244  
FXUS02 KWBC 220701  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
300 AM EDT FRI APR 22 2022  
 
VALID 12Z MON APR 25 2022 - 12Z FRI APR 29 2022  
   
..OVERVIEW
 
 
AS UPPER/SURFACE LOWS TRACK INTO SOUTH-CENTRAL CANADA AS THE  
MEDIUM RANGE PERIOD BEGINS MONDAY, THE TRAILING COLD FRONT SHOULD  
SWEEP ACROSS THE SOUTH-CENTRAL TO EASTERN U.S. AND PROVIDE A FOCUS  
FOR RAIN AND THUNDERSTORMS. UPPER TROUGHING OVER THE MIDWEST/GREAT  
LAKES SHOULD SHIFT EASTWARD AS NEXT WEEK PROGRESSES AND LIKELY  
FORM AN UPPER LOW OVER/NEAR THE NORTHEAST LATER IN THE WEEK,  
PROMOTING A SHIFT FROM WARMER TO COOLER THAN AVERAGE TEMPERATURES.  
MEANWHILE MODEL GUIDANCE SUPPORTS MEAN TROUGHING ACROSS THE WEST  
WITH LIKELY AN EMBEDDED UPPER LOW, LEADING TO POTENTIAL FOR ROUNDS  
OF PRECIPITATION IN THE NORTHWEST. BROAD UPPER RIDGING IS  
GENERALLY FORECAST IN BETWEEN, LEADING TO WARM TEMPERATURES ACROSS  
THE SOUTHWEST TO SOUTHERN/CENTRAL HIGH PLAINS.  
 
   
..MODEL GUIDANCE EVALUATION
 
 
MODEL GUIDANCE CONTINUES TO SHOW FAIRLY GOOD CLUSTERING WITH THE  
LARGE SCALE PATTERN DESCRIBED ABOVE. SOME SMALLER SCALE  
DIFFERENCES EXIST EVEN AT THE BEGINNING OF THE PERIOD,  
PARTICULARLY WITH DISTRIBUTION OF ENERGY WITHIN THE TROUGH/LOW  
NEAR THE GREAT LAKES REGION/U.S. CANADA BORDER. GFS RUNS SHOW  
UPSTREAM ENERGY COMING INTO THE TROUGH A BIT FASTER WHICH PUSHES  
ITS INITIAL SMALL CLOSED LOW EAST COMPARED TO OTHER GUIDANCE.  
ASSOCIATED SURFACE LOW POSITIONS VARY A BIT BUT WITHIN NORMAL  
SPREAD. BUT GUIDANCE AGREES IN PRINCIPLE THAT THIS UPSTREAM ENERGY  
WILL REINFORCE AND STRENGTHEN TROUGHING IN THE NORTHEASTERN U.S.  
AND TRACK EASTWARD MIDWEEK ONWARD. A CLOSED UPPER LOW WILL LIKELY  
DEVELOP--THIS IS SHOWING SOME TIMING DIFFERENCES BUT LIKELY BY  
WEDNESDAY OR THURSDAY (ECMWF RUNS HAVE BEEN THE SLOWEST). AT THE  
SURFACE, NEWER 00Z MODEL GUIDANCE IS EVEN BETTER CLUSTERED THAN  
THE PREVIOUS CYCLE WITH A LOW PRESSURE SYSTEM FORMING ALONG THE  
NEW ENGLAND COAST IN ASSOCIATION WITH THE UPPER LOW.  
 
AN UPPER LOW SPINNING CENTERED WEST OF BRITISH COLUMBIA AND  
PROMOTING PERIODS OF TROUGHING IN THE WEST IS ALSO REASONABLY  
AGREEABLE IN THE MODEL GUIDANCE, BUT MORE DIFFERENCES ARISE WITH  
INDIVIDUAL SHORTWAVES EMBEDDED WITHIN. BY WEDNESDAY ONWARD ONE  
SHORTWAVE TRACKING EAST ATOP THE RIDGE SHOWS CONSIDERABLE SPREAD  
WITH ITS EXACT TRACK/HOW MUCH IT MAY SUPPRESS THE RIDGE, WITH CMC  
RUNS BEING THE STRONGEST WITH THE ENERGY SUPPRESSING THE RIDGE,  
BUT GFS RUNS (ESPECIALLY THE 12Z) MAY NOT HAVE ENOUGH SUPPRESSION.  
LEANED TOWARD A SOLUTION IN BETWEEN THESE AT THIS POINT, CLOSER TO  
THE ECMWF AND MEANS. THEN BY THURSDAY/FRIDAY, THE TROUGH AXIS IS  
FINALLY EXPECTED TO MOVE EASTWARD SOMEWHAT, BUT THERE IS  
UNCERTAINTY WITH HOW MUCH IT MOVES INLAND GIVEN MODEL/ENSEMBLE  
MEMBER SPREAD AND RUN TO RUN DISCONTINUITIES.  
 
