FXUS63 KDMX 181127 AAA

AFDDMX



AREA FORECAST DISCUSSION...UPDATED

NATIONAL WEATHER SERVICE DES MOINES IA

625 AM CDT THU MAR 18 2010



...UPDATED AVIATION DISCUSSION...



.SHORT TERM /TODAY/...

SFC HIGH PRESSURE SETTLING SOUTH OVER THE ARKLATEX REGION AND A COLD 

FRONT APPROACHING NW IA FROM THE NORTHERN PLAINS WILL SET UP A 

SEASONALLY MILD DAY UNDER SW TO W FLOW. WITH DECENT MIXING UP TO 875 

MB OR SO AND A MODEST WARM NOSE ALOFT AT THIS HEIGHT...SHOULD SEE 

TEMPS OVER 60 DEGREES FOR MUCH OF THE AREA SAVE THE NORTHWEST 

QUARTER WHERE A HIGHER PERCENTAGE OF CLOUD COVER WILL LIKELY KEEP 

TEMPS SOMEWHAT IN CHECK.



.LONG TERM /TONIGHT THROUGH WEDNESDAY/...

FOCUS OF THE LONG TERM FORECAST REMAINS THE STORM SYSTEM SET TO 

AFFECT THE AREA ON FRIDAY AND SATURDAY. ABOUT 24 HOURS AGO THE MODEL 

SUITE BEGAN TRENDING TO A MORE PROGRESSIVE/SOUTHEASTWARD SOLUTION 

AND THIS TREND HAS CONTINUED TONIGHT. WHILE THE OVERALL THINKING 

REGARDING THE EVOLUTION OF THIS SYSTEM HAS NOT CHANGED...THE MORE 

PROGRESSIVE NATURE OF PRECIP HAS RESULTED IN A DECREASE IN QPFS AND 

DURATION OF POPS AT ANY GIVEN POINT. HAVE LOWERED POPS RATHER 

SIGNIFICANTLY ACROSS THE NORTHWEST AFTER DAYTIME FRIDAY AS THE 

SYSTEM HAS SHIFTED SOUTHEAST AND DRY LOW LEVEL AIR STREAMING IN FROM 

THE NORTH APPEARS LIKELY TO INHIBIT PRECIP IN THIS AREA. 

OTHERWISE...HAVE CONTINUED CAT POPS AT TIMES FOR THE REMAINDER OF 

THE CWA AS MOISTURE AND FORCING ARE STILL FAIRLY IMPRESSIVE. PRIMARY 

CONCERN WITH THIS SYSTEM WILL LIKELY BE AMOUNT OF PRECIPITATION AND 

ITS EFFECTS ON ONGOING FLOODING AS DISCUSSED BELOW.



OF COURSE THE OTHER BIG QUESTION IS HOW MUCH OF THE PRECIP WILL FALL 

AS SNOW. WITH THE SOUTHEASTWARD QPF SHIFT INTO RELATIVELY WARMER 

TEMPERATURES THE SNOWFALL POTENTIAL HAS DECREASED SOMEWHAT...AND 

THIS IS ESPECIALLY TRUE WHEN ONE CONSIDERS THAT GROUND TEMPS ARE IN 

THE LOWER 40S IN MOST LOCATIONS DUE TO THE FACT THAT TEMPERATURES 

HAVE NOT FALLEN BELOW FREEZING IN THE LAST WEEK AND A HALF OR SO. 

TODAYS EXPECTED HIGHS IN THE MID 60S WILL ONLY ENHANCE THIS EFFECT. 

SO EVEN AFTER PRECIP MODE CHANGES TO SNOW...LIKELY SOMETIME FRIDAY 

NIGHT...IT WILL TAKE A WHILE FOR THE SNOW TO BEGIN TO ACCUMULATE. 

THE ONLY CAVEAT HERE IS THAT A NARROW BAND OF CONVECTIVELY ENHANCED 

SNOW IS POSSIBLE AND THIS WOULD MITIGATE THE WARM GROUND EFFECTS AND 

RESULT IN SOMEWHAT MORE SUBSTANTIAL ACCUMULATIONS. HOWEVER...THE 

OCCURRENCE OF SUCH A FEATURE IS FAR FROM CERTAIN...AND EVEN IF IT 

DOES OCCUR IT WILL LIKELY BE FAIRLY PROGRESSIVE LIMITING SNOWFALL 

AMOUNTS AT ANY GIVEN POINT. IN LIGHT OF ALL THIS...HAVE TAKEN 

SNOWFALL TOTALS DOWN INTO THE COUPLE OF INCHES RANGE...AND EXPECT 

THAT EVEN IF SOME ENHANCED HEAVIER AMOUNTS DO OCCUR THEY WILL BE 

ISOLATED WITHIN THE AFOREMENTIONED NARROW BAND FEATURE.



