January 16, 2003 Winter Storm

Event Summary
National Weather Service, Raleigh NC

January 16, 2003 Winter Storm

Event Overview - Snow ( 2-6 inches) began falling across the North Carolina mountains on 16 January 2003. A trace to 3 inches of snow fell across central North Carolina during the evening of 16 January 2003. The snow/rain line was oriented from southwest to northeast, generally across the dividing line between the Piedmont and Coastal Plain. A narrow transition zone of mixed freezing rain separated areas with accumulating snow from areas with just rain. No significant glazing from the mixed freezing rain was reported.

Synoptic Overview - The snow was produced by a quick moving upper level disturbance that tracked from the northern Pacific coast into the northern plains. From there, the disturbance charged southeastward into Arkansas before tracking eastward toward North Carolina. A weak surface low accompanied the upper level system tracking from Arkansas through Tennessee during the day on the 16th. On the evening of the 16th, cyclogenesis shifted from east Tennessee into central South Carolina.

Snow Accumulation Map - The largest snowfall totals were in the mountains closer to the track of the upper level vorticity impulse. The eastern extent of the snow was limited by low level warm air advection ahead of the developing surface low in central South Carolina and with exiting surface high pressure off the Virginia coast.

Liquid Equivalent Precipitation - The ratio of snow to rain was 10 to 1 east of the mountains. In the mountains, the ratio was higher. The narrow yellow band of lesser amounts across the far western Piedmont is small in scale. Its cause is subject to speculation; however the band could be, in part, a reflection of the better dynamics associated with the vorticity impulse passing to the northwest and the favorable low level baroclincity setting up southeast of the lesser amount area. For a resembling pattern covering a much larger scale - refer to the Dec 2-3 2000 snow event case.

Visible Satellite Imagery from 1401Z Friday January 17, 2003 - Shows those areas in North Carolina receiving measurable snow.

Upper Air Maps

00Z 2003/01/17 300 mb Heights, Isotachs, and Winds (kts) - Eta Initialized Data
Other than providing a source of lift, the strong west to east jet across North Carolina limited snowfall amounts. The fast moving upper winds confined the precipitation to about a 6 hour period. The dry air intrusion accompanying the jet produced a sharp back edge to the precipitation. The rapid drying aloft may have also contributed to snow ending as light freezing rain in some locations. As the depth of the moisture column diminished from aloft, the temperatures through the cloud deck warmed above the preferred temperatures cold enough to produce snow crystals (generally about -10 C in central NC).

00Z 2003/01/17 300 mb Heights, Isotachs, and Winds (kts) - Eta Initialized Data, - Click to enlarge

(Click the image to enlarge.)

00Z 2003/01/17 500 mb Heights and Geostrophic Absolute Vorticity - Eta Initialized Data
Lift associated with the 500 mb short-wave and the accompanying vorticity impulse was best realized in the mountains of North Carolina where 2 - 6 inches of snow fell.

00Z 2003/01/17 500 mb Heights and Geostrophic Absolute Vorticity - Eta Initialized Data, - Click to enlarge

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00Z 2003/01/17 700 mb Heights, Relative Humidty and Omega - Eta Initialized Data
Precipitation (see radar imagery) was marked well at 00z 1/17/03 by the maximum omega field and the best 700 mb moisture.

00Z 2003/01/17 700 mb Heights, Relative Humidty and Omega - Eta Initialized Data, - Click to enlarge

(Click the image to enlarge.)

00Z 2003/01/17 850 mb Heights, Temperatures (deg. C) and Winds (kts) - Eta Initialized Data
Winds at 850 mb show the limited amount of moisture inflow into system from the Gulf of Mexico which in turned limited the snowfall amounts. Note the 0 degree C isotherm at 850 mb is oriented in the same direction and close to the location of the snow/rain line in North Carolina.

00Z 2003/01/17 850 mb Heights, Temperatures (deg. C) and Winds (kts) - Eta Initialized Data, - Click to enlarge

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Selected Photographs from the Storm

Various images of the Raleigh-Durham area after the winter storm (Click the image to enlarge.)

Slide show of images of the Raleigh-Durham area after the winter storm

Archived Text Data from the Winter Storm

Select the desired product along with the date and click "Get Archive Data."
Date and time should be selected based on issuance time in GMT.

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Surface Data - Surface Analysis and Meteograms

NCEP Surface Analysis at the height of the storm across central North Carolina. Image is from 00Z Friday, January 17 2003.
Surface Analysis - The NCEP surface analysis (00z 17 Jan) indicates cyclogenesis was shifting from the low in Tennessee to a more favorable baroclinic zone in central South Carolina. The shifting of the low southward allowed the insitu surface cold air in central North Carolina to remain. Had the low not shifted southward and/or had there been a stronger and better organized surface low, warm air advection would have caused the snow/rain line to be located farther northwest. Note there was no supporting cold air high pressure system to the north. Measurable snow in central North Carolina without a supporting cold air high pressure system to the north is relatively infrequent.

