Area Forecast Discussion
Issued by NWS Des Moines, IA

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191
FXUS63 KDMX 072139
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
339 PM CST SUN FEB 7 2016

.SHORT TERM /TONIGHT/...
ISSUED AT 334 PM CST SUN FEB 7 2016

PRIMARY CONCERN OBVIOUSLY REMAINS SNOW AND WIND TRENDS...AND
RESULTANT BLIZZARD POTENTIAL. LONG WAVE TROUGH CONTINUES TO DROP
INTO THE UPPER MS VALLEY WITH SHORT WAVE/PV ANOMALIES THROUGH THE
SIOUXLAND AREA AND NRN MN. FORCING WITH THESE FEATURES IS
GENERALLY WEAK...BUT RESULTS IN A SATURATED COLUMN...ESPECIALLY
BY LATER TONIGHT. THIS SHOULD RESULT IN FAIRLY WIDESPREAD
SNOW...BUT MOSTLY LIGHT...SIMILAR TO WHAT IS NOW OCCURRING FROM
THE DAKOTAS INTO MN. THE LIFT IS NOT GREAT BUT THE DENDRITIC LAYER
SHOULD BE QUITE DEEP LATER TONIGHT...EXCEEDING 2KM AT TIMES...SO
AT LEAST SOME SNOW PRODUCTION AND ACCUMS ARE QUITE LIKELY. THIS
SYNOPTIC SCALE FORCING WILL ALSO EVENTUALLY COMBINE WITH
CONVECTIVE SNOW SHOWERS AS LAPSE RATES STEEPEN...WHICH ARE
DEPICTED IN MOST HI RES CONVECTION ALLOWING MODELS /CAMS/. THE NAM
EVEN DEPICTS SOME TOKEN MLCAPE TONIGHT. ALTHOUGH A MORE GENERAL
BROAD BRUSH APPROACH IS SHOWN IN QPF TONIGHT DUE TO LOW SPACIAL
PREDICTABILITY...CAMS SHOW POTENTIAL FOR VERY NARROW BANDED QPF TO
REACH 0.10 OR MORE IN NW-SE STRIPES ORIENTED ALONG THE THERMAL
GRADIENT. THUS EXPECT BROAD SNOWFALL AND BANDS TO COMBINE FOR A
DUSTING TO AN INCH BY 12Z WITH LOCALLY HIGHER AMOUNTS IN BANDS.
REGARDING WIND...20Z SURFACE ANALYSIS SHOWS GRADIENT TIGHTENING
WITH WEAK TROUGH THROUGH THE SIOUXLAND AREA...AND MORE PRONOUNCED
COLD FRONT MOVING THROUGH ND AND MN. LAPSE RATES ARE STEEPENING
BEHIND THE SIOUXLAND TROUGH WITH SOME GUSTS REACHING 40-50 MPH.
ALTHOUGH THE PEAK GUSTS WILL REMAIN WEST OF OUR FORECAST
AREA...SOUNDINGS SUGGEST A BLEND OF PROJECTED MEAN MIXED LAYER
WIND AND TOP OF THE LAYER MAY GENERATE GUSTS 40 MPH OR MORE INTO
THE NIGHT.

