River Flood Warning 27, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
251 PM CDT TUE APR 1 2008

.SHORT TERM /TONIGHT/...
SURFACE HIGH PRESSURE OVER THE HIGH PLAINS WILL MOVE QUICKLY
EASTWARD ACROSS IOWA OVERNIGHT. WINDS WILL LIGHTEN AROUND AND AFTER
SUNSET...BECOMING LIGHT AND VARIABLE BY MIDNIGHT AS THE HIGH PASSES
THROUGH...THEN COMING AROUND TO SOUTH AND PICKING UP AGAIN AS THE
HIGH MOVES AWAY BY TOMORROW MORNING. NO PRECIPITATION IS EXPECTED
OVERNIGHT AS IS REFLECTED IN THE LACK OF POPS. THE TWO MOST
DIFFICULT ELEMENTS TO PREDICT TONIGHT WILL BE CLOUD COVER THROUGH
THE EVENING AND MINIMUM TEMPERATURES OVERNIGHT.

LOW-LEVEL STRATUS WHICH HAS PLAGUED THE STATE FOR THE PAST COUPLE OF
DAYS IS HAVING TROUBLE MOVING OUT OF THE AREA THIS AFTERNOON. THE
TWO NORTHERN TIERS OF COUNTIES ARE VIRTUALLY CLEAR...BUT THE
SOUTHERN TWO THIRDS OF OUR SERVICE AREA ARE STILL SOCKED IN. WHAT
LOOKED LIKE RAPID SOUTHWARD PROGRESS OF THE BACK EDGE THIS MORNING
HAS SLOWED CONSIDERABLY AS STRATUS HAS CONTINUED TO FILL IN ON THE
BACK SIDE. THIS CLOUD REDEVELOPMENT SHOULD DIMINISH AS WIND SPEEDS
DECREASE THIS EVENING...ALLOWING THE CLOUD SHIELD TO MOVE OUT
THEREAFTER.

THE MINIMUM TEMPERATURE FORECAST OVERNIGHT IS DOMINATED BY THE
SPECTER OF RADIATIONAL COOLING. WITH HIGH PRESSURE PASSING
OVERHEAD...CLEARING SKIES...AND LIGHTENING WINDS...DEWPOINT
DEPRESSIONS WILL DROP TO NEAR ZERO DURING THE EARLY MORNING HOURS.
OBSERVED DEWPOINTS THIS AFTERNOON HAVE RUN SEVERAL DEGREES HIGHER
OVER MUCH OF OUR AREA THAN THE MODELS ARE PICKING UP ON...POSSIBLY
DUE TO AIR COMING OFF THE SNOWPACK UPSTREAM. AM ALSO CONCERNED THAT
IF THE LOW CLOUDS TAKE LONGER TO CLEAR OUT OF THE FAR SOUTH THAN
EXPECTED IT WILL KEEP TEMPS UP THERE. HAVE OPTED TO NUDGE MINIMUM
TEMPS UPWARD A DEGREE OR TWO...WITH THE COLDEST TEMPS LIKELY IN THE
NORTH WHERE CLOUD COVER WILL BE LEAST...DEWPOINTS WILL BE
LOWEST...AND WINDS WILL BE LIGHTEST.

.LONG TERM /WEDNESDAY-TUESDAY/...
MUCH ENERGY OVER THE EASTER PACIFIC AT VARIOUS LATITUDES WILL SWOOP
OVER THE ROCKIES BY WED NIGHT AND CONVERGE OVER THE CENTRAL PLAINS
BY THURSDAY. THE MODELS ARE CONSISTENT IN MAINTAINING SEPARATION
BETWEEN THE NORTHERN AND SOUTHERN STREAM SYSTEMS...BUT THERE IS AN
OBVIOUS ABSORPTION OF THE SOUTHERN STREAM UPPER LEVEL SYTEM INTO THE
SOUTHWEST FLOW AHEAD OF DIGGING NORTHERN STREAM TROUGH THURSDAY. THE
CONSENSUS IS TO ALSO KEEP THE ASSOCIATED SFC LOW TRACK AND BULK OF
MOISTURE SOUTH OF IA. HOWEVER...ISENTROPIC LIFT...QG FORCING AND MID
LEVEL FRONTOGENETICAL FORCING NORTH OF THE LOW TRACK WILL BRING
CHANCES FOR RAIN TO MUCH OF THE CENTRAL IOWA...THOUGH BEST CHANCES
WILL BE SOUTH OF INTERSTATE 80. THURSDAY WILL BE A TOUCH COOLER THAN
WEDNESDAY WITH THE CLOUD COVER...AND ESPECIALLY OVER SRN IA WHERE
RAIN CHANCES ARE GREATEST.

QUIET WEATHER AND NEAR NORMAL TEMPERATURES FRIDAY AND SATURDAY UNDER
NW FLOW ALOFT. THE WEATHER PATTERN/FORECAST BECOMES MUCH MORE
MUDDLED LATE IN THE WEEKEND AND EARLY NEXT WEEK. 12Z GFS IS NOW BACK
TO A MORE AMPLIFIED UPPER LEVEL SYSTEM TRACKING THROUGH THE CENTRAL
PLAINS. MEANWHILE THE 12Z ECMWF IS NOW FLATTER. BOTH SHOW A SFC LOW
PRESSURE OF DIFFERING MAGNITUDES MOVING THROUGH OR NEAR IOWA FROM
SUNDAY INTO MONDAY...THEN PERHAPS A HIGHER AMPLITUDE SYSTEM
APPROACHING THE AREA BY THE MIDDLE OF NEXT WEEK. SO FAR...THE LATE
WEEKEND SYSTEM DOES NOT APPEAR TO TAP INTO MUCH COLD AIR...SO PRECIP
TYPE WILL LIKELY BE RAIN. WILL CONTINUE TO MONITOR THOUGH BECAUSE
DEPENDING ON THE LOW TRACK AND STRENGTH OF DYNAMICS...THERE COULD BE
ENOUGH COLD AIR OR COOLING PROCESSES OCCURRING TO RESULT IN SOME
SNOW. OVERALL...THE BROAD WINDOW OF CHANCE POPS LATE IN THE EXTENDED
PERIOD REFLECT MUCH UNCERTAINTY IN THE EXACT TIMING OF THE VARIOUS
PRECIPITATION CHANCES.

&&

.AVIATION...01/18Z
THE LOW CLOUDS WHICH HAVE PLAGUED OUR AREA FOR THE PAST 36 HOURS OR
SO ARE FINALLY MOVING OUT. KMCW IS ALREADY VIRTUALLY CLEAR AND KFOD
WILL BE SOON...WITH THE OTHER STATIONS CLEARING OUT THIS AFTERNOON
AND EVENING. SURFACE HIGH PRESSURE WILL MOVE IN TONIGHT...RESULTING
IN A QUICK DROP IN WIND SPEEDS TO LIGHT AND VARIABLE. WINDS WILL
COME AROUND TO SOUTH SOUTHWEST AND PICK UP A BIT AS THE HIGH
PRESSURE MOVES EASTWARD AWAY FROM US TOMORROW.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE

SHORT TERM/AVIATION...LEE
LONG TERM...MOYER

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
330 PM CDT TUE APR 1 2008

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-022030-
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-
330 PM CDT TUE APR 1 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED.