS) APPEAR  
QUITE SLOW/SOUTH.  
 
CLUSTERING IS STILL GOOD FOR THE STRONG STORM FORECAST TO BE  
OFFSHORE THE PACIFIC NORTHWEST BY THURSDAY. THERE IS INCREASING  
SPREAD BOTH ALOFT AND AT THE SURFACE BY FRIDAY, AS ENERGY ROUNDING  
THE BASE OF THE UPPER LOW ALREADY IN PLACE CAUSES POTENTIAL FOR A  
SURFACE LOW FARTHER SOUTH TO TAKE OVER FOR THE NORTHERN ONE.  
ENSEMBLE MEANS INDICATE ONE SURFACE LOW IN BETWEEN BUT THIS COULD  
BE DUE TO AVERAGING OUT ENSEMBLE MEMBERS SHOWING BOTH LOWS. MOST  
DETERMINISTIC GUIDANCE BRIEFLY SHOW TWO LOWS. REGARDLESS, AN UPPER  
TROUGH WITH AN EMBEDDED LOW IS MOST LIKELY TO REACH THE VICINITY OF  
CALIFORNIA BY THE WEEKEND, ALONG WITH A LOW AT THE SURFACE. THE  
ECMWF OPERATIONAL RUN AND MANY OF ITS ENSEMBLE MEMBERS ARE SLOWER  
THAN THE CMC/GFS SUITES. ECMWF-BASED AI MODELS ARE FASTER THAN THE  
OPERATIONAL RUN, SO FAVORED A BLEND NOT AS SLOW AS THE EC ITSELF.  
SHORTWAVES FARTHER EAST ARE VARIABLE BUT IN GENERAL DO NOT SEEM AS  
FOCUSED IN THE NORTH-CENTRAL U.S. COMPARED TO SOME PREVIOUS MODEL  
RUNS.  
 
THE WPC FORECAST USED A MULTI-MODEL DETERMINISTIC BLEND EARLY IN  
THE PERIOD, AND WITH REASONABLE CLUSTERING FOR THE LARGE SCALE  
FEATURES WAS ABLE TO MAINTAIN A MAJORITY DETERMINISTIC BLEND  
THROUGH DAY 6. BY DAY 7 THE GEFS AND EC ENSEMBLE MEANS REACHED JUST  
OVER HALF THE BLEND.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A COLD FRONT OR TWO AND DEVELOPING LOW PRESSURE AT THE SURFACE  
COMBINING WITH A STRONG JET AND ITS RIGHT ENTRANCE REGION TO THE  
EAST OF AN UPPER TROUGH WILL SUPPORT POTENTIALLY HEAVY RAIN ACROSS  
PORTIONS OF THE SOUTHEAST/CAROLINAS ON WEDNESDAY. THOUGH RECENT  
MODEL GUIDANCE HAS BACKED OFF SOME FROM SOME OF THE EXTREMELY HIGH  
RAIN TOTALS FROM A DAY AGO, INGREDIENTS ARE IN PLACE FOR SOME  
LOCALLY HEAVY RAIN THAT COULD CAUSE FLOODING ISSUES. A MARGINAL  
RISK REMAINS IN PLACE IN THE WEDNESDAY EXCESSIVE RAINFALL OUTLOOK,  
AND AN EMBEDDED SLIGHT RISK CANNOT BE RULED OUT IN FUTURE UPDATES.  
SOME POTENTIALLY HEAVY RAIN COULD LINGER INTO THURSDAY, CURRENTLY  
MOST LIKELY OVER EASTERN NORTH CAROLINA, BUT WITH CONTINUED  
UNCERTAINTY. WILL START WITH A MARGINAL RISK THERE WITH WHAT SEEMS  
TO BE A COMPROMISE IN COVERAGE OF THE GUIDANCE (SOME SHOW HEAVY  
RAIN WELL WEST AND SOUTH OF THE MARGINAL, WHILE SOME REALLY ONLY  
HIT THE OUTER BANKS). THERE IS ALSO A BROAD RANGE OF POSSIBLE  
OUTCOMES FOR HOW MUCH RAINFALL EXTENDS INTO THE MID-  
ATLANTIC/NORTHEAST MID-LATE WEEK, DEPENDING ON THE EVOLUTION AND  
TRACK OF WESTERN ATLANTIC LOW PRESSURE. IN THIS FORECAST CYCLE,  
PRECIPITATION HAS TRENDED DOWN THERE IN FAVOR OF A FOCUS OFFSHORE.  
THE SURFACE LOW MAY PRODUCE A PERIOD OF BRISK WINDS OVER NEW  
ENGLAND.  
 
