Preliminary Forecasts
Issued by NWS

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000
FXUS02 KWNH 270719
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
218 AM EST FRI FEB 27 2015

VALID 12Z MON MAR 02 2015 - 12Z FRI MAR 06 2015

...GUIDANCE/UNCERTAINTY ASSESSMENT...

MEDIUM-RANGE MODEL AND ENSEMBLE FORECAST SPREAD HAS OVERALL
DECREASED WITH THE LATEST COUPLE RUN CYCLES...BOLSTERING OVERALL
FORECAST CONFIDENCE. MODEL GUIDANCE OFFERS A REASONABLY SIMILAR
MID-LARGER SCALE PATTERN EVOLUTION...BUT BY NATURE THE MODELS
OFFER UNCERTAIN EMBEDDED SYSTEM TIMING DIFFERENCES AND LARGER RUN
TO RUN CONTINUITY ISSUES THAN ENSEMBLE MEANS.

ACCORDINGLY...THE WPC MEDIUM-RANGE PRODUCT SUITE HAS BEEN
PRIMARILY DERIVED FROM A BLEND OF THE REASONABLY COMPATABLE 06 UTC
GEFS MEAN AND 00 UTC NAEFS/ECMWF ENSEMBLE MEANS. HEAVIER WEIGHTING
WAS PLACED ON ECMWF ENSEMBLES IN THIS BLEND FOR AN OVERALL
SOLUTION SLIGHTLY ON THE MORE AMPLIFIED/LESS PROGRESSIVE SIDE OF
THE FULL ENVELOPE OF SOLUTIONS ACROSS THE LOWER 48. THIS TAKES
INTO ACCOUNT THE HIGH AMPLITUDE OF THE UPSTREAM MID-UPPER LEVEL
ERN PACIFIC TO ALASKAN RIDGE THAT IS COMMONLY SUPPORTED.

...PATTERN OVERVIEW AND SENSIBLE WEATHER HIGHLIGHTS...

MID-UPPER LEVEL TROUGHING AND SURFACE LOW PRESSURE DUG INTO THE
NERN US LIFTS TO THE CANADIAN MARITIMES MON/TUE. COOLING SURFACE
BASED HIGH PRESSURE SINKS ACROSS THE CENTRAL THEN ERN US IN THE
WAKE OF A LEAD AND PCPN FOCUSING FRONTAL SYSTEM.

UPSTREAM...AN AMPLIFIED SRN STREAM MID-UPPER LEVEL TROUGH MON/TUE
OVER THE SWRN US WILL FOCUS A SIGNIFICANT WINTER PCPN THREAT WITH
HEAVIER SNOWS ALSO WORKING INTO THE S-CENTRAL ROCKIES AS AIDED BY
UPSLOPE FETCH...LINGERING MIDWEEK.

MEANWHILE...SIGNIFICANT NRN STREAM IMPULSE DIGGING IS EXPECTED
OVERTOP THROUGH WRN CANADA TO THE LEE OF THE AMPLIFIED ERN
PACIFIC/ALASKAN RIDGE. THIS TROUGHING FEEDS INTO THE N-CENTRAL US
AND UNCERTAIN EXTENT OF SUBSEQUENT PHASING WITH SRN STREAM
ENERGIES LEADS INTO AN OVERALL TRANSLATION OF A MEAN TROUGH OVER
THE CENTRAL THEN NERN STATES MID-LATER NEXT WEEK. COLD NRN STREAM
HIGH PRESSURE SINKS ACROSS THE WRN THEN CENTRAL US DURING THIS
PERIOD...EVENTUALLY SPREADING ACROSS THE SRN AND ERN US. A LEAD
AND WAVY FRONT ASSOCIATED WITH PIECES OF ENERGY EJECTING ENEWD OUT
FROM THE SWRN US WILL ACT TO POOL MOISTURE AND FOCUS A POTENTIALLY
LARGE SWATH OF MODERATE TO HEAVIER PCPN MON-WED ACROSS THE CENTRAL
THEN ERN US IN ADVANCE AND WRAPPING BACK INTO THE TRAILING MAIN
ARCTIC AIRMASS. THIS OFFERS YET ANOTHER SIGNIFICANT WINTER PCPN
THREAT ON THE NRN PERIPHERY OF THE OVERALL PCPN SHIELD AND HEAVY
WARM SECTOR RAINS WITH INCREASED GULF INFLOW.

SCHICHTEL

$$





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