Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXUS02 KWBC 011600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT SUN MAY 01 2016

VALID 12Z WED MAY 04 2016 - 12Z SUN MAY 08 2016

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

THE BEST CONSENSUS OF GUIDANCE CONTINUES TO ADVERTISE A VERY
BLOCKY PATTERN DURING THE PERIOD... WITH ONE UPR LOW CLOSING OFF
NEAR THE CA COAST THEN MOVING INTO THE WEST AND ANOTHER CLOSED LOW
LIKELY TO BE EMBEDDED WITHIN A DEEP ERN TROUGH.  OVERALL THE THE
WRN UPR LOW STILL EXHIBITS THE BEST CLUSTERING AND CONTINUITY
WHILE SIGNIFICANT QUESTION MARKS REMAIN FOR ERN U.S./WRN ATLC
DETAILS AND THEN FROM LATE WEEK ONWARD FROM THE NERN PAC ACROSS
CANADA.

FOR MOST OF THE WED-SUN TIME FRAME AN AVG OF LATEST GUIDANCE
PROVIDES A REASONABLE FCST FOR THE UPR LOW PROGRESSING INTO THE
WEST.  THE PAST DAY OF SOLNS HAS BECOME A LITTLE MORE STABLE ON
TIMING DURING THE FIRST HALF OF THE PERIOD WHILE A SLIGHTLY SLOWER
TREND BECOMES EVIDENT BY NEXT WEEKEND.  UPSTREAM LATE IN THE
PERIOD THE PAST TWO ECMWF RUNS DISPLAY A SIGNIFICANT BREAK IN
CONTINUITY FROM PRIOR RUNS AND ESTABLISHED MODEL/ENSEMBLE
CONSENSUS AS THEY BRING NERN PAC TROUGHING INTO WRN CANADA/NWRN
CONUS WHERE MEAN RIDGING HAS BEEN FCST.  RELATIVE TO THE FULL 00Z
ENSEMBLE SPREAD THE 00Z ECMWF RUN IS FAIRLY EXTREME BUT EVEN THE
00Z ECMWF ENSEMBLE MEAN HAS ADJUSTED TO THE IDEA OF BREAKING DOWN
THE WRN CANADA MEAN RIDGE.  GIVEN THIS ABRUPT AND PRONOUNCED
CHANGE... PREFER TO LEAN AWAY FROM THE 00Z ECMWF/ECMWF MEAN WITH
THIS ASPECT OF THE FCST AFTER DAY 5 FRI.  THE OLD 12Z ECMWF MEAN
WOULD BE PREFERRED BASED ON BETTER MAINTENANCE OF THE WRN CANADA
RIDGE ALOFT.

SOME SPECIFICS FOR ERN U.S./WRN ATLC EVOLUTION REMAIN UNCERTAIN.
BESIDES THE UNCERTAINTY OF EXACTLY HOW INITIAL GRTLKS ENERGY WILL
ULTIMATELY CLOSE OFF ITS UPR LOW OVER THE APLCHNS/EAST COAST...
THERE ARE STILL SIGNIFICANT MODEL DIFFS IN THE DEPICTION OF SHRTWV
ENERGY ROUNDING THE SRN/ERN SIDE OF THE OVERALL TROUGH ALOFT
DURING THE FIRST HALF OF THE PERIOD.  THE 00Z UKMET STILL OFFERS
POTENTIAL FOR A STRONG INTERACTION THAT WOULD LEAD TO A
DEEP/INLAND SFC LOW AS PER THE TWO ECMWF RUNS PRIOR TO THE 00Z
RUN.  REMAINING GUIDANCE IS NOW HINTING THAT INITIAL WAVINESS NEAR
THE EAST COAST WILL CONSOLIDATE INTO A COMPACT LEADING WAVE THAT
WILL MOVE QUICKLY NWD AND BY DAY 5 FRI GIVE WAY TO A SECOND WRN
ATLC SFC SYSTEM ASSOC WITH THE UPR LOW... WITH THIS LATTER FEATURE
PERSISTING THROUGH THE WEEKEND.  PREFER TO INCLUDE SOME 00Z
GFS/ECMWF ALONG WITH THE ENSEMBLE MEANS TO ADJUST TOWARD THE DAYS
3-5 DETAILS WHILE OTHERWISE MAINTAINING REASONABLE OVERALL
CONTINUITY.  NOTE THAT THE 06Z GFS IS CONSIDERED ONE OF THE LESS
PROBABLE SOLNS WITH ITS FARTHER SWD ERN CANADA UPR LOW AND QUICK
EJECTION OF THE ERN TROUGH.  THE 06Z GEFS MEAN HAS ENOUGH ELEMENTS
OF THIS SCENARIO NOT TO BE FAVORED EITHER.

