Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 011202
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
602 AM CST SUN FEB 1 2015

.SHORT TERM /TODAY/...
ISSUED AT 342 AM CST SUN FEB 1 2015

MAIN CONCERN REMAINS TREND OF ONGOING WINTER STORM WHOSE HAZARDS ARE
BECOMING MORE WORRISOME WITH TIME.  WIDESPREAD LIFT AND MODERATE TO
HEAVY SNOWFALL CONTINUES IN RIGHT ENTRANCE REGION OF GREAT LAKES/SE
CANADA JET SEGMENT.  KINEMATIC AND THERMODYNAMIC FORCING IS DEEP AND
IMPRESSIVE WITH DPVA NOTED AHEAD OF KS SHORT WAVE/PV ANOMALY AND
SIOUXLAND DEFORMATION ZONE ASSOCIATED WITH PARENT WAVE. THETA-E
ADVECTION AND MOISTURE TRANSPORT ARE MORE ELEVATED THAN SOME STORMS
WITH PEAK AT H7/H5 AND IS COINCIDENT WITH THE DENDRITIC ZONE FOR THE
TIME BEING. LUCKILY...STATIC STABILITIES ARE FAIRLY HIGH IN THIS
LAYER SO THUNDERSNOW OR ADDITIONAL ELEVATED CONVECTIVE LIFT
CONTRIBUTIONS ARE NOT EXPECTED.

THE THERMODYNAMIC ASPECT OF THIS STORM WILL WANE TOWARD MIDDAY AND
THE KINEMATIC FORCING WILL DIMINISH SOMEWHAT AS WELL.  HOWEVER IT
WILL STILL REMAIN QUITE DEEP AND REMAIN COINCIDENT WITH THE
DESCENDING DENDRITIC GROWTH ZONE /DGZ/. THIS WILL KEEP ACCUMULATING
SNOWS GOING THROUGHOUT THE DAY AND HAVE RAISED POPS ACCORDINGLY. THE
COLUMN WILL COOL SUFFICIENTLY THAT THE DGZ DEPTH MAY APPROACH 3KM BY
THIS AFTERNOON WITH LOW LEVEL LAPSE RATES STEEPENING IN THE COLD
ADVECTION. CONVECTIVE SNOW SHOWERS MAY BEGIN CONTRIBUTING TO THE
SNOWFALL BY LATE MORNING. WINDS MAY GUST TO 35 MPH OR SO RIGHT ON
THE BRINK OF NEEDING A BLIZZARD WARNING. CONFIDENCE IS NOT THERE TO
ISSUE AS OF YET...BUT HAVE CERTAINLY HIT THAT WORDING HARDER IN
RECENT WSW. WOULD EXPECT TRAVEL TO BE QUITE DIFFICULT IF NOT
IMPOSSIBLE OVER THE WRN AND NRN HALVES OF IA BY LATE AFTERNOON WITH
PLENTY OF SNOW TO BLOW AROUND.

A PERSISTENT BAND OF HIGHER REFLECTIVITIES AND DENDRITIC SNOW HAS
SETUP ALONG THE I80 AND HIGHWAY 30 CORRIDORS AND THERE IS ALREADY IN
EXCESS OF SEVEN INCHES HERE AT THE OFFICE.  NOW HAVE WIDESPREAD
STORM TOTAL AMOUNTS OF 8-12 FORECAST AREA WIDE WITH LOCALIZED 12-14
POSSIBLE FROM CENTRAL IA EASTWARD ALONG THE AFOREMENTIONED
CORRIDORS.  TREE DAMAGE IS ALREADY PRODUCING POWER OUTAGES AND WOULD
EXPECT THIS PROBLEM TO CONTINUE AND BECOME MORE WIDESPREAD AS WINDS
INCREASE LATER TODAY.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 342 AM CST SUN FEB 1 2015

THE LARGE WINTER STORM SYSTEM CURRENTLY AFFECTION THE REGION WILL
PUSH AWAY TO THE SOUTHEAST TONIGHT...WITH SNOW AND BLOWING SNOW
LINGERING WELL INTO THE EVENING AS REFLECTED IN THE WINTER STORM
WARNING AND THE SHORT TERM DISCUSSION ABOVE. BY MONDAY MORNING
TEMPERATURES WILL PLUMMET WELL BELOW ZERO ACROSS MOST OF THE AREA
AND HAVE LOWERED THE FORECAST BY A COUPLE OF DEGREES FROM THE
PREVIOUS PACKAGE. WITH A SURFACE RIDGE BUILDING IN...CLEAR SKIES
AND A DEEP FRESH SNOW PACK IN PLACE...WE MAY NEED TO GO EVEN LOWER
BUT THERE IS SOME DOUBT AS TO WHETHER WINDS WILL GO FULLY CALM OR
NOT.

