Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 281553
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
953 AM CST SUN DEC 28 2014

.SYNOPSIS...
ISSUED AT 317 AM CST SUN DEC 28 2014

HIGH PRESSURE RIDGE WILL MOVE ACROSS THE STATE TODAY WITH THE NEXT
POLAR FRONT POISED TO DROP SOUTH ACROSS THE REGION TONIGHT AND
MONDAY VERY COLD HIGH PRESSURE WILL BUILD INTO THE UPPER MIDWEST IN
IT`S WAKE. UPPER AIR SYSTEM DROPPING DOWN THE WEST COAST WILL
ROTATE OUT AND AFFECT THE AREA NEXT WEEKEND.

&&

.UPDATE...
ISSUED AT 947 AM CST SUN DEC 28 2014

LOWERED TEMPS TO VARIED DEGRESS WITH MORNING UPDATE. TEMPS WERE
SOMEWHAT COOLER THAN DEPICTED...ESPECIALY OVER NRN SNOW COVER WITH
MASON CITY 15Z TEMP STILL 4F. WITH SEASONAL SOLAR MIN...SNOW COVER AND
FAIRLY LIGHT WINDS HAVE TEMPERED DIURNAL REBOUND IN SOME AREAS.

&&

.SHORT TERM /TODAY/...
ISSUED AT 317 AM CST SUN DEC 28 2014

THERE WILL ACTUALLY BE A BREAK IN THE WEATHER TODAY AS IOWA FINDS
ITSELF BETWEEN THE SYSTEM THAT MOVED ACROSS YESTERDAY AND IS NOW TO
OUR EAST AND THE NEXT SYSTEM MOVING IN FROM THE WEST FOR TONIGHT AND
MONDAY.  FOR TODAY THOUGH THE UPPER FLOW HAS A LITTLE MORE OF A
ZONAL COMPONENT TO IT AND IT WILL BE SEVERAL HOURS INTO THE
AFTERNOON BEFORE WE SEE CLOUD COVER DEVELOP.  OVER LOCATIONS THAT
HAVE NO SNOW COVER TEMPERATURES SHOULD CLIMB INTO THE MID 30S.
HOWEVER...ACROSS NORTHERN LOCATIONS WHATEVER SNOW IS ON THE GROUND
COMBINED WITH CLOUD COVER DEVELOPING OVER THE AREA AND THE FACT THAT
THESE LOCATIONS WILL HAVE TO RECOVER FROM EARLY MORNING TEMPERATURES
FROM 5 TO 10 DEGREES...WILL HAMPER HIGH TEMPS.  I AM NOT EXPECTING
HIGHS TO CLIMB MUCH MORE THAN THE MID 20S.

THERE IS SOME DISCREPANCY BETWEEN MODEL SOUNDINGS WITH THE NAM BEING
A LITTLE MORE AGGRESSIVE WITH MOISTURE MOVING BACK IN.  THE GFS IS
LESS SO BUT STILL DOES TRY TO DEVELOP LOW LEVEL MOISTURE BY MID TO
LATE AFTERNOON.  SOUNDINGS SHOW MID LEVELS TO REMAIN DRY THROUGH 00Z
BUT NEAR PEAK HEATING BOTH MODEL FORECAST SOUNDINGS TRY TO DEVELOP
SOME LOW LEVEL MOISTURE THUS TRYING TO DEVELOP SOME STRATOCU WITH
PEAK HEATING MUCH LIKE WHAT OCCURRED YESTERDAY.  THE EXCEPTION IS
THAT YESTERDAY WE WERE UNDER DECENT COLD ADVECTION WHICH WILL BE
ABSENT OR NOT AS STRONG TODAY.  ACROSS SOUTHERN LOCATIONS I WOULD
NOT EXPECT MORE THAN SOME SCATTERED TO POSSIBLY AN OCCASIONAL BROKEN
DECK OF CLOUDS.  ACROSS THE WEST AND NORTH HOWEVER SOME FORCING
ENTERS THE AREA WITH THE WAVE MOVING IN.  WITH MID LEVELS REMAINING
FAIRLY DRY WE SHOULDN`T SEE A LOT OF MID CLOUD COVER BUT THE FORCING
MAY BE DEEP ENOUGH TO TAP THE LOWER LAYERS WHERE THE SOUNDINGS
INDICATE THE MOISTURE IS AND THUS WE WOULD GET SOME LOWER CLOUD
DEVELOPMENT AFTER 21Z.  NOT LOOKING AT ALL FOR PRECIP THIS
AFTERNOON...JUST CLOUD COVER.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 317 AM CST SUN DEC 28 2014

