Flooding in Iowa, March 2 to 7, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1225 PM CST SUN MAR 2 2008

UPDATED TO ADD 18Z AVIATION FORECAST DISCUSSION.

.SYNOPSIS...
LONG WV TROUGH APPROACHING ROCKIES WITH MATURING JET SEGMENT FROM WY
INTO ND.  ASSOCIATED DIVERGENCE HELPING UVM CO INTO SD.  PRIMARY
SHORT WV OVER CO PRODUCING QG FORCING INTO HIGH PLAINS BUT LACK OF
MOISTURE KEEPING IT FROM RESULTING IN TOO MUCH FOR NOW.
THERMODYNAMIC FORCING ALSO NOTED FARTHER E INTO UPR MO VALLEY AND
BUFFALO RIDGE AREAS BUT AGAIN LACKING MOISTURE.  MUCAPE AXIS IN THE
HUNDREDS IS ALREADY EVIDENT FROM TX/OK INTO SERN NE WITH ISOLATED
OTHER INSTANCES OVER NE/SD.  08Z SFC ANLYS PLACES LOW OVER SERN NE
WITH FRONTAL BOUNDARY FROM CO INTO CENTRAL DAKOTAS...AND WRM FRONT
DOWN MO RIVER.  NICE ISALLOBARIC COUPLET TAKING SHAPE BUT NO
SIGNIFICANT COLD AIR SURGE EVIDENT YET.

&&

.DISCUSSION...
PRIMARY CONCERN WILL BE DRAMATIC NW SHIFT IN 00Z DOMESTIC MODELS
BRINGING SIGNIFICANT PCPN THROUGH MUCH OF FCST AREA TONIGHT.  IN THE
MEAN TIME...MOISTURE TO CONTINUE TO INCREASE ALONG AND SOUTH OF THE
WRMFNT TODAY...WITH SOUTHERLY FLOW OFF THE GULF. 40F TO 50F
DEWPOINTS ALREADY INTO ERN NE/NW MO...WITH MID 30S ACROSS THE
SOUTHERN HALF OF THE CWA.  AS SFC LOW DEEPENS THROUGH THE
DAY...MOISTURE TRANSPORT TO INCREASE INTO THE AREA WITH THE LOW
LEVELS SATURATING BRINGING LOW STRATUS DECK/DRIZZLE/FOG TO THE AREA.
HOWEVER MODELS CONTINUE TO TREND SLOWER WITH THE TIMING...SO HAVE
BACKED OFF DRIZZLE/FOG MENTION NOW UNTIL THE LATE MORNING HOURS WHEN
RUC/NAM/GFS ALL IN AGREEMENT THAT SHOULD HAVE SATURATION BY THAT
TIME. AS UPPER LEVEL TROUGH BEGINS TO EXIT THE ROCKIES...AND STRONG
WAA/MOISTURE TRANSPORT INCREASES INTO THE AFTERNOON HOURS...HAVE
INCREASING CHANCES OF RAIN/SHOWERS ACROSS THE CWA. SFC FRONTAL
BOUNDARY TO BE STRETCHED FROM SW TO NE ACROSS THE CWA...WITH THE
FRONTOGENESIS MAX ALONG A CRESTON TO DES MOINES TO WATERLOO LINE BY
MID AFTERNOON.  THEREFORE HAVE GREATEST POPS IN THIS AREA. NAM AND
TO SOME EXTENT THE GFS ADVERTISING AREA ALONG AND TO THE SOUTHEAST
OF THE AFOREMENTIONED AREA TO BECOME UNSTABLE BY MID/LATE AFTERNOON.
NAM COMPLETELY ERODES THE CAP...BRINGING 500-100J/KG CAPE INTO THE
SOUTH CENTRAL/SOUTHEASTERN CWA BY 21-00Z...WHILE THE GFS STILL
SHOWING SOME CIN. BUFKIT ALSO SHOWING POTENTIAL FOR ELEVATED
INSTABILITY...SO HAVE INCREASED MENTION OF ISO T TO SCT T ACROSS
THIS AREA...WITH THE GREATEST CHANCE FOR T IN THE KOTM AREA.
OTHERWISE FRONTAL BOUNDARY TO SLIDE THROUGH CWA BY LATE DAY...WITH
BREEZY TO WINDY CONDITIONS EXPECTED ACROSS THE AREA AS NORTHWEST
WINDS PICK UP BEHIND THE FRONT. POSSIBILITY OF RAIN MIXING WITH SNOW
ACROSS THE FAR NORTHWEST BY LATE THIS AFTERNOON...BUT SFC TEMPS TO
HOVER AROUND FREEZING SO EXPECT MUCH OF IT TO MELT AS IT REACHES THE
GROUND.

