Prognostic Meteorological Discussion
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FXUS02 KWBC 251457
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1056 AM EDT SUN JUN 25 2017

VALID 12Z WED JUN 28 2017 - 12Z SUN JUL 02 2017

...HEAVY RAIN POTENTIAL EXISTS FROM THE CENTRAL PLAINS TO THE
UPPER GREAT LAKES LATE THIS WEEK THROUGH THE WEEKEND...

***PATTERN OVERVIEW AND MODEL PREFERENCES***

THE MODELS CONTINUE TO SHOW A SIMILAR LARGE SCALE PATTERN ON
WED-THU WITH A LEAD UPPER TROUGH PROGRESSING OUT OF THE UPPER MS
VALLEY TOWARDS THE UPPER GREAT LAKES THAT HAS POTENTIAL TO PRODUCE
A ROUND OF HEAVY SHOWERS/STORMS. BOTH THE GFS AND ECMWF SHOW
DIFFERENCES FROM RUN TO RUN AND WITH EACH OTHER...AS WELL AS
DIFFERENCES WITH THEIR ENSEMBLE MEANS.  AN EQUALLY WEIGHTED
FORECAST WAS USED AMONG BOTH THE OPERATIONAL AND MEANS UNTIL
BETTER AGREEMENT DEVELOPS. THE 06Z GFS WAS A SLOW OUTLIER SO THE
00Z RUN WAS USED INSTEAD.

ON THU-FRI...THE INITIAL LEAD WAVE CROSSES THE GREAT LAKES INTO
SOUTHEAST CANADA WITH THE FRONT EXTENDING ACROSS NORTHERN NEW
ENGLAND.  THE BETTER OVERLAP WITH THE MEANS FROM THE GEFS AND
ECMWF LED TO THESE SOLUTIONS TO PLACE LOW PRESSURE AND THE FRONTAL
AXIS/ORIENTATION.

THE MODELS/ENSEMBLES SHOW A WAVE ROTATING AROUND THE CLOSED LOW
MOVING EAST FROM ALBERTA...WITH THE WAVE PROGRESSING ACROSS THE
NORTHERN PLAINS FRI TO THE UPPER MS VALLEY AND UPPER LAKES SAT.
THIS WAVE SPURS DEVELOPMENT OF A WAVE OF LOW PRESSURE ALONG THE
FRONT ROUGHLY IN KS THU TO EASTERN IOWA FRI AND ACROSS LOWER MI
FRI NIGHT TO ONTARIO SAT MORNING.  ANOTHER ROUND OF HEAVY
SHOWERS/STORMS IS POSSIBLE WITH THIS WAVE.  WITH THIS WAVE THE 00Z
ECMWF BROKE CONTINUITY BY HAVING A HIGHER AMPLITUDE SHORTWAVE AND
DOWNSTREAM RIDGE...FORCING LOW PRESSURE TO BE FURTHER WEST THAN
THE PRIOR 12Z RUN AND 00Z ECMWF ENSEMBLE MEAN/GFS/GEFS MEAN.  A
LITTLE MORE WEIGHTING WAS GIVEN THE GEFS MEAN/ECMWF MEAN AND LESS
TO THE OPERATIONAL ECMWF AND GFS GIVEN THEIR OPERATIONAL
VARIABILITY RUN TO RUN.

ACROSS THE WESTERN US...THE AFOREMENTIONED WAVE MOVING EAST ACROSS
THE NORTHERN ROCKIES AND PLAINS WILL SUPPRESS THE UPPER LEVEL
RIDGE SOUTHWARD INTO MEXICO.  BY NEXT WEEKEND, UPPER LEVEL
TROUGHING DOWNSTREAM FROM A CLOSED LOW OVER THE NORTHERN PACIFIC
WILL MOVE ONSHORE AND INLAND...WITH LOW PRESSURE DEVELOPING ON THE
PLAINS DAY 7 SUN 02 JULY.  THE 00-06Z GFS WERE ON THE HIGHEST
AMPLITUDE SIDE OF THE GUIDANCE DISTRIBUTION OF THE 500 MB
WAVE...SO MORE WEIGHTING WAS GIVEN TO THE 06Z GEFS MEAN/00Z ECMWF
ENSEMBLE MEAN AND 00Z ECMWF. ADDITIONAL RAINFALL WILL DEVELOP IN
THE CENTRAL PLAINS TO UPPER MS VALLEY...WHICH COULD BE A PROBLEM
IF RAINFALL OCCURS IN AREAS IMPACTED FROM THE PRIOR WAVES CROSSING
THE REGION.


***SENSIBLE WEATHER***

THE MULTIPLE WAVES OF LOWER HEIGHTS/PRESSURE CROSSING FROM THE
CENTRAL PLAINS TO UPPER MS VALLEY AND UPPER GREAT LAKES SHOULD
PRODUCE AT LEAST A COUPLE OF ROUNDS OF HEAVY SHOWERS/STORMS.
SIGNIFICANT FLOODING POTENTIAL IS POSSIBLE IF THERE IS OVERLAP OF
BOUTS OF SHOWERS AND STORMS.  THIS WILL BE WATCHED CLOSELY DUE TO
MULTI-DAY TOTALS OF SEVERAL INCHES OF RAIN POSSIBLE FROM EASTERN
KANSAS AND NEBRASKA ACROSS NORTHERN MISSOURI AND IOWA TO NORTHERN
ILLINOIS...INCLUDING THE CHICAGO AREA.  AREAS OF EXCESSIVE
RAINFALL CAPABLE OF PRODUCING FLASH FLOODING APPEAR INCREASINGLY
LIKELY.

THE SUCCESSION OF UPPER TROUGHS CROSSING THE UPPER MS VALLEY AND
UPPER LAKES SHOULD HELP KEEP TEMPERATURES WELL BELOW NORMAL
THROUGH NEXT WEEKEND...WITH ANOMALIES NEAR 10 DEGREES BELOW NORMAL
RECURRING IN AREAS NEAR LAKE SUPERIOR IN THE ARROWHEAD OF MN TO
THE KEWEENAW PENINSULA/ UPPER PENINSULA OF MICHIGAN.

ANOMALIES SHOW FORECAST HIGH TEMPERATURES SLIGHTLY ABOVE AVERAGE
IN THE SOUTHWEST AND SOUTHERN GREAT BASIN TO THE SOUTHERN
ROCKIES...WITH AREAS OF 3-5 DEGREES ABOVE THE 30 YEAR MEAN
TEMPERATURES EXPECTED THROUGH THE WEEKEND. A WARM STRETCH IS ALSO
EXPECTED OVER THE MID ATLANTIC STATES LATER THIS WEEK THROUGH THE
WEEKEND...WITH 3-5 DEGREES ABOVE NORMAL COMMON.

PETERSEN


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