Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 271747
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1147 AM CST SAT DEC 27 2014

.SYNOPSIS...
ISSUED AT 328 AM CST SAT DEC 27 2014

LOW PRESSURE MOVING INTO WISCONSIN WILL BE NORTHEAST OF THE GREAT
LAKES BY TONIGHT. WEAK HIGH PRESSURE WILL MOVE OVER IA TONIGHT.
STRONGER HIGH PRESSURE WILL BUILD INTO THE UPPER MIDWEST FOR THE
FIRST PART OF THE WEEK AS AN UPPER LEVEL SYSTEM BRUSHES THE AREA
MONDAY.

&&

.UPDATE...
ISSUED AT 715 AM CST SAT DEC 27 2014

WE HAVE CURRENTLY LOST MOST OF THE ICE INTRODUCTION ACROSS
NORTHWEST AND NORTHERN IOWA WHICH IS LEADING TO PRECIP BEING MORE
VERY LIGHT AND PATCHY FREEZING DRIZZLE. THIS SYSTEM IS PULLING OUT
AND NOT EXPECTED TO BE MUCH OF A PROBLEM. SOUTHEAST OF A LINE FROM
ALO TO DSM PRECIP IS MORE DRIZZLE OR FREEZING DRIZZLE AND RAIN.
SATELLITE IMAGERY IS SHOWING SOME DEEPER MOISTURE STREAMING UP
ACROSS THE SOUTHEAST HALF OF THE FORECAST AREA HOWEVER WITH THE
LACK OF APPRECIABLE FORCING PRECIP IS MOSTLY DRIZZLE. THE FREEZING
DRIZZLE IS MOST LIKELY FOR THE NEXT COUPLE OF HOURS IN A NARROW 30
MILE ZONE SOUTHEAST OF A LINE FROM ALO TO DSM WHERE SURFACE TEMPS
ARE JUST BELOW FREEZING. ADJUSTMENTS WERE MADE TO PTYPE THROUGH
15Z. AFTER THAT TIME PRECIP SHOULD BE DEPARTING.

&&

.SHORT TERM /TODAY/...
ISSUED AT 328 AM CST SAT DEC 27 2014

PRECIPITATION TYPE CONTINUES TO BE AN ISSUE AND WILL CONTINUE TO BE
AN ISSUE THROUGH THE EVENT.  ANOTHER PROBLEM WILL BE THE TIMING OF
ANY CLEARING.  THE MAIN BAND OF SNOW ACROSS THE WEST AND NORTH
OCCURRED PRETTY MUCH AS FORECAST HOWEVER IS IT CLEAR THAT ICE
INTRODUCTION IS A PROBLEM AS PRECIP HAS SWITCHED FROM SNOW TO
FREEZING DRIZZLE AND BACK IN THIS AREA.  HERE IN DES MOINES WE HAD
DRIZZLE FOLLOWED BE A BRIEF PERIOD OF SLEET THEN SNOW AND NOW WE
SEEM TO BE LOSING ICE INTRODUCTION AS WELL AS WE ARE TRANSITIONING
BACK TO DRIZZLE/FREEZING DRIZZLE.  IT DOES APPEAR THAT NORTHWEST OF
A LINE FROM MASON CITY TO DES MOINES THE COLUMN WILL GENERALLY BE
COLD ENOUGH FOR SNOW WITH PATCHY FREEZING DRIZZLE FROM TIME TO TIME
THROUGH MID MORNING THEN WE SHOULD BE DONE AS FORCING REALLY PUSHES
OUT OF IOWA.

SOUTHEAST OF THIS LINE WILL BE A WINTRY MIX WITH RAIN AND DRIZZLE
CHANGING BRIEFLY OVER TO SNOW THEN WE APPEAR TO LOSE ICE
INTRODUCTION AND SWITCH BACK TO DRIZZLE OR FREEZING DRIZZLE AS WE
GO THROUGH THE MORNING. SURFACE LAYER TEMPS WILL DETERMINE PTYPE
AS WE GO THROUGH THE MORNING AND WE MAY WARM ENOUGH MID TO LATE
MORNING ACROSS THE FAR SOUTHEAST TO SEE RAIN IF THE ICE
INTRODUCTION REMAINS. I DO NOT EXPECT PRECIP TO REMAIN PAST 18Z
AND WE SHOULD SEE THE BULK OF THE PRECIP END BY 15Z...EXCEPT FOR
THE FAR SOUTHEAST.

