# Presentation: 827273

## Overview of 14 December 1997 Surprise Mississippi Snowstorm

- Alan Gerard                                WFO Jackson,MS

## 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

## Introduction (continued)

- Heaviest snow so early in the season at Jackson Int’l Airport (4.8 inches)
- One of the largest snowfalls in Mississippi since 1929

## The View from above...

## 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

## 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

## ZONE FORECAST                        NWS JACKSON MS                  420 PM SAT DEC 13 1997.TONIGHT...CONSIDERABLE CLOUDINESS WITH A FEW SPRINKLES OR FLURRIES.  LOW 30 TO 35. NORTHWEST WIND 5 TO 10 MPH BECOMING NORTH..SUNDAY...BECOMING PARTLY CLOUDY. A FEW SPRINKLES POSSIBLE. HIGH 45 TO 50. NORTH WIND INCREASING TO 10 TO 20 MPH..SUNDAY NIGHT...PARTLY CLOUDY. LOW NEAR 30..MONDAY...PARTLY CLOUDY. MILDER WITH THE HIGH 55 TO 60. 

## 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

## Slide 11

- 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)

## Slide 13

## Slide 14

## Slide 15

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

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

## Synopsis and Model Performance (cont’d)

- 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

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

## Synopsis and Model Performance (cont’d)

- 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

## Jackson, MS Composite Snow Sounding (Events 1”+)

- Composite Jackson Snow Raob (Events 1”+)

##  1200 UTC 14 December 1997 JAN Raob

-  1200 UTC 14 December 1997 JAN Raob

## Preliminary Summary (cont’d)

- 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

## 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

## COMET Partners Project with Jackson State University

## 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...
- What’s Eta showing in frontogenesis?
- Watch/Warning/Advisory time-frame

## Water Vapor imagery

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

## Deformation zone?

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

## Diagnosis

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

## Diagnosis

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

## Would finer scale modeling have helped?

## 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

## Ultimately...would snow have been forecast?

- Yes...more likely...
- Limited amounts and areal coverage
- Perhaps would have allowed for some advance notice...

## Conceptual Model framework...

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

## 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

## 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

## Results

- Look for paper in upcoming issue of *Weather and Forecasting*