Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 030529
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1129 PM CST TUE FEB 2 2016

.UPDATE...
ISSUED AT 1129 PM CST TUE FEB 2 2016

A BAND OF ACCUMULATING SNOWFALL HAS BEEN PIVOTING AROUND JUST
NORTH AND WEST OF THE DES MOINES METRO...CAUSING 2 OR MORE INCHES
OF ACCUMULATION THIS EVENING WITHIN A NARROW SWATH. THIS IS ALSO
CAUSING A RAPID DETERIORATION IN ROAD CONDITIONS AS TEMPERATURES
FALL AND WINDS BEGIN TO SURGE IN FROM THE NORTHWEST. HIGH
RESOLUTION MODELS SUPPORT RADAR TRENDS IN MOVING THIS BAND VERY
SLOWLY EAST NORTHEAST OVERNIGHT...ALONG ITS OWN LENGTH UP AROUND
THE HIGHWAY 30 AND 20 CORRIDORS...SO DO NOT EXPECT ANY IMPROVEMENT
ESPECIALLY WITH THE INCREASING WINDS. THEREFORE...A WINTER WEATHER
ADVISORY HAS BEEN ISSUED ABOUT FOR TWO COUNTIES SOUTH OF AND ALL
ALONG THE WINTER STORM WARNING. THERE IS A POSSIBILITY THAT A FEW
LOCATIONS MAY EVEN SEE 5 OR 6 INCHES OF SNOW OVERNIGHT...BUT THE
PROBABILITY IS TOO LOW AND LOCATION TOO UNCERTAIN TO WARRANT
EXPANDING THE WARNING AT THIS TIME. IN ANY EVENT...A RAPID
SPREADING DETERIORATING OF ROAD CONDITIONS WILL MAKE TRAVEL VERY
DANGEROUS OVERNIGHT AND EASILY JUSTIFIES THE ADVISORY ON ITS OWN.
MEANWHILE THE AREA OF DENSE FOG IN SOUTHEASTERN IOWA HAS BEEN SLOW
TO ERODE...ONLY IMPROVING AS THE SNOW BAND MOVES IN FROM THE
WEST...SO HAVE EXTENDED ITS EASTERN PORTION THROUGH 09Z.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 301 PM CST TUE FEB 2 2016

PRIMARY CONCERN TONIGHT WILL BE PRECIP TRENDS AND HEADLINE
ADJUSTMENTS. POWERFUL LONG WAVE TROUGH WITH NOTED PV ANOMALY IN THE
CORE CONTINUES TO AFFECT IA THIS AFTERNOON WITH IMPRESSIVE 170KT JET
LEADING THE WAY. LEFT EXIT REGION DIVERGENCE AND DPVA CONTINUE TO
PUSH PRIMARY LIFT ZONE WELL NORTH AND EAST OF IOWA.
STRONG DEEP QG FORCING...INCLUDING LOWER LEVEL THERMODYNAMIC
SUPPORT...ALSO LINGERS BACK INTO IA BUT THIS IS SOMEWHAT MOISTURE
STARVED AND IS CURRENTLY GENERATING NOTHING BEYOND LIGHT SNOW AND
THEN DRIZZLE FARTHER SOUTH WHERE ICE INTRODUCTION IS LACKING. THUS
MUCH OF OUR PRECIP HAS ENDED FOR THE TIME BEING. A CONSIDERABLE
AMOUNT OF BLOWING SNOW LINGERS NORTH IN THE HEAVIER SNOW BAND
HOWEVER...6 INCHES PLUS GENERALLY ALONG AND NORTH OF SAC
CITY...WEBSTER CITY...MASON CITY LINE...WITH BLIZZARD OR NEAR
BLIZZARD CONDITIONS STILL BEING REPORTED BY LAW ENFORCEMENT...SOCIAL
MEDIA...DOT PLOW CAMS...ETC.

PRECIP MAY NOT BE FINISHED OVERALL HOWEVER AS DEFORMATION ZONE WILL
STILL LIFT THROUGH CENTRAL AND NORTHERN PORTIONS OF THE FORECAST
AREA...AND MUCH LIKE DEPICTED YESTERDAY BY THE NAM AND ASSOCIATED
NMM CORE MODELS...A LOW STATIC STABILITY BURST OF PRECIP MAY OCCUR
NEAR THE LOW CENTER WHICH IS CURRENTLY IN THE KS/NE/IA NEIGHBORING
BORDERS. TOKEN MUCAPES ARE NOTED IN THIS AREA CURRENTLY SO IT IS
QUITE POSSIBLE WE SEE ANOTHER ROUND OF SHOWERY WINTRY PRECIP LATER
THIS EVENING JUST EAST OF THE DEF ZONE. MOST DOMINATE PRECIP TYPE
SEEMS TO BE SNOW...AND WE MAY SEE ANOTHER INCH OR TWO OF SNOW WITH
ANOTHER STRONG WIND SURGE FOLLOWING IMMEDIATELY BEHIND. THUS EVEN
THOUGH WINDS MAY DIMINISH SOMEWHAT THIS EVENING AS THE LOW
APPROACHES SERN IA...EXPECT A SHARP INCREASE AGAIN OVERNIGHT.

