Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 022159
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
359 PM CST MON MAR 2 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 358 PM CST MON MAR 2 2015

PRECIP TRENDS WILL OBVIOUSLY BE THE PRIMARY CONCERNS HEADING
THROUGH THE NIGHT. ACTIVE JET STREAM OVER SRN CONUS RIDGE
CONTINUES TO STREAM MID/HIGH LEVEL MOISTURE INTO THE CENTRAL
PLAINS WITH ASSOCIATED WEAK FORCING INTO THE MO VALLEY. PATCHY
PRECIP ACROSS KS AND ALONG THE IA/MN BORDER REMAINS ALOFT HOWEVER
WITH PLENTY OF LOW LEVEL DRY AIR IN PLACE...WHICH WILL HOLD OFF
ANY PRECIP THROUGH THE EVENING HOURS.

THE FORCING WILL STRENGTHEN APPRECIABLY IN DEPTH AND MAGNITUDE BY
06Z HOWEVER AND CONTINUE THROUGH DAYBREAK. THE COMBINATION OF
DRIER AIR FROM THE SOUTHWEST AND A 1-3C WARM LAYER TO AT LEAST THE
I80 CORRIDOR /GFS/ AND POSSIBLY UP TO HIGHWAY 20 /NAM/ WILL RESULT
IN REDUCED SENSIBLE WEATHER CONFIDENCE. SOUNDINGS SHOW VARIED
DEGREES OF MOISTURE...NEVER TOTALLY SATURATING THE COLUMN IN
CENTRAL AND SRN IA WITH DEGREE OF ICE INTRODUCTION QUESTIONABLE AT
TIMES TOO. THIS WILL RESULT IN QUITE VARIABLE PRECIP TYPES IN BOTH
TIME AND SPACE WITH LOW CONFIDENCE IN DETAILS. CONFIDENT IN WINTRY
MIX TO RAIN TRANSITION SOUTH AND MAINLY SNOW NORTH...BUT LITTLE
BEYOND THAT.

SURFACE TEMPS DO NOT HELP CONFIDENCE ANY. TEMPS CONTINUE TO WARM
AT THE MOMENT WITH FREEZING LINE TO
CARROLL...PERRY...INDIANOLA...BLOOMFIELD LINE AT 21Z. THIS
SHOULD RETREAT SOUTHWARD SOMEWHAT INTO THE EARLY EVENING WITH LOSE
OF INSOLATION...BUT EXACT DEGREE PROBLEMATIC WITH STEADY S/SE
WINDS AND LOWERING CLOUD COVER. TEMPS SHOULD TRY TO LOWER TO THE
WET BULB...BUT PRECIP WILL NOT BE TOO INTENSE FOR ANY
DURATION...AND THERE SHOULD BE ANOTHER NORTHWARD REBOUND OVERNIGHT
AFTER STEADY WARM ADVECTION. ROADS TEMPS IN CENTRAL AND SRN IA ARE
CURRENTLY INTO THE 40S AND 50S AT 21Z AND SHOULD LOWER TOO WITH
PRECIP AND MINOR RADIATIONAL COOLER...BUT NOT SURE HOW MUCH.
ALTHOUGH UNCERTAINTY IS FAIRLY HIGH IN ALL DETAILS...INCLUDING
PRECIP TYPE AND EVENTUAL ROAD EFFECTS...HAVE DECIDED TO ISSUE
WINTER WEATHER ADVISORY DURING THE EARLY MORNING HOURS AND THROUGH
THE MORNING COMMUTE TO ERROR ON THE SIDE OF CAUTION...ESPECIALLY
CONSIDERING THE DEGREE OF LIFT. QPF AND PRECIP AMOUNTS WILL NOT BE
HIGH...BUT COULD BE ENOUGH TO DISRUPT DRIVING IN THE MORNING.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 358 PM CST MON MAR 2 2015

MAIN CONCERN DEALT WITH PRECIP TYPE EVENT AND WINDS TUESDAY INTO
TUESDAY NIGHT ACROSS MUCH OF THE FORECAST AREA. LEANED TOWARD THE
HIRES NMM/ARW/NAM12 FOR TIMING OF PRECIP AND WINDS DEVELOPING
TOMORROW AFTERNOON. ALTHOUGH THE ECMWF/GFS/SREF ARE IN FAIRLY GOOD
AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN TOMORROW.

