Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 291818
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
118 PM CDT FRI MAY 29 2015

.SHORT TERM /TODAY/...
ISSUED AT 348 AM CDT FRI MAY 29 2015

PRIMARY FORECAST CHALLENGE FOR TODAY IS TIMING AND COVERAGE OF
PRECIPITATION ACROSS THE AREA. CURRENTLY STORMS ARE DEVELOPING
QUICKLY ACROSS NORTHWEST IOWA...WITH A SEPARATE BAND OF LIGHT
SHOWERS AND A FEW STORMS LINGERING ACROSS EAST AND SOUTHEAST
IOWA...BUT ELSEWHERE IT HAS BEEN DRY THUS FAR. OBSERVATIONS AND
ANALYSES SHOW SOUTHWESTERLY FLOW ALOFT AND AMPLE LOW LEVEL MOISTURE
BUT ALSO THE LACK OF A FOCUSING MECHANISM OR BOUNDARY AND ONLY LIGHT
SURFACE WINDS. THE IMPLICATION IS THAT WHILE WIDESPREAD BUT MODEST
INSTABILITY AND BROAD WEAK ASCENT WILL SUPPORT ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS AT ANY GIVEN TIME...COVERAGE SHOULD REMAIN
LOW FOR MUCH OF THE DAY AS DEPICTED BY MOST SHORT TERM AND HIGH
RESOLUTION MODELS...WITH TWO EXCEPTIONS. THE FIRST IS THE NEXT
SEVERAL HOURS IN OUR NORTHWEST AND NORTH WHERE THE MORE NUMEROUS
SHOWERS AND STORMS CURRENTLY DEPICTED ON RADAR SHOULD ADVECT ACROSS
THESE AREAS. THERE IS A DISTINCT LACK OF DEVELOPMENT
UPSTREAM...ACROSS NORTHEASTERN NEBRASKA...SO FAR AND IN GENERAL THE
COVERAGE OF STORMS IN THIS AREA SHOULD DIMINISH STEADILY AFTER
SUNRISE. THE SECOND EXCEPTION IS TOWARD THIS EVENING AS A WELL
ADVERTISED COLD FRONT APPROACHES FROM THE NORTHWEST. COMBINED WITH
PEAK HEATING AND PERHAPS A WEAK SHORTWAVE IMPULSE MOVING THROUGH THE
FLOW ALOFT...EXPECT AN INCREASE IN STORM COVERAGE AND INTENSITY
AFTER 21Z OR SO BEGINNING IN THE NORTHWEST AND THEN SPREADING
SOUTHEASTWARD. INSTABILITY AND SHEAR WILL BE LIMITED SO ANY SEVERE
WEATHER THREAT SHOULD BE ISOLATED AND MARGINAL.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 348 AM CDT FRI MAY 29 2015

SENSIBLE WEATHER WILL BE RELATIVELY INACTIVE THROUGH THE PERIOD WITH
ONLY APPRECIABLE PRECIP CONCERN EARLY AND AGAIN LATE...AND EVEN
THOSE ARE NOT TOO SIGNIFICANT. WATER VAPOR IMAGERY SHOWS A BROAD
AREA OF LIFT ENTERING THE MO VALLEY WITH SCATTERED WEAK EMBEDDED
CONVECTION. THERE IS NO DISCERNIBLE KINEMATIC OR THERMODYNAMIC
FORCING MECHANISM TO PIN DOWN MUCH IN THE WAY OF LIFT
CONTRIBUTIONS. PRECIP MAINLY APPEARS TO BE UNORGANIZED IN WEAK
INSTABILITY WITH LITTLE CINH. THIS SCATTERED CONVECTION WILL
LIKELY JUST BE EXITING ERN IA AT ONSET WITH ADDITIONAL WEAK
CONVECTION DRIVEN MORE KINEMATICALLY FROM APPROACHING SRN
CANADA/ND SHORT WAVE. THERE MAY ALSO BE SOME WEAK SURFACE BASED
POTENTIAL DUE TO CONVERGENCE ALONG THE FRONT BUT MLCAPE CAPES ARE
MINIMAL SO SPC MARGINAL OUTLOOK SEEMS APPROPRIATE. COULD BE SOME
LOCALLY HEAVY RAINS AS SRN PLAINS ELEVATED PWATS PUSH INTO SERN
IA...BUT RESIDENCE TIME AHEAD OF THE FRONT WILL LIKELY PRECLUDE A
WIDESPREAD OR SIGNIFICANT CONCERN. THE AFOREMENTIONED NRN STREAM
KINEMATIC FORCING WILL LIKELY DRIVE SOME WEAK POST-FRONTAL
CONVECTION OVERNIGHT...LINGERING INTO SAT MORNING SE.

