Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 301646
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1146 AM CDT THU APR 30 2015

.SHORT TERM /TODAY/...
ISSUED AT 256 AM CDT THU APR 30 2015

SFC HIGH TO DOMINATE THE REGION TODAY...WITH THE RIDGE AXIS MOVING
THROUGH THE CWA. WEAK CAA ALOFT...WITH NORTHERLY SURFACE FLOW. SOME
MID CLOUD CREEPING SOUTH ACROSS EASTERN MINNESOTA EXPECTED TO NOSE
INTO THE EASTERN CWA THIS MORNING AND MAY BREAK INTO A MID LEVEL CU
DECK ACROSS THE FAR EAST THIS AFTERNOON. WITH THE WEAK CAA AND THE
POSSIBILITY OF SOME CLOUDS HAVE DROPPED HIGHS A FEW DEGREES ACROSS
THE FAR EAST. OVERALL SHOULD SEE TEMPS SIMILAR TO SLIGHTLY COOLER
FROM THE READINGS WEDNESDAY WITH HIGHS RANGING FROM THE UPPER 60S
TO LOWER 70S ACROSS THE CWA.

.LONG TERM /TONIGHT THROUGH TUESDAY/...
ISSUED AT 256 AM CDT THU APR 30 2015

MAIN CHALLENGES REMAIN THE SAME IN THE EXTENDED. EXPECTING A WHOLESALE
TRANSITION TO A WET PATTERN AFTER SATURDAY WITH A SHIFT TO WEST
SOUTHWEST UPPER LEVEL PATTERN FOR MOST OF NEXT WEEK. SUBTROPICAL
HIGH SETS UP OVER THE ATLANTIC...RESULTING IN MORE GULF MOISTURE
ENTERING THE PICTURE AS WAVES BEGIN TO DEEPEN EAST OF THE ROCKIES.
MODELS DIFFER ON SOME OF THE FEATURES AND TIMING...BUT TRENDS ARE
SIMILAR. OVER THE NEXT 24 HOURS...HIGH AMPLITUDE RIDGE THAT ESTABLISHED
ITSELF ACROSS THE REGION TODAY WILL SLOWLY EDGE EAST OVERNIGHT.
THIS WILL ALLOW A WEAK PACIFIC BOUNDARY OVER THE WESTERN PLAINS TO
ENTER NORTHWEST IOWA BY 12Z FRIDAY. SHOWERS SHOULD HOLD OFF UNTIL
AFT 12Z NORTHWEST AREAS THEN SLOWLY WORK THROUGH THE AREA DURING
THE DAY FRIDAY. WITH THE LACK OF ANY REAL MOISTURE AND DRY ATMOSPHERE
WILL HOLD OFF ON THUNDER UNTIL AFT 18Z AT THIS TIME AND KEEP POP
NEAR 30 TO 40 PERCENT FOR THE DAY. CLOUDS AND POTENTIAL FOR SOME
RAIN WILL HOLD HIGHS BACK A BIT...IN THE UPPER 60S TO LOWER 70S.
SIMILAR TO PREVIOUS PACKAGES...THE FRONT WILL EVENTUALLY DRIFT
INTO NORTHERN MISSOURI AND STALL LATE FRIDAY NIGHT AND SATURDAY
MORNING PRIOR TO MIGRATING BACK NORTH THROUGH THE WEEKEND. AS A
SYNOPTIC TROUGH BECOMES MORE ESTABLISHED TO OUR WEST WEAK WARM AIR
ADVECTION AND A WEAK WAVE WILL MOVE NORTHEAST SATURDAY EVENING
INTO SUNDAY MORNING. INCREASING LOW LEVEL FLOW TO 30KTS AT H850
SHOULD FIRE ISO THUNDER SATURDAY ACROSS THE SOUTH INCREASING TO
SCT THUNDERSTORMS OVERNIGHT SAT NIGHT INTO SUNDAY MORNING BEFORE
THE JET DIMINISHES BY MID MORNING SUNDAY. WITH CLOUDS AND SOME
RAIN POTENTIAL SOUTH ON SATURDAY...HIGHS WILL RANGE FROM THE LOWER
70S SOUTH TO THE MID 70S NORTH. BY MID MORNING SUNDAY THE STORMS
