Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 111740
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1240 PM CDT FRI APR 11 2014

.SHORT TERM /TODAY/...
ISSUED AT 313 AM CDT FRI APR 11 2014

BROAD NORTHWEST FLOW ALOFT WILL PERSIST THROUGH THE DAY WITH WEAK
SHORTWAVE EDGING NORTHERN IOWA THIS MORNING. SOUTHERN EDGE OF LIFT
WILL SKIRT THE NORTH THIS MORNING WITH SOME CLOUDS AND THE THREAT OF
AN ISOLATED SHOWER.  HOWEVER...DRY LOW LEVELS WILL CONTINUE TO LIMIT
THE THREAT OF MEASURABLE PRECIPITATION AS THE SYSTEM PASSES
SOUTHEAST TODAY.  WITH THIS SYSTEM PASSING BY MIDDAY...SUNNY SKIES
SHOULD BE COMMON IN MOST AREAS THIS AFTERNOON WITH INCREASING
SOUTHWEST WINDS AS SURFACE RIDGE SLIPS INTO THE LOWER OHIO RIVER
VALLEY BY LATE THIS AFTERNOON.  HAVE STAYED ON TOP END OF GUIDANCE
GIVEN THE SUNSHINE...DRY AIRMASS...SOUTH WINDS AND GOOD MIXING INTO
THE AFTERNOON.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 313 AM CDT FRI APR 11 2014

MAIN FORECAST CONCERNS FOR THE EXTENDED REVOLVE AROUND
PRECIPITATION CHANCES FOR NEAR TERM...WITH LARGE SYSTEM SET TO
AFFECT THE AREA FOR THE WEEKEND. TWO LOW PRESSURE SYSTEM ARE SET
TO AFFECT THE AREA AND MODELS REMAIN IN BETTER AGREEMENT WITH THE
SYSTEM...THOUGH STILL SOME UNCERTAINTY MAKING FOR A CHALLENGING
FORECAST. WITH FIRST SYSTEM ANTICIPATED TO PUSH EAST FROM DAKOTAS
INTO SOUTHERN MINNESOTA BEGINNING FRIDAY NIGHT WITH FRONTAL
BOUNDARY PUSHING THROUGH IOWA. BEST FORCING WITH THIS SYSTEM WILL
BE IN NORTHERN IOWA NEAR LOW...AND HAVE KEPT FRIDAY NIGHT POPS IN
THE NORTH. WHILE MODELS INDICATE STRONG MOISTURE TRANSPORT BACK
INTO CENTRAL IOWA AHEAD OF THIS SYSTEM...FEEL THEY ARE A BIT TOO
AGGRESSIVE GIVEN AMOUNT OF DRY AIR ACROSS THE AREA. THEREFORE
HAVE CUT BACK ON TIMING AND EXTENT OF POPS TONIGHT SLIGHTLY.
FRONTAL BOUNDARY WILL CONTINUE TO DROP ACROSS CENTRAL IOWA DURING
THE DAY SATURDAY WHICH WILL CONTINUE TO BE FOCUS FOR
THUNDERSTORM DEVELOPMENT...ESPECIALLY IN THE LATE AFTERNOON
HOURS. AS MODELS DIFFER SOMEWHAT ON TIMING AND POSITIONING OF THE
BOUNDARY...HAVE TRENDED TOWARDS A GFS SOLUTION. MODELS ALSO ARE
NOT IN GOOD AGREEMENT IN AMOUNT OF INSTABILITY NEAR
BOUNDARY...THOUGH IN GENERAL SURFACE BASED CAPE VALUES OF AT OR
ABOUT 1000 J/KG ARE POSSIBLE AHEAD OF BOUNDARY...WITH NAM BEING
MOST AGGRESSIVE. IN ADDITION...SHEAR WILL BE FAVORABLE...AND MAY
SEE STRONG TO SEVERE STORMS FORM...WITH MAIN THREATS BEING HAIL
AND DAMAGING WINDS...WITH ELEVATED THUNDERSTORMS LINGERING INTO
SATURDAY NIGHT.

