Area Forecast Discussion
Issued by NWS Des Moines, IA

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249
FXUS63 KDMX 021801
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1201 PM CST TUE FEB 2 2016

.UPDATE...
ISSUED AT 1200 PM CST TUE FEB 2 2016

ADJUSTED FORECAST EARLIER THIS MORNING TO PUSH RAIN/SNOW
TRANSITION LINE FARTHER NORTH WITH DRY SLOT/WARM LAYER SURGE.
ALTHOUGH FORCING REMAINS QUITE STRONG INTO IA...MID LEVEL MOISTURE
IS BEGINNING TO LACK SO THIS WILL EITHER REDUCE OR END PRECIP
RATES...AND/OR FLIP THE PRECIP MORE TO LIQUID. ATTENTION WILL THEN
TURN TO ENHANCED BURST OF LOW STABILITY PRECIP WHICH MAY OCCUR
NEAR THE CORE OF THE UPPER LOW THIS EVENING. LOW CONFIDENCE IN
TYPE DETAILS...BUT RATES MAY BE DECENT. NO HEADLINE CHANGES RIGHT
NOW...BUT TRENDS AND POTENTIAL CANCELLATIONS AND ADJUSTMENTS WILL
CERTAINLY BE EVALUATED FOR AFTERNOON PACKAGE.

&&

.SHORT TERM /TODAY/...
ISSUED AT 418 AM CST TUE FEB 2 2016

WINTER STORM/BLIZZARD CONDITIONS STILL ONTRACK FOR TODAY OVER
WESTERN TO NORTHERN IOWA. THE MAIN FORECAST CONCERN WAS FOCUSED ON
THE DRY SLOT PUNCHING INTO SOUTH-CENTRAL TO SOUTHEAST IOWA THIS
AFTERNOON...AND HOW FAR NORTH IT WILL REACH IN THE CWA TODAY.
MODELS REMAIN IN VERY GOOD AGREEMENT WITH THE OVERALL SYNOPTIC
PATTERN AND THE TRACK OF THE SURFACE LOW ACROSS NE KANSAS INTO NW
MISSOURI AND THROUGH SOUTH-CENTRAL TO SOUTHEAST IOWA TODAY. LEANED
TOWARD A BLEND OF THE HRRR/NAM12/GFS/ECMWF TODAY FOR TIMING OF
PRECIP AND POPS.

THE LATEST HRRR/ARWWRF/4.0KM WRF/HOPWRF BRING THE WAA SNOW BAND INTO
THE AREA B/T 12-17Z THIS MORNING...WITH THE WEST TO NORTHWEST
REMAINING THE DEFORMATION ZONE DURING MUCH OF THE DAY. EXPECTING THE
SNOW TO PERSIST THROUGH THIS EVENING ONCE IT BEGINS IN THE BLIZZARD
WARNING (EXCEPT A BRIEF STINT OF FZRA...MORE ON THIS BELOW).
AGAIN...THERE REMAINS PLENTY OF INSTABILITY AS MUCAPES B/T 700-500MB
RANGE FROM 50-100MB AND LAPSE RATES ARE IN THE 6-7 C/KM RANGE THIS
MORNING. ALREADY SEVERAL LIGHTNING STRIKES OCCURRING IN NORTHEAST
KS/SOUTHEAST NE/NORTHERN MO AS OF 0945Z. CONFIDENCE IS HIGH FOR A
BRIEF PERIOD HEAVY SNOW...WITH THE POTENTIAL FOR THUNDERSNOW ALONG
AND SOUTH OF I-80 PROVIDING A BRIEF BURST OF EFFICIENT SNOW
DURING THE MORNING COMMUTE.

THE DREADED DRY SLOT LOOKS TO PUNCH INTO SOUTH-CENTRAL IOWA TOWARDS
MIDDAY AND LIKELY AS FAR NORTH ALONG A LINE FROM DES MOINES TO
WATERLOO PAST 18Z. HENCE...EXPECTING A BREAK IN PRECIP THIS
AFTERNOON AND THUS LOWERED POPS ACROSS THE SOUTHEAST. THE OTHER
SCENARIO IS FOR SNOW TO CHANGE TO RAIN ALONG AND SOUTH OF I-80 THIS
AFTERNOON. FURTHER NORTH AND WEST...SOUNDINGS LOSE ICE INTRODUCTION
FOR A SHORT TIME FRAME AND HAVE KEPT MENTION OF FZRA THIS AFTERNOON
FROM A LINE NEAR AUDUBON NORTHEAST THROUGH FORT DODGE TO MASON CITY.
NOT ANTICIPATING A LARGE AMOUNT OF ICE ACCUMS...BUT ANY ICE ONTOP OF
SNOW TYPICALLY LEADS TO DIFFICULT TRAVEL CONDITIONS.

