Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 250955
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
355 AM CST WED FEB 25 2015

.SHORT TERM /TODAY/...
ISSUED AT 354 AM CST WED FEB 25 2015

BIGGEST CONCERN THROUGH TODAY WILL OBVIOUSLY BE TRACK AND AMOUNTS.
TRACK WISE GUIDANCE SUITE HAS CONTINUED TO DRIFT HEAVIEST AXIS NORTH
AND EAST WITH TIME...BUT QUESTION WILL BE HOW FAR. BLEND OF MAIN
OPERATIONAL DETERMINISTIC RUNS NOW PLACES HIGHEST AMOUNTS ALONG
EMMETSBURG TO TAMA OR GRINNELL LINE THROUGH 00Z.  THIS IS ALSO
SUPPORTED BY 00Z SPC SSEO BLEND OF VARIOUS HI RES SOLUTIONS.
CONFIDENCE IS STILL NOT TOO HIGH HOWEVER AS MOST RECENT RAP...HRRR
AND HOPWRF SOLUTIONS...DIFFICULT TO INJECT INTO THE FORECAST AT
POINT...ARE EVEN FARTHER NORTH OF THIS TRACK. THUS FEEL FORECAST IS
HEADING IN THE RIGHT DIRECTION...AT LEAST FOR MAX AMOUNTS AND THEIR
PLACEMENT...BUT POTENTIALLY NOT QUITE THERE YET. THIS THINKING HAS
RESULTED IN A NORTHWARD EXPANSION OF WINTER STORM WARNING...NOW
INCLUDING ALGONA...MASON CITY AND WATERLOO.  CONFIDENCE IN SRN EDGE
OF WARNING IS DECREASING HOWEVER AT THE SAME TIME.

DEGREE OF FORCING REMAINS UNCHANGED HOWEVER AND EXPLODES INTO IA
THROUGH THE DAY...INITIAL KINEMATICALLY DOMINATED BUT EVENTUALLY AIDED
BY MORE THERMODYNAMIC FORCING AS FRONTOGENETICAL RESPONSE INCREASES
INTO THE AFTERNOON. THIS CAN BE SEEN QUITE NICELY IN THE HI RES
SIMULATED REFLECTIVITY WITH MATURING SW-NE LOBE OF SNOW PASSING
THROUGH LATE. SNOWFALL RATES ACROSS NRN IA SHOULD BE 1 IN/HR PLUS
WITH NOTED MODEL OMEGA AND QG FORCING IN 290-300K OR H7/H6 DENDRITIC
GROWTH ZONE. 1-2KM DRY AIR MAY INITIALLY LIMIT PRECIP...BUT SNOWFALL
RATES ARE EXPECTED TO OVERCOME THAT.  SURFACE OBS ARE ALREADY
SHOWING VISIBILITIES 3/4 TO 2SM JUST UPSTREAM AND THE SYSTEM REALLY
HAS NOT MATURED YET.

HAVE NOT CANCELLED ANY HEADLINES...BUT MORE NRN TRACK WILL ALSO
LEAVE SNOW AMOUNTS IN DOUBT SW DUE TO WARMER AIR WITH A PERIOD OF
RAIN EVEN POSSIBLE. SNOWFALL RATES MAY STILL BE INTENSE FOR A SMALL
WINDOW HOWEVER SUPPORTING A HEADLINE EVEN THOUGH TOTAL SNOW CRITERIA
MAY NOT BE MET.  FARTHER SOUTH SNOW RATIOS LOOK LOWER WITH MAX LIFT
WARMER THAN -10C.  WARMER COLUMN WILL LIKELY RESULT IN WETTER SNOW
SOUTH VS MORE FLUFFY NORTH. HAVE ALSO PUSHED BACK SOME HEADLINES IN
TIME TO BETTER ACCOUNT FOR SLOWER TIMING AND HITTING THOSE MAIN
IMPACTS.