NCEP Surface Analysis from 06Z Thursday December 5, 2002.

Java Loop of Surface Analysis from Surface Analysis from 00Z Thursday January 16 through 12Z Friday January 17, 2003.

Surface Meteogram for Raleigh (KRDU)

KRDU Meteogram.

Surface Meteogram for Greensboro (KGSO)

KGSO Meteogram.

RAOB Data - Selected KGSO RAOB Plots (Skew-T Diagrams)

KGSO RAOB Plot (Skew-T Diagram) from 12Z Thursday January 16, 2003.
12 hours before the onset of snow at GSO (Greensboro, NC), the GSO RAOB was dry below 700 mb and cold enough to support snow. Low level northeasterly winds may have been supplying weak cold air advection; however, the chief source for maintaining enough cold air to support snow would come from evaporative cooling below 700 mb.

KGSO RAOB Plots (Skew-T Diagram) - Click to enlarge

Click the image to enlarge.

KGSO RAOB Plot (Skew-T Diagram) from 18Z Thursday January 16, 20032.
6 hours before the onset of snow at GSO, the GSO RAOB indicated that the low level winds had become southerly leaving the insitu cold air and limited potential for evaporative cooling as the principal means to support the onset of precipitation as snow. The increase of moisture aloft ensured that temperatures in the cloud layer would be cold enough (i.e., colder than -10 C) to support snow crystals.

Click the image to enlarge.

KGSO RAOB Plot (Skew-T Diagram) from 00Z Friday January 17, 2003.
As the snow began at GSO, mid level winds had increased ahead of the approaching short wave. The sounding was cold enough to support snow despite southeasterly surface winds.

Click the image to enlarge.

Nomogram -

The actual thickness from the Greensboro (GSO) upper air data indicated that this would be an all-snow event.

RAH P-type Nomogram from January 16 and 17, 2002.

Click the image to enlarge.

Radar Imagery - Selected KRAX Base Reflectivity Imagery

The quick movement of the mid level short-wave and the sharp back edge to the precipitation shield limited the duration of the precipitation to around a 6 hour period. This largely accounted for keeping the snowfall totals to 3 inches or less in central North Carolina. Warm air advection ahead of the weak surface wave produced bright band melting seen in the radar imagery. Low level convergence (850 mb) assisted in producing the enhancement seen in the precipitation imagery. The enhanced areas corresponded to those locations in central North Carolina that received the slightly higher snowfall totals.

Note the area of heavier precipitation (yellow) near Raleigh. This is an area of brief moderate snow. Raleigh (KRDU) reported moderate snow for a brief time (see METAR's below).

SPECI KRDU 170058Z VRB04KT 2SM -SN BKN001 OVC019 00/M05 A3002 RMK AO2 P0000
SPECI KRDU 170105Z 07004KT 1 1/4SM -SN BR OVC001 M01/M03 A3002 RMK AO2 TWR VIS 2 P0000
SPECI KRDU 170119Z 06003KT 3/4SM -SN BR OVC001 M02/M02 A3002 RMK AO2 TWR VIS 2 P0001
METAR KRDU 170151Z 06004KT 3/4SM -SN BR OVC001 M02/M02 A2998 RMK AO2 TWR VIS 2 SLP157 P0004 T10171017
METAR KRDU 170151Z COR 06004KT 3/4SM -SN BR OVC001 M02/M02 A2998 RMK AO2 SNINCR 1/1 PRESFR TWR VIS 2 SLP157 P0004 T10171017
SPECI KRDU 170203Z 03005KT 1 1/4SM -SN BR OVC001 M02/M02 A2997 RMK AO2 P0001

KRAX Base Reflectivity Imagery - Click to enlarge

Click the image to enlarge.

Java Loop of KRAX Base Reflectivity Imagery Animation from Approximately 2202Z Thursday January 16 through 0558Z Friday January 17, 2003.

Final Thoughts - Using real-time data to closely monitor the evolution of the meteorological features and the accompanying weather as the system tracked into the northern and central plains proved to be critical to the timely issuance of snow advisories correctly calling for 1-3 inches of snow in central North Carolina. Comparing these real time trends to the projections made by the numerical models (especially qpf) provided confidence in the model�s projections that measurable snow would occur in central North Carolina despite a number of limiting factors. Those limited factors included.... a very fast moving system with limited moisture and the lack of a sustained low level cold air advection source (i.e., high pressure to the north). P-type climatology stratified by patterns of cyclogenesis coupled with the staff�s skillful use of the station�s partial thickness technique (TRENDs) lead to the nearly exact placement of the snow/rain line that fell across central North Carolina.

Case study team -
Jonathan Blaes
Phil Badgett
Gail Hartfield
Kermit Keeter

For questions regarding the web site, please contact Jonathan Blaes.

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