Prognostic Meteorological Discussion
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FXUS02 KWBC 240642
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 AM EDT SUN JUL 24 2016

VALID 12Z WED JUL 27 2016 - 12Z SUN JUL 31 2016

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

THERE IS STILL RELATIVE AGREEMENT UPON THE LARGE SCALE EVOLUTION
BUT CONSIDERABLE MODEL AND ENSEMBLE SPREAD FOR EMBEDDED SHRTWV
DETAILS.  CONTINUE TO PREFER A FCST APPROACH THAT INCORPORATES
IDEAS FROM THE OPERATIONAL RUNS AND ENSEMBLE MEANS TO REFLECT
CONSENSUS FEATURES WHILE YIELDING AN INTERMEDIATE SOLN WHERE
TIMING/AMPLITUDE DIFFS ARISE.  THIS CYCLE MAKES USE OF THE 12Z-18Z
GFS/12Z ECMWF AND 18Z GEFS/12Z ECMWF MEANS.

GUIDANCE REMAINS CONSISTENT IN DEVELOPING A MEAN TROUGH NEAR THE
MS VLY... DOWNSTREAM FROM A PERSISTENT GREAT BASIN UPR HIGH AND
MODEST WRN CANADA MEAN RIDGE.  CURRENT CONSENSUS SUGGESTS THE AXIS
OF THE MS VLY TROUGH MAY BEGIN TO MOVE EWD LATE IN THE PERIOD
WHILE A NERN PAC TROUGH REACHES WRN CANADA AND THE NRN HALF OF THE
WEST COAST.  FROM FAIRLY EARLY IN THE FCST PERIOD ENSEMBLE
SPAGHETTI PLOTS SHOW A WIDE VARIETY OF SOLNS FOR INDIVIDUAL
SHRTWVS WITHIN THE SRN CANADA/NRN U.S. FLOW... REFLECTING THE LOW
PREDICTABILITY OF SMALLER SCALE DETAILS IN THIS PATTERN.  ONE
ASPECT OF IMPROVING CONFIDENCE INVOLVES THE LATE PERIOD WEST COAST
TROUGH AS TRENDS HAVE GENERALLY GRAVITATED TOWARD ECMWF/ECMWF MEAN
RUNS THAT INITIALLY SIGNALED THE AN EARLIER ARRIVAL OF THE TROUGH.
 TIMING/AMPLITUDE DIFFS THAT REMAIN ARE WITHIN TYPICAL ERROR FOR
DAYS 6-7 FCSTS THUS FAVORING THE MODEL/ENSEMBLE BLEND.  FROM THE
PLAINS INTO THE EAST... THE UNCERTAINTY OF SHRTWV DETAILS ALOFT
LEADS TO LOW CONFIDENCE IN THE EXISTENCE/TIMING/TRACK OF ONE OR
MORE SFC WAVES THAT SHOULD TRACK WITHIN A CORRIDOR EXTENDING FROM
THE CNTRL PLAINS INTO THE OH VLY/LWR GRTLKS.  ANOTHER FAVORED AREA
OF WAVINESS AT THE SFC SHOULD EXTEND ALONG THE MID ATLC/NERN COAST.


...WEATHER HIGHLIGHTS/THREATS...

BROADLY SPEAKING THE FCST IS CONSISTENT FOR EVOLUTION OF FLOW
ALOFT AND SFC FRONTS/WAVES TO PROMOTE AREAS OF ORGANIZED
CONVECTION FROM THE NRN-CNTRL PLAINS INTO THE MID ATLC/NORTHEAST.
UNCERTAINTY IN IMPORTANT SHRTWV DETAILS... ALONG WITH DEPENDENCE
ON MESOSCALE DETAILS THAT MAY NOT BE EVIDENT UNTIL A FEW HRS AHEAD
OF TIME... CONTINUE TO MAKE IT DIFFICULT TO PINPOINT THE MOST
FAVORED LOCATIONS FOR HIGHEST RNFL TOTALS IN THE EXTENDED TIME
FRAME.  THE SAME IS THE CASE FOR DETERMINING SEVERE THREATS.
MONSOONAL MSTR AND IMPULSES ALOFT WILL CONTRIBUTE TO DIURNAL
CONVECTION OVER THE SOUTHWEST AND ROCKIES WHILE PORTIONS OF THE
GULF COAST AND FLORIDA SHOULD SEE PERIODS OF SHWRS/TSTMS AS WELL.

WRN U.S. HEAT WILL EXPAND INTO THE NORTHWEST WITH GREATEST
COVERAGE OF HIGHS 10F OR MORE ABOVE NORMAL ACROSS THE WEST LIKELY
TO BE ON THU-FRI.  WEST COAST STATES WILL SEE A NOTICEABLE COOLING
TREND DURING THE WEEKEND AS AN UPR TROUGH ARRIVES.  MUCH OF THE
EAST COAST WILL SEE ABOVE NORMAL TEMPS MID-LATE WEEK.  THE NRN
HALF OF THE EAST COAST SHOULD THEN TREND CLOSER TO NORMAL BUT
PARTS OF THE SRN MID ATLC/SOUTHEAST MAY REMAIN 5-10F ABOVE NORMAL
THROUGH THE WEEKEND.  NRN INTO CNTRL PLAINS LOCATIONS SHOULD SEE A
PERIOD OF BELOW NORMAL HIGHS WITH A WARMING TREND BY NEXT WEEKEND.

RAUSCH

$$





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