Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 091743
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1243 PM CDT WED APR 9 2014

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 334 AM CDT WED APR 9 2014

STRONG WARM ADVECTION WILL BE ARRIVING OVER THE WESTERN HALF OF
THE STATE EARLY THIS MORNING AND WILL RAPIDLY SPREAD EAST. GOOD
SOUTHWEST WINDS WILL DEVELOP AND SHOULD HAVE A SIGNIFICANT DIURNAL
SWING FROM THE COOL LOWS THIS MORNING WITH TEMPERATURES RISING 35
TO 40 DEGREES. THIS WILL BE AIDED BY DEEP MIXING AND LOW DEWPOINTS
THAT WILL BE IN THE 20S AND 30S. SOUTHWEST WINDS THIS AFTERNOON
WILL BE IN THE 20 TO 30 MPH RANGE WITH HIGHER GUSTS. HIGH
TEMPERATURES ARE FORECAST TO BE IN THE 70S ACROSS THE ENTIRE
AREA. SIGNIFICANT SUNSHINE IS EXPECTED WITH A FEW PASSING HIGH
LEVEL CLOUDS.

.LONG TERM /TONIGHT THROUGH TUESDAY/...
ISSUED AT 334 AM CDT WED APR 9 2014

MODELS SHOWING MARKEDLY GOOD AGREEMENT IN BRINGING A WEAK...VERY
FAST MOVING...COLD FRONT THROUGH THE DMX CWA THURSDAY MORNING.
MODELS SUGGEST FRONT WILL ENTER NW COUNTIES OF CWA BY 06Z THU AND BE
EXITING THE DMX CWA BY 12Z. BIGGEST CHALLENGE WITH GENERATING PRECIP
WITH THIS FRONT IS LACK OF MOISTURE IN LOW LEVELS. HIGH PRESSURE OFF
SOUTHERN EDGE OF LOUISIANA PREVENTING GULF MOISTURE FROM BEING
ADVECTED NORTHWARD INTO IOWA BY THE TIME OF THE FROPA THURSDAY AM.
THERE IS SOME Q VECTOR CONVERGENCE IN MID LEVELS TO HELP GENERATE
SOME LIFT AND 0 TO 6 KM SHEAR VALUES OF 30 TO 35 KTS...BUT LIMITED
MOISTURE AVAILABILITY TO HAMPER SIGNIFICANT PRECIP/STORM CHANCES.

HIGH PRESSURE TO MOVE IN BEHIND THE FROPA WHICH WILL ADVECT SOME
COOLER AIR INTO THE REGION AND DROP TEMPS FROM WEDNESDAY. ENSEMBLE
SHOWING H850 TEMPS IN THE +3C TO +5C RANGE DURING THE DAY. GIVEN
SUNSHINE LIKELY PLUS MONDAY/S AFOREMENTIONED CONDITIONS AND
TEMPS...IT SEEMS REASONABLE TO GO A FEW DEGREES WARMER THAN MONDAY/S
TEMPERATURES AND GUIDANCE.

MODELS ARE IN GOOD AGREEMENT WITH PUSHING A WEAK...FAST MOVING
SHORTWAVE THROUGH THE CWA FRIDAY AM. CHALLENGE FOR THE SHORTWAVE
SIMILAR TO THURSDAY/S FRONT IN THAT THERE IS A NOTABLE LACK OF
MOISTURE TO SUPPORT SIGNIFICANT PRECIP/STORMS. THE HIGH PRESSURE
AREA FROM THURSDAY WILL HAVE PROPAGATED INTO ILLINOIS BY FRIDAY AM
AND SUBSEQUENT NORTHEASTERLY FLOW WILL MAKE IT INTO
MISSOURI...SERVING TO BLOCK GULF MOISTURE FROM MAKING IT INTO IOWA
TO SUPPORT THE SHORTWAVE. KEEPING SLIGHT POPS IN FCST AS HIGH BASED
LIGHT RAIN POSSIBLE IN MORNING...BUT FRIDAY PM SHOULD BE DRY IN DMX
CWA AS MODELS...ESPECIALLY THE GFS SHOWING SUBSIDENCE AND DRY AIR
ENTRAINMENT IN THE MID LEVELS...WHICH WILL LEAD TO MID LEVEL CLOUD
DECAY.

