000
FXUS63 KDMX 100548
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1148 PM CST MON DEC 9 2013

.UPDATE...
ISSUED AT 1148 PM CST MON DEC 9 2013

HAVE UPDATED THE FORECAST TO ADD IN A MENTION OF SOME LIGHT SNOW
LATE TONIGHT WITH THE UPPER WAVE PUSHING THROUGH. SOUNDINGS
SATURATE FOR AN HOUR OR TWO...SO COULD SEE A TRACE TO A FEW TENTHS
ACROSS EXTREME NORTHERN/NORTHEASTERN CWA. STILL EXPECTING GUSTY
WINDS AND AREAS OF BLOWING SNOW LATE TONIGHT INTO TUESDAY MORNING.

UPDATE ISSUED AT 606 PM CST MON DEC 9 2013

TEMPERATURE HAVE ALREADY DROPPED BELOW FORECAST MIN TEMPS...SO
HAVE DROPPED MIN TEMPS ESPECIALLY ACROSS THE NORTHEAST WHERE WILL
TAKE LONGER FOR WAA TO SET IN. EXPECTING TEMPS TO DROP FOR A FEW
MORE HOURS...BEFORE WAA SETS IN WITH STRONGER SOUTHERLY TO
SOUTHWESTERLY WINDS ALLOWING TEMPS TO GRADUALLY RISE THROUGH LATE
TONIGHT INTO EARLY TUESDAY MORNING.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 310 PM CST MON DEC 9 2013

MAIN CONCERN OVERNIGHT WILL BE ARRIVAL OF FAST MOVING CLIPPER SYSTEM
FROM THE NORTHWEST. WINDS HAVE ALREADY SHIFTED TO THE WEST WITH
WARMING ALOFT. THOUGH WE HAVE NOT WARMED SIGNIFICANTLY TODAY
NORTH... LOOKS LIKE THE TEMPS WILL STEADY OFF AFTER FALLING A FEW
DEGREES AND THEN WARM THOUGH THE EVENING HOURS. INCREASING SOUTHWEST
WINDS WILL BEGIN TO CREATE AREAS OF PATCHY BLOWING SNOW IN ADVANCE
OF THE SYSTEM. THE LOW IS EXPECTED TO DROP SOUTHEAST ACROSS MN WITH
A STRONG TRAILING COLD FRONT THAT ARRIVES BY 08-09Z NORTHWEST AND
SWEEPS SOUTHEAST THROUGH THE FORECAST AREA BY 12Z. INITIALLY MIXING
WILL NOT BE IMPRESSIVE BEHIND THE FRONT...BUT TOWARD 12Z LAPSE RATES
BECOME NEARLY ADIABATIC WITH INCREASING MIXING THROUGH EARLY TUES
MORNING. BY SUNRISE NORTHWEST WINDS LIKELY TO BE INCREASING WITH
BLOWING SNOW BECOMING MORE PREVALENT. THOUGH SNOW PACK NOT VERY DEEP
FLUFFY NATURE OF YESTERDAYS SNOW MAY BECOME A PROBLEM IN RURAL AREAS
ONCE WINDS PICK UP BY MORNING.  LOWS WILL DROP TO SINGLE DIGITS
ABOVE AND BELOW ZERO INITIALLY THEN STEADY OFF AND SLOWLY RISE INTO
LATE OVERNIGHT AHEAD OF THE LOW. NOT EXPECTING ANY PRECIP WITH MID
LEVEL CLOUD DECK MOVING OVER THE REGION.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 310 PM CST MON DEC 9 2013

WE WILL REMAIN BENEATH BROAD CYCLONIC FLOW THROUGH
WEDNESDAY...RESULTING IN A CONTINUATION OF COLDER THAN NORMAL
TEMPERATURES ACROSS THE AREA. ON TUESDAY MORNING A SURFACE LOW
PRESSURE AREA MOVING QUICKLY ACROSS MINNESOTA WILL TIGHTEN THE
PRESSURE GRADIENT ACROSS IOWA...RESULTING IN STRONG WINDS FOR A
PERIOD OF SEVERAL HOURS. THE STRENGTH OF THE WIND AND GUSTS WILL
BE DETERMINED BY THE EXTENT TO WHICH THE MIXED LAYER WILL DEEPEN
AFTER SUNRISE...CONCURRENT WITH A STEADY DECREASE IN WIND SPEEDS
ALOFT BY LATE MORNING...SO THE WINDOW OF OPPORTUNITY FOR STRONG
WINDS WILL BE RELATIVELY NARROW. HOWEVER...IT WILL LIKELY RESULT
IN SOME BLOWING SNOW ESPECIALLY IN FLAT AND OPEN AREAS AND COULD
LEAD TO TRAVEL DIFFICULTIES. HAVE INCLUDED BLOWING SNOW IN THE
FORECAST ACCORDINGLY AND INCLUDED THIS POTENTIAL IN THE HAZARDOUS
WEATHER OUTLOOK AS WELL.

