Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 301136
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
636 AM CDT SAT MAY 30 2015

.SHORT TERM /TODAY/...
ISSUED AT 340 AM CDT SAT MAY 30 2015

A COLD FRONT HAS PUSHED ACROSS THE AREA OVERNIGHT AS ANTICIPATED AND
WILL MOVE OFF TO THE SOUTHEAST TODAY. IN WAKE OF THE FRONT
CONSIDERABLY COOLER TEMPERATURES WILL FLOW IN ON NORTH BREEZES.
HOWEVER...THIS AIRMASS WILL BE RELATIVELY SHALLOW TODAY WITH
PERSISTENT LOW LEVEL MOISTURE LINGERING PER CROSS SECTIONS AND
FORECAST SOUNDINGS. A 500 MB TROUGH WILL MOVE IN FROM THE
NORTHWEST...PROVIDING IMPETUS FOR PERSISTENT LOW CLOUDS ACROSS THE
AREA FOR MUCH OF THE DAY AND HOLDING TEMPERATURES DOWN EVEN FURTHER.
NEARLY ALL HIGH RESOLUTION SHORT TERM FORECAST MODELS PREDICT THE
REDEVELOPMENT OF LIGHT RAIN OR DRIZZLE/SPRINKLES WITHIN THIS LOW
CLOUD FIELD TODAY...AND REGIONAL RADAR SHOWS SOME INKLING OF THIS
WITH LIGHT RETURNS BLOSSOMING OVER NORTHEASTERN NEBRASKA AT THIS
HOUR. HAVE THUS MAINTAINED SLIGHT CHANCE POPS WITH ISOLATED LIGHT
SHOWER WORDING FOR MUCH OF THE DAY. WHILE THIS WILL MAKE FOR A
COOL...GRAY...AND SOMETIMES DAMP SATURDAY IT WILL BE OF LITTLE
IMPACT AS ANY RAINFALL AMOUNTS WILL BE VERY LIGHT AND STRUGGLE TO
EVEN MEASURE.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 340 AM CDT SAT MAY 30 2015

LARGE CANADIAN HIGH PRESSURE OVER THE FAR NORTHERN PLAINS TODAY
WILL SHIFT EAST THEN ENTRENCH ACROSS THE WESTERN GREAT LAKES
THROUGH THE MID PORTION OF NEXT WEEK. THEREFORE...THE SYSTEM WILL
HAVE A SIGNIFICANT IMPACT ON THE WEATHER ACROSS IOWA DURING THIS
TIME. IN THE MID LEVELS...NORTHWEST FLOW WILL TRANSITION TO ZONAL
TUESDAY THE GRADUALLY EVOLVE INTO AN OMEGA BLOCK LATE IN THE WEEK
AS AN UPPER LEVEL SYSTEM DIGS ACROSS THE WESTERN CONUS WHILE
ANOTHER UPPER LOW REMAINS PARKED OVER THE SOUTHEAST CONUS. THE
CONSENSUS WOULD LEAVE A SFC BOUNDARY STALLED JUST WEST OF IOWA MID
WEEK. UPPER LEVEL SHORT WAVES RIPPLING THROUGH THE FLOW STILL
LIKELY TO IMPACT THE STATE. THE COMBINATION OF CONVECTION AND THE
SHORT WAVE ENERGY MAY HELP PUSH A BOUNDARY THROUGH LATE IN THE
WEEK.

IN THE NEAR TERM...HAVE DRY CONDITIONS OVERNIGHT THOUGH STILL NOT
COMPLETELY CONFIDENT THAT A FEW PATCHES OF LINGERING DRIZZLE STILL
ARE NOT PRESENT THROUGH 03Z OVER SOUTHERN IOWA. ANOTHER FACTOR
OVERNIGHT INTO EARLY SUNDAY IS THE BACK DOOR BOUNDARY MOVING IN
FROM THE NORTHEAST AS THE AREA OF HIGH PRESSURE MOVES OVER LAKE
SUPERIOR AND ONTARIO. THIS WILL BRING DRIER AIR WHICH WILL HELP
ERODE THE MOISTURE DEPTH THROUGH THE LOWER LEVELS. SUNDAY IS
EXPECTED TO BE MOSTLY DRY HOWEVER A STRONG SHORT WAVE WILL
APPROACH NORTHWEST IOWA DURING THE AFTERNOON WITH GOOD QG FORCING
ARRIVING. THE FLOW ORIGINATING FROM THE HIGH PRESSURE WILL KEEP
PROFILES BELOW 600 MB QUITE DRY THEREFORE THE QUESTION WILL BE IF
THERE WILL BE ENOUGH FORCING AND MOISTURE ABOVE THIS LAYER TO
PRECIP LOAD THE DRY LAYERS BELOW TO SUFFICIENTLY FOR
PRECIPITATION TO REACH THE GROUND. CAN NOT DISCOUNT SPRINKLES AT
THIS POINT OVER THE NORTHWEST BEFORE DIMINISHING. THE AREA OF HIGH
PRESSURE WILL DROP SOUTH MONDAY AND TUESDAY AND WILL REINFORCE THE
DRY AIR OVER IOWA WITH MOSTLY DRY CONDITIONS PREVAILING. THE
AFOREMENTIONED BOUNDARY WILL DRAW CLOSER TO IOWA BY WEDNESDAY WITH
PRECIPITATION CHANCES INCREASING...ESPECIALLY WEST. THUNDERSTORM
CHANCES WILL EXPAND FURTHER EAST THURSDAY AND FRIDAY. TEMPERATURES
WILL REMAIN COOL SUNDAY AND MONDAY THEN WARMING THROUGH THE 70S TUESDAY
WITH SOME 80S BY WEDNESDAY.

&&

.AVIATION...30/12Z
ISSUED AT 636 AM CDT SAT MAY 30 2015

LOW CIGS AND SOME -RA CURRENTLY AFFECTING THE AREA WILL SLOWLY
CLEAR OUT FROM NW TO SE TODAY. THIS WILL RESULT IN SOME IFR IN THE
NEXT FEW HOURS...WITH MVFR FOR SEVERAL HOURS AFTER THAT BEFORE VFR
CONDITIONS RETURN THIS AFTN/EVE. HAVE TAKEN BEST GUESS AT TIMING
THESE TRANSITIONS IN THE 12Z TAFS BUT AMENDMENTS ARE PROBABLE
TODAY. ONCE THE CLOUDS DO CLEAR OUT...WE SHOULD SEE VFR CONDITIONS
FOR QUITE SOME TIME FROM TONIGHT ONWARD.

&&

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

&&

$$

SHORT TERM...LEE
LONG TERM...DONAVON
AVIATION...LEE


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