TUESDAY INTO WEDNESDAY...STRONG WAA AND THETA-E ADVECTION
CONTINUES INTO MUCH OF CENTRAL IOWA TUESDAY MORNING AHEAD OF A
POTENT SHORTWAVE TO PUNCH INTO THE STATE BY THE AFTERNOON.
TEMPERATURE WISE...WENT ABOVE GUIDANCE FOR HIGHS TOMORROW WHICH
WILL LIKELY OCCUR EARLY IN THE DAY AND HAVE MENTION OF A NON-
DIURNAL TEMPERATURE TREND TUESDAY AFTERNOON. LOW CONFIDENCE WITH
MUCH OF THE WAY OF FZRA PAST 15Z WITH THE STRONG WAA AND EVEN B/T
12-15Z TUESDAY. ANY FZRA WILL BE SHORT-LIVED AND MORE CONFIDENT
PRECIP WILL BE IN THE FORM OF RAIN/SLEET IN THE MORNING AND
POSSIBLY SOME DRIZZLE AS THE FORECAST SOUNDINGS LOSE THE DEEP
SATURATION AND THUS THE ICE INTRODUCTION THE MORNING HOURS.
CERTAINLY LOOKS TO BE A BRIEF PERIOD OF THE WINTRY MIX SOUTH OF
HIGHWAY 30 TO THE INTERSTATE 80 CORRIDOR DURING THE MORNING
COMMUTE TUESDAY BUT THIS WINTRY MIX QUICKLY ENDS BY MID- MORNING
AS SURFACE TEMPS AND THE BOUNDARY LAYER WARM UP ENOUGH TO MELT
ANYTHING BEFORE REACHING THE SURFACE. THAT BEING SAID...POTENTIAL
IS THERE FOR MUCH OF THE WEST-CENTRAL TO SOUTHWEST FORECAST AREA
BEING IN THE DRY SLOT TUESDAY...AND HENCE POPS/PRECIP AMOUNTS
MIGHT BE OVER DONE IN THIS AREA.

FURTHER NORTH...HAVE ISSUED WINTER WEATHER ADVISORY TO HANDLE SNOW
AND BLOWING SNOW DURING THE AFTERNOON HOURS ACROSS NORTHERN
IOWA. THE PROBLEM IS THE BETTER POTENTIAL FOR ANY DENDRITIC SNOW
AND ACCUMULATING SNOW WILL BE DURING THE MORNING HOURS TUESDAY AND
AMOUNTS REMAIN LESS THAN 2 INCHES NORTH OF HIGHWAY 20. THE
STRONGEST FORCING...INSENTROPIC LIFT...AND THE DEEP MOISTURE
QUICKLY PUSH EAST BY 18Z TUESDAY AND LIKELY EVEN SOONER. CUT DOWN
ON POPS/QPF DURING THE AFTERNOON HOURS CONSIDERABLY. ONLY HAVE A
FEW TENTHS OF AN INCH OF SNOW ACROSS THE NORTH TUESDAY AFTERNOON.
HOWEVER THERE IS A DECENT PV ANOMALY AND THE STRONG PUSH OF CAA
IN THE AFTERNOON PUSHING WINDS ATOP THE MIXED LAYER TO INCREASE
TO 33 TO 38 KNOTS. MUCH OF THAT WIND SHOULD BE REALIZED AT THE
SURFACE OVER NORTHERN IOWA. THERE IS A THIN LAYER OF SATURATION
WITHIN THE SNOW GROWTH REGION TUESDAY AFTERNOON PER MCW/FRM/ALO
SOUNDINGS AND SUGGEST SNOW SQUALL POTENTIAL IN THIS AREA THROUGH
THE EARLY EVENING TUESDAY. CURRENTLY SNOW DEPTH STILL RANGES IN
THE 4-8 INCHES BUT NOT CONFIDENT WINDS WILL BE STRONG BREAK
THROUGH THE CRUST AND CAUSE VISIBILITY RESTRICTIONS FROM SNOW
CURRENTLY ON THE GROUND. MORE CONFIDENT WITH THE SNOW SQUALL
POTENTIAL CAUSING BRIEF PERIODS OF NEAR BLIZZARD CONDITIONS FROM
18Z TUESDAY TO 03Z WEDNESDAY. A SIMILAR SET UP TO JANUARY 8 EVENT
BUT TOMORROW THE WINDS ARE SLIGHTLY WEAKER AND HAVE LOWER
CONFIDENCE WITH PROLONG PERIODS OF BLIZZARD CONDITIONS AND THUS
LEANED TOWARDS ISSUING THE WINTER WEATHER ADVISORY.

