433  
FXUS02 KWBC 170710  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
310 AM EDT TUE OCT 17 2017  
 
VALID 12Z FRI OCT 20 2017 - 12Z TUE OCT 24 2017  
 
...GUIDANCE/UNCERTAINTY ASSESSMENT AND SENSIBLE WEATHER  
HIGHLIGHTS/THREATS...  
 
MODELS AND ENSEMBLES REMAIN IN REASONABLE AGREEMENT INTO THE  
WEEKEND AND FORECAST CONFIDENCE IS ABOVE NORMAL DURING THIS PERIOD  
WITH GOOD RUN TO RUN GUIDANCE CONTINUITY.  
IN THIS PERIOD THE MAIN FORECAST FOCUS WILL BE ACROSS THE WRN US.  
DEEP PACIFIC TROUGH RELATED HEIGHT FALLS SLAM INTO THE WEST COAST  
FRI THAT WORK INLAND ACROSS MUCH OF THE WRN US AND ROCKIES INTO  
SAT. EXPECT HEAVY PCPN OVER THE NWRN US INTO CA WITH INITIAL  
MOISTURE FEED THAT COULD PRODUCE SOME RUNOFF ISSUES. DYNAMICALLY  
DRIVEN/TERRAIN ENHANCED AMOUNTS THEN PROGRESS ACROSS THE N-CENTRAL  
INTERMOUNTAIN WEST/ROCKIES. COOLING TEMPS WITH FRONTAL PASSAGE AND  
HIGH PRESSURE SURGE WILL SUPPORT SOME HEAVY TERRAIN ENHANCED SNOWS  
IN A PERIOD WITH LOWERING SNOW LEVELS. ADDITIONAL UPSTREAM PACIFIC  
ENERGIES PUNCHING INTO THE NWRN US SHOULD ADD ANOTHER SHOT OF  
MODERATE PCPN INTO THE REGION OVER THE WEEKEND. MID-UPPER LEVEL  
RIDGE BUILDING SHOULD THEN USHER IN A DRY PATTERN WITH MODIFYING  
TEMPS NEXT WEEK.  
 
FORECAST SPREAD AND UNCERTAINTY INCREASES SIGNIFICANTLY BY LATER  
WEEKEND INTO EARLY NEXT WEEK DOWNSTREAM ACROSS THE CENTRAL AND ERN  
US. GUIDANCE HAS NOT OFFERED STELLAR RUN TO RUN CONSISTENCY WITH  
THE FORECAST OF SUBSEQUENT STREAM SEPARATION AS AFOREMENTIONED WRN  
US TROUGH ENERGIES PROGRESS INTO THE CENTRAL US AND LATER THE ERN  
US. RECENT RUNS OF THE ECMWF HAS BEEN SHOWING DEEP CLOSED LOW  
DEVELOPMENT THAT HAS SHIFTED OVER THE PAST FEW DAYS FROM AS FAR  
WEST AS THE SRN ROCKIES TO THE SRN PLAINS THEN LOWER MS VALLEY.  
ENSEMBLE SUPPORT FOR THIS HAS BEEN MARGINAL...AND THE LATEST 00  
UTC ECMWF RUN CONTINUES TRENDING TO A MUCH WEAKER LOW SHIFTED  
PROGRESIVELY EASTWARD UNDERNEATH INCREASINGLY DOMINANT AND NRN  
STREAM TROUGH ENERGIES DIGGING SEWD FROM THE N-CENTRAL US MON TO  
THE E-CENTRAL US TUE. ACCORDINGLY...THE NOTION THAT THE HIGHER  
RESOLUTION ECMWF MIGHT BE CATCHING ONTO A MORE SIGNIFICANT SRN  
STREAM SYSTEM NOT SHOWN WELL IN OTHER GUIDANCE HAS DWINDLED.  
INSTEAD EXPECT THERE MAY WELL BE STREAM SEPARATION TO SOME  
DEGREE...BUT OVERALL EXPECT A POTENT AND WAVY COLD FRONT AND  
EMERGING DEEP INFLOW FROM THE GULF OF MEXICO INLAND AND NORTHWARD  
TO FUEL A PROGRESSIVE AND WIDESPREAD SWATH OF MODERATE TO HEAVY  
RAINS ACROSS THE CENTRAL THEN ERN US NEXT WEEK WITH THE EMERGING  
NRN STREAM AMPLITUDE LIFTING ACTIVITY RAPIDLY NORTHWARD ACROSS THE  
ERN THIRD OF THE NATION WITH ACTIVITY ADDING WRN ATLANTIC INFLOW  
OEVR TIME. MOST GUIDANCE NOW SUPPORTS THIS SCENARIO AND WPC PROGS  
WERE PRIMARILY DERIVED WITH A COMPOSITE MODEL AND ENSEMBLE BLEND  
THAT DE-EMPHASIZED MUCH OF THE EARLIER ECMWF POTENTIAL.  
 
SCHICHTEL  
 

 
 
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