A ROBUST 500 MB SHORTWAVE WILL MOVE OVER THE REGION TUESDAY NIGHT
AND WEDNESDAY...SPREADING A SWATH OF LIGHT SNOW AHEAD OF A SHARP
COLD FRONT THAT WILL SURGE ACROSS OUR FORECAST AREA DURING THE DAY
ON WEDNESDAY. THE SNOW WILL FALL ACROSS MOST OF IOWA ON TUESDAY
NIGHT...HOWEVER THE PERIOD OF COLUMN SATURATION WILL BE FAIRLY
BRIEF/PROGRESSIVE AND THE BROAD SCALE FORCING IS MODEST AND NOT
WELL FOCUSED. THERE MAY BE BRIEF BURSTS OF MODERATE SNOWFALL IN
SOME AREAS...BUT GIVEN THE QUICK HITTING NATURE OF THE SYSTEM
AMOUNTS ARE EXPECTED TO BE LIGHT...GENERALLY AROUND AN INCH
CENTRAL UP TO TWO INCHES NORTHEAST. WINDS WILL BE LIGHT WHILE SNOW
IS FALLING AND LITTLE IMPACT IS ANTICIPATED...THOUGH INCREASING
WINDS BEHIND THE FRONT ON WEDNESDAY COULD CAUSE SOME SHALLOW
BLOWING SNOW. THE INCREASING WINDS AND MUCH COLDER AIR SURGING IN
ON WEDNESDAY MORNING WILL ALSO LIKELY RESULT IN DANGEROUS WIND
CHILLS ESPECIALLY ACROSS THE NORTH AND NORTHWEST...AND ANOTHER
WIND CHILL ADVISORY MAY BE NECESSARY AT SOME POINT.

AFTER A VERY COLD DAY ON WEDNESDAY THE CYCLONIC FLOW ALOFT WILL
FINALLY PUSH OFF TO THE EAST...ALLOWING FOR WEAK RIDGING TO BUILD
ACROSS THE REGION AND BEGIN A SLOW WARMING TREND. THE WARMING WILL
BE TEMPERED BY THE SNOW ON THE GROUND BUT NEVERTHELESS SOUTHERN
IOWA SHOULD APPROACH FREEZING/MELTING TEMPERATURE ON FRIDAY
AFTERNOON. BY THE END OF THE WORK WEEK A DEEP BUT BROAD 500 MB
TROUGH WILL BE MOVING OVER THE ROCKIES AND WILL BRING A RETURN OF
SNOW CHANCES FOR THE FIRST HALF OF THE WEEKEND. AT THIS TIME THE
TROUGH APPEARS TO NOT BE VERY WELL PHASED...WITH THE BULK OF ITS
ENERGY PASSING BY TO OUR NORTH AND SOUTH AND A RELATIVE GAP IN THE
PRECIPITATION MOVING ACROSS IOWA WHICH WOULD RESULT IN ONLY LIGHT
AMOUNTS AT BEST. HOWEVER...THE EVOLUTION OF THIS SYSTEM WILL BE
MONITORED OVER THE NEXT SEVERAL DAYS.

&&

.AVIATION...10/06Z
ISSUED AT 1148 PM CST MON DEC 9 2013

GUSTY WINDS STILL EXPECTED TO PICK UP LATER TONIGHT...WITH AREAS
OF BLOWING SNOW. POSSIBILITY OF VSBYS DROPPING TO MVFR AND
POSSIBLY IFR AT NORTHERN TAF SITES WHERE WINDS WILL BE STRONGEST
TOWARD SUNRISE TUESDAY TO MID MORNING TUESDAY. WINDS DIMINISH
TOWARD TUESDAY AFTERNOON...WITH ANOTHER SYSTEM PUSHING INTO THE
CWA SPREADING SNOW INTO THE AREA TUESDAY EVENING. HAVE INCLUDED
SNOW MENTION AT NORTHERN TAF SITES...WITH BEST CHANCES FOR SNOW AT
SOUTHERN TAF SITES JUST BEYOND THE CURRENT TAF FORECAST PERIOD.

&&

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

&&

$$

UPDATE...BEERENDS
SHORT TERM...REV
LONG TERM...LEE
AVIATION...BEERENDS