COLD FRONTAL PASSAGE WILL BRING APPRECIABLY COOLER AND ESPECIALLY
DRIER AIR INTO THE WEEKEND WITH BAROCLINIC TROUGH INTO IA SUN AND H85/H7
RETURN FLOW STARTING AN EXTENDED PERIOD OF WARM ADVECTION THROUGH
THE MID/UPPER MO VALLEY EARLY NEXT WEEK. THIS WILL BE ENHANCED BY
SOME KINEMATIC SUPPORT FROM SHORT WAVE EJECTED OUT OF CURRENT BC
TROUGH. INSTABILITY AND MOISTURE RETURN ARE FAIRLY WEAK BUT
300-310K ISENT LIFT SEEMS STRONG ENOUGH TO GENERATE SOME WEAK
CONVECTION AND WITH ESE MEAN WIND FLOW WOULD NOT BE SURPRISED TO
SEE SOMETHING DRIBBLE INTO NRN IA FROM MN...ESPECIALLY
NOCTURNALLY. THESE CONDITIONS GO FROM SUN NIGHT INTO TUE NIGHT AND
DO NOT HAVE THE CONFIDENCE TO ADD THAT EXTENDED OF WORDING YET SO
HAVE OPTED TO KEEP THINGS DRY UNTIL CONFIDENCE INCREASES.
SOMETHING TO MONITOR. SURFACE PATTERN DOES NOT CHANGE MUCH WITH
WEAK SELY LOW LEVEL FLOW...GRADUALLY BECOMING MORE SLY WITH TIME
INTO WED. THERE REALLY IS NOT ANYTHING TO HANG YOUR HAT ON FOR
POPS AGAIN UNTIL LATE IN THE PERIOD...WED NIGHT OR THU AND EVEN
THIS MAY BE OVERDONE. IT WOULD LIKELY BE ELEVATED WITH ANY SURFACE
CONVERGENCE STILL TOO FAR WEST. THIS PATTERN WILL ALSO RETURN MORE
SEASONAL TEMPERATURES AS WELL.

&&

.AVIATION...29/18Z
ISSUED AT 118 PM CDT FRI MAY 29 2015

SOME SCATTERED SHOWERS AROUND CURRENTLY WITH ACTIVITY EXPECTED TO
INCREASE ACROSS THE NORTH AND SOUTHEAST THIS AFTERNOON AND IMPACT
MOST SITES THROUGH THIS EVENING AS A STRONG COLD FRONT SWEEPS
THROUGH THE STATE TONIGHT. SOME MVFR/LOW VFR CIGS AROUND AND
EXPECT ALL MVFR CONDITIONS BY LATE TONIGHT WITH STRATUS BEHIND THE
FRONT. STRATUS WILL LINGER INTO SATURDAY...BUT IS EXPECTED TO LIFT
SOME AND START TO BREAK UP TOWARD THE END OF THE PERIOD. WINDS TO
SHIFT AROUND TO THE NORTHWEST BEHIND THE FRONT...AND PICK UP TO
BECOME BREEZY.

&&

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

$$

SHORT TERM...LEE
LONG TERM...SMALL
AVIATION...BEERENDS



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