000
FXUS63 KDMX 082346
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
546 PM CST SAT MAR 8 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 335 PM CST SAT MAR 8 2014

RELATIVELY QUIET WEATHER TONIGHT AS SUBSIDENCE ASSOCIATED WITH A
SURFACE RIDGE PASSES OVER THE STATE. ONLY EXCEPTION WILL BE THE
FAR NORTH THIS EVENING WHERE SOME MID LEVEL CLOUDS ASSOCIATED
WITH WEAK WARM ADVECTION/ISENTROPIC LIFT SCOOTS ACROSS THE NORTH.
OTHERWISE...CLEAR SKIES WILL ABOUND OVERNIGHT AS THE RIDGE PASSES
OVERHEAD. WINDS WILL GENERALLY BE LIGHT WITH WEAK PRESSURE
GRADIENT....HOWEVER AN INCREASE WILL BEGIN IN THE WEST LATE
TONIGHT AND THIS WILL LIKELY LEAD TO STEADY IF NOT SLOWLY RISING
TEMPERATURES TOWARD DAYBREAK AS MIXING INCREASES...THEREFORE HAVE
INCLUDED A NON-DIURNAL CURVE IN THE WEST IN THE EARLY MORNING
HOURS.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 335 PM CST SAT MAR 8 2014

MAIN FORECAST CONCERN IS WITH WARMER TEMPERATURES SUNDAY AND
MONDAY...AND WITH MIXED PRECIPITATION POTENTIAL TUESDAY INTO
TUESDAY NIGHT.

SUNDAY AND MONDAY...GENERALLY WENT 2 TO 4 DEGREES ABOVE THE
WARMEST GUIDANCE FOR MAX TEMPS SUNDAY AND SEVERAL DEGREES WARMER
FOR MAX TEMPS ON MONDAY...ESPECIALLY ACROSS THE SOUTH TO
SOUTHWEST WHERE THE SNOW PACK IS LIMITED OR COMPLETELY GONE.
TEMPERATURES LOOK TO RISE WELL INTO THE 50S SUNDAY IN THE CENTRAL
TO SOUTHWEST AS 850MB TEMPS WARM TO +8C TO +9C SUNDAY AFTERNOON
AND MIXING TO ABOUT 925MB AND POSSIBLY A BIT DEEPER. GOOD
SOUTHWEST FLOW PERSISTS SUNDAY NIGHT INTO MONDAY AND RAISED
MINIMUM TEMPS A COUPLE OF DEGREES AS TEMPS SHOULD HAVE A TOUGH
TIME DROPPING OFF. BY MONDAY THE WARM NOSE LOOKS TO NUDGE INTO
WESTERN AND CENTRAL IOWA BY 12Z MONDAY AND PUSHES EAST THROUGHOUT
THE DAY. 850MB TEMPS WARM TO +14C ACROSS THE WEST AND MIXING
SHOULD BE TO AROUND 925MB THROUGH THE AFTERNOON AND WITH THE
WARMER START MONDAY MORNING...TEMPS LOOK TO HAVE NO PROBLEM
REACHING WELL INTO THE 60S IN THE CENTRAL TO SOUTHWEST PORTIONS OF
THE FORECAST AREA. WEAK SURFACE HIGH MOVES INTO THE STATE BY THE
LATE AFTERNOON MONDAY AND MAINLY SHIFTING WINDS NORTHWEST CLOSER
TO 00Z. THE SNOW PACK RIDDEN AREAS WILL REMAIN COOLER...BUT STILL
LOOK TO RISE ABOVE GUIDANCE SUNDAY AND MONDAY.

TUESDAY...SURFACE LOW PRESSURE DEVELOPS OVER THE CENTRAL ROCKIES
AND MOVES SOUTHEAST ACROSS THE PLAINS INTO MISSOURI BY TUESDAY
MORNING. GOOD ISENTROPIC LIFT ALONG THE 295K TO 300K SURFACES
BRINGS A DECENT AMOUNT MOISTURE TRANSPORT INTO THE STATE BY 18Z
TUESDAY. GFS SHOWING A BAND OF FRONTOGENETICAL FORCING BETWEEN
850MB TO 600MB TUESDAY AFTERNOON ON THE BACKSIDE OF THE SURFACE
LOW. WENT COOLER FOR TEMPERATURES PER GFS/ECMWF SUGGESTING THE
CAA TO DEVELOP SOONER THAN PREVIOUSLY ANTICIPATED. AS A
RESULT...HAVE A NON-DIURNAL TEMPERATURE TREND TUESDAY AND THUS
INCREASED SNOW AMOUNTS ACROSS THE NORTH AS PRECIP SHOULD TEETER
BACK AND FORTH FROM RAIN TO SNOW DURING DAY. NAM IS MORE BULLISH
WITH THE CAA AND THUS HAS MUCH HIGHER SNOW AMOUNTS ACROSS THE
NORTH. LEANED TOWARD THE GFS/ECMWF UNTIL ANOTHER RUN OR TWO OF THE
NAM TO SEE IF CONTINUES WITH ITS 12Z SOLUTION. THE CENTRAL AND
SOUTH LOOK TO REMAIN WARM ENOUGH FOR RAIN UNTIL TUESDAY EVENING.
BY THEN THE DEEPER MOISTURE AND BEST FORCING WILL HAVE MOVED OFF
TO THE SOUTHEAST...SO ANY SNOW AMOUNTS LOOK TO BE MINIMAL ATTM.

WEDNESDAY THROUGH FRIDAY...SURFACE HIGH PRESSURE REMAINS ACROSS
THE REGION DURING THIS TIME FRAME AND 500MB FLOW TRANSITIONS FROM
NORTHWEST FLOW TO MORE ZONAL FLOW BY FRIDAY. TRENDED WARMER ON
THURSDAY AND FRIDAY AS SURFACE RIDGE PROVIDES SOUTHERLY TO
WESTERLY FLOW LOOKS TO REMAIN IN PLACE ACROSS THE STATE.

&&

.AVIATION...09/00Z
ISSUED AT 545 PM CST SAT MAR 8 2014

BROKEN HIGH MVFR CU FIELD OVER SOUTHERN IOWA WILL DISSIPATE AFTER
SUNSET...AND OTHERWISE VFR CONDITIONS WILL CONTINUE THROUGH THE
TAF PERIOD. LIGHT NORTHWESTERLY WINDS WILL SWITCH TO THE SOUTHWEST
AND INCREASE TO 10 TO 15 KTS TOMORROW DURING THE DAY. THERE WILL
LIKELY BE A FEW HIGHER GUSTS OVER 20 KTS...ESPECIALLY ACROSS
SOUTHERN IOWA WHERE THE LACK OF A SNOW PACK WILL INDUCE FURTHER
MIXING.

&&

.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 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...COGIL
LONG TERM...PODRAZIK
AVIATION...SKOW
HYDROLOGY...ZOGG