River Flood Warning 9, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1221 PM CST MON MAR 8 2010

.UPDATE...
BIGGEST POINT IS UPCOMING CHANGES IN HYDRO PRODUCTS.  SEE HYDRO
SECTION BELOW FOR MORE DETAILS.

ONLY MINOR CHANGES TO PREVIOUS FORECAST...MAINLY CLIPPING MAXES A
FEW DEGREES AS SUGGESTED BY EVEN THE MOST AGGRESSIVE GFS FORECAST
SOUNDINGS.  ALTHOUGH LOW CLOUDS ARE ERODING SOMEWHAT SOUTH...EXPECT
CLOUDS FROM APPROACHING SYSTEM TO KEEP ANY CLEARING BRIEF.  NAM/WRF
CONTINUE TO BE TOO COOL...OVERLY INFLUENCED BY SNOW COVER.  ALSO
UPDATED 18Z AVIATION DISCUSSION.

&&

.SHORT TERM /TODAY/...
LOW LEVEL MOISTURE IS HOLDING TIGHT OVER IOWA EARLY THIS MORNING
WITH LOW LEVEL STRATUS COVERING NEARLY THE ENTIRE STATE. CEILINGS AT
3 AM ARE RANGING FROM 100-800 FT. VSBYS HAVE BEEN HOLDING THE PAST
SEVERAL HOURS FROM 1/4SM TO 2 1/2SM. WILL KEEP THE DENSE FOG
ADVISORY INTACT THOUGH AS SHOULD STILL SEE SOME LOWERING TOWARD DAY
BREAK. PRIMARY QUESTION OF THE DAY IS WILL THE STRATUS HOLD STRONG
AND BEGIN TO GIVE DURING THE DAY. THE 00Z NAM WAS ADAMANT THAT THE
STRATUS WOULD REMAIN INTACT OVER CENTRAL IA WHILE ERODING FROM THE
EAST AND SOUTH. THE 06Z NAM HAS BACKED OFF SOMEWHAT. WITH WARM
ADVECTION GOING ON NEAR 900 MB...THE LOW LEVEL INVERSION CONTINUES
TO STRENGTHEN AND WITH SNOW MELT CONTINUING BELOW WITH LIGHT SFC
FLOW...THERE IS LITTLE HOPE OF ERODING THE STRATUS COMPLETELY. THE
RESULT WILL BE FOG LINGERING THIS MORNING AND LIKELY WILL BE HAZY
MUCH OF THE DAY WITH STRATUS REMAINING MUCH OF THE DAY OVER CENTRAL
AND NORTHERN IA. BEST CHANCE FOR SUN WILL BE OVER THE SOUTH.

THE NAM IS A LITTLE BEHIND THE CURVE REGARDING SFC DEWPOINTS AND
TEMPERATURES EARLY THIS MORNING WITH THE GFS MEAN FIELDS PERFORMING
BETTER. TEMPERATURES AT 3 AM ARE NEAR MET GUIDANCE HIGHS WHICH IS
NOT REALISTIC AS THERE WILL AT LEAST BE SOME DIURNAL RESPONSE
SIMILAR TO SUNDAY. HAVE KEPT THE PERIOD DRY WITH THE EXCEPTION OF
SOME PATCHY DRIZZLE EARLY. PRECIPITATION WILL BE NEARING FAR
SOUTHWEST IA BY 00Z BUT SHOULD NOT AFFECT THE FORECAST AREA UNTIL
AFTER THAT TIME WHEN BETTER SATURATION THROUGH THE MID LEVELS
OCCURS.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
NOT TOO MANY CHANGES NOTED IN THE EXTENDED WITH MODELS CONTINUING
TO SHOW GOOD AGREEMENT WITH EACH OTHER AND FROM RUN TO RUN. STILL
EXPECTING A PROLONGED PRECIPITATION EVENT...WITH A FEW DIFFERENT
WAVES IMPACTING THE CWA. FIRST WAVE OF INTEREST PUSHING THROUGH
ARIZONA AT THE MOMENT...AND WILL CONTINUE ITS EASTWARD
TRACK...BEGINNING TO TURN MORE NORTHEASTWARD AS IT MOVES THROUGH
THE SOUTHERN HIGH PLAINS TONIGHT INTO CENTRAL KANSAS BY 12Z TUESDAY.
FEW BATCHES OF ENERGY ROTATING AROUND THE MAIN LOW TO BE RESPONSIBLE
FOR MAIN PUSHES OF MOISTURE/EXPECTED RAIN ACROSS THE AREA. FIRST ONE
TO ROTATE INTO THE CWA BY THIS EVENING AND MOVE NORTHWARD INTO
TUESDAY MORNING. HAVE CONTINUED WITH CATEGORICAL POPS...BUT HAVE
SLOWED THE INITIAL ONSET SOME ACROSS THE AREA. SFC WINDS TO REMAIN
MORE EASTERLY TO ONLY SLIGHTLY SOUTHEASTERLY OVERNIGHT...SUGGESTING
SOME DRIER AIR TO OVERCOME ESPECIALLY ACROSS THE NORTHERN CWA. AS
MAIN UPPER LOW WOBBLES ACROSS NORTHEASTERN KANSAS WEDNESDAY...NEXT
SHORTWAVE ROTATES INTO SOUTHERN IOWA BY LATE TUESDAY
AFTERNOON...PUSHING NORTHWARD THROUGH THE CWA TUESDAY NIGHT INTO
EARLY WEDNESDAY. SHOULD SEE ANOTHER ROUND OF RAIN WITH THIS BATCH OF
ENERGY. MAY THEN SEE A BREAK IN THE PRECIP LATER WEDNESDAY INTO
WEDNESDAY EVENING...WITH CLOUD COVER REMAINING ACROSS THE AREA. MAIN
UPPER WAVE WEAKENS...AS NEXT WAVE DIGGING THROUGH THE SOUTHERN
PLAINS TAKES SHAPE AND PHASES WITH THE CURRENT SYSTEM IN PLACE. THIS
SYSTEM IS EXPECTED TO PUSH INTO IL THURSDAY AND RETROGRADE SOMEWHAT
INTO MISSOURI THURSDAY NIGHT INTO FRIDAY. WARMER AIR/MOISTURE
WRAPPING INTO THE SYSTEM ALLOWS FOR LIFT ACROSS THE CWA THURSDAY
INTO THURSDAY NIGHT. HAVE INCREASED POPS FOR THIS TIME PERIOD...WITH
ANOTHER ROUND OF PRECIP EXPECTED. SOUNDINGS/THERMAL PROGS INDICATE
ALL RAIN FOR NOW...WITH COLDER AIR REMAINING JUST TO THE WEST OF THE
CWA. RIGHT NOW LOOKS LIKE MAJORITY OF THE PRECIP TO BEGIN TO MOVE
OUT OF THE CWA BY LATER FRIDAY INTO FRIDAY NIGHT...WITH UPPER
RIDGING BUILDING INTO THE AREA FOR THE WEEKEND. BLENDED QPF FORECAST
WITH HPC GUIDANCE AND THE GFS/EC WHICH INDICATES AROUND AN INCH FOR
MOST SITES THROUGH THE WEEK...WITH LOCALLY HIGHER AMOUNTS POSSIBLE.
NAM TRIES TO BRING SOME INSTABILITY INTO THE CWA TUESDAY AFTERNOON
INTO TUESDAY NIGHT...BUT GFS/EC KEEP IT TO THE SOUTH OF THE CWA.
HAVE THEREFORE LEFT IT OUT OF THE FORECAST...BUT IF GET SOME
CONVECTIVE DEVELOPMENT LOCALLY HIGHER PRECIP AMOUNTS ALSO EXPECTED.
OTHERWISE TEMPERATURES TO REMAIN MILD THROUGH THE WEEK...ALTHOUGH
DID CONTINUE TO UNDERCUT GUIDANCE WITH CLOUDS/PRECIP KEEPING TEMPS
DOWN SOME. TRENDED OVERNIGHT TEMPERATURES WARMER...WITH DEWPOINTS
MAINLY IN THE UPPER 30S TO LOWER 40S THROUGHOUT MUCH OF THE WEEK
WILL KEEP TEMPS UP AT NIGHT. THEREFORE EXPECT A SMALLER DIURNAL
RANGE THROUGHOUT THE WEEK. THESE MILD TEMPERATURES WILL CONTINUE THE
SNOWMELT PROCESS...AND WHEN COMBINED WITH THE ADDITIONAL RAINFALL
WILL LIKELY LEAD TO FLOODING ACROSS MUCH OF THE AREA BY LATE WEEK
INTO THE WEEKEND.