POTENTIAL FOR STRONG TO POSSIBLY SEVERE THUNDERSTORMS THE BIGGEST
THREAT. A LARGE...NEGATIVELY TILTED TROUGH IS SLATED TO MOVE ACROSS
THE NORTHERN CONUS. MODELS SHOWING A BOUNDARY COMING OFF OF THE LOW.
00Z GFS AND 12Z EURO IN GOOD AGREEMENT THROUGH 12Z SATURDAY...AND
THEN HAVE MAJOR DISAGREEMENT THEREAFTER. THE 00Z GFS SEEMS TO BE A
FAST OUTLIER WHEN COMPARED WITH OTHER MODELS SO LEANING TOWARDS
BLEND FAVORING THE EURO FOR TIMING. THE GULF IS OPEN WITH STRONG
MOISTURE TRANSPORT INTO THE CWA. ENSEMBLE RUNS HAVE +1.5 STD DEV
FOR PWAT VALUES SATURDAY. CAPE VALUES...ESPECIALLY IN SOUTHERN
IOWA...EXCEED 1000 J/KG DURING THE AFTERNOON. 0 TO 6 KM SHEAR
AROUND 30 KTS. BEST MOISTURE CONVERGENCE AND FORCING ALONG THE
BOUNDARY...SO THE LOCATION OF THE BOUNDARY WILL BE AN IMPORTANT
FOCUS FOR CONVECTION. MODELS HAVE BOUNDARY IN NORTHWESTERN IOWA
DURING THE DAYTIME...AND SLOWLY SAG IT SOUTHEASTWARD DURING THE
DAY. POSSIBLY ENOUGH CAPE...INSTABILITY...AND MOISTURE IN THE
ENVIRONMENT AHEAD OF THE BOUNDARY TO GENERATE STORMS. IN LEANING
TOWARDS THE EURO SOLUTION...THE BOUNDARY IS STILL OVER THE CWA
SUNDAY MORNING...SO STORMS MAY PERSIST INTO SUNDAY AS WELL.

FURTHERMORE...THE SLOWER EURO IS ESPECIALLY HINTING AT SNOW CHANCES
AS SYSTEM LINGERS INTO MONDAY MORNING. EURO HAS PRECIP GENERALLY OUT
OF CWA BY SUNRISE MONDAY...SO AS OF NOW...IT DOES NOT APPEAR THAT
THERE WILL BE MUCH IN TERMS OF IMPACT TO THE MONDAY MORNING
COMMUTE...BUT THE EVOLUTION OF THIS SYSTEM BEARS WATCHING. MODELS
HINTING AT HIGH PRESSURE MOVING ACROSS THE MIDDLE OF THE CONUS. THIS
SHOULD BRING DRY CONDITIONS AND SLIGHTLY COOLER TEMPS AS CWA WILL BE
IN NORTHWESTERLY FLOW INTO WEDNESDAY.

&&

.AVIATION...09/18Z
ISSUED AT 1239 PM CDT WED APR 9 2014

STRONG WINDS WILL CONTINUE TO MIX THIS AFTERNOON BEFORE DECOUPLING
BY AROUND 00Z TONIGHT. PRESSURE GRADIENT REMAINS TIGHT ENOUGH TO
KEEP SUSTAINED WINDS AOA 12 KNOTS THROUGH THE OVERNIGHT HOURS.
COLD FRONT WILL MOVE ACROSS THE STATE EARLY THURSDAY MORNING AND
WILL SEE SOME CAA TOWARDS THE END OF THE FORECAST PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 334 AM CDT WED APR 9 2014

HIGH TEMPERATURES IN THE 70S TODAY COMBINED WITH DEWPOINTS IN THE
UPPER 20S TO LOWER 30S THIS AFTERNOON...WILL CREATE RELATIVE
HUMIDITY VALUES LESS THAN 25 PERCENT. THIS FOLLOWS TUESDAY WHEN
RELATIVE HUMIDITY WERE IN THE 20S OVER CENTRAL AND SOUTHWEST IOWA
WHICH HELPED DRY FUELS FURTHER. THE FUELS ACROSS ALL OF CENTRAL
IOWA ARE STILL 85 TO 95 PERCENT CURED WITH GREEN UP NOT HAVING
OCCURRED YET. THE DRY FUELS...VERY LOW RELATIVE HUMIDITY VALUES
AND SOUTHWEST WINDS OF 20 TO 30 MPH WITH HIGHER GUSTS WILL CREATE
RED FLAG CONDITIONS FOR THE AFTERNOON HOURS. THEREFORE A RED FLAG
WARNING HAS BEEN ISSUED FOR THE ENTIRE FORECAST AREA FROM NOON TO
7 PM TODAY. THE STATE HAS HAD SEVERAL GRASS FIRES THE PAST FEW
WEEKS UNDER LESS FAVORABLE CONDITIONS. IN ADDITION...DATA FROM
PAST YEARS IOWA GRASS FIRES SUGGEST CONDITIONS TODAY WILL BE
SIMILAR TO THOSE EVENTS. OFTEN THESE CAN BE LINKED WITH THE PUBLIC
BURNING DURING SPRING CLEAN UP DURING THE FIRST MILD DAYS OF THE
SPRING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 7 PM CDT THIS EVENING FOR ADAIR-ADAMS-
APPANOOSE-AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-
CASS-CERRO GORDO-CLARKE-CRAWFORD-DALLAS-DAVIS-DECATUR-EMMET-
FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-
JASPER-KOSSUTH-LUCAS-MADISON-MAHASKA-MARION-MARSHALL-MONROE-PALO
ALTO-POCAHONTAS-POLK-POWESHIEK-RINGGOLD-SAC-STORY-TAMA-TAYLOR-
UNION-WAPELLO-WARREN-WAYNE-WEBSTER-WINNEBAGO-WORTH-WRIGHT.

&&

$$

SHORT TERM...DONAVON
LONG TERM...KOTENBERG
AVIATION...PODRAZIK
FIRE WEATHER...DONAVON



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