WITH THE SURFACE LOW TRACKING ACROSS SOUTH-CENTRAL TO SOUTHEAST IOWA
THIS AFTERNOON...A LULL IN THE WINDS ARE ANTICIPATED OVER MUCH OF
THE WINTER STORM WARNING AREA. THE PRESSURE GRADIENT AND MIXED LAYER
WINDS STAY STRONG ENOUGH OVER THE WEST TO NORTHWEST TO CONTINUE TO
PROVIDE SIGNIFICANT VISIBILITY RESTRICTIONS.

.LONG TERM /TONIGHT THROUGH MONDAY/...
ISSUED AT 418 AM CST TUE FEB 2 2016

UPPER LOW WILL TRAVERSE THE STATE TONIGHT WITH SURFACE LOW
PASSING FROM NEAR LAMONI THIS EVENING TO DUBUQUE BY DAYBREAK
WEDNESDAY. DRY SLOT WILL BE IN PLACE ACROSS THE SOUTH AND EAST AT
BEGINNING OF THE PERIOD WITH DEFORMATION PRECIPITATION ONGOING
ACROSS THE FAR NORTH AND WEST. GIVEN THE LOSS OF SATURATION
ALOFT...THERE WILL BE A THREAT OF FREEZING DRIZZLE ACROSS
PORTIONS OF AREA INTO THIS EVENING...MAINLY EAST OF I35 AND NORTH
OF I80. MODELS ARE INDICATING DEVELOPMENT OF A SECONDARY ENHANCED
AREA OF PRECIPITATION ON SOUTHERN FLANK OF DEFORMATION AREA WHERE
STATIC STABILITY IS RELATIVELY WEAK AND LIFT IS STRONG. ANTICIPATE
A RAIN/SNOW MIX INITIALLY...BUT AS PRECIPITATION RATES
INCREASE...SNOW WILL BECOME PREDOMINANT AS SOUNDINGS GENERALLY
ISOTHERMAL ALONG 0C. SNOW WILL CONTINUE FARTHER NORTH AS WELL BUT
WILL BE DECREASING IN COVERAGE AND INTENSITY AS BEST FORCING AND
LIFT SHIFTS NORTHEAST. ADDITIONAL SNOWFALL AMOUNTS WILL BE FROM 1
TO 3 INCHES OVERNIGHT WITH HIGHEST AMOUNTS IN THE BAND RUNNING
FROM CENTRAL INTO NORTHEAST IOWA. WINDS WILL BE IN A RELATIVELY
LULL EARLY THIS EVENING FOR MUCH OF THE FORECAST AREA WITH THE LOW
TRACKING THROUGH THE SOUTH AND EAST. HOWEVER...THE FAR NORTH AND
WEST WILL CONTINUE TO SEE STRONG WINDS THIS EVENING WITH THESE
STRONGER NORTHWEST WINDS EXPANDING OVERNIGHT AS THE LOW MOVES
TOWARD DUBUQUE. THE THREAT OF BLOWING SNOW WILL INCREASE AND
SPREAD SOUTHEAST ACROSS THE FORECAST AREA OVERNIGHT WITH THE
INCREASING COLD ADVECTION.

THE REMAINDER OF THE FORECAST IS RELATIVELY DRY...AT LEAST THROUGH
THE WEEKEND WITH GRADUAL MODERATION. THERE WILL BE A COLD DAY OR
TWO THROUGH THURSDAY BUT SURFACE FLOW BECOMES WESTERLY WITH
READINGS CLIMBING INTO THE WEEKEND AS MEAN POSITION OF EASTERN
TROF SHIFTS SLIGHTLY EASTWARD. HOWEVER...BY THE END OF THE
FORECAST PERIOD...AN ARCTIC FRONT WILL SURGE INTO THE MIDWEST
WITH TEMPERATURES CRASHING INTO EARLY NEXT WEEK.

&&

.AVIATION...02/18Z
ISSUED AT 1200 PM CST TUE FEB 2 2016

IFR/LIFR CONDITIONS STILL PREVAIL OVER MOST AREAS AND SHOULD
REMAIN SO THROUGH THE PERIOD OUTSIDE OF A POSSIBLE SHORT BREAK
TOWARD KOTM THIS EVENING. DRY MID LEVEL AIR WILL PRODUCE A BREAK
FROM PRECIP UNTIL THE CORE OF THE LOW PRESSURE SYSTEM ALOFT MOVES
THROUGH TONIGHT. WINDS WILL INCREASE AGAIN TONIGHT POSSIBLY
PRODUCING ADDITIONAL BLOWING SNOW FOR NRN TAF SITES...AND ANOTHER
ROUND OF WINTRY PRECIP.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 AM CST WEDNESDAY FOR ADAIR-ADAMS-
AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CASS-DALLAS-GRUNDY-
GUTHRIE-HARDIN-MADISON-MARSHALL-POLK-STORY.

WINTER WEATHER ADVISORY UNTIL 6 AM CST WEDNESDAY FOR CLARKE-
JASPER-POWESHIEK-RINGGOLD-TAMA-TAYLOR-UNION-WARREN.

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...SMALL
SHORT TERM...PODRAZIK
LONG TERM...COGIL
AVIATION...SMALL



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