...2006 NATIONAL FLOOD SAFETY AWARENESS WEEK...

NATIONAL FLOOD SAFETY AWARENESS WEEK CONTINUES WITH THE THEME OF...ICE JAMMING AND SNOWMELT FLOODING.

SPRING RUNOFF RESULTS IN ONE OF THE MOST COMMON FLOOD THREATS IN SOUTHERN AND SOUTHEAST MONTANA...ICE JAMMING AND SNOWMELT FLOODING OCCUR AFTER THE WINTER SEASON.

ICE JAMMING DEVELOPS WHEN PROLONGED SUB ZERO WEATHER IS FOLLOWED BY SIGNIFICANT WARMING...ALLOWING THE ICE ON RIVERS TO BREAK FREE AND FLOW DOWNSTREAM. ICE JAMS TYPICALLY FORM AS ICE ACCUMULATESAT BENDS IN RIVERS OR AT OTHER OBSTACLES SUCH AS BRIDGE SUPPORTS. WATER QUICKLY BACKS UP BEHIND THE JAM AND CAN CAUSE LOCALIZED FLOODING. JAMS CAN RELEASE VERY QUICKLY ANDFLASH FLOODING IS OFTEN THE RESULT...AS THE WATER STORED BEHIND THE ICE JAM THEN RUSHES DOWNSTREAM.

SNOWMELT FLOODING OCCURS ASWARMER SPRING TEMPERATURES MELTSNOW OVER THE MOUNTAINS AND THE RUNOFF OVERFILLS CREEKS AND RIVERS. SNOWMELT FLOODING MAY BE WORSENEDBY SPRING RAINS FALLING OVER THE MOUNTAIN SNOW PACK ADDING TO THEWATER FLOWING INTO CREEKS AND RIVERS.

SNOWMELT AND THE BREAKUP OF RIVER ICE OFTEN OCCUR IN TANDEM. ICE JAMS RESPOND TO FLUCTUATING RIVER FLOWS ASSOCIATED WITH SNOWMELT AND CAN AS A RESULT INTENSIFY SNOWMELT FLOODING.

THE NATIONAL WEATHER SERVICE PROVIDES EXTENSIVE INFORMATION ON SNOWPACK CONDITIONS ACROSS THE COUNTRY. A WIDE ARRAY OF GROUND, AIRBORNE AND SATELLITE OBSERVATIONS ARE USED TO MONITOR SNOW CONDITIONS. YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE ROUTINELY PROVIDES FLOOD FORECASTS…WHETHER OR NOT THEY ARE RELATED TO SNOWMELT OR ICE JAMS.

MORE INFORMATION MAY BE OBTAINED FROM YOUR LOCAL NATIONAL WEATHER SERVICE…

WEATHER.GOV/GLASGOW

WEATHER.GOV/BILLINGS

WEATHER.GOV/GREATFALLS

WEATHER.GOV/MISSOULA