Prognostic Meteorological Discussion
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000
FXUS10 KWNH 050418
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 AM EDT WED AUG 05 2015

VALID AUG 05/0000 UTC THRU AUG 08/1200 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO DEGRADE THEIR SHORT
RANGE FORECASTS.


CLOSED LOW MOVING INTO THE WEST FRIDAY
DEEP CYCLONE APPROACHING HAIDA GWAII LATE FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE GUIDANCE REMAINS IN GOOD AGREEMENT WITH THESE SYSTEMS.


POSSIBLE CLOSED LOW NEAR THE CENTRAL US/CAN BORDER FRI
PRECEDING SHORTWAVE MOVING INTO LAKE SUPERIOR FRI NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: CLOSE TO THE CANADIAN
CONFIDENCE: BELOW AVERAGE

THE GUIDANCE SHOWS CONSIDERABLE SPREAD WITH THIS SYSTEM.  THE 00Z
GFS IS THE MOST NORTHERLY WHILE THE 12Z UKMET IS THE MOST
SOUTHERLY AND ONE OF THE STRONGER SOLUTIONS WITH THE SHORTWAVE
KICKING OUT AHEAD OF IT.  THE 12Z ECMWF RESEMBLED THE 12Z UKMET AT
THE SURFACE WITH THE DEPTH OF THE WAVE MOVING INTO LAKE SUPERIOR
EARLY SATURDAY, WHICH WAS PROBLEMATIC.  ANY SYSTEMS MOVING OVER
THE TOP OF THE SLOWLY AMPLIFYING RIDGE IN THE SOUTHERN PLAINS
SHOULD NOT BE OVERLY STRONG MOVING OVER ITS APEX DUE TO
SUPERGEOSTROPHIC/QUICK FLOW, WHICH RULES OUT THE UKMET/ECMWF FROM
CONSIDERATION.  THE 12Z GLOBAL ENSEMBLE GUIDANCE FAVORED A
SOLUTION CLOSE TO THE 12Z CANADIAN, WHICH IS PREFERRED WITH BELOW
AVERAGE CONFIDENCE.


EASTERN TROUGH
SURFACE LOW NEAR THE EAST COAST SATURDAY MORNING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: CLOSE TO THE NAM
CONFIDENCE: AVERAGE

THE 12Z UKMET WAS WEAKER THAN THE OTHER GUIDANCE WITH THIS TROUGH
-- ONE OF ITS USUAL BIASES.  BOTH THE 12Z CANADIAN/12Z UKMET
APPEAR TO GENERATE A CONVECTIVE WAVE WHICH DEEPENS AS IT PASSES
THE 40N 70W BENCHMARK -- THEIR USUAL BIAS.  OTHERWISE, THE 12Z
GLOBAL ENSEMBLE GUIDANCE IS SPREAD BETWEEN THE NORTHERLY 12Z ECMWF
(WHICH SOMETIMES HAS THIS BIAS THREE DAYS INTO THE FUTURE WITH
COASTAL LOWS) AND THE SOUTHERLY 00Z GFS.  A COMPROMISE OF THE TWO,
NOT FAR FROM THE 00Z NAM, APPEARS BEST WITH AVERAGE CONFIDENCE.


...MODEL TREND GRAPHICS AT
www.wpc.ncep.noaa.gov/html/model2.shtml...

...500 MB FORECASTS AT
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...

ROTH
$$





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