Wintertime INstability inDEX Version 2'0

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Wintertime INstability inDEX Version 2.0
WINDEX V2.0

• An operational solution for assessing the
  potential for bursts of heavy snow within an
  atmosphere which is unstable with respect to
  shallow upright convection in winter

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WINDEX
Quantitative Parameters
For snow squalls with visibility less than 3 miles

• INSTABILITY - T1 T5 Temp Diff gt 10
• MOISTURE - R1 gt 50 percent
• Lifting Mechanism - LI increase of 8 or greater

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WINDEX
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Wintertime INstability inDEX Version 2
WINDEX V2.0
Over ten years later
- Significant advances in readily available
gridded data and software platforms in which to
display this data
- Model resolution has improved and has allowed
for better detection of mesoscale features
- Better understanding of cloud microphysics and
the role of dendritic growth and its ability to
produce efficient accumulating snowflakes.
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Wintertime INstability inDEX Version 2
WINDEX V2.0

• New parameters to help in forecasting bursts of
  heavy snow. Those instances where visibility is
  expected to be reduced to 1/2SM or less.

• Oh my gosh its like a blizzard outside !

• Improves on the original WINDEX study through the
  use of BUFKIT.. A software application tool
  for analyzing model data
• - Identify dendritic growth layers
• - Omega fields
• - Low Level Cape ( LLC )

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BUFKIT
http//wdtb.noaa.gov/resources/projects/BUFKIT

• Assess temperature and moisture profile to
  determine dendritic growth potential
• Low Level Cape ( LLC ) helps assess atmospheric
  buoyancy and snow intensity
• Assess Omega and associated lift in atmosphere on
  an hourly basis

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SNOWFLAKE PHYSICS
TEMPERATURE RANGE -12 TO -18 C
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WINDEX V2.0
THE NEW PARAMETERS

• INSTABILITY AND LIFT
• - Low Level Cape ( LLC ) of 30 or greater
• - If LLC of 30 or greater is not present,
  then Omega of
• -5 or less is needed

2. MOISTURE AND DENTRITIC GROWTH Within the
instability layer there is RH of 70 or greater
in the dendritic temperature range. ( -12C to
-18C )
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WINDEX V2.0
Snow bursts with visibility of 1/2SM or less can
be expected if

• T1-T5 temperature difference is 10C or greater
• LLC of 30 or greater, if not present, then an
  OMEGA of (-5) or less
• Within the instability layer, RH of 70 or
  greater in the maximum dendritic growth
  temperature range

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WINDEX SPIKE
Classic signature on BUFKIT of a heavy snow burst

• T1-T5 Temperature difference is 10C or greater
• Rapid spike or stretching of the vertical column
  of low level moisture accompanied by an omega of
  (-5) or less piercing through a dendritic growth
  layer of 70 or greater RH
• LLC of 30 or greater is preferred, but not
  necessary

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A CASE STUDY JANUARY 6TH 2004
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12Z ETA MODEL FOUS
TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5
BOS//515736 00423 132814 24009388 06000645315
09517 142817 15009385 12000482808 00415 152821
09958882 18000404306 00715 222822
03938579 24000365213 -2012 152820 98948677
30000405112 -5313 182719 97938677
36000525013 -4716 192818 01928577
42000665312 -3018 172909 04928679
48000423918 -1527 182921 10938579
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Limitations

• Scale of Phenomena - too small for models?
• Inconsistency of models and low level RH
• Spatial Coverage of snow squalls - can be
  scattered in nature
• Duration, and resulting accumulation

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Why is important to know state of the lower
layers of the Atmosphere in Winter?
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Final Thoughts

• Windex was originally designed as a simple
  forecast method to quickly assess the threat of
  instability snow showers or snow squalls along an
  approaching frontal boundary in winter.
• My hope is WINDEX V2.0 can now be used to further
  refine the potential intensity of those snow
  squalls
• The 850MB temperature range of between -10 to -15
  can be used as a corridor of where best location
  of most intense snow showers/squalls may exist if
  LLC is 30 or greater and there is a noticeable
  frontal boundary.

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