WE WILL REMAIN BENEATH GENERALLY NORTHWESTERLY 500 MB FLOW FOR THE
ENTIRE WEEK PREVENTING ANY SIGNIFICANT WARMING ESPECIALLY WITH SO
MUCH SNOW ON THE GROUND. A SERIES OF IMPULSES TRAVELING THROUGH
THIS FLOW WILL PROVIDE INTERMITTENT CHANCES FOR ADDITIONAL
SNOWFALL. HOWEVER...MOST OF THESE WAVES WILL BE MODEST AND QUICKLY
MOVING SO ANY ACCUMULATIONS WILL BE LIGHT. THE POSSIBLE EXCEPTION
COMES IN THE FORM OF A 500 MB TROUGH SWINGING ACROSS THE UPPER
MIDWEST FROM LATE TUESDAY INTO WEDNESDAY. AT THE SURFACE...THE
APPROACH OF THIS SYSTEM WILL BE REFLECTED IN THE DEVELOPMENT OF A
WEAK INVERTED TROUGH STRETCHING FROM KANSAS AND MISSOURI UP TOWARD
IOWA BY TUESDAY MORNING. AS A LEADING 500 MB IMPULSE ROCKETS
ACROSS OUR FORECAST AREA AROUND TUESDAY AFTERNOON MOST MODELS
DEPICT A NICE CORE OF LIFTING OVER THE REGION JUST NORTH OF THE
SURFACE TROUGH YIELDING A GOOD SET UP FOR ACCUMULATING SNOWFALL.
THE NAM IS ANOMALOUSLY FAR NORTH WITH ITS SOLUTION OF THE SURFACE
TROUGH AND RESULTING SNOW FIELD AND LARGELY DISCOUNTED ITS
SOLUTION IN FAVOR OF THE MORE CONSISTENT GFS AND ECMWF WHICH PAINT
A COUPLE OF TENTHS OF AN INCH OF QPF ACROSS AREAS NORTH OF
I-80...WHICH WOULD PROBABLY TRANSLATE INTO SOMETHING ON THE ORDER
OF A FEW INCHES OF SNOW. FORTUNATELY IT APPEARS THAT WINDS WILL BE
FAIRLY LIGHT ON TUESDAY AFTERNOON SO THE IMPACTS ARE NOT
ANTICIPATED TO BE SIGNIFICANT AT THIS TIME.

BY WEDNESDAY A LARGE AREA OF HIGH PRESSURE WILL BE BUILDING FROM
SOUTHERN CANADA DOWN INTO THE DAKOTAS...SWEEPING A SURGE OF
NORTHWEST WINDS DOWN ACROSS IOWA EARLY IN THE DAY. MEANWHILE THE
PRIMARY 500 MB TROUGH WILL SWING OVER THE REGION...SPREADING A
SWATH OF ACCUMULATING SNOW FROM AROUND THE BLACK HILLS DOWN ACROSS
NEBRASKA AND INTO KANSAS AND MISSOURI BY WEDNESDAY EVENING. THERE
IS SOME QUESTION AS TO HOW MUCH THIS SWATH WILL AFFECT OUR
SOUTHWESTERN/SOUTHERN COUNTIES DURING THE DAY ON WEDNESDAY...BUT
THE MODEL SOLUTIONS HAVE HAD A WIDE SPREAD IN THIS SCENARIO AND
FOR NOW HAVE JUST HELD LOW CHANCE POPS. IN ANY EVENT AS THE
AFOREMENTIONED HIGH PRESSURE BUILDS IN ON WEDNESDAY NIGHT
TEMPERATURES WILL LIKELY FALL EVEN FURTHER...WITH TEENS BELOW ZERO
A DISTINCT POSSIBILITY BY EARLY THURSDAY MORNING. HAVE ONCE AGAIN
ADJUSTED WEDNESDAY NIGHT LOWS DOWNWARD BY SEVERAL DEGREES AND THIS
TREND WILL LIKELY CONTINUE IN THE COMING DAYS. WINDS WILL BE
DIMINISHING ON WEDNESDAY NIGHT BUT IT REMAINS TO BE SEEN WHETHER
WIND CHILLS WILL HIT ADVISORY CRITERIA AND IT IS QUITE POSSIBLE
GIVEN THE ANTICIPATED LOW TEMPERATURES. TOWARD THE END OF THE WEEK
THERE ARE SOME INDICATIONS THAT WE MAY SEE A BRIEF PERIOD OF WEAK
RIDGING AND WARM AIR ADVECTION...BUT GIVEN THE DEPTH OF THE SNOW
PACK IN PLACE AT THAT TIME IT IS DIFFICULT TO IMAGINE ANY REALLY
SIGNIFICANT WARMING/MELTING AND HAVE CONTINUED TO ADJUST
TEMPERATURES DOWNWARD DURING THAT TIME.

&&

.AVIATION...01/12Z
ISSUED AT 602 AM CST SUN FEB 1 2015

WIDESPREAD IFR/LIFR CONDITIONS ARE EXPECTED TO PERSIST THROUGH THE
MORNING WITH STEADY SNOW...AND ADDITIONAL BLOWING SNOW
RESTRICTIONS OVER NRN IA. THE SNOW SHOULD WEAKEN IN INTENSITY
SOMEWHAT BY LATE MORNING...BUT STILL IMPROVE NO BETTER THAN
WIDESPREAD IFR THROUGH MUCH OF THE DAY IN LIGHT SNOW AND BLOWING
SNOW. THE SNOW AND BLOWING SNOW SHOULD DIMINISH FURTHER AND
SUFFICIENT FOR MVFR IMPROVEMENT INTO THE EARLY EVENING BEFORE
GOING CLEAR INTO THE NIGHT.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR ADAIR-ADAMS-
APPANOOSE-AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-
CASS-CERRO GORDO-CLARKE-CRAWFORD-DALLAS-DAVIS-DECATUR-EMMET-
FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-
JASPER-KOSSUTH-LUCAS-MADISON-MAHASKA-MARION-MARSHALL-MONROE-PALO
ALTO-POCAHONTAS-POLK-POWESHIEK-RINGGOLD-SAC-STORY-TAMA-TAYLOR-
UNION-WAPELLO-WARREN-WAYNE-WEBSTER-WINNEBAGO-WORTH-WRIGHT.

&&

$$

SHORT TERM...SMALL
LONG TERM...LEE
AVIATION...SMALL



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