Overview of 14 December 1997 Surprise Mississippi Snowstorm

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Overview of 14 December 1997 Surprise Mississippi
Snowstorm

• Alan Gerard WFO
  Jackson,MS

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Introduction

• Occurred between 0600 UTC and 2100 UTC 14
  December 1997
• 4 to 8 inches of snow in a swath across central
  Mississippi
• Associated with an upper low passing to the
  south of the area

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Introduction (continued)

• Heaviest snow so early in the season at Jackson
  Intl Airport (4.8 inches)
• One of the largest snowfalls in Mississippi since
  1929

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The View from above...
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Overview and Forecasts

• Synoptic pattern through the week characterized
  by a large upper low to the west of MS which
  medium range models were forecasting to move
  slowly east
• NWSFO JAN forecast carried threat of snow for
  several days prior to the event

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Overview and Forecasts

• As the event approached, short range models
  (particularly the Eta) backed off of the
  precipitation threat
• Zone forecasts issued the day of the event
  indicated little in the way of snow

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ZONE FORECAST NWS JACKSON
MS 420 PM SAT DEC 13
1997.TONIGHTCONSIDERABLE CLOUDINESS WITH A FEW
SPRINKLES OR FLURRIES. LOW 30 TO 35. NORTHWEST
WIND 5 TO 10 MPH BECOMING NORTH..SUNDAYBECOMING
PARTLY CLOUDY. A FEW SPRINKLES POSSIBLE. HIGH 45
TO 50. NORTH WIND INCREASING TO 10 TO 20
MPH..SUNDAY NIGHTPARTLY CLOUDY. LOW NEAR
30..MONDAYPARTLY CLOUDY. MILDER WITH THE HIGH
55 TO 60.
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Synopsis and Model Performance

• Main synoptic feature associated with this event
  was a deep low in the middle and upper
  troposphere
• Model performance in handling this feature had a
  major impact on forecasts for the event

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• 12Z 13 Dec Eta run had a 160 m error for the
  depth of the 500 mb low at the 24 hour forecast
  period
• Other models were better, but still had poor
  forecasts (15Z Meso-eta 110 m, 12Z NGM 75 m, 12Z
  AVN 40 m)

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• 00 H Eta Model 1200 UTC 14 December 1997
  1000-500 mb Mean RH and Thkns

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Synopsis and Model Performance (contd)

• 12Z 13 Dec Eta and NGM models showed no QPF
  amounts across MS during the time of the snow
  event
• 15Z 13 Dec Meso-eta and 12Z 13 Dec AVN models did
  show some QPF amounts, but too light and too far
  southeast

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• 1500 UTC 13 Dec 1997 Meso-eta 850 mb T, 2M T, and
  12hr QPF Valid 1200 UTC 14 Dec 1997

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Synopsis and Model Performance (contd)

• This event was highly unusual synoptically in
  Mississippi
• A recently completed climatological study
  indicated that no significant snow events had
  occurred in central Mississippi due to an upper
  low passing south of the area in the last 50 years

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• Jackson, MS Composite Snow Sounding (Events 1)

• Composite Jackson Snow Raob (Events 1)

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• 1200 UTC 14 December 1997 JAN Raob

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Preliminary Summary (contd)

• The combination of the unusual nature of the
  event and the lack of model signals led to only a
  minor mention of snow in the forecast for this
  event
• The 0000 UTC 14 Dec model runs showed much more
  clearly the snow potential this, however, was
  too late to provide any significant lead time

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Preliminary Summary

• The snow event of 14 December 1997 was a highly
  unusual event synoptically
• Model guidance from the 13 December 1997 model
  suite showed very few clear signals that a major
  winter storm was impending for the 14th

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COMET Partners Project with Jackson State
University
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Concepts Examined

• Water Vapor/IR imagery
• Long range versus short range snow expectations
  and recent busts
• Early season climatology say no
• Cold, no moisture, no features...
• Whats Eta showing in frontogenesis?
• Watch/Warning/Advisory time-frame

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Water Vapor imagery

• 2315 UTC 12/13
• Moisture pool to the east
• Upper low digging into region

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Deformation zone?

• IR View
• Per work by Beckman
• Was visible in imagery before snow started

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Diagnosis

• 250 mb Fronto-genesis
• Eta 12hr Forecast valid at 12Z 12/14

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Diagnosis

• 290K Surface
• Strong Pressure Advection
• Axis of higher mixing ratios
• Clearly evident on 00Z model runs not on the 12Z
  model runs

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Would finer scale modeling have helped?
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Mesoscale Model Results

• Apply MM5
• 20 km outer grid 9 km inner grid
• Runs for 12Z Saturday and 00Z Sunday (forecast
  versus nowcast)
• Intent Would it have made a difference?
• Investigate moisture and vertical motion fields

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Ultimatelywould snow have been forecast?

• Yesmore likely...
• Limited amounts and areal coverage
• Perhaps would have allowed for some advance
  notice...

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Conceptual Model framework...

• Upper level frontogenesis
• Think Carlson conveyor belts
• Think of active layer from 700mb upwards
• More common than one might think???

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Conclusions

• Mesosnowfall event of 14 December 2001 was a
  highly unusual event in Mississippi
  climatologically
• Early in the winter season
• Associated with upper low
• Numerical models operational at the time provided
  few clues that an event would occur

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Conclusions

• COMET Partners Project showed some tools that
  could have been used...
• Monitoring satellite images for development of
  deformation zone and moisture pools with
  greater moisture than implied by models
• Monitoring upper level frontogenesis
• Use of mesoscale models may have improved
  numerical forecasts
• Looking at developing conceputal model of this
  type of event

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Results

• Look for paper in upcoming issue of Weather and
  Forecasting