WHAT THIS MEANS FOR HEADLINES IS THAT WINTER WEATHER ADVISORY AND A
TIER OF THE WINTER STORM WARNING WILL BE CANCELLED. THERE WILL BE A
CONSIDERABLE LULL IN SENSIBLE WEATHER INTO THE EVENING IN THESE
LOCATIONS. ADDITIONAL HEADLINES COULD POTENTIALLY BE NEEDED
AGAIN...BUT THIS WOULD BE DEPENDENT ON ADDITIONAL PRECIP. THE SNOW
CONSISTENCY IN CENTRAL IA IS VERY WET AND NOT CONDUCIVE FOR
SIGNIFICANT BLOWING SNOW. FARTHER NORTH WHERE THE SNOW IS DEEPER AND
DRIER AND CURRENTLY BLOWING...ANOTHER INCREASE IN WINDS WITH GUSTS
LIKELY 35-40 MPH WILL LOOK TO PRODUCE ANOTHER ROUND OF BLIZZARD OR
NEAR BLIZZARD CONDITIONS. SO EVEN THOUGH THERE MAY BE A LULL...WILL
LEAVE THE BLIZZARD WARNING UNCHANGED AS TO NOT INJECT CANCELLED
WORDING AND FALSE MESSAGING.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 301 PM CST TUE FEB 2 2016

RELATIVELY QUIET IN THE LONG TERM PERIOD. FOR THE START OF THE
PERIOD...THE LAST OF THE DEFORMATION ZONE PRECIP WILL BE EXITING
THE EASTERN PORTION OF THE FORECAST AREA AND WILL BE OUT OF THE
AREA BY 18Z. LITTLE TO NO ACCUMULATION EXPECTED AFTER 12-13Z.
WINDS HOWEVER WILL STAY UP. WE ARE LOOKING AT WINDS IN THE MORNING
IN THE RANGE OF 15 TO 30 MPH AND THIS WILL CONTINUE TO PRODUCE
AREAS OF BLOWING SNOW...ESPECIALLY NW WHERE WE HAVE THE MOST NEW
SNOW. IT WILL ALSO BE MUCH COLDER SO EVEN THOUGH WE WILL NOT HAVE
SNOW TO CONTEND WITH IT WILL BE A RAW DAY. THERE MAY ALSO BE SOME
RESIDUAL TRAVEL CONCERNS AS MELTED ROADWAYS SLICKEN UP WITH THE
COLDER TEMPS AND WHEEL TRACK PRODUCE A GLAZE FROM DRIFTING SNOW
ACROSS THE ROADS.

ON THURSDAY THERE IS ANOTHER SHORTWAVE THAT GRAZES THE FORECAST
AREA ACROSS THE NORTHEAST. AT THIS POINT I LEFT THE FORECAST DRY
BUT WE COULD SEE A DUSTING OF SNOW IN THE MASON CITY AREA AND
LOCATIONS SOUTH AND EAST OF THE CITY.

FOR THE REST OF THE PERIOD UPPER RIDGING WORKS INTO THE AREA AND A
MORE WESTERLY FLOW DEVELOPS BRINGING IN WARMER...OR AT LEAST
MODERATING TEMPERATURES BACK TO THE AREA. SOUTHERN LOCATIONS COULD
SEE READINGS IN THE 40S WITH MID TO UPPER 30S NORTH OVER THE
WEEKEND.

THEN FOR SUNDAY THROUGH TUESDAY THE MODELS DROP ANOTHER DEEP
TROUGH OVER THE UPPER MIDWEST BRINGING COLDER TEMPERATURES BACK TO
CENTRAL IOWA ALONG WITH A CHANCE FOR SOME LIGHT SNOW. THIS SYSTEM
WILL LACK THE GULF MOISTURE TAP SO DESPITE THE SYSTEM BEING STRONG
AND MUCH COLDER AIR MOVING IN...WE ARE NOT LOOKING AT A LOT OF
SNOW WITH THE SYSTEM.

&&

.AVIATION...03/06Z
ISSUED AT 1129 PM CST TUE FEB 2 2016

IFR CONDITIONS WILL CONTINUE THROUGH THE NIGHT BETWEEN THE
FOG...LOW CEILINGS...SNOW AND BLOWING SNOW. GRADUAL IMPROVEMENT
WILL OCCUR ON WEDNESDAY AS THE SNOW MOVES OUT AND WINDS SLOWLY
SUBSIDE. THERE IS UNCERTAINTY AS TO THE EXTENT TO WHICH CIGS MAY
CLEAR OUT/RISE ON WEDNESDAY...AND BELIEVE AT LEAST MVFR CIGS WILL
PROBABLY PERSIST THROUGH THE DAY.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 AM CST WEDNESDAY FOR ADAIR-ADAMS-
BLACK HAWK-CASS-CLARKE-GRUNDY-JASPER-MADISON-MARSHALL-POLK-TAMA-
UNION-WARREN.

DENSE FOG ADVISORY UNTIL 3 AM CST WEDNESDAY FOR CLARKE-JASPER-
LUCAS-MAHASKA-MARION-MONROE-POLK-POWESHIEK-WAPELLO-WARREN.

WINTER STORM WARNING UNTIL 6 AM CST WEDNESDAY FOR AUDUBON-BOONE-
BREMER-BUTLER-DALLAS-GUTHRIE-HARDIN-STORY.

BLIZZARD WARNING UNTIL 6 AM CST WEDNESDAY FOR CALHOUN-CARROLL-
CERRO GORDO-CRAWFORD-EMMET-FRANKLIN-GREENE-HAMILTON-HANCOCK-
HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-SAC-WEBSTER-WINNEBAGO-
WORTH-WRIGHT.

&&

$$

UPDATE...LEE
SHORT TERM...SMALL
LONG TERM...FAB
AVIATION...LEE


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