Prognostic Meteorological Discussion
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FXUS02 KWBC 190700
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT THU OCT 19 2017

VALID 12Z SUN OCT 22 2017 - 12Z THU OCT 26 2017

...HEAVY RAINFALL POTENTIAL IN THE ERN U.S. WITH RECORD HEAT IN
THE SOUTHWEST...


...PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENTS...

MODELS AND ENSEMBLES AGREE TO DEVELOP AN AMPLIFIED FLOW PATTERN
OVER THE LOWER 48 NEXT WEEK. A LEAD CLOSED LOW POTENTIALLY PEELING
OFF FROM THE FLOW MAY AFFECT THE GULF COAST EARLY NEXT WEEK AS
DEEPENED MOISTURE FROM THE GULF OF MEXICO THEN ATLANTIC FEEDS
INCREASINGLY INLAND. GIVEN SUBSEQUENT PHASING WITH A DIGGING NRN
STREAM TROUGH...A RESULTANT NEGATIVELY-TILTED TROUGH LEADS TO
500MB HEIGHT DEPARTURES UPWARDS OF 3 STANDARD DEVIATIONS BELOW
NORMAL BY THE MIDDLE OF NEXT WEEK OVER THE EAST. THIS SCENARIO
OFFERS WIDESPREAD HEAVY RAIN POTENTIAL OVER THE E-CENTRAL TO ERN
US. PREFER A COMPOSITE 12 UTC GFS/ECMWF AND GEFS/ECMWF ENSEMBLE
MEAN GIVEN RECENT MODEL UNCERTAINTY.

AS A SHARP NEGATIVE HEIGHT ANOMALY ENCOMPASSES THE ERN THIRD OF
THE NATION...PRONOUNCED UPSTREAM RIDGING OVER THE WEST WILL USHER
IN WARM/DRY CONDITIONS TO THE REGION. A COMPOSITE GUIDANCE
SOLUTION SEEMS REASONABLE INTO TUE...BUT PREFER TO LEAN WEIGHTING
TOWARD THE MORE AMPLIFIED/LESS PROGRESSIVE ECMWF AND ECMWF
ENSEMBLE MEAN UPSTREAM OVER THE PACIFIC TO THE WEST COAST BY LATER
NEXT WEEK WITH THE ANTICIPATION OF WELL DOWNSTREAM EFFECTS FROM
THE ENTRAINMENT OF WRN PACIFIC TYPHOON LAN INTO THE WESTERLIES.


...SENSIBLE WEATHER HIGHLIGHTS/THREATS...

ZONAL FLOW OVER THE NWRN US SUPPORTS SOME HEAVY PRECIPITATION OVER
THE OROGRAPHICALLY FAVORED LOCATIONS OF THE OLYMPICS AND CASCADES
THIS WEEKEND. THIS WESTERLY FLOW REGIME SHOULD BE DEVOID OF
APPRECIABLE COLD AIR WHICH MAINTAINS SNOW OVER THE HIGHER
ELEVATIONS. WITH HEIGHTS BUILDING IN TIME...THE ACTIVE STORM TRACK
WILL LIFT UP INTO BRITISH COLUMBIA NEXT WEEK. FARTHER
EAST...WIDESPREAD RAINFALL SHOULD BE ONGOING WITH A WAVY COLD
FRONT MOVING THROUGH THE E-CENTRAL U.S. SUN/MON. ACTIVITY WILL
PICK UP IN COVERAGE AND INTENSITY AS THE SRN STREAM SHORTWAVE
DEVELOPS WITH HEAVIER AMOUNTS POSSIBLE IF THE SYSTEM SLOWS. A
HEAVY RAINFALL SIGNAL THEN EXISTS FOR THE ENTIRE ERN SEABOARD
OCTOBER 23-25 ONCE THE UPPER TROUGH STRENGTHENS AND A SERIES OF
SURFACE LOWS FORM. THERE IS A THREAT OF RUNOFF ISSUES.

SCHICHTEL

$$





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