Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 112028
AFDDMX

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

.SHORT TERM /TONIGHT/...
ISSUED AT 328 PM CDT FRI APR 11 2014

WINDS WILL ONCE AGAIN DIMINISH THIS EVENING WITH MOSTLY CLEAR SKIES.
VERY LOW DEWPOINTS WILL ALLOW TEMPERATURES TO FALL AFTER SUNSET...
BUT NOT FOR LONG AS WINDS WILL INCREASE BY MIDNIGHT AHEAD OF A LOW
PRESSURE SYSTEM APPROACHING RAPIDLY FROM SOUTH DAKOTA. AS THIS LOW
PRESSURE NEARS THE NORTHWEST CORNER OF IOWA AROUND SUNRISE
SATURDAY WINDS WILL TURN THROUGH SOUTHEAST TO SOUTH AND INCREASE
NOTICEABLY...ALONG WITH LOW LEVEL MOISTURE AS INDICATED BY
FORECAST SOUNDINGS. GIVEN THE RESULTING INSTABILITY SOME SHOWERS
AND THUNDERSTORMS ARE POSSIBLE EARLY SATURDAY MORNING...MAINLY
ACROSS NORTHERN IOWA CLOSER TO THE LOW...BUT NO SIGNIFICANT
IMPACTS ARE ANTICIPATED. HAVE MAINTAINED CHANCE POPS TO ACCOUNT
FOR THE PRECIP THREAT BUT THE BIG SHOW WILL WAIT FOR LATER
TOMORROW AND INTO SUNDAY AS DISCUSSED IN THE LONG TERM SECTION
BELOW.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 328 PM CDT FRI APR 11 2014

