Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 152330
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
630 PM CDT TUE APR 15 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 335 PM CDT TUE APR 15 2014

RIDGE OF HIGH PRESSURE MOVING EAST THROUGH CENTRAL IOWA THIS
AFTERNOON. SOUTHERLY FLOW OVER WESTERN IOWA WILL INCREASE ACROSS THE
REMAINDER OF THE AREA OVERNIGHT. EXPECT TEMPERATURES TO BEGIN TO
RISE AFTER MIDNIGHT WITH ALL LOCATIONS ABOVE FREEZING BY 12Z. STRONG
MID LEVEL THETA-E ADVECTION WILL ALSO COMMENCE THIS EVENING. THIS
WILL MAINLY RESULT IN INCREASING MID LEVEL CLOUDS THROUGH THE
PERIOD. VERY DEEP DRY LAYER MAINTAINS AND IS STILL NEAR 11 KFT BY
12Z. WHILE THE THERMODYNAMICS ARE IN PLAY OVERNIGHT...THE PRIMARY
KINEMATICS ARE DELAYED A BIT AND JUST MOVING INTO WESTERN IOWA AT
THE END OF THE PERIOD. OVERALL...THIS SYSTEM HAS A MOISTURE
DISCONTINUITY WITH THE LOW LEVEL MOISTURE NOT ARRIVING UNTIL AFTER
THE MID LEVEL FORCING PASSES THROUGH INTO WED MORNING AND THE MID
LEVEL DRY SLOT ARRIVES. POSSIBLE SPRINKLES OCCUR BY 12Z BUT AT THIS
TIME...THE POTENTIAL NOT HIGH ENOUGH TO MENTION.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 335 PM CDT TUE APR 15 2014

THE LONG TERM FORECAST IS FAIRLY DYNAMIC AND ACTIVE AT LEAST THROUGH
THIS WEEKEND. ON WEDNESDAY A SURFACE LOW PRESSURE CENTER WILL MOVE
ALONG THE SOUTH DAKOTA/NEBRASKA BORDER AND OVER FAR NORTHERN IOWA BY
THE EVENING. THIS LOW WILL BE TRAILING A COLD FRONT...BUT AHEAD OF
IT WINDS WILL TURN TO SOUTH SOUTHWEST AND INCREASE IN A VERY TIGHT
PRESSURE GRADIENT...WITH THE STRONGEST WINDS LIKELY ACROSS OUR
CENTRAL AND SOUTHEAST FURTHER AWAY FROM THE LOW CENTER IN THE LATE
MORNING AND EARLY AFTERNOON. AT THIS TIME IT APPEARS THAT WIND
SPEEDS AND GUSTS WILL BE VERY CLOSE TO WIND ADVISORY CRITERIA AND
THIS WILL BE MONITORED ON THE OVERNIGHT SHIFTS IN CASE AN ADVISORY
BECOMES NECESSARY. IN ADDITION...UPSTREAM OBS AND RECENT CLIMATOLOGY
FROM LAST WEEK INDICATE THAT THE MODELS ARE TOO MOIST WITH SURFACE
DEWPOINTS DURING THIS TIME...ESPECIALLY GIVEN THE DEEP MIXED LAYER
ILLUSTRATED BY FORECAST SOUNDINGS. THERE ARE ALSO INCREASING SIGNS
THAT TEMPERATURES COULD WARM MORE THAN PREVIOUSLY THOUGHT...SIMILAR
TO WHAT WE EXPERIENCED ON SATURDAY BUT TO A MUCH LESSER EXTENT WITH
FORECAST HIGHS NOW IN THE MID 60S ACROSS THE SOUTHERN HALF OF IOWA.
GIVEN THIS COMBINATION OF FACTORS THERE IS NOW A DISTINCT
POSSIBILITY THAT RELATIVE HUMIDITY COULD FALL BELOW 25 PERCENT
ESPECIALLY ACROSS OUR SOUTHEAST...WHICH WITH WINDS OVER 25 MPH WOULD
NECESSITATE A RED FLAG WARNING IN THOSE AREAS. GIVEN THE POSSIBILITY
OF EITHER OR BOTH OF THESE HEADLINES...AND AN ELEVATED FIRE DANGER
IN ANY EVENT...HAVE ISSUED A FIRE WEATHER WATCH FROM LATE MORNING
THROUGH THE AFTERNOON ON WEDNESDAY ACROSS ABOUT THE SOUTHEAST HALF
OF THE FORECAST AREA. THERE IS ALSO SOME POTENTIAL FOR LIGHT RAIN
ACROSS NORTHERN IOWA CLOSER TO THE LOW TRACK...BUT IT IS EXPECTED TO
HAVE NO REAL IMPACT.