.LONG TERM /TONIGHT THROUGH TUESDAY/...
ISSUED AT 354 AM CST WED FEB 25 2015

TODAYS SNOWFALL EVENT...DISCUSSED IN THE SHORT TERM SECTION
ABOVE...WILL CONTINUE INTO TONIGHT AS THE SYSTEM EXITS TO THE
SOUTHEAST. FORECAST SOUNDINGS INDICATE A DEEP DENDRITIC GROWTH
ZONE FOR SEVERAL HOURS AS THE COLUMN COOLS...AND DESPITE A STEADY
DECREASE IN FORCING HAVE HELD POPS LONGER THROUGH THE EVENING AS
SNOW SHOULD PERSIST UNTIL THE DRY AIR CAN REALLY WORK IN FROM THE
NORTH. DUE TO THE SNOW LINGERING LONGER THROUGH THE EVENING...PART
OF THE WINTER STORM WARNING IN OUR SOUTHEAST HAS BEEN EXTENDED TO
06Z.

FROM THURSDAY INTO SATURDAY MUCH COLDER WEATHER WILL PREVAIL AS A
LARGE HIGH PRESSURE AREA BUILDS DOWN FROM CANADA ACROSS THE
DAKOTAS AND IOWA. HIGH TEMPERATURES ON THURSDAY WILL NOT BE VERY
FAR ABOVE MORNING LOWS...THEN ON THURSDAY NIGHT AS THE CENTER OF
THE HIGH MOVES NEAR SOUTHWEST IOWA TEMPERATURES SHOULD PLUMMET
ESPECIALLY WITH THE FRESH SNOW PACK FROM WEDNESDAYS SYSTEM
COVERING MUCH OF THE AREA. ON FRIDAY THE HIGH WILL BE SLOW TO PULL
AWAY...LIMITING ANY OPPORTUNITY FOR MODERATION...THEN ON FRIDAY
NIGHT ITS INFLUENCE WILL KEEP WINDS LIGHT OR CALM EARLY IN THE
NIGHT ESPECIALLY ACROSS OUR NORTHEAST AND EAST WHERE THE NEW SNOW
WILL LIKELY BE DEEPEST. IN LIGHT OF THESE FACTORS...HAVE LOWERED
THE TEMPERATURE FORECAST BY SEVERAL DEGREES FOR EACH PERIOD FROM
THURSDAY THROUGH FRIDAY NIGHT. WE ARE NOW PREDICTING THURSDAY
HIGHS AND THURSDAY NIGHT LOWS BOTH NEAR RECORD COLD LEVELS FOR THE
DATE. WIND CHILL HEADLINES ARE A NEAR CERTAINTY FOR MUCH OF THIS
PERIOD AS WELL.

