Prognostic Meteorological Discussion
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000
FXUS02 KWBC 221545
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1145 AM EDT SAT JUL 22 2017

VALID 12Z TUE JUL 25 2017 - 12Z SAT JUL 29 2017

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

THE MOST CONSTANT FEATURE DURING THE MEDIUM RANGE PERIOD WILL BE A
RIDGE OF HIGH PRESSURE THAT STARTS OVER THE FRONT RANGE OF THE
CENTRAL/SOUTHERN ROCKIES ON TUES. THIS FEATURE WILL STRENGTHEN
THROUGHOUT THE FORECAST PERIOD, BUILDING INTO THE FOUR CORNERS
REGION AND DOWNSTREAM INTO THE CENTRAL/SOUTHERN PLAINS AND LOWER
MS VALLEY BY NEXT SAT. ALSO AROUND THURS/FRI, THIS RIDGE WILL
BEGIN TO EXPAND NORTHWARD UP INTO THE NORTHERN PLAINS AND CENTRAL
CANADA.

MEANWHILE, THE WESTERLIES GENERALLY NEAR THE U.S./CANADIAN BORDER
WILL FEATURE A SERIES OF SHORTWAVES DURING THE NEXT WEEK. HOWEVER,
TOWARD THE END OF NEXT WEEK INTO THE WEEKEND, A FEW OF THESE
IMPULSES WILL HELP ESTABLISH AN AMPLIFIED ANOMALOUS UPPER TROUGH
OVER THE EAST, EXTENDING FROM QUEBEC TO THE COASTAL CAROLINAS.

FIRST, AN ELONGATED AREA OF TROUGHING EXTENDING ALONG THE NERN
COAST ON TUESDAY WILL QUICKLY LIFT OUT AND GIVE WAY TO MODEST
SHORTWAVE RIDGING IN THE WAKE. MEANWHILE LOOKING TOWARD CENTRAL
CANADA ON TUES, A BOWLING BALL MID TO UPPER LOW AND SHARPENING
BAND OF HEIGHT FALLS WILL ROLL DOWNSTREAM AND BEGIN TO INTRODUCE A
LARGE CLOSE VORTEX OVER NORTHERN QUEBEC AND HEIGHT FALLS ACROSS
THE GREAT LAKES INTO THE NERN QUAD OF THE COUNTRY. THIS WILL BE
FOLLOWED UP A REINFORCING PAC SHORT WAVE AND POLAR SHORT WAVE,
REACHING THE OH VALLEY AND UPPER/EASTERN GREAT LAKES RESPECTIVELY
BY NEXT SAT MORNING TO SET UP A AN ANOMALOUS UPPER TROUGH 1.5 TO 2
STANDARD DEVIATIONS BELOW AVG.

FINALLY THE LAST OF THE SHORT WAVE FEATURES WILL GENERALLY IMPACT
THE PACIFIC NORTHWEST WITH DOWNSTREAM RIDGING ACROSS THE CENTER OF
THE COUNTRY. THE FIRST SET OF HEIGHT FALLS WILL APPROACH THE PAC
NW WED/THURS, WHILE A WEAKNESS NEAR CENTRAL CA GETS CAUGHT UP IN
THE WESTERLIES AND LIFTS NORTH AND EAST THROUGH THE INTERIOR
NW/NORTHERN ROCKIES. THIS ASSORTMENT OF UPPER DYNAMICS WILL LIFT
OVER THE RIDGE AND BEGIN REACHING CENTRAL CANADA/UPPER MIDWEST
THURS/FRI. THE MAIN UPPER TROUGH AND DECAYING 500MB CIRCULATION
WILL SPREAD INTO THE PAC NW AND BRITISH COLUMBIA, WHILE RIDGING
DOWNSTREAM ENHANCES.

AS WHOLE, WPC THE GUIDANCE AND ENSEMBLES ARE IN SOLID AGREEMENT.
WPC USED ABOUT 80 PERCENT OPERATIONAL GUIDANCE OF THE 00Z ECMWF
WITH THE 00Z/06Z VERSIONS OF THE GFS THROUGH NEXT THURS. BY NEXT
FRI AND SAT, A GRADUAL INCREASE IN THE 00Z ECMWF MEAN AND 06Z GEFS
MEAN WAS NEEDED WITH THE STABLE OPERATIONAL ECMWF TO COUNTERACT
THE GROWING DETAIL DIFFERENCES WITH THE 00Z AND 06Z GFS. THUS 75
PERCENT OF THE BLEND THESE TWO DAYS IS ECMWF/EC MEAN AND GEFS MEAN
WITH ONLY 25 PERCENT TO THE GFS.


...WEATHER HIGHLIGHTS...

FORECAST TEMPERATURES ACROSS THE NATION SHOULD REMAIN WITHIN
ROUGHLY 10 DEGREES OF CLIMATOLOGY THROUGHOUT THE PERIOD. THE 5 DAY
WPC MEAN FOR MAX TEMPS SUGGEST THE COOL SPOTS BEING OVER THE
INTERIOR NORTHEAST WITH GRADUAL LOWERING UPPER HEIGHTS, ALONG THE
WEST COAST WITH ONSHORE FLOW OFF THE COOLER PACIFIC WATERS AND
ACROSS THE FOUR CORNERS REGION WITH CONTINUED MONSOONAL FEED INTO
THE REGION. THE HOT SPOTS FROM THE MEAN 5 DAY MAX TEMPS WILL BE
ACROSS THE CENTRAL/SOUTHERN PLANS UNDERNEATH THE DOME OF HIGH
PRESSURE AND ACROSS THE INTERIOR NW/NORTHERN ROCKIES/PLAINS WITH
THE ANTICIPATED UPPER RIDGING REACHING THE AREAS LATE NEXT WEEK.

ANOMALOUS MONSOONAL MOISTURE PUMPING INTO THE DESERT
SOUTHWEST/FOUR CORNERS REGION SHOULD KEEP THE REGION WET
THROUGHOUT THE PERIOD. ANTICYCLONIC FLOW AROUND THE RIDGE WILL
EVENTUALLY CARRY THESE FEATURES AND SURFACE COLD FRONT THROUGH THE
NORTH-CENTRAL U.S. AND THE GREAT LAKES/OH VALLEY INTO THE
EASTERN/CENTRAL AND SOUTHERN TIER OF THE COUNTRY WITH THE
POSSIBILITY OF MORE MESOSCALE CONVECTIVE SYSTEMS. ELSEWHERE...THE
SOUTHERN TIER OF THE COUNTRY SHOULD BE WET...ESPECIALLY DURING THE
PEAK IN THE DIURNAL HEATING CYCLE. SOME ENHANCEMENT IS LIKELY AS
ONE FRONTAL ZONE GIVES WAY TO ANOTHER.


MUSHER/RUBIN-OSTER


$$





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