WILL DIMINISH. A PLUME OF WARMER AIR WILL MOVE INTO WESTERN AND
NORTHWEST IOWA SUNDAY. H850 TEMPS APPROACH 15 TO 20C BY AFTERNOON
WITH DECENT MIXING. WILL BE RAISING HIGHS NORTHWEST TO THE LOWER
TO MID 80S. THOUGH RATHER WARM ALOFT...CLOUD COVER...INCREASING
SFC DEW POINTS AND NEW FOLIAGE MAY HINDER TEMPS TO GO ANY HIGHER.
WILL MONITOR TRENDS OVER THE NEXT DAY OR TWO. MUCAPE SUNDAY SHOULD
BE PRETTY HIGH ACROSS THE AREA WITH 1500 TO 2500 J/KG DUE TO THE
WARM READINGS AND HIGHER MOISTURE CONTENT OF THE AIRMASS. SHOWERS
AND THUNDERSTORMS ARE ANTICIPATED TO DEVELOP NORTH OF THE APPROACHING
BOUNDARY WITH INCREASING ISENTROPIC LIFT. AS THE FRONT SAGS SOUTH
SUNDAY AFTERNOON...A FEW STRONGER STORMS LIKELY TO DEVELOP OVER
NORTHERN IOWA PRIOR TO INSTABILITY LESSENING THROUGH THE LATE EVENING.
THIS LOOKS TO BE THE BEST POTENTIAL FOR SVR STORMS THROUGH THE WEEKEND.
BY MONDAY THE FRONT MAY HANG UP OVER CENTRAL OR SOUTHERN
IOWA|NORTHERN MISSOURI AND REMAIN IN THE AREA THROUGH WEDNESDAY
BEFORE A STRONGER WAVE DEVELOPS OVER THE WESTERN PLAINS. A PROTRACTED
PERIOD OF SHOWERS AND THUNDERSTORMS IS ANTICIPATED...SO GENERALLY
MILD AND HUMID WEATHER WITH HIGHS IN THE 70S AND LOWS IN THE 50S
WITH PERIODS OF THUNDERSTORMS EACH DAY MONDAY THROUGH WEDNESDAY.
PRELIMINARY MODEL QPF OUTPUT THROUGH THE PERIOD SUNDAY NIGHT
THROUGH WEDNESDAY SUGGESTS 1 TO UP TO 3 INCHES OF RAINFALL ACROSS
THE REGION MOSTLY FOCUSED ALONG THE QUASI STATIONARY BOUNDARY. FOR
NOW THERE IS TOO MUCH UNCERTAINTY TO FOR ANY ACCURATE PLACEMENT OF
THE MAX RAINFALL...BUT THE WEEK APPEARS TO BE SHAPING UP TO BE
SOGGY AND GENERALLY CLOUDY. WIND FIELDS AND INSTABILITY LOOK FAIRLY
MODEST UNTIL LATE IN THE PERIOD ON WEDNESDAY...SO THE THREAT FOR
ANY SEVERE STORMS LOOKS LIMITED UNTIL WEDNESDAY OR LATER.

&&

.AVIATION...30/18Z
ISSUED AT 1142 AM CDT THU APR 30 2015

HIGH PRESSURE RIDGE OVER IOWA WILL MOVE EAST WITH FLOW BECOMING
SOUTHERLY OVERNIGHT. COLD FRONT FROM ND INTO WY WILL APPROACH
NORTHWEST IOWA BY 18Z. VFR CONDITIONS THROUGH THE TAF PERIOD.

OUTLOOK...COLD FRONT WILL MOVE SOUTHEAST INTO IA AND DISSIPATE.
SOME SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH THE
FRONT...BUT WIDESPREAD ACTIVITY IS NOT LIKELY. ANOTHER FRONTAL
SYSTEM WILL MOVE IN BY SUNDAY NIGHT AND STALL OUT...LEAVING
SEVERAL DAYS OF UNSETTLED WEATHER OVER IOWA.

&&

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

$$

SHORT TERM...BEERENDS
LONG TERM...REV
AVIATION...MS APR 5


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