THE STORM SYSTEM/PRECIP SHOULD CLEAR OUR SOUTHEASTERN COUNTIES LATE 

SATURDAY...AFTER WHICH RIDGING WILL BE IN PLACE INTO EARLY NEXT 

WEEK. HAVE LOWERED MIN TEMPS ACROSS MUCH OF THE AREA SAT NIGHT AS 

WINDS WILL LIKELY BE LIGHT AND SKIES SHOULD CLEAR OUT AT LEAST 

ACROSS THE NORTHWEST. SUNDAY APPEARS DRY AND NOT TOO COOL AS THERE 

SHOULD NOT BE MUCH SNOW COVER FROM THE FRI/SAT STORM AND RIDGING 

APPEARS TO BE BRINGING IN SOME DEGREE OF WAA ALOFT. AS 500 MB FLOW 

GOES ZONAL AROUND MONDAY NIGHT ONWARD SOME MODEL RUNS ATTEMPT TO 

BRING LIGHT PRECIP ACROSS WITH LITTLE SHORTWAVES...HOWEVER THE NEXT 

SUBSTANTIAL PRECIP CHANCES DO NOT ENTER THE FORECAST UNTIL AROUND 

MIDWEEK WHEN A DEEPER WAVE MAY APPROACH THE AREA.



&&



.AVIATION...

18/12Z...CIRRUS MOVING ACROSS IOWA IS PUTTING AN END TO THE AREAS OF 

DENSE FOG. HOWEVER...KOTM WILL HAVE ANOTHER HOUR OR SO OF POTENTIAL 

VLIFR CONDITIONS. OTHERWISE...VFR CONDITIONS ARE EXPECTED DURING THE 

BALANCE OF THE FORECAST PERIOD. SOUTHWESTERLY WINDS WILL PICK UP TO 

12 KT OR SO...WITH POTENTIAL FOR HIGHER GUSTS AFT 14-15Z. A COLD 

FRONT WILL SLIP THROUGH NORTHWEST TO SOUTHEAST AFT 00Z...SHIFTING 

WINDS TO THE NORTHWEST. CEILINGS WILL GRADUALLY COME DOWN BEHIND THE 

FRONT...BUT NOT EXPECTING ANYTHING BELOW 050 UNTIL AFT 12Z FRIDAY.



&&



.HYDROLOGY...

WIDESPREAD MODERATE TO MAJOR FLOOD EVENT CONTINUES. THE FLOOD THREAT 

IS MIGRATING FROM SOUTH TO NORTH WITH TIME. BASINS OF MOST CONCERN 

ARE FIRST THE DES MOINES/RACCOON...FOLLOWED BY THE CEDAR/IOWA THEN 

SKUNK. MODERATE TO MAJOR FLOODING EXPECTED AT MANY LOCATIONS IN THE 

DES MOINES/RACCOON RIVER BASINS. ICE JAM PROBLEMS CONTINUE TO 

DIMINISH.



SOME STREAMS ARE NEAR CREST NOW...WITH OTHERS EXPECTED THROUGH EARLY 

NEXT WEEK. THERE IS A POSSIBILITY OF MODERATE TO HEAVY RAINFALL LATE 

THIS WORK WEEK. LOOKING ON THE POSITIVE SIDE...IF THIS RAIN DOES 

MATERIALIZE THEN IT WILL HAVE FALLEN AFTER THE CRESTS OCCUR...WHICH 

MEANS IT WOULD HAPPEN DURING THE HYDROGRAPH RECESSIONS. ONCE THE 

HYDROGRAPHS GO INTO RECESSION...IT TAKES A LOT OF EXTRA WATER TO 

TURN THEM AROUND. WE WILL HAVE TO KEEP AN EYE ON THINGS.



MANY STREAMS WILL BE SLOWER THAN NORMAL TO RECEDE POST-CREST AND 

FALL BELOW STAGE...AS THE RUNOFF FROM SNOW MELT AS WELL AS EXCESS 

SOIL MOISTURE TAKES A WHILE TO FIND ITS WAY INTO THE STREAMS.



&&



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



$$



SHORT TERM...MOYER

LONG TERM...LEE

AVIATION...MOYER

HYDROLOGY...ZOGG