Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 270926
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
326 AM CST FRI FEB 27 2015

.SHORT TERM /TODAY/...
ISSUED AT 326 AM CST FRI FEB 27 2015

ARCTIC HIGH PRESSURE IS CENTERED OVER THE CENTRAL MISSOURI RIVER
VALLEY INCLUDING WESTERN IOWA. A COUPLE RECORD LOWS HAVE ALREADY
BEEN SET AT MASON CITY AND WATERLOO THIS MORNING AND WILL CONTINUE
TO LOWER THOSE RECORDS OVER THE NEXT SEVERAL HOURS AS WINDS
GRADUALLY DIMINISH. TEMPERATURES ARE THE PRIMARY FORECAST CHALLENGE
TODAY. EXPECT A SLOW RECOVERY THIS MORNING AND IT WILL REMAIN COLD
ALL DAY WITH HIGH TEMPERATURES 25-30 DEGREES BELOW NORMAL IN THE
SINGLE DIGITS TO LOWER TEENS. SOME LOW LEVEL MOISTURE IS STILL
AVAILABLE FOR THE POTENTIAL FOR ICE CRYSTAL/CLOUD STREAMERS TO
DEVELOP AS AFTERNOON MIXING OCCURS. THE LACK OF GOOD COLD ADVECTION
ONGOING AND A LESS FAVORABLE LIGHT WEST TO SOUTHWEST WIND BY THE
AFTERNOON SHOULD LIMIT POTENTIAL.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 326 AM CST FRI FEB 27 2015

ONE MORE COLD NIGHT IS IN STORE FOR MOST OF THE AREA TONIGHT AS
THE HIGH PRESSURE AREA SLIDING ACROSS IOWA TODAY WILL STUBBORNLY
CLING TO ESPECIALLY EASTERN IOWA AFTER DARK. THIS WILL RESULT IN
ANOTHER ROUND OF PLUMMETING TEMPERATURES AFTER SUNSET GIVEN THE
CLEAR SKIES AND NEARLY CALM WINDS EXPECTED...PARTICULARLY WITH
TEMPERATURES ONLY IN THE SINGLE DIGITS EVEN BEFORE THE SUN SETS.
HAVE CONTINUED THE TREND OF FORECASTING BELOW GUIDANCE LOWS
TONIGHT ACROSS MUCH OF OUR FORECAST AREA. A WIND CHILL ADVISORY
COULD BE NEEDED ONCE AGAIN...ALTHOUGH SIMILARLY TO FRIDAY MORNING
THE WINDS WILL BE VERY LIGHT SO IT WOULD BE A MARGINAL SITUATION.

AFTER THE INTENSE COLD THAT WILL PERSIST INTO SATURDAY
MORNING...THE LONG TERM FORECAST BECOMES A TALE OF TWO SYSTEMS AS
GENERAL 500 MB TROUGHINESS ACROSS THE WESTERN U.S. SPITS OUT
SEVERAL UPPER LEVEL STORM SYSTEMS THAT WILL TRAVEL ACROSS THE
CENTRAL U.S. FOR IOWA THERE WILL BE TWO PRIMARY SYSTEMS OF
INTEREST...THE FIRST COMING THIS WEEKEND AND THE SECOND AROUND
TUESDAY OF NEXT WEEK. REGARDING THE FIRST SYSTEM...THERE HAS BEEN
A CONSISTENT SIGNAL IN MODEL SOLUTIONS DEVELOPING A WEAK SURFACE
TROUGH ROUGHLY FROM KANSAS UP TO NEAR THE IOWA MISSOURI BORDER AND
INTO ILLINOIS ON SATURDAY NIGHT...COINCIDENT WITH THE APPROACH OF
A 500 MB TROUGH PROVIDING A BROAD AREA OF LIFT. THIS WILL RESULT
IN A SWATH OF SNOW AROUND THE SURFACE FRONTAL ZONE...BLEEDING INTO
MUCH OF IOWA BUT MAINLY THE SOUTH AND SOUTHEAST. THE SNOW SHOULD
BEGIN IN OUR SOUTHERN COUNTIES ON SATURDAY AFTERNOON AND SPREAD
ACROSS MOST OF THE AREA SATURDAY NIGHT...BEFORE ENDING ON SUNDAY
AS THE 500 MB TROUGH HELPS PUSH THE SURFACE FRONT AWAY TO THE
SOUTHEAST AND BRINGS COOLER NORTHWEST FLOW TO IOWA BY LATE SUNDAY.
HAVE CONTINUED TO FORECAST HIGH POPS ACROSS ABOUT THE SOUTHEASTERN
HALF OF THE FORECAST AREA ON SATURDAY NIGHT AND INTO SUNDAY
MORNING AS SNOW APPEARS VERY LIKELY...HOWEVER FORECAST SOUNDINGS
INDICATE THAT THE CLOUD LAYER WILL MOSTLY RESIDE BELOW THE
DENDRITIC GROWTH ZONE AND FORCING ASSOCIATED WITH THE UPPER LEVEL
SYSTEM. IN ADDITION...SOUNDINGS ALSO SHOW POCKETS OF DRY AIR
ENTRAINING INTO THE COLUMN AT TIMES. IN LIGHT OF THESE
FACTORS...THE SNOW SHOULD BE FAIRLY LIGHT EXCEPT PERHAPS IN OUR
SOUTHERN AND SOUTHEASTERN COUNTIES AND GENERALLY LIGHT TO MODERATE
ACCUMULATIONS ARE EXPECTED WITH VERY LITTLE IN THE NORTHWEST.
GIVEN VERY COLD GROUND AND PAVEMENT TEMPERATURES AND THE ABSENCE
OF WIND FOR MOST OF THIS EVENT...LITTLE IMPACT IS ANTICIPATED AT
THIS TIME.

