Prognostic Meteorological Discussion
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000
FXUS02 KWBC 221600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT THU JUN 22 2017

VALID 12Z SUN JUN 25 2017 - 12Z THU JUN 29 2017

...PATTERN OVERVIEW/MODEL EVALUATION...

AN AMPLIFIED WRN RIDGE/ERN TROUGH PATTERN WILL TREND FLATTER WITH
TIME, AS ERN/NERN PAC TROUGH ENERGY ERODES THE WRN RIDGE WITH THIS
EVOLUTION EVENTUALLY LEADING TO A WEAKER ERN U.S. MEAN TROUGH.
DOMINANT UNCERTAINTIES CARRY OVER FROM PREVIOUS CYCLES.  THESE
INCLUDE TRACK/TIMING OF THE NERN PAC UPR LOW MOVING INTO CANADA,
DETAILS OF THE TROUGH TO THE S OF THE UPR LOW, AND FARTHER EWD THE
SHRTWV DETAILS WITHIN THE ERN U.S. MEAN TROUGH.

FROM THE ERN PAC INTO THE CENTRAL PART OF THE CONTINENT, GFS/GEFS
RUNS CONTINUE TO TRACK THE NERN PAC UPR LOW SOMEWHAT FARTHER SWD
THAN MOST OTHER SOLNS THUS LEADING TO LOWER HGTS ALOFT OVER THE
WEST.  WHILE THE SRN TRACK HAS BEEN SOMEWHAT CONSISTENT OVER THE
PAST DAY OR TWO IN THE GFS, TIMING HAS VARIED CONSIDERABLY.  THIS
INCLUDES THE 00Z/06Z GFS RUNS WHICH ARE SLOWER/FASTER
RESPECTIVELY.  TROUGHING TO THE S OF THE UPR LOW WILL INCORPORATE
A LOWER LATITUDE UPR LOW FCST TO BE OFFSHORE THE WEST COAST AROUND
40N LATITUDE AS OF 12Z MON.  THE COMBINATION OF THIS ENERGY WILL
SUPPORT SRN CANADA/NRN TIER LOW PRESSURE AND ASSOC FRONTAL SYSTEM.
 THERE APPEARS TO BE A GENERAL TREND OVER RECENT ENSEMBLE MEAN
RUNS TOWARD A SLIGHTLY FASTER BUT BETTER DEFINED SYSTEM.  THE
FASTER TREND SEEMS REASONABLE GIVEN THE EVOLUTION TOWARD FLATTER
FLOW ALOFT.  STILL PREFER TO TILT THE FCST BLEND TO THE N OF THE
GFS FOR THE UPR LOW TRACKING INTO CANADA BUT THERE HAS BEEN ENOUGH
PERSISTENCE TO GIVE ITS SOLNS PARTIAL MINORITY CONSIDERATION.
TELECONNECTIONS RELATIVE TO THE ALEUTIANS NEG HGT ANOMALY CENTER
AND NERN PAC POS ANOM CENTER IN D+8 CHARTS CONTINUE TO SUPPORT
POTENTIAL FOR SOME DEGREE OF MEAN TROUGHING ALONG OR INLAND FROM
THE WEST COAST.  THIS ALSO FAVORS AN INTERMEDIATE SOLN WITH A
LITTLE MORE WRN TROUGHING THAN THE ECMWF/ECMWF MEAN LATE IN THE
PERIOD, THOUGH IT SHOULD BE NOTED THAT THE ECMWF MEAN DOES
EVENTUALLY DEVELOP SOME TROUGHING AFTER DAY 7 THU.

OVER THE EAST THE THEME CONTINUES TO BE ABOVE AVG CONFIDENCE IN
THE MEAN TROUGH BUT LOW CONFIDENCE IN THE DETAILS.  MODELS ARE
STILL SHUFFLING AROUND FROM RUN TO RUN FOR EXACTLY HOW ONE OR MORE
SFC WAVES EVOLVE NEAR THE EAST COAST INTO EXTREME ERN CANADA IN
ASSOC WITH SHRTWV ENERGY ALOFT.  THE GENERAL CONSENSUS FROM THE
PAST COUPLE DAYS OF GUIDANCE HAS BEEN FOR SFC FEATURES TO BE
FAIRLY WEAK.  THERE IS BETTER AGREEMENT ON TRAILING HIGH PRESSURE
BUILDING FROM THE PLAINS INTO THE EAST.  AFOREMENTIONED
TELECONNECTIONS YIELD A HINT OF FLAT CYCLONIC FLOW OVER THE EAST
FOR LATE PERIOD AND BEYOND.