ON WEDNESDAY NIGHT...BEHIND THE COLD FRONT...HIGH PRESSURE WILL
BUILD DOWN THE MISSOURI RIVER VALLEY WITH COOLER TEMPERATURES
SURGING INTO IOWA AND NORTH NORTHWEST WINDS GRADUALLY DIMINISHING
THEN BECOMING LIGHT AND VARIABLE BY THURSDAY NIGHT AS THE RIDGE
MOVES OVERHEAD. A SOUTHERN STREAM WAVE WILL MOVE ACROSS MISSOURI
DURING THIS TIME...BUT IT IS FAR LESS PHASED WITH THE WEDNESDAY
NORTHERN STREAM SYSTEM THAN IN FORECAST SOLUTIONS OF PREVIOUS DAYS
AND IT NOW APPEARS LIKELY THAT THE RAIN FROM THESE TWO SYSTEMS WILL
SPLIT MOST OF THE AREA WITH THE WEDNESDAY RAIN CONFINED TO NORTHERN
IOWA AS DISCUSSED ABOVE AND THE THURSDAY/THURSDAY NIGHT RAIN
CONFINED TO THE SOUTHEAST AND AGAIN HAVING NO REAL IMPACT IN TERMS
OF ANY HAZARDS. THE PRIMARY CONSEQUENCE IS THAT POPS HAVE BEEN
GREATLY LOWERED FROM PREVIOUS FORECASTS FOR THURSDAY AND THURSDAY
NIGHT.

THIS WEEKEND THERE HAS BEEN A FORECAST CHANGE IN THE OPPOSITE
DIRECTION...AS LONG RANGE PROGNOSTIC MODELS ARE NOW UNANIMOUSLY
INDICATING MUCH BETTER PHASING OF THE STREAMS AND WIDESPREAD RAIN
FROM LATE SATURDAY THROUGH SUNDAY. IT REMAINS TO BE SEEN WHETHER OR
NOT THIS WILL MATERIALIZE...BUT GIVEN THE STRONG AND RECENTLY
CONSISTENT SIGNAL HAVE INCREASED POPS FOR THIS PERIOD ALTHOUGH
FORECAST INSTABILITY PROFILES INDICATE ONLY A LOW CHANCE FOR THUNDER
SO HAVE LEFT IT OUT OF THE FORECAST FOR NOW.

&&

.AVIATION...16/00Z
ISSUED AT 630 PM CDT TUE APR 15 2014

SOME MID CLOUDS EXPECTED TO STREAM ACROSS THE CWA TONIGHT...AND
CONTINUE INTO WEDNESDAY ASSOCIATED WITH AN AREA OF LOW PRESSURE
CENTERED OVER CENTRAL SD. SOUTHERLY WINDS INCREASING AHEAD OF THIS
LOW PRESSURE AREA...WITH WINDS STAYING UP TONIGHT AND BECOMING
MORE SOUTHEASTERLY. BREEZY CONDITIONS WITH GUSTY WINDS THEN
EXPECTED AS WINDS SHIFT AROUND TO THE SOUTHWEST FOR WEDNESDAY WITH
SOME STRONGER WINDS MIXING DOWN FROM ALOFT BY LATE MORNING INTO
THE AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 335 PM CDT TUE APR 15 2014

SOUTH SOUTHWEST WINDS WILL INCREASE SUBSTANTIALLY ON WEDNESDAY
MORNING...REACHING SPEEDS OF 25 TO 30 MPH WITH GUSTS TO NEAR 40
MPH INTO THE AFTERNOON. RELATIVE HUMIDITY WILL PLUMMET AFTER
SUNRISE...BOTTOMING OUT AT 25 TO 30 PERCENT ACROSS CENTRAL AND
SOUTHEAST IOWA DURING THE AFTERNOON. WHILE THERE IS SOME
UNCERTAINTY AS TO WHETHER RED FLAG WARNING CRITERIA WILL BE
MET...IT IS A DISTINCT POSSIBILITY AND IN ANY EVENT THERE WILL BE
AN ELEVATED FIRE DANGER. TO HIGHLIGHT THIS THREAT...AND THE
POTENTIAL FOR A RED FLAG WARNING...A FIRE WEATHER WATCH HAS BEEN
ISSUED FOR THE LATE MORNING THROUGH AFTERNOON HOURS ON WEDNESDAY.
BURNING IS STRONGLY DISCOURAGED ON WEDNESDAY.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
EVENING FOR ADAIR-ADAMS-APPANOOSE-BOONE-CASS-CLARKE-DALLAS-DAVIS-
DECATUR-GREENE-GRUNDY-GUTHRIE-HAMILTON-HARDIN-JASPER-LUCAS-
MADISON-MAHASKA-MARION-MARSHALL-MONROE-POLK-POWESHIEK-RINGGOLD-
STORY-TAMA-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-WEBSTER.

&&

$$

SHORT TERM...DONAVON
LONG TERM...LEE
AVIATION...BEERENDS
FIRE WEATHER...LEE



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