Preliminary Forecasts
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FXUS02 KWNH 290648
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EDT WED MAR 29 2017

VALID 12Z SAT APR 01 2017 - 12Z WED APR 05 2017

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

TOWARD THE END OF THE PERIOD AND BEYOND MOST GUIDANCE IS STARTING
TO SUGGEST AN EWD SHIFT OF THE OVERALL PATTERN AS A DEEPENING MEAN
TROUGH SETTLES OVER THE NERN PACIFIC.  THIS EVOLVING TROUGH SHOWS
BETTER THAN AVG AGREEMENT FOR A DAY 7 FCST.  IN THE MEANTIME THERE
ARE STILL SIGNIFICANT MODEL/ENSEMBLE DIFFS FOR INDIVIDUAL FEATURES
WITHIN THE ONGOING SPLIT FLOW REGIME WHICH INTO NEXT WEEK SHOULD
SUPPORT PAC ENERGY FLOWING INTO A WRN CONUS MEAN TROUGH BEFORE
CONTINUING ONWARD ACROSS THE LOWER 48.

IN RECENT DAYS GUIDANCE HAS DIFFERED GREATLY WITH THE
PROGRESSION/TRACK OF AN UPR LOW FCST TO MOVE OUT OF THE SRN
ROCKIES DAY 3 SAT ONWARD ALONG WITH SPECIFICS OF INCOMING PAC
ENERGY.  THE 12Z-18Z GFS/12Z CMC AND THEIR MEANS MADE A NOTABLE
FASTER ADJUSTMENT WITH THE SRN PLAINS LOW, BRINGING THAT CLUSTER
CLOSER TO THE ECMWF/ECMWF MEAN WHICH HAVE TENDED TO BE ON THE
FASTER SIDE OF THE SPREAD.  THE OPERATIONAL 12Z ECMWF IN
PARTICULAR STILL LOOKED TOO FAST AS IT OUTRAN ITS MEAN TO THE E OF
THE MS VLY.  MEANWHILE THERE ARE OPPOSING CONSIDERATIONS FOR THE
INCOMING PAC ENERGY.  MOST NON-ECMWF GUIDANCE HAS GENERALLY
TRENDED FASTER VS 1-2 DAYS AGO BUT A SLOWER/SHARPER WRN TROUGH VS
THE ECMWF/ECMWF MEAN WOULD BE MORE CONSISTENT WITH PRECEDING
FEATURES WITHIN THE ESTABLISHED MEAN PATTERN.  AS WITH THE
DOWNSTREAM UPR LOW, THE 12Z ECMWF STRAYS FASTER THAN ITS MEAN AS
THE UPR TROUGH MOVES INTO THE PLAINS.  TAKEN AS A WHOLE THE
PLAUSIBILITY OF VARIOUS SOLNS SEEMS TO HAVE BECOME A LITTLE MORE
BALANCED THAN APPEARED TO BE THE CASE PREVIOUSLY.  THEREFORE THE
UPDATED FCST ADJUSTED TO A NEARLY EVEN BLEND AMONG THE FASTER AND
SLOWER IDEAS, WITH MORE OPERATIONAL WEIGHTING EARLY-MID PERIOD AND
MORE ENSEMBLE MEAN WEIGHTING LATE.  INCOMING 00Z MODELS STRONGLY
SUGGEST PROGRESSION THAT IS AT LEAST SLOWER THAN THE 12Z ECMWF.


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

THE GREATEST FOCUS FOR ACTIVE WEATHER DURING THE PERIOD WILL BE
WITH THE UPR LOW AND ASSOC SFC SYSTEM TRACKING EWD/NEWD OUT OF THE
SRN ROCKIES/PLAINS.  SPREAD FOR TIMING/TRACK OF THIS SYSTEM IS
STILL ENOUGH TO TEMPER CONFIDENCE IN SPECIFICS OF THE EVENT BUT
THERE STILL APPEARS TO BE A FAIRLY HIGH PROBABILITY OF
HEAVY/EXCESSIVE RAIN EXTENDING FROM THE SRN PLAINS THROUGH THE
SOUTH WITH SPC ALSO MONITORING POTENTIAL FOR SEVERE CONVECTION.
ACTIVITY SPREADING NEWD ACROSS THE REMAINDER OF THE EAST SHOULD
NOT BE AS HVY BUT MAY STILL CONTAIN POCKETS OF MDT-HVY INTENSITY.
ERN SLOPES OF THE COLORADO ROCKIES WILL LIKELY SEE AN EPISODE OF
HVY SNOW/LOWER ELEV RAIN ENHANCED BY UPSLOPE FLOW TO THE N OF THE
SRN ROCKIES UPR LOW DURING THE WEEKEND.  LOCATIONS FROM THE PAC NW
INTO THE NRN-CNTRL ROCKIES SHOULD SEE ONE OR MORE PERIODS OF
LOCALLY ENHANCED RAIN/HIGHER ELEV SNOW WITH SHRTWV ENERGY FLOWING
INTO THE WEST.  ON SAT NEW ENGLAND WILL SEE LINGERING RAIN AND
SOME INLAND SNOW WITH A DEPARTING SYSTEM.

A MAJORITY OF THE COUNTRY SHOULD SEE ABOVE NORMAL TEMPS FOR THE
OVERALL FCST PERIOD.  MOST NOTABLE ANOMALIES ON THE WARM SIDE ARE
LIKELY TO BE OVER THE NRN PLAINS CENTERED AROUND SUN AND OVER THE
SOUTH DURING THE WEEKEND.  EXCEPTIONS WILL BE FOR CHILLY READINGS
OVER THE CNTRL-SRN ROCKIES/PLAINS WITH THE UPR LOW DURING THE
WEEKEND AND OVER THE NORTHEAST WHICH WILL BE IN THE COLD SECTOR OF
A DEPARTING SYSTEM SAT AND THEN SEE A CANADIAN FRONTAL PASSAGE IN
ANOTHER DAY OR SO FOLLOWED BY ONSHORE FLOW BY TUE-WED.

RAUSCH

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