Preliminary Forecasts
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FXUS02 KWNH 290635
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
234 AM EDT MON AUG 29 2016

VALID 12Z THU SEP 01 2016 - 12Z MON SEP 05 2016

...OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT...

DOWNSTREAM FROM A STRONG E-CNTRL PACIFIC RIDGE EXPECT A MEAN
TROUGH TO MOVE GRADUALLY INLAND FROM THE WEST COAST.  THE
DOWNSTREAM CNTRL U.S. RIDGE AND ERN TROUGH WILL MAKE STEADY EWD
PROGRESS... ULTIMATELY LEAVING THE ERN PART OF NORTH AMERICA WITH
ABOVE AVG HGTS ALOFT AS FAVORED BY TELECONNECTIONS RELATIVE TO THE
ERN PAC/WRN U.S. PATTERN BY LATE IN THE PERIOD.  THE NATIONAL
HURRICANE CENTER IS ISSUING ADVISORIES ON TWO SYSTEMS OF INTEREST
TO THE LOWER 48.  T.D. EIGHT MAY BRUSH THE NORTH CAROLINA COAST
DURING THE SHORT RANGE IN THE PROCESS OF RECURVING WHILE T.D. NINE
IS FCST TO TRACK THROUGH THE GULF OF MEXICO AND THROUGH NRN
FLORIDA INTO THE ATLANTIC.  CONSULT LATEST NHC PRODUCTS FOR
FURTHER INFO ON THESE SYSTEMS.

AWAY FROM T.D. NINE THE MANUAL FCST MAINTAINS THE STRATEGY OF
BLENDING LATEST MODEL AND ENSEMBLE GUIDANCE... 12Z-18Z GFS/18Z
GEFS MEAN AND 12Z ECMWF/ECMWF MEAN... EARLY-MID PERIOD BEFORE
TRENDING TOWARD THE TWO ENSEMBLE MEANS BY DAY 7 MON AS CONFIDENCE
IN MODEL DETAILS DECREASES.

WITHIN THE WRN U.S. MEAN TROUGH THERE IS FAIR AGREEMENT THAT THE
INITIAL CORE OF ENERGY ALOFT TRACKING ACROSS VANCOUVER ISLAND
THU-FRI SHOULD EJECT NEWD AND SUPPORT LOW PRES TRACKING TOWARD
HUDSON BAY WITH THE TRAILING FRONT PROGRESSING INTO THE NRN
PLAINS.  BY THE LATTER HALF OF THE PERIOD UNCERTAINTIES WITH EXACT
DETAILS OF ENERGY FLOWING ACROSS THE NRN PAC AND FEEDING INTO THE
MEAN TROUGH LEAD TO LOWER CONFIDENCE IN SPECIFICS AND FAVOR
INCREASING EMPHASIS ON THE ENSEMBLE MEANS ESPECIALLY BY THE START
OF NEXT WEEK.  ALSO AT THAT TIME THE NRN PLAINS FRONT MAY
DECELERATE/BECOME STNRY AS HGTS ALOFT STABILIZE WITH A PERSISTENT
SWLY ORIENTATION.  BY LATE IN THE PERIOD PREFS LEAN SLIGHTLY
TOWARD THE ECMWF MEAN VS THE GEFS MEAN AS RECENT MULTI-DAY TRENDS
HAVE TENDED TO BRING THE GEFS TOWARD THE EC MEAN ON DAYS WHEN THE
FORMER HAPPENED TO BE THE SLOWER/MORE AMPLIFIED SOLN AS IS THE
CASE TODAY AT SOME FCST HRS.

YET TO BE RESOLVED DETAILS OF THE ERN U.S. TROUGH HEADING INTO THE
ATLC WILL BE CRUCIAL FOR THE FCST OF T.D. NINE ONCE IT TRACKS
BEYOND FLORIDA.  GUIDANCE HAS BEEN QUITE DIVERSE WITH TRACK/TIMING
AFTER FRI IN JUST THE PAST 12-24 HRS OF RUNS LET ALONE PRIOR TO
THAT.  EXTRAPOLATION BEYOND THE PERIOD OF TIME COVERED BY THE 0300
UTC NHC ADVISORY MAINTAINS CONTINUITY WITH RESPECT TO DECELERATION
TO ACCOUNT FOR GUIDANCE SPREAD WHILE AT A GREATER DISTANCE OFF THE
SERN COAST DUE TO FASTER EWD MOTION THROUGH LATE WEEK.  00Z
GUIDANCE THUS FAR IS SUGGESTING A MORE PROGRESSIVE SCENARIO COULD
HOLD AFTER FRI.


...WEATHER HIGHLIGHTS/THREATS...

T.D. NINE... FCST TO STRENGTHEN TO TROPICAL STORM STATUS BEFORE
REACHING FLORIDA... WILL LIKELY BE ACCOMPANIED BY A PERIOD OF HVY
RAIN AND STRONG WINDS.  EFFECTS ALONG THE SOUTHEAST COAST AFTER
THE SYSTEM TRACKS ACROSS NRN FL WILL DEPEND ON PRECISE
TRACK/TIMING.  THE UPR TROUGH ENTERING THE WEST WILL BRING SOME
TERRAIN ENHANCED PCPN TO THE NRN PAC NW/NRN ROCKIES.  LEADING COLD
FRONT REACHING THE NRN PLAINS SHOULD PROMOTE INCREASED CONVECTION
DURING THE WEEKEND AND EARLY NEXT WEEK.  BEST POTENTIAL FOR SOME
HVY RNFL SHOULD BE WITHIN AN AREA FROM THE CNTRL PLAINS INTO THE
UPR MS VLY/UPR GRTLKS.  POTENTIAL DECELERATION/STALLING OF THE SFC
FRONT LATE IN THE PERIOD COULD ALLOW FOR TRAINING/REPEAT ACTIVITY.
 FARTHER EWD THE FRONT CROSSING THE EAST EARLY IN THE PERIOD MAY
BRING SOME SHWRS/TSTMS.  COOL TEMPS OVER THE WEST COAST STATES AS
OF LATE THIS WEEK WILL PUSH GRADUALLY FARTHER INLAND.  AHEAD OF
THE COLD FRONT EMERGING FROM THE NORTHWEST... ON THU-FRI PARTS OF
THE NRN PLAINS SHOULD SEE TEMPS 10-15F ABOVE NORMAL AND PERHAPS
LOCALLY HIGHER.  HIGH PRESSURE BUILDING INTO THE EAST WILL BRING A
COUPLE DAYS OR SO OF NEAR/SLIGHTLY BELOW NORMAL TEMPS AROUND LATE
WEEK/EARLY WEEKEND.  THE WARMING TREND THAT FOLLOWS MAY BRING
ANOMALIES BACK UP TO AT LEAST PLUS 5-10F FROM THE OH VLY/APLCHNS
INTO THE NORTHEAST.

RAUSCH

$$





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