Prognostic Meteorological Discussion
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059
FXUS02 KWBC 230646
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EDT SAT JUL 23 2016

VALID 12Z TUE JUL 26 2016 - 12Z SAT JUL 30 2016

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

MODELS AND ENSEMBLES REMAIN SIMILAR FOR MOST ASPECTS OF THE LARGE
SCALE EVOLUTION... DOMINATED BY A PERSISTENT GREAT BASIN/FOUR
CORNERS RIDGE AND A SLOWLY AMPLIFYING/SHARPENING MEAN TROUGH OVER
THE VICINITY OF THE MS VALLEY.  HOWEVER THE RELATIVELY SMALL SCALE
OF IMPORTANT EMBEDDED DETAIL DIFFS WILL CONTRIBUTE TO LOW
PREDICTABILITY FOR SPECIFICS THAT WILL IMPACT SENSIBLE WEATHER
OVER SOME AREAS.

THE EVOLVING E-CNTRL U.S. MEAN TROUGH SHOULD BEGIN TO TAKE SHAPE
WITHIN FLOW TO THE S/SW OF A CLOSED LOW CROSSING ERN CANADA WHILE
REINFORCEMENT COMES FROM ERN PAC/WRN CANADA ENERGY PASSING THROUGH
A MODEST MEAN RIDGE OVER WRN CANADA.  THERE IS RELATIVE AGREEMENT
THAT FLOW ALOFT WILL REFLECT AT THE SFC AS TWO WAVY SFC FRONTS FOR
A MAJORITY OF THE PERIOD... ONE FROM THE MID ATLC WWD INTO THE
PLAINS AND A SECOND THAT BEGINS TO DRIFT SWD INTO THE NRN TIER AT
THE START OF THE PERIOD ON TUE.  INDIVIDUAL WAVES ALONG THESE
FRONTS WILL BE SENSITIVE TO IMPULSES ALOFT THAT MAY NOT BE FCST
WITH A REASONABLE DEGREE OF CONFIDENCE UNTIL WELL WITHIN THE SHORT
RANGE TIME FRAME.  WITH ONLY MODEST IMPACT ON THE DOWNSTREAM
TROUGH SO FAR... TOWARD DAYS 6-7 FRI-SAT THE PAST 12-24 HRS OF
ECMWF MEAN RUNS SHOW A NOTICEABLE TREND TOWARD QUICKER AND/OR MORE
AMPLIFIED EJECTION OF NERN PAC/GULF OF ALASKA TROUGHING TOWARD WRN
CANADA AND THE PAC NW.  THROUGH THE 12Z/18Z CYCLES OTHER GUIDANCE
DID NOT YET SHOW MUCH EVIDENCE OF THE ECMWF MEAN TREND.  SOME
WEIGHTING OF THE ECMWF MEAN IDEA SEEMS REASONABLE AS IT IS
PLAUSIBLE FOR UPSTREAM FLOW TO EJECT THE FEATURE.  IN FACT THE UPR
SYSTEM NOW REACHING THE GULF OF ALASKA HAD BEEN FCST TO EJECT MORE
SLOWLY IN SOME EXTENDED GUIDANCE.

THE UPDATED FCST USED VARIOUS ATTRIBUTES OF THE 12Z-18Z GFS/12Z
ECMWF AND 18Z GEFS/12Z ECMWF MEANS INTO DAY 6 FRI TO CAPTURE THE
MOST AGREEABLE ASPECTS OF GUIDANCE WITH MUCH GREATER EMPHASIS ON
THE MEANS BY DAY 7 SAT.  GEFS/ECMWF MEAN WEIGHTING AT THAT TIME
WAS KEPT AROUND EVEN SINCE THE ECMWF MEAN SCENARIO IS PLAUSIBLE
BUT OTHER SOLNS WERE NOT YET STRONGLY TRENDING THAT WAY.  THE 00Z
GFS/CMC HAVE ADJUSTED TO A COMPROMISE BTWN THE ECMWF MEAN AND
SLOWER 00Z GEFS MEAN WITH THE NERN PAC TROUGH.


...WEATHER HIGHLIGHTS/THREATS...

EXPECT EVOLVING FLOW ALOFT AND WAVY FRONTS AT THE SFC TO SUPPORT
AREAS OF ORGANIZED CONVECTION WITHIN AN AREA FROM THE NRN-CNTRL
PLAINS INTO THE OH/TN VALLEYS AND PERHAPS EWD INTO THE APLCHNS.
UNCERTAINTY OF IMPORTANT SMALL SCALE DETAILS LOWERS CONFIDENCE IN
FURTHER REFINING HEAVIEST RNFL POTENTIAL WITHIN THIS AREA... BUT
IT SEEMS LIKELY THAT MULTI-DAY TOTALS COULD BE SIGNIFICANT AT SOME
LOCATIONS.  SOME OF THIS CONVECTION MAY ALSO BE STRONG TO SEVERE
SO CONSULT SPC OUTLOOKS FOR FURTHER INFO AS THE SUPPORTING DETAILS
COME INTO CLEARER FOCUS.  ELSEWHERE... THE SOUTHWEST AND ROCKIES
SHOULD SEE DAILY EPISODES OF CONVECTION WITHIN A BAND OF MONSOONAL
MSTR WHILE CONVECTION OVER THE GULF COAST AND VICINITY MAY BE
ENHANCED BY ONE OR MORE MID LVL IMPULSES RETROGRADING AROUND THE
SRN SIDE OF THE SRN TIER RIDGE ALOFT.

THE MOST EXTREME TEMPS RELATIVE TO NORMAL SHOULD BE FROM THE WEST
COAST STATES INTO THE NRN ROCKIES WITH SOME HIGHS REACHING 10-20F
ABOVE NORMAL ON ONE OR MORE DAYS.  ISOLD RECORD HIGHS AND/OR
RECORD WARM LOWS MAY BE PSBL WITHIN THIS AREA.  ALBEIT WITH LESSER
ANOMALIES THE EAST COAST STATES WILL LIKELY REMAIN VERY WARM AHEAD
OF THE DEVELOPING MS VLY MEAN TROUGH ALOFT.  THE NRN PLAINS/UPR MS
VLY SHOULD BE MOST CONSISTENTLY BELOW NORMAL WITH SOME MINUS 5-10F
ANOMALIES FOR HIGHS.

RAUSCH

$$





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