NOW FOR CLOUDS.  SOUNDINGS INDICATE MID LEVELS DRYING OUT BETWEEN 15
AND 18Z BUT AN INVERSION SETS UP AROUND 700MB AND LOW LEVEL MOISTURE
STUBBORNLY REMAINS IN PLACE.  WITH COLD ADVECTION STRENGTHENING
THROUGH THE DAY I DON`T SEE MUCH CHANCE OF CLEARING.  AT BEST WE
WILL SEE BREAKS IN THE OVERCAST AND MAY GET SUN AT TIMES BUT THEN
STRATUS OR STRATOCU SHOULD RE-DEVELOP.  TEMPS WILL OF COURSE BE
AFFECTED BY THIS AS WELL.  IF WE BREAK OUT ESPECIALLY ACROSS THE FAR
SOUTHEAST WHERE LITTLE IF ANY SNOW IS EXPECTED THEN TEMPS SHOULD
RESPOND SOME AND COULD BE A BIT WARMER THAN THE CURRENT FORECAST.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 328 AM CST SAT DEC 27 2014

HIGH PRESSURE RIDGE WILL MOVE ACROSS THE STATE TONIGHT WITH A
WEAK UPPER LEVEL SYSTEM MOVING THROUGH THE AREA MONDAY AS IT EXITS
THE SOUTHWESTERN U.S. TROUGH. DO NOT EXPECT A GREAT DEAL OF
PRECIPITATION OUT OF THIS SYSTEM WITH SNOWFALL AMOUNTS LIKELY
UNDER AN INCH. LARGER HIGH PRESSURE WILL BUILD INTO THE UPPER
MIDWEST FOR THE MIDDLE OF THE WEEK IT WILL DRAW DOWN A DECENT
CHUNK OF COLD AIR...BUT THERE ARE SOME CONCERNS. WITH THE HIGH
PRESSURE PASSING WELL WEST OF THE STATE THE TENDENCY OF THE MODELS
IS TO OVER FORECAST THE COLD. WENT A FEW DEGREES ABOVE MOS FOR
WED. EVEN SO...WIND CHILL VALUES WILL BE IN THE ADVISORY CATEGORY
OVER THE NORTH IN THE -20 TO -25 RANGE.

THE NEXT WEATHER SYSTEM FOR NEXT WEEKEND IS NOT CLEAR CUT BY ANY
MEANS. A LARGE DIFFERENCE BETWEEN THE ECMWF AND THE GFS WITH THE
ECMWF KEEPING THE NORTHERN AND SOUTHERN STREAM MORE SPIT AND THUS
KEEPING THE PRECIP OUT OF IA. THE GFS IS MORE CONSOLIDATED AND
WOULD PAINT MORE SNOWFALL FOR THE STATE. FOR THE TIME BEING...WILL
GO WITH A CHANCE CATEGORY EVENT AND WATCH FOR LATER DEVELOPMENTS.

&&

.AVIATION...27/18Z
ISSUED AT 1146 AM CST SAT DEC 27 2014

PRECIP HAS ENDED ACROSS TAF SITES BUT LINGERING MAINLY MVFR CIGS
REMAIN A CONCERN. IMPROVEMENT WILL BE GRADUAL...BUT EXPECT
TRANSITION TO VFR AND MOSTLY CLEAR SKIES LATER THIS AFTERNOON AND
EARLY EVENING AS STRATUS SLOWLY DEPARTS IN BROAD CYCLONIC FLOW.

&&

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

&&

$$

UPDATE...FAB
SYNOPSIS...MS DEC 14
SHORT TERM...FAB
LONG TERM...MS DEC 14
AVIATION...SMALL


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