THERE IS A RELATIVELY HIGH CONFIDENCE IN METEOROLOGICAL TRENDS
NOTED ABOVE...BUT IT HAS DECREASED RELATING TO HOW THIS WILL
MODULATE INTO VISIBILITY RESTRICTIONS AND A POTENTIAL BLIZZARD.
TEMPS HAVE REACHED THE MID/UPPER 30S ACROSS THE CURRENT BLIZZARD
WARNING AREA WITH SOME SUNSHINE...AND A FEW MANUAL OBSERVATIONS
INDICATE THAT THE SNOW IS SOMEWHAT WET AND COMPACTED. THE LATEST
SNOW DEPTH ESTIMATES /WWW.NOHRSC.NOAA.GOV/ SHOW THE STRONGEST
WINDS ARE JUST BEGINNING TO REACH THE DEEPEST UPSTREAM SNOWPACK
OVER SRN MN...SO IT IS SOMEWHAT UNKNOWN WHETHER THIS AREA WILL BE
CAPABLE OF PRODUCING SIGNIFICANT BLOWING SNOW UNTIL THE WINDS WORK
FOR SEVERAL HOURS. FEEL FALLING SNOW...ESPECIALLY THE BANDED
SNOW...WILL PRODUCE DRAMATICALLY REDUCED VISIBILITIES FOR SOME
SHORTER PERIODS BUT CONFIDENCE IN WHETHER THIS CAN COMBINE WITH
EXISTING SNOW DOWN TO A 1/4SM OR LESS HAS DIMINISHED. CERTAINLY DO
NOT WANT TO RISK CANCELING OR DOWNGRADING CURRENT WARNING AND THEN
HAVING TO FLIP FLOP BACK TO WARNING...SO WILL LEAVE CURRENT
HEADLINE RIDE UNTIL CONFIDENCE IN 1/4SM VISIBILITY INCREASES. THE
WIND COMPONENT WILL CERTAINLY BE THERE. EITHER A WIND ADVISORY OR
WINTER WEATHER ADVISORY WILL LIKELY BE NEEDED IN THE SOUTHERN NON-
WARNING AREA...BUT WILL HOLD OFF UNTIL IT BECOMES CLEARER WHICH
FLAVOR OR HEADLINE IS MORE APPROPRIATE...AGAIN NOT WANTING TO FLIP
FLOP.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 334 PM CST SUN FEB 7 2016

FORECAST CONCERN REMAINED FOCUSED ON CONTINUED BLIZZARD AND WINDY
CONDITIONS MONDAY INTO MONDAY NIGHT. LEANED TOWARD A BLEND OF THE
NAM/GFS/HIRES NMM FOR POPS/WX TIMING MONDAY...THEN A GFS/ECMWF
BLEND THROUGH THE REST OF THE FORECAST PERIOD.

MONDAY INTO TUESDAY...THE LARGE SURFACE LOW PRESSURE LOOKS TO BE
CENTERED OVER THE GREAT LAKES BY SUNRISE MONDAY MORNING PLACING
IOWA REMAINS WELL WITHIN THE STRONG NORTHERLY FLOW THROUGH MUCH
OF THE DAY MONDAY. 850MB TEMPS/WINDS BOTTOM OUT B/T -13C TO -17C
WITH WINDS HOWLING AT 40-55 KNOTS. THESE WINDS ARE AT OR NEAR THE
MIXED LAYER AND EXPECT THEM TO REACH THE SURFACE WITH SUFFICIENT
MOMENTUM TRANSFER THROUGH THE DAY TOMORROW. BUFR SOUNDINGS
CONTINUE TO KEEP MUCH OF THE FORECAST AREA WITHIN A DEEP AND
SATURATED DENDRITIC LAYER THROUGH THE MORNING...AND EVEN EAST OF
I-35 THROUGH THE AFTERNOON. MOST SOUNDINGS ARE COMPLETELY WITHIN
THE DGZ UP TO ROUGHLY 600MB..SO EXPECTING SNOW TO CONTINUE TO FALL
THROUGH THE MORNING HOURS. VERY LITTLE OMEGA PRESENT BUT WITH VERY
STEEP LAPSE RATES AND A SMALL AMOUNT OF FRONTOGENETICAL FORCING
AVAILABLE...EXPECTING SNOW SHOWERS TO PERSIST THROUGH THE MORNING
HOURS AND EVEN INTO THE AFTERNOON. A DRY INTRUSION BEGINS TO PUNCH
INTO THE WESTERN PORTION OF THE STATE BY THE AFTERNOON AND SHOULD
FINALLY CUTOFF THE ICE INTRODUCTION AND SNOW PRODUCTION WEST OF I-
35.