SCENARIO TONIGHT SIMILAR TO WHAT WAS SEEN ON 01/00Z MODELS BUT
SHIFTING ABOUT 140MI NWWD WITH MORE CONVECTIVE POTENTIAL.  BIGGEST
DIFFERENCE BETWEEN NAM AND GFS APPEARS TO BE THERMALLY WITH NAM
COOLER AND SHOWING MORE SNOW.  WILL FOLLOW GFS FOR SEVERAL
REASONS...ALTHOUGH 00Z ECMWF HAS NOT BUDGED ADDING TO CONCERN.  NAM
APPEARS TO BE TOO AGGRESSIVE WITH COLD AIR SURGE VS CURRENT
OBS...ALTHOUGH OBVIOUSLY NOT GREAT GFS HAS SHOWN BETTER RUN TO RUN
CONTINUITY BEING MORE NWLY IN PAST RUNS...GFS IS NOT AS BIG A SHIFT
FROM PERSISTENCE...AND BEING HESITANT TO FAVOR NAM OVER GFS WHEN IN
DOUBT DUE TO PAST PERFORMANCE.  MUCH LIKE YESTERDAY...GFS SHOWS VERY
STRONG UPWARD VERTICAL MOTION IN DENDRITIC LAYER H5/H6 OR 305-310K
ISENT SFCS.  OVERALL QG FORCING NOTHING SPECIAL...BUT NARROW BAND OF
OMEGA IS...APPARENTLY A REFLECTION OF FRONTOGENETICAL FORCING IN
VERY LOW STABILITIES UNDER RIGHT ENTRANCE REGION OF MN JET SEGMENT.
EPV AND THETA-E LAPSE RATES CERTAINLY SUGGEST CONVECTIVE ELEMENTS
TONIGHT SO WE SHOULD SEE NARROW HEAVY BANDED PCPN RATHER THAN
BROADER DEFORMATION ZONE AS MID LEVEL SATURATION PATCHY.  FOLLOWING
GFS BUFR SOUNDINGS...PCPN SHOULD MAINLY BE RAIN THIS EVE...GOING TO
RAIN/SNOW AND THEN MAINLY SNOW 06-09Z.  WILL LIKELY ALSO SEE SLEET
MIX IN AFTER 03Z AS COLD AIR DEEPENS SOMEWHAT AND CONVECTION COMES
INTO PLAY.  PEAK UVM LOOKS TO BE 03Z-09Z PLACING GREATEST SNOW
POTENTIAL IN BAND FROM FROM AIO-IFA.  ALTHOUGH GFS COBB AMOUNTS
SUGGEST UP TO 9 INCHES POSSIBLE AT CRL...HAVE TRIMMED THAT BACK
SOMEWHAT TO ACCOUNT FOR MELTING AND UNCERTAINTY IN PCPN TYPE.
ISOLATED AREAS COULD CERTAINLY END UP WITH THOSE AMOUNTS...BUT
COVERAGE WILL BE LIMITED SO GOING MORE CONSERVATIVE WILL LIKELY BE
MORE REPRESENTATIVE...HIGHER POD AND LOWER FAR.  WITH UNCERTAINTY IN
MODEL TRENDS...CONVECTION AND THERMAL PROFILE THIS FORECAST IS
ADMITTEDLY RATHER LOW CONFIDENCE AND LIKELY OPEN TO REVISIONS AS
EVENT NEARS.  BECAUSE OF FORECAST SHIFT AND EVEN WARNING POTENTIAL
FEEL SOME SORT OF HEADLINE IS WARRANTED SO FOR A START WILL GO WITH
GENERAL WINTER WX ADVY TONIGHT FROM SW INTO NE IOWA.

SYSTEM SHOULD EXIT MON MORNING WITH LITTLE ADDITIONAL ACCUMS.
LOWERED TEMPS SOMEWHAT TONIGHT...ALTHOUGH NOT AS AGGRESSIVELY AS MOS
DEPICTS.  SHOULD SEE LITTLE REBOUND TOMORROW WITH CONTINUED CAA.
NAM ENDS UP COOLER WITH MORE LOW CLOUDS MON NIGHT INTO TUE.  FEEL
THIS IS A BIT TOO EXTREME BUT DID SHADE THINGS DOWNWARD IN THESE
PERIODS FROM A COMPROMISE TO JUST BELOW GFS MOS.  WITH FOCUS ON NEAR
TERM...DID NOT CHANGE LATER PERIODS MUCH BUT DID BUMP POPS UP
SLIGHTLY N TUE NIGHT/WED AS SYSTEM DROPS DOWN MO VALLEY.

&&

.HYDROLOGY...
BASINS BETWEEN DSM AND OTM HAVE SNOW WATER EQUIVALENTS OF 2-4 INCHES
BASED ON NOHRSC ESTIMATES.  WITH WARM TEMPS AND RAIN THIS AFTERNOON
AND EVE...WITH MAY ACCELERATE MELTING.  WILL CONTINUE MENTION IN
THE HWO REGARDING CHARITON...S SKUNK AND DES RIVER TRIBS IN THESE
AREAS. COULD BE PLENTY OF STANDING WATER TOO THAT HAS DIFFICULTY
DRAINING DUE TO FULL SNOWPACKED DITCHES.

