National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KDMX 070556
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1156 PM CST THU MAR 6 2014

.UPDATE...
ISSUED AT 1156 PM CST THU MAR 6 2014

WINDS WILL BE SUBSIDING OVER THE NEXT COUPLE OF HOURS ACROSS
NORTHERN IOWA AND REPORTS INDICATE THAT THERE HAS BEEN SLIGHT
IMPROVEMENT IN MOST AREAS ALREADY. BLOWING SNOW SHOULD DIMINISH
FURTHER THOUGH ICY PATCHES ON THE ROADS WILL PERSIST THROUGH THE
NIGHT. THE ADVISORY WILL BE ALLOWED TO EXPIRE AT MIDNIGHT AND
FOLLOWED UP WITH SPECIAL WEATHER STATEMENTS AS NEEDED.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 403 PM CST THU MAR 6 2014

APPROACHING FRONTAL BOUNDARY CURRENTLY LOCATED IN WESTERN DAKOTAS
WILL PUSH SOUTHEAST THROUGHOUT THE NIGHT. WINDS WILL REMAIN UP
THROUGH MUCH OF THE EVENING WITH PRESSURE GRADIENT...COMBINED WITH
WAA WHICH WILL HELP TO KEEP TEMPERATURES WARMER THROUGH THE
OVERNIGHT. HAVE ADJUSTED TEMPERATURES UP SLIGHTLY...THOUGH HAVE KEPT
COOLEST TEMPERATURES IN THE NORTHEAST WHERE HIGHS TODAY DID NOT WARM
AS MUCH AS EXPECTED. ANTICIPATE CLOUDS TO INCREASE OVERNIGHT ACROSS
THE NORTHWEST AHEAD OF BOUNDARY.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
ISSUED AT 403 PM CST THU MAR 6 2014

THE PRIMARY FORECAST CHALLENGE REMAINS PRECIPITATION CHANCES AND
PRECIPITATION TYPE MOVING IN WITH SYSTEM. THE PRIMARY SYSTEM IS
WELL TO THE WEST WITH THE PRIMARY FORCING NOT ARRIVING UNTIL LATE
FRIDAY AFTERNOON AND INTO THE EVENING. THE SYSTEM WILL BE RELIANT
ON PACIFIC MOISTURE WITH THE GULF LOW PRESSURE CUTTING OFF THE
SOUTHERN MOISTURE FLOW. THE AREA OF DEEP MOISTURE WILL BE NARROW
AND STILL CONDITIONS NOT REAL FAVORABLE FOR ANY DRIZZLE/FREEZING
DRIZZLE WITH A LACK OF LOW LEVEL MOISTURE ADVECTION WITH THE
SOUTHERN MOISTURE FLOW NEARLY NON-EXISTENT. THERE WILL BE SOME LOW
CHANCES FOR FREEZING RAIN DURING TRANSITION AS MID LEVEL PROFILES
REMAINING WARM THROUGH THE DRY LAYER. THE WETBULB TEMPERATURES
THROUGH THIS LAYER ARE BELOW FREEZING THOUGH THUS ONCE SATURATION
OCCURS OR EVEN BEFORE...THE TRANSITION TO SNOW WILL COMMENCE. ONCE
SNOW DOES DEVELOP...UP TO 2 INCHES OF SNOW MAY OCCUR MAINLY SOUTH
OF INTERSTATE 80 BEFORE THE SYSTEM MOVES OUT FRIDAY NIGHT.

SATURDAY WILL BE THE COOL DAY WITH CANADIAN HIGH PRESSURE PASSING
THROUGH. WARM ADVECTION WILL COMMENCE BY SUNDAY WITH TEMPERATURE
PUSHING TO NEAR 40 NORTHEAST TO THE LOWER 50S SOUTHWEST. AN EVEN
WARMER DOWNSLOPE COMPONENT WILL ARRIVE ON MONDAY AS THE THERMAL
RIDGE PASSES THROUGH. HIGHS SHOULD REACH THE 60S OVER PORTIONS OF
THE SOUTHWEST TO THE MID 40S NORTHEAST. THIS SHOULD SET OFF THE
ICE JAM POTENTIAL DISCUSSED IN THE HYDRO SECTION BELOW. CHANCES
FOR PRECIPITATION ARE INCREASING ON TUESDAY THOUGH THE
PRECIPITATION TYPE STILL NOT A CERTAIN WITH WARMER LOW LEVELS
POSSIBLY KEEPING THE EVENT AS ALL RAIN. MODEL CONSENSUS OF THE GENERAL
UPPER LEVEL PATTERN IS GOOD TOWARD THE END OF THE EXTENDED WITH
SOME DIFFERENCES ON THE STRENGTH OF THE SOUTHERN PLAINS SHORT WAVE
AND ASSOCIATED DIGGING BY WEDNESDAY. NEAR SEASONAL TEMPERATURES
FOR THE MID PORTION OF THE WEEK.