BEST CHANCE FOR PRECIPITATION WILL COME SUNDAY AS SECONDARY LOW
ACROSS KS BEGINS TO PUSH EAST WITH BOUNDARY LIFTING INTO SOUTHERN
IOWA. MOISTURE IS A BIT MORE CONFINED TO SOUTHERN IOWA...THOUGH
ANTICIPATE WIDESPREAD PRECIPITATION ACROSS THE CWA SUNDAY AS
SYSTEM CONTINUES TO LIFT NORTH. ENOUGH INSTABILITY FOR
THUNDERSTORMS TO REMAIN IN THE FORECAST...THOUGH SEVERE CHANCES
ARE SOMEWHAT LIMITED SUNDAY. SOUNDINGS INDICATE DEEP
SATURATION...AND COULD SEE HEAVY RAIN AT TIMES WITH THUNDERSTORMS.
SYSTEM WILL QUICKLY PUSH EAST...WITH PRECIPITATION ENDING SWIFTLY
FROM NORTHWEST TO SOUTHEAST AS LARGE UPPER LEVEL LOW ACROSS
NORTHERN CANADA DIGS TROUGH ACROSS IOWA...WITH ONLY LINGERING
LIGHT PRECIPITATION EARLY MONDAY. HOWEVER...STRONG CANADIAN LOW
WILL ALLOW FOR YET ANOTHER PUSH OF MUCH COOLER AIR INTO THE
NORTHERN PLAINS. THIS WILL ALLOW FOR PRECIPITATION TO SWITCH TO
SNOW ON BACK SIDE OF SYSTEM...HOWEVER STILL UNCERTAINTY IN TIMING
OF END OF PRECIPITATION AND PRECIPITATION MAY END BEFORE COLD
ENOUGH AIR PUSHES IN TO SWITCH TO SNOW. NONETHELESS...HAVE KEPT
SNOW AND RAIN/SNOW MENTION SUNDAY NIGHT.

COLD AIR WILL LINGER THROUGH THE BEGINNING OF THE WEEK BEFORE LOW
LIFTS NORTHEAST BY LATE WEEK...WITH WEAK ZONAL FLOW RETURNING
ACROSS IOWA. MAY SEE BRIEF CHANCES FOR PRECIPITATION IN NORTHERN
IOWA AT TIMES AS SHORTWAVES WORK AROUND UPPER LEVEL LOW...THOUGH
HAVE ONLY KEPT MENTION FOR WEDNESDAY NIGHT. ANOTHER LOW PRESSURE
SYSTEM WILL DEVELOP IN LEE OF ROCKIES AND LIFT PRECIPITATION INTO
IOWA FOR LATE IN THE PERIOD...THOUGH TEMPERATURES ARE WARM ENOUGH
FOR PRECIPITATION TO BE RAIN.

&&

.AVIATION...11/18Z
ISSUED AT 1240 PM CDT FRI APR 11 2014

VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. NEARLY CLEAR
SKIES WILL BE THE RULE THROUGH MIDNIGHT WITH WINDS DIMINISHING IN
THE EVENING. LATE TONIGHT AS A LOW PRESSURE SYSTEM APPROACHES FROM
NORTH DAKOTA WINDS WILL TURN TO SOUTH AND INCREASE AGAIN ALONG
WITH MID LEVEL CLOUDS...THEN SATURDAY MORNING THE WIND AND CLOUD
INCREASE WILL CONTINUE WITH A FEW SHOWERS AND STORMS BECOMING
POSSIBLE. HOWEVER...THE RELATIVELY LOW PROBABILITY OF RAINFALL
PRECLUDES MENTION IN THE TAFS AT THIS RANGE. CONVECTION WILL
BECOME MORE LIKELY LATER SATURDAY AND THIS WILL BE ASSESSED IN
FUTURE TAF ISSUANCES.

&&

.FIRE WEATHER...
ISSUED AT 313 AM CDT FRI APR 11 2014

ANOTHER DAY WHERE CONDITIONS FOR FIRE WILL BECOME ELEVATED BY
AFTERNOON.  SUNNY SKIES WILL INCREASE MIXING THROUGH THE DAY WITH
WARMING AT 850MB.  AIRMASS CONTINUES TO BE RELATIVELY DRY ALLOWING
THE NEAR SURFACE TEMPERATURES TO WARM QUICKLY AND GENERALLY WARMER
THAN GUIDANCE.  ANTICIPATE RELATIVE HUMIDITY VALUES TO DROP INTO THE
LOW TO MID 20S BY THIS AFTERNOON DURING PEAK HEATING. LIMITING
FACTOR IN RED FLAG CONDITIONS WILL BE THE WIND WHICH REMAINS
SUSTAINED IN THE MID TEENS THIS AFTERNOON.  WILL CONTINUE TO MENTION
ELEVATED FIRE CONDITIONS IN HWO AND SPS AS NECESSARY.

&&

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

&&

$$

SHORT TERM...COGIL
LONG TERM...AWB
AVIATION...LEE
FIRE WEATHER...COGIL



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