Preliminary Forecasts
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065
FXUS02 KWNH 250642
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EDT SAT MAR 25 2017

VALID 12Z TUE MAR 28 2017 - 12Z SAT APR 01 2017

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

THE PRIMARY FOCUS OF THE FCST CONTINUES TO BE ON THE SERIES OF
FAIRLY VIGOROUS SYSTEMS AMPLIFYING INTO AND EJECTING FROM A
W-CNTRL U.S. MEAN TROUGH, WHILE DETAILS OF NRN STREAM FLOW ACROSS
THE NRN TIER STATES/SRN CANADA WILL ALSO REQUIRE MONITORING.
THERE ARE PERSISTENT DIFFS WITH A SYSTEM CROSSING THE NORTHEAST
EARLY-MID WEEK BUT THE MOST CONTENTIOUS PART OF THE FCST IS IN THE
LATTER HALF OF THE PERIOD WHEN SOLNS DIVERGE FOR SHRTWV ENERGY
HEADING INTO THE WEST BY THU WITH DOWNSTREAM EFFECTS ON AN UPR LOW
TRACKING OUT OF THE FOUR CORNERS REGION INTO THE PLAINS TUE-THU.

THE FIRST FEATURE OF INTEREST IS AN AREA OF DIFFUSE LOW PRESSURE
HEADING TOWARD THE NORTHEAST AS OF EARLY TUE, WITH UPR SUPPORT
PROVIDED BY A COMBINATION OF ENERGY EJECTING FROM THE WEST IN THE
SHORT RANGE AS WELL AS UPR TROUGH ENERGY CROSSING ERN CANADA.
THIS SYSTEM WILL LIKELY CONSOLIDATE TOWARD THE CANADIAN MARITIMES
AS THE ERN CANADIAN TROUGH CLOSES OFF AN UPR LOW.  FOR MULTIPLE
RUNS GFS-BASED GUIDANCE HAS TENDED TO BE SOMEWHAT SLOWER THAN THE
ECMWF AND MOST OTHER SOLNS TO VARYING DEGREES.  LACK OF
CONVERGENCE OVER THE PAST DAY SEEMS TO FAVOR AN INTERMEDIATE SOLN
LEANING SLIGHTLY MORE IN THE ECMWF DIRECTION REFLECTING AVG TIMING
OF GUIDANCE AS A WHOLE.  THE NEW 00Z GUIDANCE THUS FAR MAINTAINS
THE AFOREMENTIONED TIMING SPREAD.

THE SYSTEM NEAR THE FOUR CORNERS REGION AS OF EARLY TUE SHOWS
DECENT CLUSTERING INTO WED, WITH MOST GUIDANCE SHOWING A SOMEWHAT
FASTER TREND OVER THE PAST 24-36 HRS.  BEYOND WED THE PATH AND
TIMING OF THIS SYSTEM DIVERGE IN RESPONSE TO INCREASING SPREAD IN
THE HANDLING OF INCOMING PACIFIC ENERGY LATE IN THE WEEK.  THE
ECMWF/CMC AND THEIR MEANS REPRESENT THE MOST STABLE CLUSTERING AT
THE MOMENT, RAPIDLY AMPLIFYING THE WRN TROUGH WITH A CLOSED LOW,
OR AT LEAST A HINT OF ONE IN THE CASE OF THE CMC MEAN, REACHING
THE FOUR CORNERS/SRN ROCKIES BY NEXT SAT.  AT THE SAME TIME THE
LEADING PLAINS SYSTEM WOULD PROGRESS NEWD IN A FASHION CONSISTENT
WITH THE ESTABLISHED MEAN PATTERN.  HOWEVER INDIVIDUAL MODEL RUNS
HAVE DIFFERED FOR THE TRACK OF BOTH THE LATE WEEK WRN CLOSED LOW
AND SYSTEM TRACKING OUT OF THE PLAINS.  THE 18Z GFS DIFFERED THE
MOST FROM MOST OTHER SOLNS IN PULLING OFF AN UPR LOW OFFSHORE CA
WHILE BRINGING MOST REMAINING TROUGH ENERGY INTO THE PLAINS/MS
VLY, RESULTING IN A SLOW/SWD EVOLUTION OF THE LEADING PLAINS
SYSTEM.  THE 12Z GFS WAS CLOSER TO THE MAJORITY CLUSTER.  THE NEW
00Z GFS HAS RETURNED CLOSER THOUGH NOT YET TO REMAINING GUIDANCE
OVER THE WEST WHILE PSBLY BEING TOO EAGER TO SHEAR THE PLAINS
SYSTEM AND OVER-AMPLIFY NRN STREAM SHRTWV ENERGY APPROACHING THE
EAST.  USING SOME INPUT FROM YDAY`S 12Z AND 00Z ECMWF RUNS ALONG
WITH THE ECMWF MEAN/CMC/12Z GFS YIELDED A GOOD INTERMEDIATE SOLN
ALOFT WITH A DEEPER WRN CLOSED LOW THAN THE MEANS AND A TRACK
CLOSEST TO THE ECMWF MEAN THAT HAS HAD THE MOST STABLE TRACK OVER
THE PAST DAY.  FOR THE PLAINS SYSTEM EJECTING INTO THE NORTHEAST
IN THE SAME LATE WEEK TIME FRAME, THIS BLEND HELPED TO KEEP SYSTEM
TIMING BTWN THE POTENTIALLY FAST 12Z ECMWF AND SLOWER/SWD 12Z GFS.
 THIS BLEND WAS USED FOR DAYS 5-7 THU-SAT.  SOME 18Z GFS WAS
INCLUDED WITH THE OTHER SOLNS WHEN BETTER CONSENSUS EXISTED DAYS
3-4 TUE-WED.