AFTER A BRIEF QUIET PERIOD FROM LATE SUNDAY INTO MONDAY AS ANOTHER
HIGH PRESSURE CENTER MOVES ACROSS THE REGION...THE SECOND STORM
SYSTEM WILL APPROACH IOWA. THIS SECOND SYSTEM WILL BE MUCH MORE
ENERGETIC AS SOUTHWESTERLY 500 MB FLOW DEVELOPS A SURFACE LOW
PRESSURE SYSTEM IN THE LEE OF THE ROCKIES ON MONDAY NIGHT AND
PUSHES IT UP ACROSS IOWA ON TUESDAY. AS THE LOW WRAPS UP IT WILL
DRAW IN DEEP ATMOSPHERIC MOISTURE FROM THE SOUTH AND DEVELOP AN
INVERTED TROUGH STRETCHING FROM KANSAS UP ACROSS OUR FORECAST AREA
BY LATE MONDAY NIGHT. VERTICAL PROFILES INDICATE STRONG FORCING
ASSOCIATED WITH THE APPROACH OF THIS SYSTEM AND ALL SYSTEMS ARE GO
FOR A WIDESPREAD PRECIPITATION EVENT...WITH IMPRESSIVE QPF FOR THE
SEASON INDICATED PARTICULARLY ACROSS OUR SOUTHEAST AND DOWN INTO
MISSOURI AND KANSAS ALONG THE SURFACE BOUNDARY. GFS FORECAST
SOUNDINGS HAVE BEEN PERSISTENT IN THEIR PROGNOSIS OF PRECIPITATION
TYPE FOR THIS EVENT...WHICH SHOULD START AS SNOW WHEN THE COLUMN
FIRST SATURATES...THEN TRANSITION TO SLEET AND FREEZING RAIN AS A
PRONOUNCED WARM NOSE DEVELOPS...FOLLOWED BY RAIN NEAR THE SOUTH OF
THE FRONT AS SURFACE TEMPERATURES RISE THROUGH THE 30S...WHILE
REMAINING SNOW ACROSS THE NORTHWEST FOR THE ENTIRE EVENT. AS THE
LOW SHOOTS BY AND STRONG NORTHWEST FLOW PUSHES THE SURFACE FRONT
OUT OF OUR AREA ALL PRECIPITATION WILL CHANGE TO SNOW BY LATE
TUESDAY BEFORE CLEARING OUT OF THE AREA. WHILE THIS GENERAL
SOLUTION HAS BEEN CONSISTENT AND IS REASONABLE GIVEN THE SYNOPTIC
SET UP...THE DEVIL WILL BE IN THE DETAILS OF TIMING...LOCATING THE
RAIN/MIX/SNOW BOUNDARY AT ANY GIVEN TIME...AND DETERMINING HOW
MUCH PRECIPITATION FALLS AS SNOW...ICE...OR RAIN. AT THIS RANGE
PREDICTIONS OF THESE DETAILS ARE NOT STABLE...BUT GIVEN THE STRONG
SIGNAL FOR BOTH ROBUST QPF AND A ZONE OF ICING...AS WELL AS
POSSIBLY PROLONGED SNOW ACROSS THE NORTHWEST AND STRONG WINDS ON
THE BACK SIDE OF THE SYSTEM...SOME KIND OF HEADLINE LEVEL EVENT IS
LIKELY. PLEASE MONITOR THIS POSSIBILITY CLOSELY IN THE COMING
DAYS.

THE GOOD NEWS IS THAT AFTER THE EARLY WEEK SYSTEM CLEARS OUT
AROUND TUESDAY NIGHT...THERE IS FINALLY SOME INDICATION THAT WE
MAY SEE AT LEAST SOME BREAK FROM OUR PROLONGED COLD SNAP LATER
NEXT WEEK. OF COURSE THIS MAY BE TEMPERED DEPENDING ON HOW MUCH
SNOW THE TUESDAY SYSTEM DOES OR DOES NOT PRODUCE...BUT AT LEAST
LONG RANGE MODEL SOLUTIONS ARE CONSISTENTLY SHOWING A PERIOD OF
WEAK RIDGING ALOFT AND SOUTHWEST SURFACE FLOW...THOUGH THIS PERIOD
COULD BE UNFORTUNATELY SHORT LIVED.

&&

.AVIATION...27/06Z
ISSUED AT 1126 PM CST THU FEB 26 2015

WIDESPREAD VFR CONDITIONS ARE EXPECTED FOR MUCH OF THE FORECAST
PERIOD. ONLY ISSUE WOULD BE ON FRIDAY AFTERNOON WITH LOW LEVEL
CLOUDS AND A FEW FLURRIES WITH SOUNDINGS SHOWING SOME SATURATION JUST
ABOVE 1KFT. OTHERWISE...SKIES WILL BE CLEAR WITH UNRESTRICTED
VISIBILITIES AND CEILINGS. LIGHT NORTHWEST WINDS WILL BECOME LIGHT
SOUTHWEST WINDS ON FRIDAY AND EVENTUALLY SOUTHEAST BY LATE FRIDAY
EVENING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING FOR BLACK HAWK-
BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CERRO GORDO-EMMET-FRANKLIN-
GREENE-GRUNDY-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-JASPER-KOSSUTH-
MARSHALL-PALO ALTO-POCAHONTAS-POWESHIEK-SAC-STORY-TAMA-WEBSTER-
WINNEBAGO-WORTH-WRIGHT.

&&

$$

SHORT TERM...DONAVON
LONG TERM...LEE
AVIATION...COGIL



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