930  
FXUS02 KWBC 251557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 AM EDT THU OCT 25 2018  
 
VALID 12Z SUN OCT 28 2018 - 12Z THU NOV 01 2018  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
THE GUIDANCE FORECASTS TROUGHING TO REDEVELOP MID-CONTINENT TO THE  
EAST OF A POSITIVE MID-LEVEL HEIGHT ANOMALY IN THE NORTHEAST  
PACIFIC/WEST COAST, DOWNSTREAM OF A NEGATIVE ANOMALY CLOSER TO THE  
INTERNATIONAL DATELINE. THE GUIDANCE SHOWS GOOD AGREEMENT AT 500  
HPA, BUT THIS DOES NOT EXTEND TO THEIR SURFACE PATTERNS. FOR  
SUNDAY, A BLEND OF THE 00Z CANADIAN, 00Z UKMET, 00Z ECMWF, AND 06Z  
GFS IS FINE. THE CANADIAN/ECMWF GUIDANCE DEPART FROM THE ENSEMBLE  
MEAN SOLUTIONS MID-CONTINENT, WITH THE ECMWF TOO FAR NORTH WITH A  
LOW IN CANADA AND THE CANADIAN TOO FAR SOUTH/TOO PROGRESSIVE WITH  
ITS LOWS IN THE LOWER 58. FOR MONDAY AND TUESDAY, A COMPROMISE OF  
THE 06Z GFS AND 00Z UKMET WAS PREFERRED. ONCE THE UKMET RUN ENDS,  
A COMPROMISE OF THE 06Z GFS/00Z ECMWF ENSEMBLE MEAN/00Z NAEFS MEAN  
WAS USED FOR WEDNESDAY INTO NEXT THURSDAY WHICH WERE AGREEABLE.  
THIS LED TO A SPEEDIER FRONTAL PROGRESSION THAN OVERNIGHT  
CONTINUITY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
REGARDING PRECIPITATION, THE MOST ACTIVE AREA WILL BE OVER THE  
PACIFIC NORTHWEST GIVEN THE SEMI-PERMANENT ONSHORE/ZONAL FLOW  
REGIME THROUGH THE PERIOD. THIS WILL BE AUGMENTED DURING THE  
PASSAGE OF ANY NOTABLE SHORTWAVES, ESPECIALLY THE ONE ARRIVING  
LATE THIS WEEKEND. SEVERAL INCHES OF RAINFALL ARE LIKELY ACROSS  
THE OLYMPICS AND CASCADES GIVEN FAVORABLE UPSLOPE TRAJECTORIES  
WITH SNOW EXPECTED OVER THE HIGHER ELEVATIONS EXTENDING INTO THE  
INTERIOR MOUNTAINOUS TERRAIN. ACROSS THE NORTHEAST, IT WILL BE  
INTERMITTENTLY WET OVER THE REGION WITH SNOW POSSIBLE OVER  
PORTIONS OF THE APPALACHIANS. A HEAVY STRIPE OF PRECIPITATION WILL  
BE EXITING NORTHERN MAINE ON SUNDAY MORNING AS A WAVE EXITS THE  
REGION WHILE BROAD CYCLONIC FLOW AND ADDITIONAL FORCING KEEPS  
SHOWERS IN THE PICTURE INTO EARLY NEXT WEEK. REGARDING THAT NEXT  
TROUGH CROSSING THE CENTRAL U.S. BY MID-WEEK, POLEWARD MOISTURE  
RETURN SHOULD ALLOW RAINFALL TO BREAK OUT ALONG THE SLOW-MOVING  
FRONTAL ZONE ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY.  
UNCERTAINTY REMAINS HIGH AS THE HEAVIER AMOUNTS WILL BE DRIVEN BY  
WHERE INSTABILITY IS MORE PREVALENT.  
 
TEMPERATURES REMAIN COOL OVER LARGE SECTIONS OF THE EASTERN U.S.  
GIVEN THE LOWER HEIGHTS TRAVERSING THE REGION. FORECAST ANOMALIES  
SHOULD BE AROUND TO 10 TO 15 DEGREES BELOW CLIMATOLOGY,  
PARTICULARLY OVER THE OHIO VALLEY INTO THE NORTHEASTERN U.S.  
THROUGH EARLY NEXT WEEK. EVENTUALLY NUMBERS SHOULD RETURN CLOSER  
TO AVERAGE FOR LATE OCTOBER GIVEN MID-SOUTHWESTERLY FLOW BECOMING  
ESTABLISHED. OUT TO THE WESTERN U.S., TEMPERATURES WILL BE AROUND  
10 TO 15 DEGREES ABOVE AVERAGE, PARTICULARLY OVER THE CENTRAL  
GREAT BASIN INTO THE ROCKIES GIVEN THE RIDGING ALOFT. AS HEIGHTS  
LOWER FROM TUESDAY ONWARD, A COOL DOWN IS EXPECTED TO SHIFT  
EASTWARD TOWARD THE CENTRAL U.S. FOR MUCH OF NEXT WEEK.  
 
WE WISH BRENDEN WELL ON HIS UPCOMING ADVENTURE IN SACRAMENTO AFTER  
12 YEARS AT HPC/WPC. WE'LL MISS HIM. :)  
 
ROTH/RUBIN-OSTER  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page