Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 260958
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
358 AM CST WED NOV 26 2014

.SHORT TERM /TODAY/...
ISSUED AT 355 AM CST WED NOV 26 2014

THE APPROACHING WINTER STORM AND SNOW EVENT HAVE UNFOLDED VERY MUCH
AS EXPECTED OVERNIGHT...WITH A BANDING FEATURE TRANSLATING SLOWLY
EASTWARD ACROSS THE AREA AND AFFECTING A BROAD SWATH ROUGHLY DOWN
THE I-35 CORRIDOR AT THIS TIME. SNOWFALL AMOUNTS WITHIN THIS BAND
HAVE ALREADY REACHED BETWEEN 1 AND 3 INCHES ACCORDING TO SPARSE
REPORTS. THE PARENT SURFACE LOW IS STILL LOCATED ACROSS FAR
NORTHWEST IOWA...AND WILL SLIDE SOUTHEASTWARD TODAY. THE EARLY
MORNING SNOW BAND SHOULD CONTINUE TO SLOWLY PROGRESS EAST AND
NORTHEAST THIS MORNING...CLEARING OUT OF CENTRAL IOWA...THEN STALL
AND GRADUALLY WEAKEN AS THE SURFACE LOW SLIDES THROUGH. THIS WILL
RESULT IN SLIGHTLY LESS INTENSE SNOWFALL RATES ACROSS OUR NORTHEAST
LATER THIS MORNING...BUT A LONGER DURATION OF SNOWFALL AS THE BAND
PIVOTS AROUND THE LOW RESULTING IN HIGHER SNOWFALL TOTALS IN THOSE
AREAS. DOWN TOWARD THE DES MOINES METRO MOST OF THE ACCUMULATING
SNOW SHOULD FALL WITHIN THE PROGRESSIVE BAND...ENDING AROUND 5 OR
PERHAPS 6 AM...WITH JUST LIGHT ACCUMULATIONS THEREAFTER.

THE TEMPERATURE FORECAST FOR TODAY IS ALSO PROBLEMATIC...AS IN THE
NORTHWEST HIGHS WILL PROBABLY BE THE TEMPERATURE AT 12Z...WHEREAS IN
THE SOUTH AND SOUTHWEST WARM AIR ADVECTION ON THE LEADING FLANK OF
THE LOW SHOULD ALLOW TEMPERATURES TO CLIMB TO A COUPLE DEGREES ABOVE
FREEZING IN THE LATE MORNING AND AFTERNOON...POTENTIALLY RESULTING
IN A CHANGE OF PRECIP OVER TO LIGHT RAIN AT TIMES. IN ANY EVENT
ACCUMULATIONS WILL BE LIGHT IN THOSE AREAS BY THAT TIME...BUT AT
LEAST IT WILL KEEP ROADS WET INSTEAD OF ICY. THE OTHER FORECAST
CONCERN IS THE WINDS COMING IN BEHIND THE LOW THIS AFTERNOON AND
EVENING...ESPECIALLY ACROSS OUR NORTHERN AND WESTERN
COUNTIES...WHICH COULD RESULT IN SOME BLOWING SNOW EFFECTS. THE
PRECIP SHOULD END BEFORE THE STRONGER WINDS ARRIVE AND THE NEW SNOW
ON THE GROUND WILL BE FAIRLY WET AND STICKY. THIS WILL MITIGATE
BLOWING SNOW IMPACTS...BUT THERE COULD STILL BE SOME SHALLOW
BLOWOVER ON THE ROADS WHICH...COMBINED WITH RAPIDLY FALLING
TEMPERATURES THIS EVENING...MAY RESULT IN REFREEZE ISSUES AFTER
DARK. FOR NOW THE WINTER WEATHER ADVISORY LINES UP WELL WITH
FORECAST SNOWFALL AMOUNTS SO NO CHANGES HAVE BEEN MADE...BUT THESE
POSSIBLE THREATS WILL BE ASSESSED THROUGHOUT THE DAY IN CASE CHANGES
TO THE ADVISORY AREA/TIMING BECOME NECESSARY.

.LONG TERM /TONIGHT THROUGH TUESDAY/...
ISSUED AT 355 AM CST WED NOV 26 2014

THE COLD ADVECTION SURGE WILL CONTINUE TO MOVE INTO IOWA THIS
EVENING AND THIS WILL BE THE PERIOD OF PEAK MIXING AND WIND GUST
POTENTIAL. WIND GUSTS TO 35 MPH ARE LIKELY AND THIS WILL CREATE
SOME AREAS OF BLOWING SNOW. POTENTIAL IS THERE THAT HEADLINES MAY
NEED TO BE EXTENDED INTO THE EVENING FOR THE BLOWING SNOW. A
SECONDARY SHORT WAVE DROPPING THROUGH SOUTHERN MN AND INTO
NORTHERN IA THIS EVENING WILL KEEP THE POTENTIAL FOR LIGHT SNOW
GOING OVER THE EAST/SOUTHEAST BEFORE ENDING WITH ADDITIONAL
ACCUMULATIONS LESS THAN ONE INCH.

