Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 302059
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
359 PM CDT THU JUL 30 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 357 PM CDT THU JUL 30 2015

SURFACE HIGH WILL REMAIN IN PLACE OVER FAR SOUTHERN IOWA TONIGHT
WHILE ALOFT WE WILL REMAIN IN NORTHWEST FLOW.  THE NAM IS SUGGESTING
A SUBTLE SHORTWAVE CROSSING SOUTHWEST IOWA OVERNIGHT AS A WEAK COLD
FRONT SINKS INTO THE NORTHWEST QUARTER OR SO OF THE STATE.  THERE IS
SOME POSSIBILITY THAT A SPRINKLE OR TWO COULD BE ASSOCIATED WITH
EITHER OF THESE FEATURES BUT INSTABILITY IS RATHER MINIMAL AND
FORCING IS TIED MORE TO THE FRONTAL BOUNDARY THAN THE SUBTLE WAVE
ACROSS THE SOUTH...WHERE THE BETTER INSTABILITY LIES.  CONFIDENCE AS
TO WHERE ANY PRECIP MAY OCCUR IS VERY LOW AND AS SUCH I DO NOT HAVE
A MENTION OF POPS IN THE FORECAST.  HI-RES CONVECTION ALLOWING
MODELS ARE IN POOR AGREEMENT AS WELL AS THE HRRR CURRENTLY IS
FORECASTING SHOWERS ACROSS THE NORTHERN HALF OF IOWA WHERE THERE ARE
BARELY A FEW CLOUDS.  THE NAM 12 HAS SPITS OF PRECIP OVER BOTH THE
SOUTH AND NORTHWEST WHILE THE OTHER MODELS DO THIS OVER THE SOUTH.
COVERAGE WOULD BE SPARSE AND POPS MAY NEED TO BE ADJUSTED IN LATER
SHIFTS IF SOMETHING IS ABLE TO DEVELOP.  AS FOR TEMPS...NORTHWEST
IOWA SHOULD BE THE COOLEST AS THE FRONT WILL BE THROUGH THEM BUT IT
IS DOUBTFUL THAT IT WILL MAKE IT TOO FAR INTO OUR FORECAST AREA BY
12Z.  AS A RESULT I HAVE KEPT LOWER 60S NORTH TO MID 60S SOUTH FOR
TONIGHT`S LOWS.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
ISSUED AT 357 PM CDT THU JUL 30 2015

GENERAL PREMISE OF LONG TERM LOOKING SIMILAR TO YESTERDAY/S OUTPUT.
DIFFERENCE IS THAT TODAY/S RUNS ARE A LITTLE MORE AMPLIFIED AND
CONFIDENCE INCREASED IN MULTIPLE ROUND OF PRECIP OF THE NEXT SEVEN
DAYS. FROM 12Z UNTIL 18Z FRIDAY...A WEAK BOUNDARY WILL BE PASSING
THROUGH OUR CWA FROM NW TO SE. PWATS WITH THIS BOUNDARY BARELY GO
ABOVE 1 INCH AND MOISTURE CONV AT THE SFC IS MINIMAL. TIME OF DAY
ALSO TYPICALLY NOT FAVORABLE FOR CONVECTION. THEREFORE...AM
KEEPING CWA DRY WITH THIS BOUNDARY PASSAGE. EXPECT ANOTHER MAINLY
CLOUD- FREE DAY WITH 850MB TEMPS IN THE 17C TO 20C RANGE TO MIX
DOWN AND YIELD MID TO UPPER 80S.