&&

.AVIATION...02/18Z
LOTS OF LOW LEVEL MOISTURE IS STREAMING NORTH AHEAD OF COLD
FRONT...BUT IT IS SHALLOW. AFTER LONG TRACK OVER MELTING SNOW ...IT
IS PRODUCING LOW CLOUDS AND FOG IN NRN IA...WITH IFR CONDITIONS.
DRIZZLE AND LIGHT RAIN ARE EXPECTED TO DEVELOP THROUGH THE AFTERNOON
INTO EARLY EVENING...PROLONGING IFR IN NORTH. FARTH S...SHOWERS OR
THUNDERSTORMS ARE EXPECTED TO DEVELOPED SE OF KDSM...WITH MVFR
ASSOCIATED. AFTER THE FRONT...MAINLY 03Z-09Z A BAND OF SNOW WILL
SPREAD EWD ACROSS CENTRAL IA PRODUCING IFR CIGS AND VISIBILITIES.
MVFR FOLLOWING THEN CLEARING MON MORNING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...WINTER WX ADVY TONIGHT
CERRO GORDO-WRIGHT-FRANKLIN-BUTLER-BREMER-CALHOUN-WEBSTER-HAMILTON-
HARDIN-GRUNDY-CRAWFORD-CARROLL-GREENE-BOONE-STORY-MARSHALL-AUDUBON-
GUTHRIE-DALLAS-POLK-CASS-ADAIR-MADISON-ADAMS-UNION-TAYLOR-

&&

BSS/KJ

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1100 AM CST SUN MAR 2 2008

IAZ004>007-015-016-023-024-033-031100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-POCAHONTAS-
HUMBOLDT-SAC-
1100 AM CST SUN MAR 2 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL AND
NORTHWEST IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

LIGHT RAIN WILL CHANGE TO LIGHT SNOW DURING THE LATE AFTERNOON AND
EVENING HOURS. ACCUMULATIONS SHOULD VARY FROM A DUSTING TO TWO
INCHES BEFORE THE PRECIPITATION ENDS AFTER MIDNIGHT.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED.

IAZ017-025>028-034>038-044>049-057>060-070>072-081-082-092-031100-
CERRO GORDO-WRIGHT-FRANKLIN-BUTLER-BREMER-CALHOUN-WEBSTER-
HAMILTON-HARDIN-GRUNDY-CRAWFORD-CARROLL-GREENE-BOONE-STORY-
MARSHALL-AUDUBON-GUTHRIE-DALLAS-POLK-CASS-ADAIR-MADISON-ADAMS-
UNION-TAYLOR-
1100 AM CST SUN MAR 2 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST...CENTRAL
AND NORTHEAST IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

RAIN DURING THE LATE AFTERNOON WILL MIX WITH SLEET...AND THEN CHANGE
TO ALL SNOW THIS EVENING. ACCUMULATIONS SHOULD VARY FROM TWO TO FOUR
INCHES...BUT LOCALLY HIGHER AMOUNTS ARE POSSIBLE. MOST OF THE SNOW
WILL FALL IN JUST A FEW HOURS.  WITH BRISK NORTHWEST WINDS AT SPEEDS
OF 15 TO 30 MPH...VISIBILITIES MAY BE REDUCED TO A HALF MILE OR LESS
DURING THE PERIODS OF MORE INTENSE SNOW.

A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE AREA. PLEASE REFER
TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES
FOR MORE DETAILS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED...BUT SNOWFALL REPORTS ARE
ALWAYS APPRECIATED AND ENCOURAGED.

IAZ039-050-061-062-073>075-083>086-093>097-031100-
BLACK HAWK-TAMA-JASPER-POWESHIEK-WARREN-MARION-MAHASKA-CLARKE-
LUCAS-MONROE-WAPELLO-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
1100 AM CST SUN MAR 2 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHERN AND
EASTERN IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

FOR AREAS SOUTH OF I-80...ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE
LATE THIS AFTERNOON AND EARLY THIS EVENING...WITH POTENTIAL FOR
DAMAGING WINDS OR LARGE HAIL.

LATER IN THE EVENING...RAIN WILL MIX WITH SLEET AND SNOW...AND THEN
CHANGE TO ALL SNOW AFTER MIDNIGHT. ACCUMULATIONS SHOULD VARY FROM
ONE TO TWO INCHES...BUT LOCALLY HIGHER AMOUNTS MAY OCCUR. MOST OF
THE SNOW WILL FALL IN JUST A FEW HOURS...REDUCING VISIBILITY AND
CAUSING SLICK CONDITIONS.

IN ADDITION...WARM TEMPERATURES AGAIN TODAY ARE CAUSING SNOW
MELT...SO SMALL STREAMS AND TRIBUTARIES MAY REACH BANK FULL.
LOCALIZED MINOR FLOODING MAY OCCUR DUE TO PONDING OF WATER.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED FOR A SHORT TIME LATE THIS
AFTERNOON AND EARLY THIS EVENING...AND SNOWFALL REPORTS ARE ALWAYS
APPRECIATED AND ENCOURAGED.

JUNGBLUTH