Prognostic Meteorological Discussion
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FXUS02 KWBC 231547
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1146 AM EDT SUN JUL 23 2017

VALID 12Z WED JUL 26 2017 - 12Z SUN JUL 30 2017

...PATTERN OVERVIEW/GUIDANCE EVALUATION/PREFERENCES...

THE MEAN LARGE SCALE PATTERN STARTS OFF WITH A MEAN RIDGE OVER THE
FOUR CORNERS REGION INTO THE CENTRAL/SOUTHERN PLAINS, WHILE MAIN
WESTERLIES AND UPPER JET REMAIN NEAR THE US/CANADIAN BORDER OR
EVEN NORTH. HOWEVER BY D+8, THE PATTERN TRANSITIONS FROM TROUGH
OVER THE PAC, ANOMALOUS RIDGE OVER THE WEST INTO WESTERN CANADA
AND A AMPLIFIED UPPER TROUGH EXTENDING FROM EASTERN CANADA SOUTH
TO THE SOUTHEAST/EAST-CENTRAL GULF COAST STATES.

THE SYNOPTIC-SCALE PATTERN STARTS OFF WITH UPPER DYNAMICS
DEPARTING THROUGH THE CANADIAN MARITIMES AND TRAILING
COLD/STATIONARY FRONT EXTENDING BACK INTO THE SOUTHEAST. MEANWHILE
A RATHER POTENT SHORT WAVE OVER CENTRAL CANADA WITH TRAILING COLD
FRONT DROPPING THROUGH UPPER MIDWEST/UPPER MS VALLEY WILL ROLL
DOWNSTREAM AND SLICE THROUGH THE NERN QUAD OF THE COUNTRY
THURS/FRI. THIS WILL HELP LOWER UPPER HEIGHTS OVER THE EASTERN
PORTION OF THE COUNTRY, WHILE HEIGHTS BEGIN TO BUILD NORTHWARD
INTO THE NRN INTER-MOUNTAIN WEST AND NORTHERN ROCKIES. FOLLOWING
THIS SYSTEM WILL BE AN ASSORTMENT OF SMALL SCALE SHORT WAVE
IMPULSES ALONG THE NRN STREAM AND ONE WEAKNESS THAT ORIGINATES
FROM THE CENTRAL WEST COAST. THIS SHOULD HELP SLOWLY USHER THE
MAIN 500MB TROUGH AXIS TO JUST OFFSHORE OR ALONG THE NERN SEABOARD
TO THE OH/TN VALLEYS AND SOUTH, AS BLOCKING UPPER RIDGE DOWNSTREAM
OF THE ATLANTIC PROHIBITS FAST PROGRESSION AND A FURTHER
AMPLIFICATION OF THE EASTERN TROUGH. MEANWHILE THE FINAL SYSTEM
ALONG THE WESTERLIES WILL BE THE UPPER TROUGH DIGGING SOUTH AND
EAST TOWARD BRITISH COLUMBIA, WHILE WEAKNESS NEAR NRN CA BEGINS TO
FEEL INFLUENCE OF WESTERLIES. THIS WHOLE SYSTEM ALONG WITH OTHER
SMALL SCALE MARITIME IMPULSES LIFT NORTH AND EAST TOWARD CENTRAL
CANADA BEFORE DRIVING ANOTHER DECENT COLD FRONT INTO THE UPPER
MIDWEST FOR NEXT WEEKEND. THIS ALLOWS UPPER RIDGE BUILDING OVER
THE ENTIRE WESTERN CONUS TO BEGIN EXPANDING NORTH INTO WESTERN
CANADA. SO BY THE END OF THE FCST PERIOD BASED ON THE EC MEAN, A 1
TO 2 STANDARD DEVIATION OF ABOVE AVG 500MB HEIGHTS WILL EXTEND
FROM THE ENTIRE WEST INTO WESTERN CANADA, WHILE A NEG ANOMALY OF 1
STANDARD DEVIATION BELOW AVG HEIGHTS SETTLE INTO THE SERN SECTION
OF THE COUNTRY.

THE GUIDANCE INCLUDING ALL OPERATIONAL GUIDANCE CAPTURE THIS
SCENARIO INTO NEXT WEEKEND WITH ONLY SLIGHT SPREAD AT BEST. THIS
PROVIDED WPC CONFIDENCE IN USING 80% OPERATIONAL GUIDANCE THROUGH
D5, 60% D6 AND 40% D7. THUS MODELS USED WERE 00Z ECMWF, 00Z-06Z
GFS AND 00Z EC MEAN/06Z GEFS MEAN THROUGHOUT THE FORECAST PERIOD.


...WEATHER HIGHLIGHTS...

FORECAST HIGH TEMPERATURE ANOMALIES FOR THE WHOLE 5 DAY PERIOD
WILL FEATURE WELL ABOVE AVG HIGHS FROM THE WEST INTO THE NORTHERN
ROCKIES/PLAINS, AS COASTAL SECTIONS WILL REMAIN NORMAL TO SLIGHTLY
BELOW AVG. WHILE HIGHS SHOULD BE GENERALLY ABOVE AVG FOR A LARGE
PORTION OF TX. FOR THE REST OF THE COUNTRY, HIGHS WILL GENERALLY
BE NEAR AVG OR SLIGHTLY BELOW AVG. THE HIGHEST PROBABILITY FOR
BELOW AVG HIGHS WILL BE PARTS OF THE FOUR CORNERS REGION AND
SOUTHEAST WITH POSSIBLE DAILY RAIN/CONVECTION.

REGARDING PRECIPITATION...OTHER THAN THE FOUR CORNERS REGION WILL
CONTINUED MONSOONAL FETCH, PRECIP CHANCES WILL DWINDLE WITH THE
BUILDING UPPER RIDGE. MEANWHILE, THE MOST OPPORTUNE CHANCES FOR
HEAVY RAINFALL WILL BE EAST OF THE ROCKIES GENERALLY INVOF AND
ADVANCE OF EACH FRONTAL SYSTEM PROGGED.


MUSHER



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