A VERY COLD AIR MASS FILTERS INTO THE STATE TUESDAY NIGHT AND
CONTINUES INTO THURSDAY MORNING. THE COLDEST NIGHT WILL BE
WEDNESDAY NIGHT WITH LARGE SURFACE HIGH OVERHEAD ALLOWING FOR
CLEAR SKIES AND RADIATIONAL COOLING TO SET UP. LOWERED TEMPS
SLIGHTLY ACROSS THE NORTH FOR THURSDAY MORNING.

THURSDAY THROUGH SATURDAY...WARMER TEMPERATURES AND DRY CONDITIONS
IN STORE FOR MUCH OF THIS PERIOD WITH FRIDAY AND SATURDAY THE
WARMEST DAYS. A WEAK SHORTWAVE CUTS SOUTH SATURDAY NIGHT INTO SUNDAY
BUT WITH MINIMAL MOISTURE...LEFT FORECAST DRY ATTM. ONLY BRINGS A
BRIEF COOL DOWN IN TEMPS.

&&

.AVIATION...02/18Z
ISSUED AT 1205 PM CST MON MAR 2 2015

VFR CONDITIONS WITH LOWERING CIGS ARE IN PLACE STATEWIDE AT 18Z.
CONDITIONS SHOULD DEGRADE TO LOW END MVFR SW-NE LATE THIS EVENING
HOWEVER AS WINTRY PRECIPITATION DEVELOPS. THIS WILL LIKELY BE ON
THE LIGHT SIDE AT TAF SITES...BUT STILL MAY CAUSE ISSUES. TYPES
WILL VERY FROM RAIN/FREEZING RAIN SOUTH...TO SLEET/SNOW NORTH.
EVENT SHOULD TRANSITION TO JUST DRIZZLE OR FREEZING RAIN BY
TUESDAY MORNING AS WINDS VEER AND SYSTEM DEPARTS.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 8 AM CST
TUESDAY FOR APPANOOSE-AUDUBON-BOONE-CARROLL-CLARKE-CRAWFORD-
DALLAS-DAVIS-GREENE-GUTHRIE-JASPER-LUCAS-MADISON-MAHASKA-MARION-
MARSHALL-MONROE-POLK-POWESHIEK-STORY-TAMA-WAPELLO-WARREN-WAYNE.

WINTER WEATHER ADVISORY FROM 9 AM TO 9 PM CST TUESDAY FOR BLACK
HAWK-BREMER-BUTLER-CERRO GORDO-EMMET-FRANKLIN-GRUNDY-HANCOCK-
HUMBOLDT-KOSSUTH-PALO ALTO-WINNEBAGO-WORTH-WRIGHT.

&&

$$

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



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