AS THE NEXT COLD FRONT MOVES THROUGH TONIGHT INTO MONDAY EXPECT TO
SEE A LARGE AREA OF SNOW DEVELOP...THOUGH AMOUNTS WILL BE ON THE
LIGHT SIDE. RELATIVELY DEEP SATURATION IS SHOWN ON THE SOUNDINGS
WITH THE DGZ SATURATED. LIFT IS LIMITED AND SNOWFALL AMOUNTS WILL
THEREFORE BE LIMITED AS WELL. AT BEST GREATEST SNOWFALL WILL BE
OVER THE WEST WITH A FEW HOURS PF ONE TO TWO TENTH INCH PER HOUR
ACCUMULATION RATES. THE COLDEST AIR OF THE SEASON THUS FAR WILL
FOLLOW THIS FRONTAL PASSAGE.

STRONG HIGH BUILDS IN FOR THE MIDDLE OF THE WEEK WITH A STRONG
PUSH OF ARCTIC AIR. WITH THE HIGH PASSING SO FAR WEST...AND SNOW
COVER LIKELY TO BE MEAGER...AM CONCERNED TEMPS MAY NOT BE AS COLD
AS MON WOULD INDICATE. STILL...SINGLE DIGITS ABOVE AND BELOW ZERO
FOR LOWS LOOK GOOD.

DISCREPANCIES BETWEEN THE MODELS CONTINUE WITH THE SYSTEM FOR NEXT
WEEK. THE GFS HAS BEEN QUITE CONSISTENT AND THE ECMWF IS NOW
MOVING TOWARD THE GFS CAMP SOLUTION FRIDAY NIGHT AND SATURDAY.
THOUGH THE SYSTEM WILL BE FAST MOVING...A WIDESPREAD ACCUMULATION
OF A FEW INCHES IS A DEFINITELY POSSIBILITY. ASSUMING BY THIS
POINT WE WILL HAVE A SNOW COVER...EVEN COLDER WEATHER IS ON TAP
FOLLOWING THE EVENT.

&&

.AVIATION...28/12Z
ISSUED AT 545 PM CST SAT DEC 27 2014

VFR CONDITIONS EXPECTED THROUGH MUCH OF THE TAF PERIOD.  THE NEXT
SYSTEM TO AFFECT THE TAF LOCATIONS WILL BE SPREADING VFR CIGS IN AFT
21Z.  CIGS WILL LOWER THROUGH THE EVENING BUT THE BEST FORCING OCCURS
WHILE MOISTURE IS SHALLOW SO NOT EXPECTING MUCH IN THE WAY OF
WIDESPREAD MVFR CIGS UNTIL WELL AFTER 03Z.  A SECONDARY SHOT OF
FORCING COMES IN TOWARDS THE END OF THE PERIOD BUT IT IS NOT CLEAR
WHETHER THAT WILL THICKEN CLOUDS AND LOWER CIGS OR IF IT WILL BE
ENOUGH TO PRODUCE MEASURABLE SNOWFALL.  AT THIS POINT MODELS VARY ON
THE INTENSITY/TIMING OF THE FORCING AND THE QUALITY OF THE MOISTURE
OVER CENTRAL IOWA...ESPECIALLY THE EASTERN HALF.  I HAVE VCSH ACROSS
THE HWY 20 CORRIDOR FOR NOW.  BOTH MODELS HINT AT BREAK AFTER THE
FIRST WAVE OF FORCING THEN A SECOND WAVE ACROSS SOUTHERN IOWA AFT
THE VALID PERIOD OF THIS TAF FORECAST CYCLE.

&&

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

&&

$$

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



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