Area Forecast Discussion
Issued by NWS Des Moines, IA

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478
FXUS63 KDMX 151741
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1241 PM CDT FRI MAY 15 2015

...UPDATED AVIATION DISCUSSION...

.UPDATE...
ISSUED AT 958 AM CDT FRI MAY 15 2015

CLEANED UP GRIDS A BIT FROM THE FOG THIS MORNING AND ADJUSTED
SKY/TEMPS ACCORDINGLY. ALSO MAY SEE A BIT COOLER MAX TEMPS ACROSS
THE NORTH WITH SOME ADDED IN CIRRUS FROM A FEW POP UP
THUNDERSTORMS ACROSS NORTHWEST IOWA...SO ADJUSTED NORTHERN CWA
TEMPS DOWN A BIT. LINE OF STORMS ALREADY ACROSS ERN NE ON NOSE OF
THETA-E ADVECTION WHICH IS EXPECTED TO BE ORIENTED MORE INTO
SOUTHERN/WESTERN CWA BY THIS AFTERNOON. THEREFORE DID INCREASE
POPS A BIT IN THAT REGION AND ACROSS THE SOUTH FOR THIS EVENING.

&&

.SHORT TERM /TODAY/...
ISSUED AT 359 AM CDT FRI MAY 15 2015

DENSE FOG HAS SPREAD OVER LOCATIONS THAT RECEIVED THE MOST RAINFALL
YESTERDAY BUT VISIBILITIES ARE ALREADY BEGINNING TO IMPROVE ACROSS
THE SOUTHWEST AND EASTERN FRINGES.  THE HRRR HAS HANDLED THE DENSE
FOG LOCATION THE BEST AND AS SUCH I MADE SOME CHANGES TO THE
EXISTING ADVISORY...MAINLY TO EXTEND IT IN TIME FOR A COUPLE MORE
HOURS AND ALSO TO TRIM SOME FROM THE NORTHWEST AND AND EAST.  THE
HRRR MODEL BEGINS TO ERODE THE FOG BY 14Z AND MODEL SOUNDINGS
SUPPORT A MUCH MORE SHALLOW MOIST LOW LEVEL BY THAT TIME SO WHILE I
FELT THE ADVISORY NEEDED TO BE EXTENDED...THE EVIDENT BREAKS IN THE
DENSE FOG MADE ME HESITANT TO EXTEND IT UNTIL 15Z.

BEYOND THE MORNING FOG...LOW PRESSURE DEVELOPING ON THE LEE SIDE OF
THE ROCKIES WILL LIFT TO THE NORTH NORTHEAST TODAY COLORADO INTO
NORTH DAKOTA. A WARM FRONT EXTENDING FROM THE LOW WILL LIFT ACROSS
IOWA FROM THE SOUTHWEST THIS MORNING REACHING A STORM LAKE TO
CHARITON LINE BY LATE AFTERNOON.  WARM ADVECTION WILL OVERSPREAD THE
THE SOUTHWEST TWO THIRDS OF THE STATE THROUGH THE AFTERNOON.  MODELS
HAVE US DESTABILIZING THROUGH THE MORNING BUT DEEP MOISTURE IS A
LITTLE PROBLEMATIC AND SHEAR DOES NOT LOOK PARTICULARLY ROBUST.
THUNDERSTORMS ARE EXPECTED TO DEVELOP BY LATE MORNING AND THROUGH
THIS AFTERNOON BUT THE THREAT OF SEVERE STORMS IS LIMITED BY THE
LACK OF STRONG SHEAR.  THERE WILL BE SOME ELEVATED STORMS LIKELY IN
THE VICINITY OF THE FRONTAL BOUNDARY AND AN ISOLATED STORM WITH HAIL
CANNOT BE COMPLETELY RULED OUT BUT THE BEST INSTABILITY AND SEVERE
PARAMETERS REMAIN WEST OF THE CWA THROUGH 00Z.  WE WILL BE
CONSIDERABLY WARMER TODAY WITH HIGHS WELL INTO THE 70S.  THE CURRENT
FORECAST HAD TEMPS WELL TRENDED SO LITTLE CHANGES WERE MADE THERE.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 359 AM CDT FRI MAY 15 2015