HEADLINE CONCERNS...CERTAINLY MUCH OF THE FORECAST AREA SHOULD
REACH WIND ADVISORY CRITERIA. HOWEVER...FELT THE NEED TO HOLD OFF
ON ISSUING ATTM ACROSS IN THE SOUTH TO AVOID THE POTENTIAL FOR
UPGRADING TO A WINTER WEATHER ADVISORY ONCE THIS SYSTEM SHOWS ITS
HAND.

SNOW FLURRIES OR LIGHT SNOW SHOWERS LOOK TO CONTINUE OVER THE EAST
TOMORROW NIGHT BUT THE WINDS GRADUALLY SUBSIDE AND ANY
VISIBILITY CONCERNS WILL REMAIN MINIMAL. WIND CHILLS ARE THE MAIN
CONCERN BY LATE MONDAY NIGHT INTO TUESDAY MORNING AS THE LOOK TO
DIP INTO THE TEENS BELOW ZERO OVER THE NORTH.

WEDNESDAY THROUGH SUNDAY...SURFACE HIGH SLOWLY NUDGES ITS WAY
INTO THE REGION BY WEDNESDAY MORNING. BRISK WINDS OF 10-20 KNOTS
LOOK TO PRODUCE WIND CHILL VALUES TO 20-25 BELOW BY WEDNESDAY
MORNING AND LIKELY NEED A HEADLINE DURING THIS TIME FRAME OVER
NORTHERN IOWA. HIGH PRESSURE DOMINATES THE REMAINDER OF THE
PERIOD AND PROVIDES DRY AND COLD CONDITIONS THROUGH THE END OF THE
WEEK. GFS DOES BRING A WEAK SHORTWAVE ACROSS THE STATE THURSDAY
INTO THURSDAY NIGHT BUT ECMWF REMAINS DRY AND LEFT DRY FORECAST
ATTM UNTIL BETTER MODEL CONSENSUS.

&&

.AVIATION...07/18Z
ISSUED AT 1151 AM CST SUN FEB 7 2016

VFR CONDITIONS WILL PERSIST THROUGH MUCH OF THE AFTERNOON ALTHOUGH
MVFR/IFR CONDITIONS DUE TO A COMBINATION OF CLOUDS...SNOW AND
BLOWING SNOW WILL PROGRESS NW-SE THROUGH THE AREA INTO THE
EVENING. CONFIDENCE IS LOW IN VISIBILITY DETAILS DUE TO SNOW
SHOWER INTENSITY AND THE EFFICIENCY OF BLOWING SNOW DUE TO
RELATIVELY WET EXISTING SNOWPACK...BUT THE GENERAL CONSENSUS IS
FOR IFR VSBYS DUE TO BLOWING SNOW FOR PROLONGED PERIOD THROUGH THE
NIGHT AND INTO MONDAY MORNING. VSBYS MAY DIP TO LIFR DURING BURSTS
OF HEAVIER SNOW SHOWERS...BUT DID NOT WANT TO INCLUDE FOR 12 PLUS
HOURS. SIMILAR THINKING WITH WIND. GUSTS MAY REACH 40KTS OR MORE
FROM KDSM NORTH AND WEST...BUT DEPICTED MORE OF A LONG TERM
AVERAGE RATHER THAN PEAK.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
BLIZZARD WARNING FROM 7 PM THIS EVENING TO 6 PM CST MONDAY FOR
AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CERRO
GORDO-CRAWFORD-DALLAS-EMMET-FRANKLIN-GREENE-GRUNDY-GUTHRIE-
HAMILTON-HANCOCK-HARDIN-HUMBOLDT-KOSSUTH-MARSHALL-PALO ALTO-
POCAHONTAS-SAC-STORY-WEBSTER-WINNEBAGO-WORTH-WRIGHT.

&&

$$

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



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