.HYDROLOGY...
MAJOR CHANGES TO HYDRO PRODUCTS WILL BE FORTHCOMING THIS AFTERNOON.
WILL LIKELY ISSUE MULTIPLE RIVER FLOOD WARNINGS BASED ON SNOWMELT
AND 5 DAYS OF QPF...RATHER THAN TYPICAL 24 HOUR QPF.  THIS IS FOR
NCRFC SITES ONLY AS OF NOW.  THIS IS NOT A SIGNIFICANT CHANGE IN
THINKING FROM PREVIOUS ESF WHICH MENTIONS MINOR TO MAJOR
FLOODING...BUT SEE NO REASON TO HOLD OFF ON WARNINGS AT THIS POINT
WITH SNOWMELT AND INCREASING RAIN CONFIDENCE.

&&

.AVIATION...
08/18Z...LITTLE CHANGE FROM 12Z FORECAST PACKAGE.  MODELS ARE STILL
CONSISTENT KEEPING LOW CLOUDS LOCKED INTO MOST TAF SITES.  LOW
CLOUDS ARE ERODING ACROSS IA/MO BORDER HOWEVER...SO CONFIDENCE IS
DETERIORATING SOMEWHAT AND THIS WILL HAVE TO BE WATCHED.  IF LOW
CLOUDS INDEED HOLD IN...EXPECT PERSISTENT IFR OR LOWER CONDITIONS
THROUGH VALID PERIOD.  SHOWERS SHOULD OVERSPREAD SITES FROM SW-NE
TONIGHT AND INTO EARLY TUE.  THUNDER QUITE POSSIBLE IN THE SOUTHERN
SITES BUT HAVE ONLY INCLUDED CB WORDING FOR NOW.

&&

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

SHORT TERM...DONAVON/SMALL
LONG TERM...BEERENDS
AVIATION/HYDROLOGY...SMALL

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
219 PM CST MON MAR 8 2010

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-091200-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE-
BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-
POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-
CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-
DAVIS-
219 PM CST MON MAR 8 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MUCH OF CENTRAL IOWA.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

CHANCES OF ICE JAMS AND FLOODING ARE STILL EXPECTED WITH THE
POTENTIAL INCREASING LATER THIS WEEK. THE COMBINATION OF SNOWMELT
ASSOCIATED WITH WARMING TEMPERATURES...AND ADDITIONAL RAINFALL
TUESDAY THROUGH FRIDAY MAY RESULT INITIALLY IN ICE JAMS...AND THEN
EXPAND TO INCLUDE MORE WIDESPREAD RIVER FLOODING.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED...HOWEVER ANY REPORTS OF
FLOODING AND ICE JAMS ARE ENCOURAGED AND GREATLY APPRECIATED.

MJB/BSS