BY SATURDAY MORNING THE 500 MB PATTERN WILL BE TRANSITIONING TO A
NEW CONFIGURATION...WITH A LARGE AND BROAD TROUGH GRADUALLY
DIGGING DOWN THE PACIFIC U.S. COAST AND GENERALLY ZONAL FLOW
EXTENDING DOWNSTREAM OVER IOWA. WITHIN THIS REGIME IT IS EXPECTED
THAT SEVERAL MODEST IMPULSES WILL EJECT OUT OF THE TROUGH AND MOVE
QUICKLY OVER OUR REGION...WITH THE FLOW EVENTUALLY TURNING TO
SOUTHWEST BEFORE THE LARGE TROUGH FINALLY SWEEPS THROUGH SOMETIME
AROUND TUESDAY. AT THE SURFACE...THE INITIAL STAGES OF THE PATTERN
WILL MANIFEST IN THE DEVELOPMENT OF A BROAD QUASI-STATIONARY
FRONTAL ZONE DEVELOPING AROUND SOUTHERN IOWA OR MISSOURI OVER THE
WEEKEND. AS THE AFOREMENTIONED IMPULSES MOVE OVER THIS REGION THEY
WILL GENERATE PERIODS OF PRECIPITATION WITH SNOW THE MOST LIKELY
MODE GIVEN FORECAST TEMPERATURES AND SOUNDINGS. WHILE AMOUNTS AND
LOCATION ARE STILL UNCERTAIN...PRECIPITATION APPEARS LIKELY ACROSS
OUR SOUTHERN COUNTIES AND POPS HAVE THUS BEEN RAISED TO THE
LIKELY CATEGORY IN THIS AREA ON SATURDAY NIGHT AND SUNDAY. LOOKING
INTO EARLY NEXT WEEK...PRECIPITATION WILL AGAIN BE LIKELY SOMETIME
AROUND MONDAY NIGHT AND TUESDAY AS THE BULK OF THE ENERGY FROM THE
FORMER WESTERN U.S. TROUGH FINALLY MOVES THROUGH...BUT PREDICTIONS
AS TO TYPE AND A STORM PATH ARE HIGHLY VARIABLE AT THIS POINT TO
POPS HAVE BEEN HELD IN THE CHANCE RANGE FOR NOW. THERE IS SOME
POTENTIAL FOR A MIXED PRECIPITATION IN OUR AREA DURING THIS TIME
FRAME...BUT WE WILL NEED TO WAIT FOR A MORE STABLE SOLUTION BEFORE
ADDING MORE DETAIL TO THE FORECAST.

&&

.AVIATION...25/06Z
ISSUED AT 1140 PM CST TUE FEB 24 2015

VERY SIMILAR TO PREVIOUS DISCUSSION WITH STORM STILL ON TRACK TO
PASS THROUGH THE STATE ON WEDNESDAY INTO WEDNESDAY NIGHT. VFR
CEILINGS WILL CONTINUE TO OVERSPREAD THE STATE TONIGHT WITH
UNRESTRICTED VISIBILITIES. SURFACE WINDS WILL SWING AROUND TO THE
EAST OVERNIGHT AS SURFACE LOW DEEPENS ACROSS THE PLAINS.
CONDITIONS WILL QUICKLY BECOME IFR TO LIFR ACROSS ALL OF CENTRAL
IOWA TERMINALS ON WEDNESDAY AS SNOW OVERSPREAD THE STATE. BOTH
VISIBILITIES AND CEILINGS WILL BE SEVERELY RESTRICTED IN THE
FALLING SNOW WITH LITTLE IMPROVEMENT UNTIL LATE IN THE DAY AS THE
SNOW BEGINS TO END FROM NORTHWEST TO SOUTHEAST. SURFACE WINDS WILL
GRADUALLY SHIFT FROM EAST IN THE MORNING TO NORTHWEST BY WEDNESDAY
EVENING AS SURFACE LOW MOVES INTO MISSOURI.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 3 PM THIS AFTERNOON TO MIDNIGHT CST
TONIGHT FOR APPANOOSE-DAVIS-JASPER-LUCAS-MADISON-MAHASKA-MARION-
MONROE-POLK-WAPELLO-WARREN-WAYNE.

WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM CST
THIS EVENING FOR ADAIR-ADAMS-AUDUBON-CASS-CLARKE-CRAWFORD-
DECATUR-RINGGOLD-TAYLOR-UNION.

WINTER STORM WARNING FROM 9 AM THIS MORNING TO 9 PM CST THIS
EVENING FOR BLACK HAWK-BUTLER-CERRO GORDO-FRANKLIN-GRUNDY-HARDIN-
MARSHALL-POWESHIEK-STORY-TAMA.

WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR BOONE-
CALHOUN-CARROLL-DALLAS-EMMET-GREENE-GUTHRIE-HAMILTON-HANCOCK-
HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-SAC-WEBSTER-WRIGHT.

WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 9 PM CST THIS
EVENING FOR BREMER-WORTH.

WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR
WINNEBAGO.

&&

$$

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


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