408  
FXUS02 KWBC 302016  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
315 PM EST WED NOV 30 2022  
 
VALID 12Z SAT DEC 03 2022 - 12Z WED DEC 07 2022  
 
...BELOW NORMAL TEMPERATURES OVER THE WEST WITH RAIN/MOUNTAIN SNOW  
GRADUALLY TRENDING LIGHTER...  
   
..HEAVY RAINFALL POTENTIAL OVER THE EAST-CENTRAL U.S.
 
 
   
..OVERVIEW
 
 
MOST GUIDANCE SUGGESTS THAT THE INITIAL PATTERN CONSISTING OF  
STRONG WEST-SOUTHWESTERLY UPPER FLOW BETWEEN A GULF OF MEXICO  
RIDGE AND CENTRAL CANADA UPPER LOW, WITH A MEAN TROUGH NEAR THE  
WEST COAST, SHOULD TRANSITION TO BROADLY CYCLONIC FLOW AS THE WEST  
COAST TROUGH MOVES INLAND AND AN UPPER RIDGE BUILDS IN ITS PLACE  
BY NEXT WEDNESDAY. THIS PATTERN SHOULD PROMOTE BELOW NORMAL  
TEMPERATURES OVER MOST OF THE WEST AND NORTHERN PLAINS ON MOST  
DAYS, WHILE THE RAIN AND MOUNTAIN SNOW AFFECTING SOME PARTS OF THE  
WEST SHOULD STEADILY DECREASE IN COVERAGE AND INTENSITY WITH TIME.  
THE FIRST OF TWO PRIMARY SYSTEMS OF INTEREST WILL BE TRACKING AWAY  
FROM THE UPPER GREAT LAKES ON SATURDAY WHILE THE SECOND WILL  
INITIALLY BE NEAR THE WEST COAST AND THEN MOVE INLAND. THE SETUP  
AHEAD OF THIS SECOND SYSTEM MAY SUPPORT A PERIOD OF HEAVY RAINFALL  
OVER PARTS OF THE EAST-CENTRAL U.S., WHILE THE SOUTHERN TIER  
STATES SHOULD SEE ABOVE NORMAL TEMPERATURES.  
 
   
..GUIDANCE AND PREDICTABILITY ASSESSMENT
 
 
THE LATEST GUIDANCE THROUGH THE 00Z/06Z CYCLES SHOWS FAIRLY GOOD  
AGREEMENT ON THE INITIAL STRONG SYSTEM THROUGH THE NORTHEAST AS  
WELL AS AN UPPER LOW DROPPING DOWN THE NORTHWEST COAST. THE 00Z  
CMC AND UKMET BOTH BECOME TOO AMPLIFIED OVER THE NORTHEAST AROUND  
SUNDAY-MONDAY, WITH THE CMC OUT OF LINE WANTING TO DEVELOP A  
CLOSED LOW OVER THE CANADIAN MARITIMES WHICH LINGERS FOR A FEW  
DAYS. MEANWHILE THE UKMET IS MUCH TOO AMPLIFIED WITH SOME ENERGY  
COMING IN ON THE WESTERN SIDE OF AN UPPER LOW OVER NORTH-CENTRAL  
CANADA AT THE SAME TIME.  
 
BY AS EARLY AS DAY 5, THERE ARE SOME IMPORTANT DETAIL DIFFERENCES  
WHICH ARISE SURROUNDING ENERGY ROTATING AROUND THE CANADIAN UPPER  
LOW ACROSS THE NORTHERN TIER OF THE U.S., AS WELL AS DIFFERENCES  
IN ENERGY AS IT EJECTS FROM THE WESTERN U.S. TROUGH. THIS LEADS TO  
SOME FAIRLY IMPACTFUL DIFFERENCES IN FRONTAL PLACEMENT AND  
HEAVIEST QPF AXIS ACROSS THE EAST-CENTRAL U.S. DAYS 5-7. THE ECMWF  
IS MORE AMPLIFIED/SHARPER WITH A NORTHERN STREAM SHORTWAVE LEADING  
TO A MORE SOUTHERN SHIFT WITH THE HEAVIER QPF. THE REST OF THE  
MODELS, ALONG WITH THE NATIONAL BLEND OF MODELS AND THE ENSEMBLE  
MEANS, WOULD SUGGEST A LITTLE FARTHER NORTH FOOTPRINT ACROSS THE  
TENNESSEE VALLEY. AT LEAST THE 12Z GFS HOWEVER, AVAILABLE AFTER  
FORECAST GENERATION TIME, DID COME IN FARTHER SOUTH, SO ANY  
POTENTIAL SOUTHWARD TREND SHOULD CONTINUE TO BE MONITORED. BY DAYS  
6-7, THERE CONTINUES TO BE A WIDE ENSEMBLE MEMBER SPREAD FOR HOW  
THE WEST COAST SYSTEM EVENTUALLY PROGRESSES INLAND AS WELL AS IN  
THE CHARACTER OF UPPER TROUGHING TO THE NORTH/NORTHEAST.  
 