COLD HIGH PRESSURE WILL SETTLE INTO LATE TONIGHT AND INTO
THURSDAY. LOW TEMPERATURES WILL BE NEAR TO BELOW ZERO OVER THE
NORTHWEST TONIGHT AS THE ARCTIC AIR ARRIVES. THURSDAY WILL REMAIN
COLD UNDER THE HIGH PRESSURE HOWEVER THE SYSTEM WILL BE
PROGRESSIVE AND WILL BE PASSING EAST OF THE MISSISSIPPI RIVER BY
THE EVENING. THIS WILL RESULT IN WARM ADVECTION THROUGHOUT
THURSDAY NIGHT. THE DAILY HIGH TEMPERATURES LIKELY WILL BE AFTER
THE END OF THE HIGH TEMPERATURE GRID PERIOD OF 01Z AND BE CLOSER
TO MIDNIGHT. WARMER TEMPERATURES ARRIVE ON FRIDAY WITH MOST
LOCATIONS RISING ABOVE FREEZING AS STRONG WARMING ALOFT COMMENCES.
INITIAL ENERGY WILL BE SPENT ON MELTING THEN READINGS SHOULD RISE
INTO THE 40S OVER CENTRAL AND SOUTHERN IOWA WHILE THE NORTH
REMAINS IN THE 30S WERE DEEPER SNOW COVER IS EXPECTED. LIKELY TOO
CONSERVATIVE ON HIGHS SATURDAY OVER AREAS THAT HAVE LITTLE TO NO
SNOW COVER TO BEGIN THE DAY. THE 850 MB THERMAL RIDGE WILL BE OVER
IOWA MUCH OF THE DAY WITH TEMPERATURES OF 12C TO 15C POSSIBLE.
OBVIOUSLY MIXING WILL NOT OCCUR TO THIS LEVEL BUT WITH SOUTHWEST
WINDS...COULD WELL WARM INTO THE 50S AND APPROACH 60 OVER
SOUTHWEST IOWA WHILE COOLER OVER THE NORTH. SUSPECT TEMPERATURES
ARE STILL TOO COOL SATURDAY NIGHT INTO SUNDAY AS THE NEXT ARCTIC
BOUNDARY IS DELAYED A BIT. SUNDAY COULD APPROACH 50 IF EVERYTHING
FALLS RIGHT OVER SOUTHERN IOWA. THE BOUNDARY SHOULD ARRIVE OVER
NORTHERN IOWA DURING THE DAY WITH TEMPERATURES FALLING.

THE REMAINDER OF THE EXTENDED INCLUDES A COLD MONDAY FOLLOWED BY A
MORE SEASONAL DAY ON TUESDAY. SOME POTENTIAL FOR PRECIPITATION
AGAIN ON TUESDAY WITH THE ARRIVAL OF WARM ADVECTION.

&&

.AVIATION...26/06Z
ISSUED AT 1139 PM CST TUE NOV 25 2014

A CLIPPER SYSTEM WILL SWEEP THE STATE TONIGHT THROUGH WEDNESDAY.
CIGS WILL BECOME IFR VERY QUICKLY AS THE SYSTEM MOVES IN. THERE
MAY BE A ONE TO TWO HOUR WINDOW OF MIXED PRECIPITATION MAINLY
ACROSS SOUTHERN TAFS BUT AS THE AIR SATURATES IT WILL QUICKLY
COOL ENOUGH FOR THE PRECIP TO BE ALL SNOW. IMPROVEMENT WILL OCCUR
SLOWLY FROM WEST TO EAST AFT 15Z BUT A NORTHWEST WIND WILL
INCREASE ACROSS TAF LOCATIONS AFT 21Z THROUGH THE END OF THE TAF
PERIOD.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR BLACK
HAWK-BREMER-BUTLER-CERRO GORDO-FRANKLIN-GRUNDY-HARDIN-JASPER-
MARSHALL-POWESHIEK-STORY-TAMA-WORTH.

WINTER WEATHER ADVISORY UNTIL NOON CST TODAY FOR BOONE-EMMET-
HAMILTON-HANCOCK-HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-WEBSTER-
WINNEBAGO-WRIGHT.

&&

$$

SHORT TERM...LEE
LONG TERM...DONAVON
AVIATION...FAB



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