MAIN CHALLENGE THIS PERIOD WILL BE EVOLUTION OF SYSTEM THIS WEEKEND.
MODELS FINALLY REACHING SOME CONSENSUS ON DETAILS AND TO LESSER
EXTENT TIMING OF THE MULTIPLE PARTS OF THE SPRING STORM THIS
WEEKEND. ONGOING WARM AIR ADVECTION WILL BE IN PLACE OVER NORTHERN
IOWA BY 12Z SATURDAY WITH ELEVATED CONVECTION ON THE DECREASE NORTH
AS LOW LEVEL JET SWINGS MORE SOUTHEAST WITH TIME. WEAK SFC
FEATURE/UPPER LEVEL LOW OVER MN WILL HELP DROP COOL FRONT INTO
CENTRAL/SOUTHERN IOWA BY MID TO LATE AFTERNOON. GFS ONCE AGAIN
APPEARS FASTEST OF THE MODELS...WHILE THE GEM/EURO ARE MOST
CONSISTENT WITH LATE AFTERNOON/EVENING ARRIVAL OF FRONT INTO
SOUTHEAST IOWA. CONSEQUENTLY...BEST CHANCES FOR ORGANIZED SEVERE
CONVECTION WILL REMAIN OVER THE SOUTH THIRD ONCE MOISTURE RETURNS.
BEST UPPER LEVEL WINDS APPEAR TO BE FOCUSED OVER THE SOUTHEAST AS
WELL WITH BULK SHEAR WITH 30-40KTS THROUGH 0-6KM. EURO 0-1KM SRH
IS FORECAST TO BE 100-125 M2S2 ALONG THE WARM FRONT OVER THE EAST
AND 0-3KM SRH IS FORECAST TO BE 200-225 M2S2. DEPENDING ON THE
EVOLUTION OF THE EXPECTED WEAK SFC LOW TRACKING ACROSS THE REGION
SATURDAY AFTERNOON...THERE WILL BE A POTENTIAL FOR SUPERCELLS WITH
HAIL AND WIND BEING THE MAIN CONCERN AND A MORE CONDITIONAL ISOLATED
TOR ALONG THE WEAK WARM FRONTAL BOUNDARY IF INSOLATION IS STRONG
ENOUGH IN THE AFTERNOON. OVERALL WIND FIELDS ALOFT ARE NOT
SIGNIFICANT...WITH ONLY 35-45KTS FROM H850 TO H300. CURRENT RETURN
OF MOISTURE TODAY HAS BEEN QUITE MEAGER. MODELS HAVE CONSISTENTLY
OVERESTIMATED MOISTURE RETURN AND DEW POINTS OVER THE PAST FEW
DAYS. EVEN THIS MORNING...DRY POOL ACROSS WESTERN IOWA THROUGH
NORTH CENTRAL KS. FARTHER SOUTH...DECENT SFC MOISTURE BEGINNING TO
POOL FROM CENTRAL OK SOUTH TO GULF. ALOFT...QUITE DRY AT H850 SO
FAR BUT MOISTURE HAS MANAGED TO DRIFT NORTHEAST OF AN H850 WAVE
OVER THE PANHANDLE TO SPRINGFIELD MISSOURI. DEEPER MOISTURE
EXTENDS IN A NARROW RIBBON SOUTH TO THE GULF SETTING THE STAGE FOR
A QUICK RETURN OF DEEPER...MORE WIDESPREAD RAINFALL THROUGH THE
WEEKEND. DEBRIS AND WARM AIR ADVECTION CLOUDS AND ONGOING THUNDER
THROUGH THE DAY SATURDAY LIKELY TO CAP HIGHS AROUND THE 70-72
DEGREE MARK EXCEPT FOR THE FAR SOUTH TO SOUTHEAST WHERE MORE
INSOLATION IS ANTICIPATED AND READINGS SHOULD NEAR THE 75 DEGREE
MARK. GOOD NEWS FOR MOST AREAS...A DECENT CHANCE AND AREAL
COVERAGE OF RAINFALL WITH THUNDER IS EXPECTED FOR SATURDAY NIGHT
AND SUNDAY...PRIMARILY OVER THE SOUTHEAST HALF OF THE FORECAST
AREA WITH 1 TO 2 INCHES OF RAIN AND LOCALLY HIGHER AMOUNTS. AFTER
MILD LOWS IN THE LOWER 40S NORTHWEST TO THE UPPER 50S SOUTHEAST
HIGHS RECOVER LITTLE ON SUNDAY AS MOST OF THE AREA WILL BE IN
GUSTY NORTHERLY FLOW. THE SOUTHEAST WILL REMAIN IN THE WARM SECTOR
FOR A BIT WITH THUNDER CHANCES REMAINING OVER HALF THE AREA.
SOUNDINGS INDICATE ELEVATED INSTABILITY ACROSS MOST OF THE REGION
FROM NEAR ATLANTIC TO WATERLOO. AS THE LOW DEPARTS...THE TREND
CONTINUES FOR COLDER AIR TO GRADUALLY MIX INTO THE SYSTEM AS THE
PRECIPITATION DIMINISHES. WILL CONTINUE CHANCES FOR RASN AND LIGHT
SNOW ON THE NORTHWEST FRINGES THROUGH EARLY MONDAY MORNING. MONDAY
LOOKS MUCH BELOW NORMAL WITH SOME RESIDUAL CLOUD COVER...GUSTY
NORTHWEST WINDS AND HIGHS 15 TO 20 DEGREES BELOW NORMAL. GEM/EURO
CONTINUE TO ADVERTISE A SECOND ARCTIC COLD FRONT DROPPING SOUTH
INTO NORTHERN IOWA TOWARD EVENING WITH ANOTHER DECK OF STRATUS
LIKELY TO OVERSPREAD NORTHERN IOWA BY 03-06Z TUES. LOWS OVERNIGHT
WILL BE QUITE COLD IN THE LOWER TO MID 20S NORTH TO LOWER 30S
SOUTH. MODELS DIFFER ON TIMING OF WARM UP NEXT WEEK...BUT
PREFERENCE FOR EURO AND GEM OVER GFS DUE TO BIAS CONSIDERATIONS.
WITH THAT IN MIND...WILL DELAY ANY WARMING UNTIL WED AND THUR WITH
MORE RAPID WARMING BOTH DAYS AS HIGHER AMPLITUDE SYSTEM AGAIN
MOVES INTO THE WESTERN PLAINS. HIGHS SHOULD REACH THE LOWER 50S
NORTH WITH LOWER 60S SOUTH BOTH WED AND THURSDAY. MOISTURE SHOULD
ALSO BE ON THE INCREASE BY THE END OF THE PERIOD.

&&

.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.


&&

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

$$

SHORT TERM...LEE
LONG TERM...REV
AVIATION...LEE



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