...SENSIBLE WEATHER HIGHLIGHTS/POTENTIAL HAZARDS...

SYSTEM TRACKING OUT OF THE FOUR CORNERS REGION TUE ONWARD, AND BY
LATE IN THE PERIOD PSBL EMERGENCE OF THE NEXT AMPLIFYING WRN
SYSTEM, SHOULD PROMOTE SIGNIFICANT EPISODES OF CONVECTION OVER AND
EWD FROM THE SRN AND PERHAPS CNTRL PLAINS.  POTENTIAL FOR REPEAT
ACTIVITY WILL LIKELY LEAD TO HIGHEST RNFL TOTALS AND
EXCESSIVE/FLASH FLOOD CONCERNS OVER THE PLAINS.  ALSO SPC IS
MONITORING THE THREAT FOR SEVERE ACTIVITY FROM THE SRN PLAINS
EXTENDING AT LEAST AS FAR EWD AS THE LOWER MS VLY WITH THE FIRST
SYSTEM.  MEANWHILE AS THE SYSTEMS TRACK OVER THE WRN STATES EXPECT
SOME AREAS OF LOCALLY ENHANCED RAIN AND HIGHER ELEV SNOW.  CURRENT
INDICATIONS ARE THAT HIGHEST 5-DAY TOTALS SHOULD EXTEND FROM THE
PAC NW INTO THE NRN-CNTRL ROCKIES AND PERHAPS AS FAR S AS THE SRN
ROCKIES.  SOME POTENTIAL EXISTS FOR ENHANCED ACTIVITY OVER THE
INTERIOR WEST TO EXTEND TO THE SW OF THIS AXIS.  FAIRLY
SIGNIFICANT MODEL/ENSEMBLE SPREAD BY LATE WEEK/WEEKEND LOWERS
CONFIDENCE IN PRECIP DETAILS OVER THE WEST BY THAT TIME FRAME.
PARTS OF THE EAST WILL SEE LGT-MDT PRECIP EARLY IN THE PERIOD WITH
WINTRY WEATHER LIKELY CONFINED TO NRN NEW ENGLAND.  MSTR FROM THE
NEXT PLAINS SYSTEM SHOULD HEAD INTO/ACROSS THE EAST BY THU-SAT
WITH SOME AREAS OF HEAVIER RAIN PSBL AND WINTRY PRECIP TYPES AGAIN
CONFINED TO VERY NRN LATITUDES.

EXPECT LOCATIONS OVER THE SOUTH/SOUTHEAST AS WELL AS THE NRN
PLAINS TO SEE ABOVE NORMAL HIGHS ON THE MOST CONSISTENT BASIS
DURING THE PERIOD WITH SOME PLUS 10-20F ANOMALIES.  THERE SHOULD
BE GREATER COVERAGE OF ANOMALOUSLY WARM MIN TEMPS E OF THE ROCKIES
IN ASSOC WITH CLOUDS/PRECIP AND MULTIPLE DAYS OF LOW LVL FLOW FROM
THE GULF AHEAD OF THE EMERGING WRN U.S./PLAINS SYSTEM.  TEMPS OVER
THE WEST WILL VARY WITH SYSTEM PROGRESSION.

RAUSCH

$$





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