021  
FXUS02 KWBC 220700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST FRI FEB 22 2019  
 
VALID 12Z MON FEB 25 2019 - 12Z FRI MAR 01 2019  
   
..PATTERN OVERVIEW
 
 
LATEST GUIDANCE MAINTAINS AND TO SOME DEGREE STRENGTHENS THE REX  
BLOCK PATTERN THAT HAS GENERALLY BEEN IN PLACE OVER THE  
EAST-CENTRAL PACIFIC FOR THE PAST COUPLE WEEKS. A SIGNIFICANT  
ASPECT OF THE FORECAST EVOLUTION DURING NEXT WEEK WILL BE THE  
EXPECTED NORTHWARD DRIFT OF A STRONG UPPER HIGH LIKELY TO START  
THE WEEK NEAR THE SOUTHEASTERN COAST OF MAINLAND ALASKA. AS THIS  
OCCURS, THE CORE OF STRONGEST POSITIVE HEIGHT ANOMALIES SHOULD  
LIFT INTO THE ARCTIC. TELECONNECTIONS RELATIVE TO SUCH A  
NORTHWARD ANOMALY CENTER FAVOR A MEAN RIDGE CLOSE TO THE WEST  
COAST AND TROUGHING OVER EASTERN NORTH AMERICA. THIS TROUGH  
POSITION IS AN EASTWARD ADJUSTMENT FROM THE RECENT PATTERN BUT THE  
END RESULT KEEPS A HIGH LIKELIHOOD OF BELOW NORMAL TEMPERATURES  
ANCHORED OVER THE NORTHERN PLAINS AND VICINITY. MEANWHILE  
PROGRESSIVE MID-LATITUDE PACIFIC FLOW WILL FAVOR POTENTIAL FOR  
SIGNIFICANT FOCUSED PRECIPITATION OVER PARTS OF THE WEST COAST AND  
SOME INLAND TERRAIN. EMBEDDED ENERGY IN LOW AMPLITUDE FLOW  
CONTINUING EASTWARD MAY PRODUCE ONE OR MORE AREAS OF PRECIPITATION  
OVER THE SOUTH AND EAST--THE LATTER IN POSSIBLE COMBINATION WITH  
NORTHERN STREAM FLOW.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
MULTI-DAY MEANS INTO THE D+8 TIME FRAME AGREE QUITE WELL WITH EACH  
OTHER FOR THE OVERALL PATTERN, AND AFOREMENTIONED TELECONNECTIONS  
WITH THE POSITIVE HEIGHT ANOMALY CENTER LIFTING INTO THE ARCTIC  
YIELD A FAVORED PATTERN CONSISTENT WITH WHAT THESE MEANS ARE  
SHOWING. THUS THERE IS DECENT CONFIDENCE THAT THE GENERAL PATTERN  
SHOULD GRAVITATE TOWARD A SOLUTION CLOSE TO WHAT THE MEANS SHOW BY  
THE END OF NEXT WEEK.  
 
HOWEVER CONFIDENCE IS SIGNIFICANTLY LOWER FOR DAY-TO-DAY DETAILS.  
UPPER HIGHS OVER THE NORTHEASTERN PACIFIC/NORTHWESTERN NORTH  
AMERICA CAN CAUSE HAVOC WITH FORECAST DETAILS OVER THE EASTERN  
PACIFIC AND THE LOWER 48, DUE TO COMPLEX/HIGH-SENSITIVITY  
EVOLUTION FOR SHORTWAVE ENERGY ON THE SOUTHERN/SOUTHEASTERN SIDE  
OF THESE HIGHS. SPECIFICALLY FOR TODAY'S FORECAST, THE  
COMPLEXITIES INVOLVE A SHORTWAVE JUST OFF THE PACIFIC NORTHWEST AS  
OF EARLY MON AND AN UPPER LOW APPROACHING FROM THE WEST ALONG WITH  
THEIR POSSIBLE INTERACTION AND SUBSEQUENT MOVEMENT. DETAILS OF  
THE UPPER RIDGE WILL ALSO AFFECT THE ULTIMATE SHAPE OF CANADIAN  
FLOW THAT WILL EVENTUALLY AFFECT THE LOWER 48. CURRENTLY IT  
APPEARS THAT THE UPPER RIDGE WILL REACH FAR ENOUGH NORTH TO HAVE  
LESS INFLUENCE ON A POSSIBLE PACIFIC SYSTEM NEARING THE WEST COAST  
BY NEXT FRI.  
 
