March 10, 1999 Heavy Snow Events

On March 10th, 1999 a compact, yet locally powerful storm system blasted through northeast Wyoming and western South Dakota. A couple of narrow bands of moderate to heavy snow fell across the region. The map below depicts snowfall greater than 3". The map contours have been smoothed. The sharp cutoff on the lower left-hand portion of the map is there because that is where our reports are cutoff.

The contour map below could change if we receive late snowfall reports. Click here for a map with terrain on it.

Detailed Snowfall Reports (inches)

...WESTERN SOUTH DAKOTA...

STURGIS SHERIFF OFFICE    17-18 INCHES
FORT MEADE                17
VALE                      8-10
PHILLIP                   8-10
TILFORD WEIGH STN         8
2S ST. ONGE               7.5
10 NE QUINN               7
MIDLAND                   6-8
CRAZY HORSE MEM (CUSTER)  6-8
WASTA                     6-8
NWS OFFICE RAPID CITY     6
1/2 N NISLAND             6
3SE PIEDMONT              6
KADOKA                    5
10 NE CREIGTON            5
UNION CENTER              5
PACTOLA                   5
4 NW RAPID CITY           5
BELLE FOURCHE             4-6
LEAD                      4.5
22 NW BELLE FOURCHE       4
HOOVER STORE              4
JOHNSON SIDING            4
HOWES                     4
SPEARFISH                 4
3SE DEERFIELD             3.5
INTERIOR                  3.5
HOT SPRINGS               3.5
WHITE RIVER               3-4
23 NW EDGEMONT            3
PINE RIDGE                3
ROCHFORD                  3
3SE ELM SPRINGS           3
10 SE MARTIN              3
WINNER                    3
3 NW MILESVILLE           2-3
COTTONWOOD                2.5
5 N KYLE                  2.5
2N ARDMORE                2
MISSION                   2
WALL                      2
PRAIRIE CITY              2

...NORTHEASTERN WYOMING...

20 SE WRIGHT              10
DEVILS TOWER JCT          8
5 S SUNDANCE              6-8
GILLETTE                  6-8
WRIGHT                    6-8
SUNDANCE                  6-7
3E ROCHELLE               6
ALADDIN                   6
5SE ALVA                  5.5
HULETT                    5
MOORCROFT                 5
19 SW UPTON               4-5
12S GILLETTE              4-5
CLARETON                  3-4
7SW OSAGE                 3-4
DEVILS TOWER              3-4
13 SW UPTON               3
16 NW WRIGHT              2
RECLUSE                   1-2

Weather Maps

The storm system that affected our area on Wednesday was very similar to the storm that whipped the area on March 5th, 1999. The storm spun-up rapidly over central Wyoming late Tuesday evening on March 9th. The stormed tapped relatively benign moisture over the central plains but made use of it efficiently. The lighter snow amounts on the map were caused by the synoptic scale lift ahead of and just north of the storm track. However, as on the 5th, a narrow band of heavy snow developed.

The heaviest snow fell where the best upper level forcing and steepest lapse rates (change of temperature with height) were located. 2-3 inches of snow in 90 minutes was reported in a band of snow that moved from Pine Ridge into the northern Black Hill's foothills. The signatures on radar indicated convective snow was occurring with rates of 1-2 inches an hour in the Sturgis and Fort Meade areas on the morning of March 10th. Convective snow can be thought of as being similar to showers or thunderstorms in the summer, except that instead of rain you get heavy snow.

Take a look the Surface Map at 12Z, or 5:00 AM MST. The surface low wasn't that strong. But, you can see a red line across southern South Dakota. This was a warm front. The wind barbs are there, too, depicting surface winds. Look at the convergence of the winds ahead of the warm front. This contributes to upward vertical motion and snowfall. Also, notice the green arrow that depicts the 850-700mb flow. Check out the image showing this below.

There was a strong thermal gradient in Nebraska and South Dakota that day. When a wind crosses the isotherms (lines of constant temperature), lift results. Lift is especially strong when the winds cross the isotherms perpendicularly. Lift on this day was maximized just north of Rapid City. In the image above, the green denotes lift over the thermal boundary noted by the dashed and solid lines in degrees Celsius. The red is where there was convergence due to the wind. The wind was from the west just to the left of the red area with winds from the south to the right. All of these lifts mechanisms were maximized just north of Rapid City.

Finally, we use a computer model called the RUC2. This model runs every 3 hours. We received the 12Z (5:00 AM MST) run and used it's analysis to make the following graphic. The graphic is the 12Z (5:00 AM MST) infrared (IR) satellite image overlaid with the 500mb heights and vorticity. Notice the maximum of vorticity (spin of air parcels) over southwest South Dakota and east central Wyoming. Normally, ahead of and just north of these pieces of energy is where the "active" weather occurs. On the satellite image, note the enhanced clouds tops over western South Dakota. The scale at the left of the image shows how cold the tops were.

Radar Images

At 1353Z the images below were scanned from the KUDX WSR-88D located in New Underwood, SD. The first image below shows composite reflectivity. Note the banded structure to the returns as well as the yellows. The yellow colors correspond to 35-40dBZ returns, which is very high for snow and suggest dendritic snowflakes and heavy snow, possibly convective in nature. This is just what occurred. 16-18 inches were reported near Sturgis.

The image below is the echo tops, or tops of the clouds making the snow. The little dark blue spot to the west of Philip was 26,000 feet. Tornados have developed from thunderstorms this high in the Midwest. 26,000 foot snow producing clouds are bound to produce spirited snowfall amounts in a short amount of time.

Sequence of Forecast Events

The National Weather Service in Rapid City, SD is responsible for issuing advisories and warnings for these types of winter storms. Here are the products we issued on Tuesday and Wednesday.

• Tuesday, March 9th
• 3-4 AM - issued a Winter Storm Watch for the potential of heavy snow amounts in excess of 6 inches
• 3-4 PM - issued a Winter Storm warning for heavy snow amounts averaging 6 inches or more
• Wednesday, March 10th
• Noon - let the Winter Storm Warning expire as the heavy snow was over

The best way to hear about hazardous winter weather conditions in the Black Hills is NOAA Weather Radio. Our transmitter operates on a frequency of 162.55 MHz on station WXM-63. Our broadcasts can be heard on a scanner or via dedicated weather radios. These radios are available for purchase at your local electronics store. The information you receive will assist you in planning your day and will help you cope with winter storms.

• Animated Visible Image Loop

Click on the above link to see a long animation of the 1km visible images from our GOES-8 satellite. Warning: The animation is very large.

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