Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250004
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
604 PM CST SAT JAN 24 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 342 PM CST SAT JAN 24 2015

UPPER SHORT WAVE OVER NORTH DAKOTA WILL DROP SOUTHEAST OVERNIGHT AND
BRING INCREASING KINEMATIC FORCING TO CENTRAL IOWA. THE SFC
REFLECTION CLIPPER WILL ARRIVE OVERNIGHT AS WELL AND WILL BE OVER
CONTROL IA AROUND 06Z THEN REACH WEST CENTRAL IL BY 12Z.
PRECIPITATION WILL OVERSPREAD THE STATE OVERNIGHT WITH THE PRIMARY
CHALLENGE BEING PRECIPITATION TYPE. DOWNSLOPE SFC WARM ADVECTION
THIS AFTERNOON EXTENDS WAY BACK INTO MONTANA AND SOUTHERN
SASKATCHEWAN WITH A BACK DOOR COLD FRONT OVER THE MINNESOTA
ARROWHEAD. THE DOWNSLOPE WARMING SHOULD REACH THE SOUTHWEST HALF
TO THIRD OF THE STATE AND WILL KEEP PRECIPITATION TYPE RAIN
THROUGH MUCH OF THE NIGHT. THE COLDER AIR FROM NORTHERN MN WILL
GRADUALLY REACH NORTHERN IOWA OVERNIGHT AND EXPECT A GRADUAL
TRANSITION FROM RAIN TO SNOW. THE TRANSITION WILL BE RELIANT ON
COOLING OF NEAR SFC TEMPERATURES AND WETBULB VALUES THAT WHILE
ONLY A FEW HUNDRED FEET DEEP...WILL PROMOTE MELTING. WITH THE
SLOWER RAIN TO SNOW TRANSITION...ONLY HAVE AN INCH TO POSSIBLY
INCH AND ONE HALF OVER THE FAR NORTH THROUGH 12Z WITH LITTLE TO NO
SNOW ACCUMULATION SOUTH OF HIGHWAY 20 DURING THAT TIME. THE
STRONGER COLD ADVECTION WILL REACH FAR NORTHERN IOWA LATE TONIGHT
AND WILL BE THE START OF STRONGER AND MORE GUSTY NORTHEAST WINDS
WHICH MAY CAUSE SOME BLOWING SNOW IN LOCATIONS WITH AN INCH OR
MORE.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 342 PM CST SAT JAN 24 2015

PRECIPITATION WILL BE ONGOING ON SUNDAY AS THE CLIPPER SYSTEM
RAPIDLY DEPARTS TO THE SOUTHEAST BY 18Z.  THERE IS STILL SOMEWHAT OF
A PTYPE ISSUE WITH THE SYSTEM.  THE GFS IS CONSIDERABLY COLDER THAN
OTHER MODELS AND CONSEQUENTLY SWITCHES PRECIP OVER TO SNOW QUICKER
WHEN THE OTHERS ARE SUGGESTING EITHER A RAIN/SNOW MIX OR A WET SNOW
SOUTH WITH ALL SNOW ACROSS THE NORTH/NORTHEAST.  THE GFS ALSO HAS
QUITE A BIT MORE QPF WITH THIS SYSTEM...WHICH IF THIS WERE ALL SNOW
WOULD BE MORE OF AN ISSUE.  I NUDGED SNOW AMOUNTS DOWN IN THE SOUTH
A COUPLE TENTHS THINKING TEMPS WOULD BE A BIT WARMER AND PRECIP
WOULD BE MORE OF A MIX.  THE PRECIP SHOULD QUICKLY DEPART DURING THE
AFTERNOON WITH APPRECIABLE PRECIP ENDING BY OR SHORTLY AFTER 18Z.
WE WILL REMAIN IN COLD ADVECTION THROUGH THE DAY SO HIGHS WILL
LIKELY BE IN THE MORNING WITH SLOWLY FALLING TEMPS THROUGHOUT THE
DAY.

