Prognostic Meteorological Discussion
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895
FXUS02 KWBC 211359
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
859 AM EST TUE FEB 21 2017

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

OVERVIEW
~~~~~~~~
DOWNSTREAM OF A STRENGTHENING REX BLOCK OVER THE PACIFIC,
TROUGHING IS EXPECTED TO STRENGTHEN FROM NUNAVUT INTO THE WESTERN
STATES WHILE POSITIVE MID-LEVEL ANOMALIES/WEAK RIDGING HOLDS FIRM
ALONG THE SOUTHEAST COAST.  THE GUIDANCE IS AGREEABLE WITH THE
GENERAL FLOW PATTERN.


MODEL EVALUATION/PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SINCE YESTERDAY MORNING, THERE HAVE BEEN SIGNIFICANT SURFACE
PRESSURE CHANGES RELATING TO THE DEPTH OF THE UPPER TROUGH
EXTENDING INTO THE EASTERN PACIFIC.  ALL THE GUIDANCE FLIPPED
TOWARDS A SHARPER SOLUTION ALOFT, WHICH LED TO A SLOWER EVOLUTION
IN REGARDS TO LOW PRESSURE MOVING ACROSS THE WEST INTO THE PLAINS
-- ALMOST A DAY SLOWER THAN INDICATED YESTERDAY -- WHICH DOESN`T
INSPIRE CONFIDENCE.  HOWEVER, THE CURRENT GUIDANCE DOES RESEMBLE
CONTINUITY FROM NIGHT SHIFT.  THE 00Z UKMET AND 00Z CANADIAN WERE
SLOWER THAN THE GFS/ECMWF DETERMINISTIC AND ENSEMBLE MEAN GUIDANCE
WITH A PAIR OF SYSTEMS (THE SYSTEM CROSSING THE GREAT LAKES EARLY
AND MOVING INTO THE WEST LATE), SO THEY WERE NOT CONSIDERED USEFUL.

THE PRESSURES, WINDS, AND 500 HPA HEIGHTS WERE BASED ON A
COMPROMISE OF THE 06Z GFS/00Z ECMWF EARLY ON BEFORE INCLUDING
INCREASING AMOUNTS OF THE 00Z ECMWF AND 00Z NAEFS ENSEMBLE MEANS
FROM SUNDAY INTO NEXT TUESDAY.  THE BLEND FOR THE TEMPERATURES,
PRECIPITATION CHANCES, CLOUDS, DEW POINTS, AND WEATHER GRIDS WAS
MORE ENSEMBLE MEAN HEAVY.  THE PRELIMINARY DAYS 4-7 QPF IS A ROUGH
COMPROMISE OF THE 00Z ECMWF AND 06Z GFS FOR THE TIME BEING.
SHOULD THE 12Z GFS MASS FIELDS APPEAR USEFUL, IT COULD BE INCLUDED
IN THE QPF MIX.


WEATHER HIGHLIGHTS/THREATS
~~~~~~~~~~~~~~~~~~~~~~~~~~
IN PRINCIPLE, THE FORECAST IS STILL ON TRACK FOR THE STORM
TRACKING NORTHEAST FROM THE MIDWEST FRIDAY INTO THE WEEKEND.  THE
SPC OUTLOOK MAINTAINED A FOCUS ON AN AREA OVER AND AROUND INDIANA
AS BEST POTENTIAL FOR SEVERE CONVECTION IN THE FRI-FRI NIGHT
PERIOD.  CONSULT LATEST SPC PRODUCTS FOR UPDATED INFO.  SNOW TO
THE NORTHWEST OF THE SURFACE LOW COULD BE HEAVY AT TIMES WITHIN
THE SYSTEM`S COMMA HEAD, WITH AREAS OF MODERATE TO HEAVY RAIN
EXPECTED AHEAD OF THE COLD FRONT CROSSING THE EAST.  SOME
LOCATIONS MAY SEE STRONG WINDS.  ALONG THE WEST COAST, THE LATEST
EVOLUTION SFC/ALOFT SHOWN IN MOST GUIDANCE HAS INCREASED THE
POTENTIAL FOR A PERIOD OF HEAVIER RAIN/HIGHER ELEVATION SNOW
FOCUSED OVER CALIFORNIA (WHICH THE GUIDANCE BEGAN TO TREND TOWARDS
12Z ON MONDAY), MOST LIKELY DURING THE WEEKEND, WITH A PERIOD OF
STRONG WINDS ALSO A POSSIBLE THREAT.  SOME MOISTURE WILL EXTEND
INTO FAVORED TERRAIN OF THE INTERIOR WEST/ROCKIES.  BEYOND THE
ROCKIES, ONE OR MORE AREAS OF PCPN MAY DEVELOP WITH THE AID OF
IMPULSES EMBEDDED WITHIN AN INCREASINGLY SOUTHWEST FLOW ALOFT AS A
WAVY FRONT GRADUALLY LIFTS NWD OVER THE CENTRAL AND EASTERN
STATES.  NORTHERN AREAS MAY SEE SOME WINTRY PRECIPITATION WITH
RAIN EXPECTED FARTHER SOUTH.

ON FRIDAY, MUCH OF THE ERN U.S. SHOULD SEE TEMPS 15-30F ABOVE
NORMAL WITH WARMTH HANGING ON INTO SAT ALONG THE EAST COAST.
EXPECT SOME LOCATIONS TO SEE RECORD WARM VALUES FOR HIGH AND LOW
TEMPERATURE READINGS.  IN SPITE OF A SIGNIFICANT COOLING TREND,
TEMPERATURES SHOULD ONLY DROP TO NEAR OR SLIGHTLY BELOW NORMAL
LEVELS BRIEFLY BEFORE REBOUNDING ABOVE NORMAL AGAIN EARLY NEXT
WEEK.  THE WARMING TREND SHOULD START ON SUN OVER THE SOUTHERN
PLAINS.  MUCH OF THE WEST AND INTO THE N-CNTRL PLAINS WILL LIKELY
SEE BELOW NORMAL TEMPS WITH SOME LOCATIONS SEEING NEGATIVE 10-15F+
ANOMALIES ONE OR MORE DAYS.

ROTH/RAUSCH
$$





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