044  
FXUS02 KWBC 180631  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
231 AM EDT WED OCT 18 2017  
 
VALID 12Z SAT OCT 21 2017 - 12Z WED OCT 25 2017  
 
...A VERY ACTIVE WEATHER PATTERN FOR BOTH THE WRN U.S. AND THEN  
S-CENTRAL THROUGH ERN US...  
 
...GUIDANCE/UNCERTAINTY ASSESSMENT AND SENSIBLE WEATHER  
HIGHLIGHTS/THREATS...  
 
IT REMAINS THE CASE THAT MODELS AND ENSEMBLES ARE IN REASONABLE  
AGREEMENT THIS WEEKEND AND FORECAST CONFIDENCE IS ABOVE NORMAL  
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 QUITE 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 BY LATER WEEKEND. MID-UPPER LEVEL RIDGE BUILDING  
SHOULD THEN USHER IN A DRY PATTERN WITH MODIFYING TEMPS NEXT WEEK.  
 
FORECAST SPREAD AND UNCERTAINTY INCREASES SIGNIFICANTLY DOWNSTREAM  
NEXT WEEK ACROSS THE CENTRAL AND ERN US. GUIDANCE HAS NOT OFFERED  
STELLAR RUN TO RUN CONSISTENCY WITH THE FORECAST EXTENT 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/UKMET HAVE IN PARTICULAR PERIODICALLY SHOWN DEEP  
CLOSED LOW DEVELOPMENT THAT HAS VACILLATED OVER THE PAST FEW DAYS  
FROM THE SRN ROCKIES TO MORE RECENTLY THE SRN PLAINS...LOWER MS  
VALLEY...OR CENTRAL GULF COAST. ENSEMBLE SUPPORT HAS ALSO BEEN  
QUITE VARIED AS POTENTIALLY QUITE AMPLIFIED NRN STREAM TROUGH  
ENERGIES DIG SEWD FROM THE N-CENTRAL US MON TO THE E-CENTRAL US  
TUE TO INTERACT TO SOME DEGREE. LATEST GUIDANCE TRENDS ARE THE  
OPPOSITE FROM LAST NIGHT AND NOW SEEM TO SUPPORT TEMPORARY STREAM  
SEPARATION WITH POTENTIAL TO INDUCE A SURFACE WAVE AND DEEPER  
MOISTURE AND RAINFALL THREAT SIGNATURE. 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 S-CENTRAL THEN ERN US  
NEXT WEEK AS EMERGING NRN STREAM AMPLITUDE LIFTS AMPLE ACTIVITY  
NORTHWARD...ADDING ATLANTIC INFLOW. WPC PROGS WERE PRIMARILY  
DERIVED WITH A COMPOSITE GUIANCE BLEND TO OFFER WIDESPREAD  
S-CENTRAL TO ERN US RAINFALL CONSISTENT WITH BOTH POTENTIAL AND  
UNCERTAINTY. A QUICK PEEK AT THE 00 UTC ECMWF CONTINUES A  
TROUBLING TREND OVER THE PAST FEW DAYS FOR 00 UTC RUNS OF THE  
ECMWF TO OFFER MORE PROGRESSIVE SRN STREAM SOLUTIONS COMPARED TO  
THEIR MORE STREAM SEPARATED AND CLOSED SYSTEM 12 UTC COUNTERPARTS.  
A REASON FOR THIS IS UNCLEAR.  
 
SCHICHTEL  
 

 
 
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