THE GOOD ENOUGH AGREEMENT IN THE EARLY PERIOD ALLOWED FOR A  
GENERAL DETERMINISTIC MODEL BLEND, LED BY THE GFS AND ECMWF. AFTER  
DAY 4 THOUGH, HAD TO INCORPORATE THE ENSEMBLE MEANS IN PLACE OF  
THE CMC AND UKMET DUE TO THE DIFFERENCES DESCRIBED ABOVE WITH A  
NEARLY 50/50 DETERMINISTIC/ENSEMBLE MEAN BLEND BY DAY 7. THIS  
APPROACH KEPT FAIRLY CLOSE TO THE PREVIOUS SHIFT, WITH MAINLY ONLY  
MINOR CHANGES NEEDED FROM CONTINUITY.  
 
   
..WEATHER/HAZARD HIGHLIGHTS
 
 
LOW PRESSURE NEAR THE WEST COAST DURING THE WEEKEND WILL LIKELY  
BRING THE HIGHEST RAINFALL/MOUNTAIN SNOW TOTALS TO AREAS FROM THE  
SOUTHWEST CORNER OF OREGON THROUGH NORTHERN CALIFORNIA AND THE  
SIERRA NEVADA. LIGHTER TOTALS ARE POSSIBLE OVER THE PACIFIC  
NORTHWEST, SOUTHERN CALIFORNIA, AND PORTIONS OF THE ROCKIES. THE  
FLOW ALOFT AHEAD OF THIS SYSTEM MAY CARRY IN SOME ADDED MOISTURE  
FROM THE EASTERN PACIFIC, LEADING TO AREAS OF RAINFALL ACROSS  
ARIZONA AND NEW MEXICO. SOME OF THIS ACTIVITY COULD BE ON THE  
LOCALLY MODERATE TO HEAVY SIDE BUT CONFIDENCE IN THE DETAILS IS  
STILL FAIRLY LOW. THE SOUTHERN HALF OF THE WEST SHOULD TREND DRIER  
BY EARLY NEXT WEEK AS UPPER TROUGHING MOVES FARTHER INLAND BUT  
SOME PRECIPITATION MAY PERSIST OVER THE NORTHWEST/ROCKIES. THE  
WEST COAST SYSTEM MAY PRODUCE GUSTY WINDS OVER SOME AREAS ON  
SATURDAY.  
 
AREAS EAST OF THE ROCKIES SHOULD SEE A FAIRLY ACTIVE PATTERN BUT  
WITH SOME UNCERTAINTIES GIVEN THE SPREAD IN THE GUIDANCE FOR  
SPECIFICS. BEST CONTINUITY IS WITH A VIGOROUS SYSTEM TRACKING AWAY  
FROM THE UPPER GREAT LAKES AFTER EARLY SATURDAY WITH A BRIEF  
PERIOD OF BRISK TO STRONG WINDS CROSSING THE NORTHEASTERN QUADRANT  
OF THE LOWER 48. THE ASSOCIATED COLD FRONT COULD BRING SOME LIGHT  
TO LOCALLY MODERATE RAINFALL OVER THE EAST. THIS FRONT SHOULD  
STALL AND THEN RETURN NORTHWARD AS A WARM FRONT AHEAD OF THE NEXT  
SYSTEM EMERGING OVER THE PLAINS/MIDWEST, SERVING AS A FOCUS FOR  
INCREASING RAINFALL OVER THE MIDDLE LATITUDES OF THE EAST-CENTRAL  
U.S. SUNDAY ONWARD. BOTH LOW LEVEL FLOW FROM THE GULF AND THE  
WEST-SOUTHWESTERLY FLOW ALOFT SHOULD CONTRIBUTE MOISTURE FOR THIS  
EVENT THAT COULD PRODUCE AREAS OF MODERATE TO HEAVY RAINFALL. SOME  
RAIN MAY EXTEND BACK INTO THE PLAINS AS WELL. THE SYSTEM'S COLD  
FRONT COULD MAINTAIN AN ENHANCED RAINFALL FOCUS INTO TUESDAY. IT  
SHOULD BE NOTED THAT WHILE THE GENERAL RAINFALL SIGNAL HAS BEEN  
PERSISTENT OVER RECENT DAYS, CONFIDENCE IN THE SPECIFICS IS NOT  
GREAT IN LIGHT OF THE GUIDANCE SPREAD FOR HOW THE SURFACE SYSTEM  
EVOLVES/TRACKS EARLY NEXT WEEK. SOME SNOW COULD FALL IN THE  
NORTHERN/NORTHWESTERN PERIPHERY OF THIS SYSTEM  
 
