000
FXUS63 KDMX 080553
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1153 PM CST FRI MAR 7 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 301 PM CST FRI MAR 7 2014

COMPLEX FORECAST FOCUSES ON PRECIPITATION CHANCE AND TYPE FOR
OVERNIGHT. FRONTAL BOUNDARY HAS PUSHED SE THROUGHOUT THE AFTERNOON
AND IS CURRENTLY LOCATED ACROSS FAR SOUTHEASTERN IOWA. BEHIND THIS
BOUNDARY MOISTURE HAS CONTINUED TO INCREASE WITH WEAK FORCING WHICH
IS BEGINNING TO ALLOW FOR PRECIPITATION TO FILL IN ACROSS
NORTHWESTERN CWA. TEMPERATURES DROPPED QUICKLY BEHIND
BOUNDARY...WITH READINGS NEAR OR BELOW FREEZING IN THE NORTHWEST.
HOWEVER...SOUNDINGS INDICATE VERY WARM AND DRY AIR AT MID LEVELS.
THIS HAS CONTRIBUTED TO LIMITED DAYTIME PRECIPITATION...IN ADDITION
WARM LAYER WILL ALLOW FOR A MIX OF PRECIPITATION AT ONSET BEFORE
LAYER COOLS AND PRECIPITATION CHANGES OVER TO SNOW.

SYSTEM PUSHING SOUTH...BEFORE REACHING ADDITIONAL MOISTURE AND
FORCING IN SOUTHERN IOWA WITH WAVE PUSHING NORTH. HOWEVER...MODELS
CONTINUE TO BACK OFF ON STRENGTH OF THE SYSTEM. THEREFORE HAVE CUT
BACK ON POPS AND QPF...WITH ANTICIPATE SCATTERED NATURE OF
PRECIPITATION TO CONTINUE THROUGH THE EVENING HOURS. GIVEN
RELATIVELY SCATTERED NATURE OF PRECIPITATION AND LOW CONFIDENCE IN
PRECIPITATION AND PRECIPITATION TYPE...WITH HIGH RES MODELS
INDICATING THAT PRECIPITATION WILL GRADUALLY DIMINISH...WILL OPT TO
NOT ISSUE HEADLINES ATTM...THOUGH SYSTEM WILL NEED TO BE MONITORED
FOR POTENTIAL HEADLINES. IN ADDITION...WINDS WILL REMAIN STRONG
BEHIND BOUNDARY...WHICH MAY CONTINUE TO LEAD TO AREAS OF BLOWING
SNOW...ESPECIALLY IN THE NORTH.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 301 PM CST FRI MAR 7 2014

SATURDAY EARLY MORNING THE WILL BE SOME LINGERING PRECIP CHANCES
BUT GENERALLY CANADIAN HIGH PRESSURE WILL BE MOVING IN AND
USHERING IN SOME COOLER AIR TO CENTRAL IOWA. THE RESULT WILL BE
HIGHS THAT ARE ROUGHLY 10 T0 15 DEGREES COOLER THAN TODAY AND
DECREASING CLOUDS THROUGH THE DAY.

ON SATURDAY NIGHT THE HIGH SHIFTS TO THE SOUTH AND LITTLE TO THE
EAST SWITCHING THE FLOW TO MORE OF A WESTERLY THEN SOUTHERLY FLOW.
ALOFT AN UPPER RIDGE BEGINS TO BUILD ACROSS THE INTER-MOUNTAIN
WEST AND HIGH PLAINS. BY SUNDAY A SOUTH TO SOUTHWEST WIND
ESTABLISHES ITSELF ACROSS IOWA AND INCREASES DURING THE DAY. TEMPS
WILL RESPOND AND CLIMB INTO THE UPPER 30S NORTHEAST TO THE MID 50S
SOUTHWEST. THE WARMEST DAY WILL BE MONDAY WITH AROUND 40 NORTHEAST
AND MID 60S SOUTHWEST.

MONDAY NIGHT THROUGH WEDNESDAY IS A BIT UNSETTLED AT THIS POINT AS
A LARGE TROUGH STARTS TO CARVE OUT ACROSS THE WEST COAST AND
ROCKIES. MODELS DIVERGE ON HOW TO HANDLE THIS AND A COLD FRONT
THAT WILL PUSH ACROSS THE AREA BUT TUESDAY AND WEDNESDAY WILL
DEFINITELY BE COOLER WITH HIGHS BACK IN THE 30S AND 40S. PRECIP
WILL OCCUR WITH THE FRONT BUT WITH LACK OF CONSENSUS ON TIMING AND
LOCATION I HAVE BROAD BRUSHED POPS TO THE VICINITY OF THE FRONT.
PTYPE WILL ALSO BE OF SOME CONCERN WITH SNOW BEING MORE PROBABLE
AT NIGHT AND RAIN OR A RAIN/SNOW MIX DURING THE DAY.

THE UPPER RIDGE QUICKLY REBUILDS ACROSS THE WEST LATE IN THE WEEK
SHARPENING THE TROUGH OVER THE UPPER MIDWEST AS IT GETS SHOVED TO
THE EAST. LINGERING POPS WEDNESDAY INTO WEDNESDAY NIGHT POSSIBLE
WITH STILL COOL TEMPS THEN AS THE RIDGE EXPANDS EASTWARD TEMPS
MODERATE BACK INTO THE 40S AND 50S LATE IN THE WEEK. A FEW 60S
ACROSS THE SOUTHWEST ARE POSSIBLE BY FRIDAY.

&&

.AVIATION...08/06Z
ISSUED AT 1150 PM CST FRI MAR 7 2014

BAND OF LIGHT SNOW MOVING THROUGH CENTRAL IOWA SHOULD GRADUALLY
DIMINSH THROUGH 09Z. AREA OF STRATUS REMAINS EXPANSIVE. THE
STRATUS IS NOW MOVING SOUTHWEST OUT OF SOUTHEAST MINNESOTA AND
WISCONSIN. MVFR CIGS SHOULD GRADUALLY IMPROVE LATE TONIGHT INTO
SATURDAY MORNING. VFR THE REMAINDER OF SATURDAY WITH MAINLY NORTH
WINDS BEFORE SWITCHING TO THE WEST TO SOUTHWEST SATURDAY EVENING.

&&

.HYDROLOGY...
ISSUED AT 301 PM CST FRI MAR 7 2014

ICE JAMS AND RESULTING FLOODING WILL BECOME A CONCERN BY EARLY NEXT
WEEK AS TEMPERATURES WARM UP. AREA OF MOST CONCERN INITIALLY
INCLUDES STREAMS SOUTH OF U.S. HIGHWAY 30...BUT WILL SHIFT NORTHWARD
WITH TIME TO ENCOMPASS MUCH OF THE CWA BY THE END OF THE WEEK.
TIMING WOULD INITIALLY BE AS EARLY AS NEXT MONDAY NIGHT OR TUESDAY
FOR THE SOUTHERN CWA...AND THE MIDDLE TO LATER PARTS OF NEXT WEEK
ELSEWHERE.

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.

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 DES MOINES RIVER IN THE FORT DODGE AREA...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.

FLASH FLOOD WATCHES AND WARNINGS MAY BE ISSUED IF CONCERN BECOMES
HIGH ENOUGH FOR ICE JAM FLOODING.

&&

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

$$

SHORT TERM...AWB
LONG TERM...FAB
AVIATION...DONAVON
HYDROLOGY...ZOGG