745  
FXUS02 KWBC 231558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1058 AM EST SAT FEB 23 2019  
 
VALID 12Z TUE FEB 26 2019 - 12Z SAT MAR 02 2019  
   
..PATTERN OVERVIEW
 
 
THE REX BLOCK WILL CONTINUE TO PERSIST OVER THE EAST-CENTRAL  
PACIFIC WITH RIDGING STRETCHING INTO ALASKA AND NORTHWESTERN  
CANADA, ALLOWING FEATURES TO DROP QUICKLY ACROSS THE WESTERN U.S.  
THAT FEATURE, ALONG WITH TROUGHING OVER EASTERN NORTH AMERICA, HAS  
GOOD CONSENSUS AMONG MODELS. HOWEVER, DETAILS ABOUT SYSTEMS  
DROPPING ACROSS THE WEST AND AS THEY PROGRESS EASTWARD ARE STILL  
QUITE UNCERTAIN. THERE IS STILL A SIGNAL FOR PRECIPITATION ACROSS  
THE WEST COAST AND PARTS OF THE INTERMOUNTAIN WEST ALONG WITH VERY  
COLD TEMPERATURES IN THE NORTHERN HALF OF THE PLAINS. THE EASTERN  
U.S. CAN EXPECT AN ACTIVE PERIOD WITH PRECIPITATION--BUT  
UNCERTAINTIES WITH THE MULTIPLE SYSTEMS IMPACTING THIS REGION DOES  
NOT BRING CONFIDENCE IN THE DETAILS AT THIS TIME.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
IN THE BEGINNING OF THE MEDIUM RANGE PERIOD, A MID-LEVEL CLOSED  
LOW/TROUGH WILL REMAIN OVER WESTERN BRITISH COLUMBIA/PACIFIC  
NORTHWEST THROUGH DAY 5 (THURSDAY). THE DETAILING OF THIS TROUGH  
AND THE TIMING OF THIS FEATURE MOVING INLAND IS STILL UNCLEAR. THE  
00Z CMC AND 00Z UKMET HAVE CLOSED LOWS BY DAY 3/TUE, WITH THE 06Z  
GFS AND 00Z ECMWF SHOWING AN ELONGATED OPEN TROUGH. BY DAY 4,  
THESE MODELS SHOW THE MID-LEVEL LOW CLOSING OFF AND BEGINNING TO  
MEANDER INLAND. HOWEVER, THE 06Z AND 00Z GFS, ALONG WITH THE 06Z  
GEFS MEAN, ARE MUCH FASTER THAN ALL THE GUIDANCE BY DAY 5 WITH  
THIS CLOSED LOW--WITH THE UKMET MUCH SLOWER. BECAUSE OF THIS, THE  
EVOLUTION OF THIS FEATURE WITH THE GFS IS SUCH AN OUTLIER (EVEN  
THE 06Z GEFS MEAN)--BY DAY 7/SAT, THE GFS HAS A 1050 MB HIGH  
PRESSURE SPILLING INTO THE PLAINS WITH A VERY STRONG SURFACE LOW  
MOVING INTO THE OHIO VALLEY. ONCE AGAIN, THE OTHER PIECES OF  
GUIDANCE ARE MORE IN AGREEMENT NOT TO BE AS POTENT AS THE GFS.  
WITH THE SHORTWAVES DROPPING SOUTHWARD ALONG THE EDGE OF THE REX  
IN THE PACIFIC THROUGH THE EASTERN U.S., THE TIMING AND DETAILS OF  
THESE FEATURES ALSO DIFFER AMONG THE 00Z ECMWF/06Z GFS/00Z CMC AND  
00Z UKMET THROUGHOUT THE MEDIUM RANGE PERIOD.  
 
