Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 220836
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
336 AM CDT FRI APR 22 2016

.SHORT TERM.../TODAY/
ISSUED AT 336 AM CDT FRI APR 22 2016

MAIN CONCERN TODAY WILL BE STRATUS AND TEMPERATURES. SHORT WAVE OVER
THE GREAT LAKES CONTINUES TO PUSH COLDER AIR ALOFT INTO IOWA EARLY
TODAY. A SECONDARY SFC WEAK TROUGH IS ALSO MOVING INTO THE AREA WITH
STRATUS RAPIDLY INCREASING BEHIND IT. OVER THE SOUTHEAST EARLY TODAY
DEW POINTS REMAIN IN THE UPPER 40S TO NEAR 50...SOME FOG POTENTIAL
STILL EXISTS INTO THE EARLY MORNING HOURS THOUGH WINDS ARE STILL
STRONG ENOUGH TO PREVENT ANY RAPID DECREASE IN VISIBILITY THUS FAR.
HIRES MODELS SUGGEST THAT SHIELD OF STRATUS WILL EXPAND ACROSS THE
AREA THROUGH AT 16Z WITH A GRADUAL SHIFT IN THE SHIELD TO THE EAST
SOUTHEAST FROM 18Z TO 00Z AS THE UPPER LEVEL SYSTEM SHIFTS EAST AND
A WEAK RIDGE OF HIGH PRESSURE BUILDS INTO THE AREA FROM THE WEST.
WITH THE EXCEPTION OF THE SOUTHEAST...MOST AREAS WILL SEE AMPLE
SUNSHINE FOR THE MID AFTERNOON TO EVENING HOURS. THIS WILL HELP
HIGHS RECOVER TO THE LOWER 60S NORTH TO THE MID TO UPPER 60S OVER
THE SOUTH. GFS/EURO SIMILAR WITH H850 COLD AIR ADVECTION STRONGER
OVER THE NORTHEAST WHERE AFTERNOON H850 TEMPS ARE PROGGED TO COOL TO
4-5C WHILE THE CENTRAL/SOUTH WILL RIDE THE 5-6C BANDWAGON. THOUGH
NOT A SIGNIFICANT DIFFERENCE...WITH THE CLOUDS AND COOLER TEMPS
ALOFT WILL MAKE FOR A 5-6F SFC TEMP DIFFERENCE BY LATE AFTERNOON
FROM NORTHEAST TO SOUTHWEST. WINDS ARE NOT A BIG FACTOR
TODAY...BUT NORTH WINDS OF 10-15 THIS MORNING WILL GIVE WAY TO NE
10 BY AFTERNOON. BY EVENING THE REGION WILL BE GENERALLY CLEAR IN
ADVANCE OF THE NEXT UPSTREAM WAVE APPROACHING FOR THE WEEKEND.

.LONG TERM.../TONIGHT THROUGH THURSDAY/
ISSUED AT 336 AM CDT FRI APR 22 2016

LITTLE OVERALL CHANGE IN FORECAST THINKING FROM PAST SEVERAL
DAYS...WITH A GENERALLY ACTIVE WEATHER PATTERN EXPECTED FOR MUCH
OF NEXT WEEK AND SEVERE WEATHER EVEN POSSIBLE AT TIMES.

FROM TONIGHT THROUGH SATURDAY NIGHT THE WEATHER ACROSS IOWA WILL
REMAIN FAIRLY QUIET AND DRY AS HIGH PRESSURE RIDGING SLIDES ACROSS
THE REGION. THE SURFACE RIDGE WILL CROSS IOWA TONIGHT AND WITH
WINDS GOING CALM AND SOME FORECAST SOUNDINGS INDICATING A SHALLOW
SATURATED LAYER...SOME FOG AND STRATUS MAY BE POSSIBLE. OTHERWISE
IT WILL REMAIN MOSTLY CLEAR THROUGH SATURDAY WHEN WINDS WILL COME
AROUND TO SOUTH AND PICK UP...BEGINNING A TREND OF WARMING AND
INCREASING MOISTURE THAT WILL PERSIST THROUGH THE WEEKEND.