THE UPDATED FORECAST BLEND STARTS WITH A COMBINATION OF 18Z GFS  
AND 12Z ECMWF/CMC/UKMET MODEL RUNS FROM DAY 3 MON INTO DAY 5 WED.  
AS OF EARLY MON THERE IS GOOD OVERALL CLUSTERING FOR THE STRONG  
STORM LIFTING AWAY FROM NEW ENGLAND AND LOW PRESSURE NEARING THE  
NORTH-CENTRAL WEST COAST. THERE IS A GENERAL THEME IN THE  
GUIDANCE THAT FEATURES OFF THE PACIFIC NORTHWEST SHOULD EVOLVE  
INTO AN UPPER LOW BUT WITH A MODERATE AMOUNT OF SPREAD FOR  
POSITION BY WED. ALSO BY WED THERE ARE HINTS IN SOME GUIDANCE  
THAT NORTHERN STREAM SHORTWAVE ENERGY MAY PRODUCE A WEAK SURFACE  
WAVE REACHING THE EAST-CENTRAL U.S. LATEST GFS RUNS AND 12Z ECMWF  
ARE ON OPPOSITE SIDES OF THE SPECTRUM WHILE A BLEND YIELDS A  
MODEST REFLECTION SIMILAR TO CONTINUITY. AS OPERATIONAL RUNS  
FURTHER DIVERGE DETAIL-WISE, THE FORECAST RAPIDLY  
INCORPORATES/INCREASES ENSEMBLE MEAN WEIGHTING (18Z GEFS/12Z ECMWF  
MEAN) SO THAT THE MEANS COMPRISE 2/3 OF THE BLEND ON DAY 6 THU AND  
100 PERCENT ON DAY 7 FRI. ON A RELATIVE BASIS THE MOST AGREEABLE  
FEATURES BY THE END OF THE WEEK APPEAR TO BE THE SYSTEM COMING  
INTO THE PICTURE OFF THE WEST COAST AND SOUTHERN CANADA LOW  
PRESSURE WHOSE TRAILING FRONT WOULD BRING A REINFORCING PUSH OF  
COLD AIR TO THE NORTHERN STATES.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE PATTERN OVER THE WEST WILL FAVOR AN AXIS OF SIGNIFICANT  
PRECIPITATION (RAIN AND HIGHER ELEVATION SNOW) FROM THE  
CENTRAL/NORTHERN WEST COAST INTO THE NORTHERN HALF OF THE ROCKIES.  
THE BEST PROBABILITY FOR HIGHEST 5-DAY TOTALS CURRENTLY COVERS  
NORTHERN CALIFORNIA/SIERRA NEVADA RANGE AND WESTERN OREGON WITH AT  
LEAST 5-10 INCHES LIQUID POSSIBLE AT SOME LOCATIONS. THE  
PRECIPITATION AXIS SHOULD EXTEND INTO FAVORED TERRAIN OF  
IDAHO/WYOMING WITH SOMEWHAT LESS EXTREME TOTALS.  
 
FARTHER EASTWARD EXPECT STRONG WINDS TO PERSIST OVER THE NORTHEAST  
QUADRANT OF THE COUNTRY INTO MON AS THE DEEP WEEKEND STORM TRACKS  
AWAY FROM NEW ENGLAND. ALSO ANTICIPATE SOME LAKE  
EFFECT/TERRAIN-ENHANCED SNOWFALL EARLY IN THE WEEK. AT LEAST ONE  
AREA OF MOISTURE MAY SPREAD MOSTLY LIGHT-MODERATE SNOW FROM THE  
NORTHERN PLAINS INTO THE NORTHEAST DURING THE WEEK, BUT WITH LOW  
CONFIDENCE IN SPECIFICS DUE TO UNCERTAINTY OVER DYNAMICS ALOFT AND  
ASSOCIATED SURFACE REFLECTION. MEANWHILE PROGRESSIVE MID-LOWER  
LATITUDE SHORTWAVE ENERGY MAY PERIODICALLY ENHANCE RAINFALL ALONG  
AND NORTH OF THE GULF COAST REGION BUT GUIDANCE SPREAD/CONTINUITY  
CHANGES DECREASE CONFIDENCE IN DETAILS. DEPENDING ON STREAM  
INTERACTION THERE IS THE POSSIBILITY THAT SOME OF THIS MOISTURE  
COULD REACH FARTHER NORTH OVER PARTS OF THE EAST BUT THE SIGNAL IS  
NOT VERY PRONOUNCED AT THIS TIME.  
 
EXPECT VERY COLD CONDITIONS TO CONTINUE OVER AND NEAR THE NORTHERN  
HALF OF THE PLAINS WITH TEMPERATURES AT LEAST 15-20F BELOW NORMAL  
MOST DAYS. SOME AREAS IN THE EXTREME NORTHERN PLAINS/EASTERN  
SLOPES OF THE ROCKIES MAY SEE HIGHS 30-40F BELOW NORMAL EARLY IN  
THE WEEK. A LATE WEEK COLD FRONT COULD BRING HIGHS BACK DOWN TO  
25-30F BELOW NORMAL ON FRI. TO A LESS EXTREME DEGREE SOME OF THIS  
CHILLY AIR SHOULD EXTEND ACROSS THE GREAT LAKES/NORTHEAST.  
PACIFIC FLOW WILL TEND TO BRING ABOVE NORMAL MINS TO ABOUT THE  
SOUTHERN 3/4 OF THE WEST WHILE DAYTIME HIGHS SHOULD BE WITHIN A  
FEW DEGREES ON EITHER SIDE OF NORMAL. THE FORECAST LOOKS SIMILAR  
OVER THE SOUTHEASTERN STATES.  
 
RAUSCH  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES 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  
 

 
 
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