AN OPERATIONAL BLEND INCORPORATING VARIOUS ASPECTS OF THE 00Z-06Z
GFS AND 00Z ECMWF/UKMET/CMC REPRESENTS FCST PREFS WELL FROM DAY 3
SUN INTO DAY 5 TUE WHILE ADDING SOME 06Z GEFS/00Z ECMWF MEAN INPUT
HELPS TO TONE DOWN DETAIL UNCERTAINTIES LATER IN THE PERIOD.  THE
RESULTING FCST IS FAIRLY CLOSE TO CONTINUITY ALOFT WHILE SFC
DETAILS ADJUST A LITTLE MORE TO REFLECT THE MOST COMMON IDEAS OF
LATEST GUIDANCE.


...WEATHER HIGHLIGHTS...

A SLOWLY MOVING OR STALLED WAVY FRONT NEAR THE GULF COAST/NRN
FLORIDA WILL PROVIDE A FOCUS FOR PERIODS OF SHWRS/TSTMS.  ALSO
HIGH PRESSURE TO THE N OF THE FRONT WILL PROMOTE A PERIOD OF LOW
LVL UPSLOPE FLOW AND POTENTIAL CONVECTIVE ENHANCEMENT ALONG THE
ERN SLOPES OF THE SRN ROCKIES/SRN HIGH PLAINS.  IN BOTH CASES SOME
LOCALLY HVY ACTIVITY IS PSBL.  ERN PAC UPR LOW ENERGY EJECTING
INLAND MAY PROVIDE A BRIEF PERIOD OF CONVECTIVE POTENTIAL OVER THE
NORTHWEST MON-TUE.  EXPECT GREATER COVERAGE/INTENSITY OF
CONVECTION TO SPREAD ACROSS THE PLAINS/MS VALLEY FROM ABOUT TUE
NIGHT ONWARD AHEAD OF ENERGY ALOFT EMERGING FROM THE WRN U.S./SWRN
CANADA AND ASSOC SFC SYSTEM.  SOME OF THIS CONVECTION MAY BE
STRONG AND/OR HEAVY BUT IT WILL TAKE SOME TIME TO RESOLVE THE MOST
FAVORED FOCUS WITH A REASONABLE DEGREE OF CONFIDENCE.  LOCATIONS
FROM THE UPR MS VALLEY THROUGH GREAT LAKES/NORTHEAST MAY SEE SOME
DIURNALLY FAVORED PRECIP UNDER THE CORE OF THE UPR TROUGH SUN
ONWARD, WITH A GRADUAL DIMINISHING OF ACTIVITY FROM WEST TO EAST
CORRESPONDING TO TROUGH PROGRESSION.

CONTINUE TO EXPECT A MODERATION OF TEMPS ACROSS MUCH OF THE LOWER
48 AS THE PATTERN ALOFT TRENDS LESS AMPLIFIED BY DAYS 6-7 WED-THU,
AT WHICH TIME MOST MIN/MAX ANOMALIES SHOULD SETTLE INTO THE SINGLE
DIGITS.  EARLIER IN THE PERIOD THE NWRN STATES MAY SEE SOME HIGHS
10-20F OR MORE ABOVE NORMAL WHILE AREAS TO THE S MAY BE 10-15F
ABOVE NORMAL.  A FEW DAILY RECORD HIGHS/WARM MINS ARE PSBL.
MEANWHILE AN AREA FROM THE CNTRL HIGH PLAINS INTO UPR MS VLY MAY
SEE HIGHS 10-20F BELOW NORMAL ON SUN WITH MUCH OF THE REST OF THE
CNTRL-ERN U.S. FAIRLY COOL AS WELL.  AN ISOLD RECORD LOW/COOL MAX
MAY BE PSBL ESPECIALLY WHERE THERE IS A SHORTER PERIOD OF RECORD.

RAUSCH

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