FRIDAY EVENING INTO SATURDAY MORNING...THE AFOREMENTIONED BOUNDARY
LOOKS TO LINGER IN NORTHERN MISSOURI TO NORTHEASTERN NEBRASKA AND
WILL SERVE AS THE FOCUSING MECHANISM FOR EVENING
CONVECTION...ESPECIALLY IN NORTHEASTERN NEBRASKA. CORFIDI VECTORS
SUGGEST STORM MOVEMENT WILL BE TO THE SE...WITH ANY RIGHT-MOVERS
MOVING MORE SOUTHERLY. WITH ENOUGH INSTABILITY PRESENT IN SOUTHERN
IOWA AHEAD OF THESE STORMS...IT SEEMS PLAUSIBLE ANY OUTFLOW
BOUNDARIES WILL PROPAGATE IN A NE/E DIRECTION INTO SOUTHERN
IOWA...POSSIBLY CLIPPING OUR SW COUNTIES. THEREFORE HAVE SOME
SLIGHT POPS GOING IN OUR SOUTH WHICH CAN OBVIOUSLY BE TWEAKED IN
NEXT UPDATES.

SATURDAY LOOKS TO BE DRY...BUT THE NEXT PRECIP CHANCES FOR ARRIVE
LATE EVENING INTO THE OVERNIGHT PERIOD FOR SUNDAY MORNING. MODELS
NOW VERY CONSISTENT IN PRODUCING A SIZABLE MCS OVER SE SOUTH DAKOTA
AND PROPAGATING THIS MCS SOUTHEASTWARD THROUGH THE CENTRAL TO
WESTERN PORTIONS OF OUR CWA. GFS SEEMING TO BE A FAST OUTLIER...SO
LEANED AWAY FROM IT FOR TIMING PURPOSES. AM STARTING TO SEE HEAVY
RAINFALL SIGNATURE AS SHORT TERM MODELS PLACING A SLUG OF 2 TO 2.25
INCH PWATS WITH THIS MCS...MIXING RATIOS OVER 8 J/KG...AND 0 TO 6 MU
CAPE OVER 1500 J/KG. IN FACT THE 18Z NAM HAD PWATS OVER 2.5
INCHES...SO RECENT MODEL TRENDS CERTAINLY POINTING UPWARDS.

BEYOND SUNDAY...YESTERDAY/S LONG TERM MODELS HINTED AT A
BAROCLINIC ZONE TRYING TO ESTABLISH ITSELF OVER OUR SOUTHERN CWA
THROUGH MID WEEK. REGION TO REMAIN IN WESTERLY TO NORTHWESTERLY
FLOW ALOFT...SUGGESTING AN OVERALL PATTERN OF SHORTWAVE
PROPAGATION THROUGH IOWA. TODAY/S MODEL RUNS YIELD A SIMILAR
SETUP TO YESTERDAY/S...WITH THE MAIN DIFFERENCE BEING HIGHER PWATS
IN THE 1.5 INCH RANGE OR SO OVER MUCH OF OUR CWA. THUS...HAVE
INCREASED POPS FURTHER NORTH FROM YESTERDAY AND UPPED CONFIDENCE
SLIGHTLY. INTERESTING THAT THE GFS...WHICH OFTEN HAS A DRY
BIAS...IS PRODUCING SO MUCH MOISTURE IN IOWA. IF UPWARD TREND
CONTINUES...NEXT WEEK COULD BE WET. WITH EXPECTED CLOUD
COVER...BEGUN TO TRIM DIURNAL RANGE...SLIGHTLY LOWERING MAX TEMPS
AND INCREASING MIN TEMPS.

&&

.AVIATION...30/18Z
ISSUED AT 1210 PM CDT THU JUL 30 2015

VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD.  WARM ADVECTION WILL
BE RESPONSIBLE FOR SOME SCT MID/HIGH LEVEL CLOUDS.  AFT 03Z A WEAK
COLD FRONT WILL SINK SOUTH ACROSS THE TAF LOCATIONS.  THIS WILL
BRING A SCT-BKN DECK BTWN 080-100KFT WHICH IS EXPECTED TO DIMINISH
LATE IN THE FCST PD.  SFC WND WILL BECOME NW AFT 03Z WITH THE FROPA
AND MAY INCREASE AFT 13Z TO 10-15KTS.


&&

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

$$

SHORT TERM...FAB
LONG TERM...KOTENBERG
AVIATION...FAB


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