COLD ADVECTION CONTINUES INTO SUNDAY EVENING BUT OVERNIGHT THE WIND
GRADUALLY BECOMES SOUTHWEST AND WARM ADVECTION SLOWLY MOVES INTO THE
WEST.  EASTERN IOWA SHOULD STILL REMAIN COLD OVERNIGHT.  ANOTHER
SYSTEM DROPS DOWN THE UPPER FLOW BUT THE LATEST MODEL RUNS BUILD A
LARGE RIDGE OVER THE ROCKIES WHICH AMPLIFIES THE PATTERN OVER US AND
RESULTS IN SHIFTING THE SHORTWAVE FURTHER TO THE EAST.  WE ALSO HAVE
A PROBLEM WITH ICE INTRODUCTION AND DONT REALLY SATURATE EXCEPT FOR
POSSIBLY A BRIEF PERIOD MONDAY MORNING.  BY THIS TIME THE RIDGE
BUILDS FURTHER EAST PUSHING THE SHORTWAVE MORE INTO ILLINOIS.  THE
RESULT WILL BE A SMALL CHANCE FOR PRECIP JUST NICKING OUR EASTERN
CWA.  THIS WAS A CHANGE FROM THE PREVIOUS FORECAST AND PTYPE WOULD
BE FREEZING DRIZZLE OR IF WE COULD SATURATE...POSSIBLY A VERY BRIEF
PERIOD OF FREEZING RAIN JUST NICKING THE FAR NORTHEAST AS THE WAVE
PASSES MONDAY MORNING.

THE AFOREMENTIONED RIDGE THEN SLIDES EAST INTO THE PLAINS AND THE
WARM UP BEGINS FOR CENTRAL IOWA.  HIGHS SHOOT INTO THE MID 30S
NORTHEAST TO AROUND 50 SOUTHWEST FOR MONDAY AND TUESDAY THEN 40S TO
MID 50S FOR WEDNESDAY.  I RAISED TEMPS FOR WEDNESDAY A FEW DEGREES
BUT WILL CONTINUE TO MONITOR AS THIS MAY NOT BE WARM ENOUGH.

THE PATTERN BECOMES ACTIVE FROM MID WEEK ON AS A SERIES OF
SHORTWAVES DROP DOWN THE FLOW AS OUR RIDGE BREAKS DOWN AND PUSHES
OFF TO THE EAST.  BY THE END OF THE WEEK A LARGE TROUGH SETS UP OVER
THE REGION AND COLD AIR WILL POUR INTO THE UPPER MIDWEST.  AFTER
SEEING 50S MIDWEEK...WE WILL BE BELOW NORMAL BY THE WEEKEND WITH
HIGHS IN THE 20S.  THE FIRST SHORTWAVE COMES ACROSS WEDNESDAY NIGHT
AND THURSDAY DELIVERING OUR FIRST SHOT OF COLDER AIR.  PRECIP SHOULD
STILL MOSTLY BE RAIN WITH A CHANGEOVER TO SNOW FAR NORTHWEST LATE.
THE COLDER AIR THEN BEGINS TO MOVE INTO THE REGION IN EARNEST FRIDAY
NIGHT AND SATURDAY. A  SECOND SYSTEM COMES IN SATURDAY INTO SUNDAY
AND THIS ONE WILL BRING SNOW TO THE AREA.

&&

.AVIATION...25/00Z
ISSUED AT 554 PM CST SAT JAN 24 2015

LOW PRESSURE SYSTEM WILL BRING RA AND SN TO SITES FOR MUCH OF
PERIOD...WITH MVFR AND IFR CONDITIONS EXPECTED WITHIN
PRECIPITATION. CONDITIONS MAY DROP TO LIFR AT TIMES AFTER 06Z.
PRECIPITATION WILL END AFTER 12Z...AND VISIBILITIES WILL
IMPROVE...THOUGH MVFR OR LOWER CEILINGS WILL REMAIN. CEILINGS WILL
IMPROVE AFTER 18Z. WINDS WILL BECOME NORTH TO NORTHEASTERLY AND
STRONG AND GUSTY NEAR 12Z...WITH GUST TO 25KTS OR HIGHER AT MOST
SITES...AND WILL REMAIN STRONG THROUGH PERIOD.

&&

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

&&

$$

SHORT TERM...DONAVON
LONG TERM...FAB
AVIATION...AWB


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