Prognostic Meteorological Discussion
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FXUS02 KWBC 210700
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST TUE NOV 21 2017

VALID 12Z FRI NOV 24 2017 - 12Z TUE NOV 28 2017

...RECORDS TEMPS FOR THE SW/WRN US AND A PROLONGED HEAVY RAIN/SNOW
PATTERN FOR THE NWRN US...


...OVERVIEW...

AN AMPLIFIED FLOW PATTERN WILL BE IN PLACE FOR THE NEXT WEEK AS
HIGHLIGHTED ALOFT BY A TROUGH OVER THE GULF OF AK/ERN PACIFIC...A
RIDGE OVER THE W-CENTRAL US...AND A TROUGH OVER THE ERN US. MUCH
OF THE PACIFIC NORTHWEST WILL REMAIN IN AN ACTIVE AND PROLONGED
WET PERIOD WITH COOLER TEMPS...AS WILL THE GREAT LAKES REGION AND
THE NORTHEAST. A VAST MAJORITY OF SRN CA...THE DESERT
SOUTHWEST...SRN ROCKIES AND SRN PLAINS WILL BE DRY WITH ABOVE
NORMAL TEMPS. SOME LOCATIONS WILL REACH OR EXCEED RECORD
TEMPS...PRIMARILY FOR LOCATIONS IN THE SOUTHWEST. THE CENTRAL U.S.
WILL BEGIN WITH ABOVE AVERAGE TEMPS PRIOR TO A WEEKEND COOLING
TREND. ADDITIONAL WET WEATHER IS LIKELY OVER FL ASTRIDE A SLOWLY
MOVING AND WAVY FRONTAL BOUNDARY.


...GUIDANCE/UNCERTAINTY PREFERENCES......

MODELS AND ENSEMBLES ARE IN GOOD AGREEMENT WITH THE LARGER SCALE
FLOW...BUT SIGNIFICANT DIFFERENCES REMAIN WITH THE TIMING AND
AMPLITUDE OF MUCH LESS PREDICTABLE EMBEDDED SMALLER SCALE SYSTEMS
THAT FOCUS YOUR LOCAL WEATHER. BLENDED REASONABLY CLUSTERED 12 UTC
GFS/ECMWF AND GEFS/ECMWF ENSEMBLES TO MITIGATE EMBEDDED SYSTEM
ERROR...LEANING A BIT MORE ON THE GEFS MEAN. THE 12 UTC GEFS MEAN
AND 12 UTC GUIDANCE OVERALL OFFERS SLIGHTLY MORE AMPLIFIED/LESS
PROGRESSIVE FLOW VS 18 UTC/00 UTC GUIDANCE. WATER VAPOR IMAGERY
SHOWS HIGHLY AMPLIFIED PACIFIC TO NOAM FLOW. WHILE SMALLER
WAVELENGTH SPACING WITH EMBEDDED IMPUSLES CAN KICK SYSTEMS
ALONG...GUIDANCE HISTORICALLY TENDS TO DE-AMPLIFY HIGHLY AMPLIFIED
FLOW TOO QUICKLY.


...WEATHER HIGHLIGHTS...

IT REMAINS THE CASE THAT HEAVY DAILY RAINS AND LOCALLY HEAVY
ELEVATION SNOWS WILL PERSIST OVER THE NWRN US FOR THE NEXT WEEK.
UPPER RIDGING SUPPORTS WELL ABOVE AVERAGE TEMPERATURES FROM THE
SOUTHWEST/SRN CA TO THE INTERMOUNTAIN WEST/ROCKY STATES. SOME
RECORD HIGHS/LOWS ARE LIKELY. MILD TEMPS WILL EXTEND EASTWARD
THROUGH THE PLAINS AHEAD OF A COLD FRONT THU AND FRI. COOLER TEMPS
WILL FILTER IN THIS WEEKEND AFTER THE FRONTAL PASSAGE. THERE IS A
GOOD CHANCE FOR APPRECIABLE PRECIPITATION ALONG THE GULF/SOUTHEAST
US COAST...ESPECIALLY FL...AS LOW PRESSURE CENTERS MEANDER ALONG A
SLOW MOVING FRONT. RAIN AND SNOW IS ALSO EXPECTED FOR THE GREAT
LAKES REGION WITH POTENT NRN STREAM CLIPPER PASSAGES AND
POST-SYSTEM LAKE EFFECT.

SCHICHTEL


$$





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