WITH THIS IN MIND, BEGAN WITH A MULTI-MODEL BLEND THROUGH DAY  
3-4/TUE-WED USING THE 06Z GFS/00Z ECMWF/00Z UKMET AND CMC. BY DAY  
5, BECAUSE OF HOW MUCH AN OUTLIER THE GFS AND THE GEFS MEAN ARE,  
OPTED TO NOT INCLUDE IT AT ALL. INSTEAD, THE 00Z CMC OVERALL HAD  
FAIR AGREEMENT WITH THE ECMWF, SO INCLUDED SOME OF IT THROUGH DAY  
7. ADDITIONALLY, FROM DAYS 5-7, INCREASED THE USAGE OF 00Z ECMWF  
ENSEMBLE MEAN AND THE 00Z NAEFS MEAN--WHICH SEEMED TO BE A NICE  
COMPROMISE BETWEEN THE 00Z ECMWF ENSEMBLE MEAN AND THE 06Z GEFS  
MEAN.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
FROM TUE-WED, EXPECT WIDESPREAD, SIGNIFICANT PRECIPITATION ACROSS  
THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA--IN THE FORM OF RAIN  
AND HIGHER ELEVATION SNOW. THIS PRECIPITATION WILL ALSO STRETCH  
INTO THE INTERMOUNTAIN WEST, INCLUDING THE NORTHERN ROCKIES. BY  
THU-FRI, A LULL IN PRECIPITATION CAN BE EXPECTED WITH POTENTIAL  
FOR LIGHT TO SCATTERED PRECIPITATION MOSTLY FOR THE PACIFIC  
NORTHWEST AND NORTHERN ROCKIES. AS THE WEEKEND COMES, ANOTHER  
ROUND OF SIGNIFICANT PRECIPITATION WILL APPROACH THE WEST  
COAST--ESPECIALLY IN CALIFORNIA/SIERRA NEVADA AND INTO THE  
INTERMOUNTAIN WEST/CENTRAL GREAT BASIN.  
 
PRECIPITATION COVERAGE AND INTENSITY FROM THE PLAINS TO EAST COAST  
CONTINUE TO BE DIFFICULT TO PINPOINT DUE TO SIGNIFICANT  
DIFFERENCES IN SHORTWAVE ENERGY AND SURFACE EVOLUTION. FROM TUE -  
WED NIGHT, EXPECT LIGHT SNOW TO PROGRESS FROM MONTANA AND INTO THE  
PLAINS, POTENTIALLY THE UPPER MIDWEST. MEANWHILE, THE SOUTHERN  
STREAM IMPULSES MAY PROMOTE PERIODS OF RAINFALL ACROSS THE GULF  
COAST STATES OVER THE COURSE OF THE PERIOD. BY FRI-SAT, THERE MAY  
BE AN EXPANSION OF PRECIPITATION COVERAGE OVER THE EASTERN STATES  
(SNOW NORTH AND RAIN SOUTH) IN ASSOCIATION WITH SOME DEGREE OF  
SURFACE DEVELOPMENT OVER THE EAST AND/OR EXTREME WESTERN ATLANTIC.  
 
WITHIN THE AREA OF MUCH BELOW NORMAL TEMPERATURES CENTERED OVER  
THE NORTHERN HALF OF THE PLAINS, COLDEST ANOMALIES (AT LEAST 30F  
BELOW NORMAL AT SOME LOCATIONS) WILL REMAIN THROUGH MIDWEEK, WITH  
A SLIGHT REBOUND IN TEMPERATURES BY THU-FRI. HOWEVER, WITH ANOTHER  
ARCTIC HIGH PRESSURE DROPPING, COLD TEMPERATURES IN THE NORTHERN  
PLAINS WILL ARRIVE ONCE AGAIN BY THE WEEKEND. FLOW FROM THE  
PACIFIC WILL KEEP MORNING LOWS ABOVE NORMAL OVER ALL BUT THE  
EXTREME NORTHERN PARTS OF THE WEST, AS WELL AS OVER THE SOUTHERN  
TIER, WHILE CLOUDS AND PRECIPITATION WILL TEND TO KEEP HIGHS  
CLOSER TO NORMAL.  
 
REINHART/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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