WARM FRONT WILL LIFT NORTHWARD FROM IOWA INTO MINNESOTA OVERNIGHT AS
SOUTHERLY FLOW DEEPENS ACROSS THE STATE.  SOME ISOLATED TO SCATTERED
CONVECTION IS EXPECTED ALONG THE BOUNDARY OVERNIGHT AS IT LIFTS
NORTHWARD...ALTHOUGH OVERALL EXTENT WILL BE KEPT IN CHECK BY LITTLE
IF ANY SYNOPTIC LIFT.  SOME OF THE STORM COULD BE QUITE STRONG GIVEN
THE INCREASING INSTABILITY BUT SHEAR REMAINS RELATIVELY WEAK AND
SHOULD LIMIT OVERALL LONGEVITY AND INTENSITY OF ANY STORMS.  THE
WARM SECTOR WILL BE IN PLACE ACROSS IOWA ON SATURDAY WITH STRONG
SOUTH WINDS.  WILL BEGIN TO SEE AN INCREASE IN SYNOPTIC FORCING BY
LATER IN THE DAY AS SHORTWAVE ROUNDS BASE OF WESTERN TROF AND BEGINS
TO HEAD NORTHEAST.  HAVE INCREASED POPS ACRS THE WEST BY LATE
AFTERNOON WITH BULK OF STORMS/PCPN ARRIVING LATE SATURDAY NIGHT WITH
APPROACH OF UPPER SYSTEM.  THIS WILL BE THE BEST THREAT FOR HEAVIER
PRECIPITATION AND SEVERE WEATHER ALTHOUGH TIMING IS BECOMING SUCH
THAT THE OVERALL SEVERE WEATHER THREAT MAY BECOME LIMITED GIVEN TIME
OF DAY.  DRY SLOT OVERSPREAD THE STATE ON SUNDAY WITH PRECIPITATION
THREAT DIMINISHING IN MOST AREAS BY AFTERNOON.  MAY SEE A BRIEF
THREAT OF MORE STORMS TOWARD MIDDAY IN THE FAR EAST AND NORTH WITH
FROPA BUT THE BULK OF STORMS WILL BE FARTHER EAST ON SUNDAY.

COLD ADVECTION INCREASES SUNDAY NIGHT INTO MONDAY WITH WINDY AND
COOL CONDITIONS.  THERE WILL BE LITTLE THREAT FOR PRECIPITATION
EARLY NEXT WEEK WITH AREA UNDER THE INFLUENCE OF CANADIAN HIGH
PRESSURE AND A DRY AIRMASS. THE NEXT BEST THREAT OF PRECIPITATION WILL
ARRIVE LATE TUESDAY NIGHT INTO WEDNESDAY AS SYSTEM APPROACHES THE
STATE FROM THE SOUTHWEST. HOWEVER...THIS SYSTEM WILL BE SHEARING
OUT WITH TIME WITH LIFT WEAKENING AND PRECIPITATION REMAINING
LIGHT. TEMPERATURES WILL REMAIN AT OR BELOW NORMAL INTO THE MIDDLE
OF THE WEEK.

&&

.AVIATION...15/18Z
ISSUED AT 1234 PM CDT FRI MAY 15 2015

VSBYS UP ACROSS THE STATE WELL WITHIN VFR WILL REMAIN THROUGH THE
REMAINDER OF THE DAY. CIGS WILL CONTINUE TO HOVER AROUND VFR/MVFR
AT MOST LOCATIONS THROUGH TAF PERIOD. STORMS WILL MOVE THROUGH
OTM/DSM/FOD/ALO SITES THIS AFTERNOON/EVENING...TEMPORARILY
DROPPING CONDITIONS INTO MVFR AND IFR...AND EXITING ALL SITES BY
AROUND 03Z. EXPECT VSBYS TO DROP AGAIN OVERNIGHT WITH FOG...BUT
WILL HOLD OFF ON DROPPING VSBYS BELOW 1 MILE.

&&

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

$$

UPDATE...BEERENDS
SHORT TERM...FAB
LONG TERM...COGIL
AVIATION...CURTIS



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