Prognostic Meteorological Discussion
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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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