BY SUNDAY MORNING A MID/UPPER LOW PRESSURE GYRE WILL BE CROSSING
THE ROCKIES...AND WILL SUBSEQUENTLY MOVE EASTWARD ACROSS SOUTH
DAKOTA AND MINNESOTA. AT THE SURFACE...LOW PRESSURE DEVELOPING
ALONG THE LEE OF THE ROCKIES SATURDAY NIGHT WILL COALESCE INTO A
CYCLONE OVER SOUTH DAKOTA BY SUNDAY...INITIALLY AHEAD OF THE
MID/UPPER LEVEL LOW BUT EVENTUALLY BECOMING STACKED. IOWA WILL BE
FIRMLY WITHIN THE WARM/MOIST SECTOR OF THE CYCLONE ON SUNDAY WITH
BROAD FORCING AND UPPER LEVEL DIFFLUENCE OVERSPREADING THE REGION
BY THE AFTERNOON. THERE HAS BEEN A CONSISTENT SIGNAL FOR A
PVA/SPEED MAX FEATURE ROTATING AROUND THE BASE OF THE GYRE AND
TRIGGERING THUNDERSTORM DEVELOPMENT ON SUNDAY AFTERNOON AND
EVENING...WITH CONVERGING MODEL SOLUTIONS PEGGING THE REGION FROM
EASTERN KANSAS UP TOWARD SOUTHWESTERN OR CENTRAL IOWA AS THE MOST
LIKELY AREA TO SEE THESE THUNDERSTORMS BEFORE SUNSET. THE DYNAMIC
FORCING FOR THESE STORMS IS PRETTY IMPRESSIVE AND INSTABILITY WILL
CERTAINLY BE SUFFICIENT FOR SOME STRONG THUNDERSTORMS...WHILE WIND
PROFILES SHOW GOOD SPEED SHEAR BUT SOMEWHAT LIMITED DIRECTIONAL
SHEAR. THIS SHOULD RESULT IN SOME ELEVATED SUPERCELL STRUCTURES
WHICH MAY REACH PARTS OF OUR FORECAST AREA LATE ON SUNDAY. THE
PRIMARY THREATS WOULD BE LARGE HAIL AND PERHAPS SOME STRONG WINDS.

IN WAKE OF THE SUNDAY SYSTEM MONDAY AND MONDAY NIGHT WILL BE
MOSTLY DRY AND SOMEWHAT COOLER WITH A WEAK SURFACE RIDGE MOVING BY
TO OUR NORTH. HOWEVER...THE NEXT LARGE STORM SYSTEM IN THE TRAIN
WILL BE CROSSING THE ROCKIES BY TUESDAY MORNING AND WILL PRODUCE
ROUGHLY A REPEAT OF THE SUNDAY SCENARIO WITH STORMS LIKELY FIRING
UP ON TUESDAY AFTERNOON SOMEWHERE OVER NEBRASKA/KANSAS/MISSOURI
AND MOVING NORTHEASTWARD ACROSS IOWA. THERE REMAIN SIGNIFICANT
DIFFERENCES IN THE TIMING OF THIS SYSTEM BETWEEN THE VARIOUS
PROGNOSTIC MODELS...WHICH WILL HAVE A SIGNIFICANT IMPACT ON WHERE
ANY SEVERE WEATHER THREAT MAY RESIDE ACROSS THE MIDWESTERN U.S.
ONCE THIS STORM SYSTEM PASSES WE WILL ONCE AGAIN SEE SOMEWHAT
COOLER AND DRIER WEATHER FOR A COUPLE OF DAYS...THEN TOWARD THE
END OF NEXT WEEK THE NEXT CYCLONE WILL APPROACH.

&&

.AVIATION.../FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT/
ISSUED AT 1202 AM CDT FRI APR 22 2016

MAIN ATTENTION WILL BE PROGRESSION OF CURRENT MN/WRN IA MVFR
STRATUS. DETAILS ARE NOT CLEAR CUT IN TIMING AND COVERAGE OF ITS
PROGRESSION...BUT HI RES MODELS SUGGEST IT WILL DROP INTO IA
EARLY THIS MORNING AND THEN DISSIPATE TOWARD MIDDAY WITH A PERIOD
OF SUB 2KFT MVFR CIGS QUITE POSSIBLE. CONFIDENCE IS NOT THERE FOR
IFR AT THIS POINT...BUT IS A POSSIBILITY AND WILL MONITOR TRENDS.
THIS SHOULD BE FOLLOWED BY VFR AS THE CLOUDS LIFT FROM MIDDAY
THROUGH THE END OF THE PERIOD. ONLY VSBY RESTRICTIONS EXPECTED
WOULD BE BRIEF MVFR TOWARD KOTM EARLY THIS MORNING.

&&

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

&&

$$

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



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