THE UPDATED FCST INCLUDES ABOUT 40 PCT TOTAL WEIGHT OF THE 00Z
GFS/ECMWF ALONG WITH THEIR ENSEMBLE MEANS INTO DAY 5 FRI TO
BALANCE EMERGING DETAILS NEAR THE EAST COAST WITH CONTINUITY WHILE
REPRESENTING CONSENSUS WITH THE WRN UPR LOW.  DAYS 6-7 ADJUST
ENTIRELY TO ENSEMBLE MEANS... FROM THE 00Z GEFS/NAEFS RUN AND OLD
12Z ECMWF MEAN BASED ON SKEPTICISM OF THE NEW ECMWF MEAN SOLN OVER
THE NERN PAC/WRN CANADA.


...WEATHER HIGHLIGHTS/THREATS...

THE DEEP UPR LOW HEADING INTO THE WEST WILL SPREAD A BROAD AREA OF
RAIN AND HIGHEST ELEVATION SNOW FROM THE WEST COAST INTO THE
ROCKIES... WITH SOME RNFL EVENTUALLY DEVELOPING OVER THE PLAINS BY
NEXT WEEKEND.  GUIDANCE IS FAIRLY CONSISTENT IN SHOWING BEST
POTENTIAL FOR HIGHEST TOTALS FROM FAVORED TERRAIN INLAND FROM THE
CENTRAL WEST COAST EASTWARD INTO THE NORTH-CENTRAL AND CENTRAL
ROCKIES/HIGH PLAINS.  NRN PARTS OF THE WEST/PLAINS SHOULD SEE
TEMPS ON THE WARM SIDE THOUGH THE NRN ROCKIES/HIGH PLAINS WILL
LIKELY COOL DOWN SOMEWHAT AROUND FRI-SUN.  MEANWHILE EXPECT A
PRONOUNCED COOLING TREND ACROSS CNTRL-SRN AREAS WITH ONE OR MORE
DAYS OF WELL BELOW NORMAL HIGH TEMPS.  DOWNSTREAM RIDGE ALOFT WILL
GRADUALLY SPREAD WARMER AIR FROM THE PLAINS INTO AND JUST BEYOND
THE MS VLY.

DEEP UPR TROUGHING AND ONE OR MORE EAST COAST/WRN ATLC SFC LOWS
WILL GENERALLY SUPPORT COOL AND UNSETTLED WEATHER OVER THE ERN
STATES.  COMBINING THE CONTINUED WIDE ARRAY OF POTENTIAL SFC
EVOLUTIONS NEAR THE EAST COAST... THE OVERALL HIGHEST PROBABILITY
FOR ONE OR MORE PERIODS OF FOCUSED/ENHANCED RNFL SHOULD EXIST FROM
THE CNTRL APLCHNS/MID ATLC INTO THE NORTHEAST.  IT WILL REQUIRE
RESOLVING FINER DETAILS OF THE FCST TO PINPOINT WHERE/WHEN RNFL
WILL BE HEAVIEST AND STRENGTH/DIRECTION OF LOW LVL WINDS.  EXPECT
THE FL PENINSULA TO SEE SOME ORGANIZED RNFL WITH A COLD FRONTAL
PASSAGE EARLY IN THE PERIOD.

RAUSCH

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.