&&

.AVIATION...07/06Z
ISSUED AT 1156 PM CST THU MAR 6 2014

STRATUS CLOUDS HAVE RECEDED UP INTO MN TONIGHT AND SHOULD HOLD UP
THERE FOR THE MOST PART THROUGH SUNRISE. MVFR VSBYS IN BR ARE
EXPECTED OVERNIGHT AT MOST TERMINALS BUT SHOULD NOT DROP MUCH
BELOW THAT DUE TO CIRRUS CLOUDS STREAMING OVERHEAD. ON FRIDAY
MORNING AS A TROUGH APPROACHES FROM THE NORTHWEST FORECAST
SOUNDINGS INDICATE THAT THE NEAR SURFACE LAYER WILL SATURATE
RAPIDLY AS HIGH DEWPOINTS MOVE IN OVER THE SNOWPACK...AND EXPECT
LOW MVFR OR IFR CIGS/VSBYS BY 11Z TO 14Z AT MOST TERMINALS AND
PERSISTING AT LEAST THROUGH MIDDAY. WHEN THE TROUGH MOVES THROUGH
IN THE EARLY TO MID AFTERNOON IT SHOULD RESULT IN A STEADY
IMPROVEMENT IN VSBY/CIG LEVELS...ESPECIALLY ALONG THE NORTH...BUT
WILL ALSO BRING A LIGHT WINTRY MIX OF PRECIP IN THE AFTN/EVE.

&&

.HYDROLOGY...
ISSUED AT 403 PM CST THU MAR 6 2014

ICE JAMS AND RESULTING FLOODING WILL BECOME A CONCERN BY EARLY NEXT
WEEK AS TEMPERATURES WARM UP. AREA OF MOST CONCERN INCLUDES STREAMS
SOUTH OF U.S. HIGHWAY 30. TIMING WOULD BE AS EARLY AS NEXT MONDAY
NIGHT OR TUESDAY.

RUNOFF FROM SNOWMELT WILL MAKE ITS WAY INTO OUR STREAMS AS
TEMPERATURES INCREASE OVER THE NEXT FEW DAYS. THE DEEP GROUND FROST
DEPTH WILL MINIMIZE INFILTRATION OF ANY WATER FROM THE
SNOWMELT...AND WOULD THUS HELP MAXIMIZE RUNOFF INTO THE STREAMS.
BASED ON CURRENT TEMPERATURE FORECASTS...RIVER LEVELS ARE EXPECTED
TO RISE ENOUGH TO RESULT IN POSSIBLE ICE JAMS AS EARLY AS NEXT
MONDAY NIGHT...PRIMARILY SOUTH OF U.S. HIGHWAY 30.

IF ICE JAMS DO OCCUR EARLY NEXT WEEK THEY WOULD BE DRIVEN PRIMARILY
BY SNOWMELT ALONE. STUDIES OF SUCH PAST ICE JAM EVENTS IN AND NEAR
THE NWS DES MOINES CWA HAVE YIELDED SOME COMMON PRECURSOR FEATURES.
FOR ICE JAMS DRIVEN TOTALLY OR PRIMARILY BY SNOWMELT ONLY...THE ICE
JAMS WERE PRECEDED BY 3 TO 5 CONSECUTIVE DAYS WITH THE DAILY MAX
TEMPERATURE IN THE 40S OR HIGHER. IN ADDITION...THE ICE JAMS
OCCURRED WITH OVERNIGHT LOWS IN THE PRECEDING 3 TO 5 NIGHTS WHICH
WERE BOTH ABOVE AND BELOW FREEZING. SOME OVERNIGHT LOWS WERE AS LOW
AS THE MIDDLE TO UPPER TEENS.

THE STUDIES ALSO SHOWED THAT WHEN THE DAILY AVERAGE TEMPERATURE
REACHED 42F OR HIGHER...ICE JAMS ALMOST ALWAYS OCCURRED WITHIN A DAY
OR TWO. THEY SOMETIMES OCCURRED DURING THE NIGHT IMMEDIATELY
FOLLOWING THE DAYTIME HIGH WHICH RESULTED IN THE DAILY AVERAGE
TEMPERATURE OF 42F OR HIGHER.

LOCATIONS THAT HAVE HISTORICALLY EXPERIENCED ICE JAMS AND RESULTING
FLOODING WOULD BE OF MOST CONCERN. THOSE LOCATIONS INCLUDE BUT ARE
NOT LIMITED TO THE RACCOON RIVER /INCLUDING IN THE DES MOINES AREA/
AS WELL AS PORTIONS OF THE SOUTH SKUNK RIVER. GIVEN THE UNUSUALLY
THICK NATURE OF THE ICE...HOWEVER...ICE JAMS AND RESULTING FLOODING
MAY OCCUR IN OTHER LOCATIONS AS WELL. AS HAS HAPPENED WITH PAST ICE
JAMS...RIVER LEVELS MAY RISE RAPIDLY THUS LEADING TO FLASH
FLOODING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

UPDATE...LEE
SHORT TERM...AWB
LONG TERM...DONAVON
AVIATION...LEE
HYDROLOGY...ZOGG