DEEPER MOISTURE STARTS TO STREAM INTO THE WEST COAST BY WEDNESDAY  
AS UPPER TROUGHING AND LOW PRESSURE APPROACH. RAIN RATES COULD BE  
HIGH ENOUGH TO BE CONCERNING FOR FLOODING ACROSS PORTIONS OF  
CALIFORNIA INTO WESTERN OREGON, SO THE DAY 5 ERO SHOWS A MARGINAL  
RISK THERE FOR WEDNESDAY. HEAVY SNOW IS LIKELY INTO THE  
CASCADES/SIERRA NEVADA AND TOWARD THE NORTHERN ROCKIES BEGINNING  
WEDNESDAY. COASTAL/LOWER ELEVATION RAIN TOTALS LOOK TO LESSEN BY  
THURSDAY BUT SNOW IS FORECAST TO EXPAND INTO THE INTERMOUNTAIN WEST  
THURSDAY AND BEYOND. THEN MODEL TRENDS HAVE CONTINUED TO INDICATE THAT  
CALIFORNIA MAY SEE INCREASING HEAVY PRECIPITATION BY FRIDAY INTO  
THE WEEKEND BASED ON WHERE AN EASTERN PACIFIC UPPER LOW/TROUGH SETS  
UP AND DIRECTS A POSSIBLE ATMOSPHERIC RIVER INTO THE STATE. THIS  
SOUTHERN SHIFT WOULD ALSO BRING PRECIPITATION INTO THE CENTRAL  
GREAT BASIN AND SOUTHWEST FOR THE WEEKEND. FARTHER EAST, SHORTWAVES  
GENERALLY RIDING ALONG THE NORTHERN SIDE OF A CENTRAL U.S. RIDGE  
COULD COMBINE WITH MOISTURE TO PRODUCE SOME LIGHT TO MODERATE  
PRECIPITATION FRIDAY INTO THE WEEKEND ACROSS THE NORTH-CENTRAL  
U.S. AND GREAT LAKES REGION AND OHIO VALLEY. CONFIDENCE IS LOW FOR  
WHERE PRECIPITATION WILL OCCUR AS WELL AS THE PRECIPITATION TYPES.  
 
COLDER THAN AVERAGE TEMPERATURES BY 15-20 DEGREES ARE LIKELY TO  
REMAIN INTO MIDWEEK FOR THE NORTH-CENTRAL PLAINS, WITH SOME GRADUAL  
MODERATION BUT REMAINING ON THE COOLER SIDE INTO THE WEEKEND. COOL  
TEMPERATURES BUT WITH LESSER ANOMALIES ARE FARTHER SOUTH IN THE  
CENTRAL U.S. WEDNESDAY, BUT THEN A NOTABLE WARMING TREND IS  
EXPECTED THERE AS UPPER RIDGING BUILDS. THE SOUTH-CENTRAL PLAINS  
INTO MISSISSIPPI VALLEY CAN EXPECT TEMPERATURES AROUND 10-15  
DEGREES ABOVE AVERAGE BY FRIDAY-SATURDAY AND CLOSER TO 20 DEGREES  
ABOVE AVERAGE BY SUNDAY. THIS BRINGS 70S AND 80S INTO KANSAS AND  
MISSOURI. MEANWHILE IN THE WEST, NEAR TO ABOVE NORMAL LOWS BUT  
NEAR TO BELOW NORMAL HIGHS ARE FORECAST, CONSISTENT WITH THE CLOUDS  
AND PRECIPITATION THERE.  
 
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