MUCH OF THE WEST SHOULD SEE BELOW NORMAL HIGH TEMPERATURES FROM  
THE WEEKEND INTO THE MIDDLE OF NEXT WEEK, WITH MOST LOCATIONS  
5-15F BELOW NORMAL. THE NORTHERN PLAINS WILL GENERALLY BE BELOW  
NORMAL, WITH SUNDAY LIKELY BEING THE MOST MODERATE DAY CLOSEST TO  
NORMAL. THEN HIGHS SHOULD DROP TO 15-25F BELOW NORMAL OVER SOME  
AREAS FOR MONDAY-TUESDAY OVER THE NORTHERN PLAINS WITH A SLIGHT  
WARMING TREND BY WEDNESDAY. SOUTHERN/EASTERN AREAS WILL TEND TO  
SEE NEAR TO ABOVE NORMAL TEMPERATURES, WITH VARIOUS AREAS OF PLUS  
10-15F ANOMALIES LIKELY DURING THE WEEKEND INTO TUESDAY (THEN  
DROPPING AS A COLD FRONT REACHES THE EAST BY WEDNESDAY). THE  
SOUTHERN TIER SHOULD SEE MULTIPLE DAYS OF PLUS 15-25F ANOMALIES  
FOR MORNING LOWS AND SOME DAILY RECORDS FOR WARM LOWS MAY BE  
POSSIBLE MONDAY-TUESDAY.  
 
SANTORELLI/RAUSCH  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE  
CENTRAL APPALACHIANS, THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI  
VALLEY, THE SOUTHERN APPALACHIANS, AND THE OHIO VALLEY, SUN-TUE,  
DEC 4-DEC 6.  
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST, MON-TUE, DEC 5-DEC  
6.  
- HEAVY SNOW ACROSS PORTIONS OF CALIFORNIA, THE CENTRAL GREAT  
BASIN, THE PACIFIC NORTHWEST, AND THE SOUTHWEST, SAT-SUN, DEC  
3-DEC 4.  
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL GREAT BASIN AND THE  
NORTHERN GREAT BASIN, SUN, DEC 4.  
- HEAVY SNOW ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE CENTRAL  
ROCKIES, AND THE CENTRAL GREAT BASIN, MON, DEC 5.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHEAST.  
- HIGH WINDS ACROSS PORTIONS OF THE GREAT LAKES, SAT, DEC 3.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL  
GREAT BASIN, THE NORTHERN PLAINS, THE NORTHERN ROCKIES,  
CALIFORNIA, THE NORTHERN GREAT BASIN, THE UPPER MISSISSIPPI  
VALLEY, AND THE GREAT LAKES, MON-TUE, DEC 5-DEC 6.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF MAINLAND ALASKA, MON-TUE,  
DEC 5-DEC 6.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF MAINLAND ALASKA, SAT-SUN,  
DEC 3-DEC 6.  
- HEAVY SNOW ACROSS PORTIONS OF MAINLAND ALASKA, SAT-MON, DEC  
3-DEC 5.  
- HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS,  
SAT-SUN, DEC 3-DEC 4.  
- HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA, SUN-TUE, DEC  
4-DEC 6.  
 
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  
 

 
 

 
 
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