OVERALL, A BLEND OF THE 12/18Z DETERMINISTIC GUIDANCE FAVORING THE  
ECMWF A BIT WORKED WELL FOR THE MEDIUM RANGE FORECAST EARLY ON,  
PHASING OUT THE CMC (AND UKMET OF COURSE) IN FAVOR THE GEFS AND EC  
ENSEMBLE MEANS. THIS PROVIDED GOOD CONTINUITY WITH THE PREVIOUS  
FORECAST.  
 
   
..SENSIBLE WEATHER/THREATS
 
 
THE COLD FRONT TRAILING FROM THE LOW MOVING ACROSS CANADA EARLY IN  
THE WORKWEEK WILL INTERSECT WITH WARM/MOIST AIR FROM THE GULF AND  
LEAD TO WIDESPREAD RAIN ALONG THE FRONT STRETCHING FROM THE GREAT  
LAKES TO OHIO/TENNESSEE VALLEYS AND INTO THE SOUTHERN PLAINS  
MONDAY, SHIFTING TO THE EASTERN SEABOARD TUESDAY. WHILE GREATER  
POTENTIAL FOR EXCESSIVE RAINFALL HAS PHASED INTO THE SHORT RANGE  
PERIOD, SOME HIGH RAIN RATES WITH UNSTABLE CONDITIONS ESPECIALLY  
IN TEXAS ON MONDAY COULD OVERCOME ONGOING DRY CONDITIONS TO CAUSE  
LOCALIZED FLASH FLOODING. ELSEWHERE, THE FRONT SHOULD ACCELERATE  
AND LEAD TO LIGHTER OVERALL RAINFALL AMOUNTS OVER THE EASTERN U.S.  
MONDAY-TUESDAY. THEN AS THE NORTHEAST UPPER LOW DEVELOPS MIDWEEK  
AND SURFACE LOW PRESSURE PIVOTS OVER THE REGION, PRECIPITATION IS  
FORECAST TO LINGER ESPECIALLY ACROSS NEW ENGLAND, WITH SOME  
POTENTIAL FOR HIGHER ELEVATIONS TO RECEIVE SNOW. MEANWHILE IN THE  
WEST, UNSETTLED WEATHER IS LIKELY AS A SERIES OF SHORTWAVES MOVE  
THROUGH THE MEAN TROUGH SOUTH OF A CLOSED UPPER LOW POSITIONED OFF  
BRITISH COLUMBIA. TIMING AND COVERAGE WITH EACH EPISODE OF  
RAIN/HIGH ELEVATION SNOW WILL TAKE ADDITIONAL TIME TO RESOLVE  
GIVEN THE TYPICAL LOWER PREDICTABILITY OF MEDIUM TO SMALLER SCALE  
OF FEATURES CONTAINED WITHIN THE MEAN FLOW.  
 
WARMER THAN NORMAL CONDITIONS FOR THE EASTERN THIRD OF THE U.S.  
MONDAY-TUESDAY WILL SWITCH TO BELOW NORMAL BEHIND THE COLD FRONTAL  
PASSAGE. THE CORE OF THAT COLD AIR IS LIKELY TO CAUSE BELOW NORMAL  
TEMPERATURES BY 15-30 DEGREES IN THE DAKOTAS AND MIDWEST TO THE  
GREAT LAKES/CENTRAL APPALACHIANS FOR THE FIRST HALF OF THE WEEK.  
THESE TEMPERATURES SHOULD MODERATE SOMEWHAT AS THEY TAKE HOLD OF  
THE NORTHEASTERN QUADRANT OF THE U.S. AS THE WEEK PROGRESSES.  
FARTHER WEST, UPPER RIDGING MIGRATING FROM THE SOUTHWEST INTO THE  
CENTRAL U.S. WILL SPREAD WARMER THAN AVERAGE TEMPERATURES FROM THE  
SOUTHWEST (WITH SOME RECORD HIGHS POSSIBLE IN SOUTHERN CALIFORNIA  
MONDAY) INTO THE FOUR CORNERS STATES AND INTO SOUTHERN/CENTRAL  
PARTS OF THE PLAINS. THE HIGH PLAINS MAY SEE TEMPERATURES AROUND  
15-20F ABOVE 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, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, 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/#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  
 

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page