Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 220610
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1210 AM CST SAT NOV 22 2014

.UPDATE...
ISSUED AT 1159 PM CST FRI NOV 21 2014

TEMPERATURES HAVE NOT FALLEN BELLOW FREEZING AT WESTERN SITES AND
GIVEN INCREASING SOUTHERLY FLOW AND WARMING TEMPERATURES HAVE
CANCELED WESTERN PORTIONS OF ADVISORY. ROAD TEMPERATURES REMAINING
NEAR OR BELOW FREEZING ACROSS REMAINDER OF ADVISORY AND STILL
ANTICIPATE -RA AND -DZ ACROSS AREA THROUGH OVERNIGHT WITH
INCREASING MOISTURE AND WITH COLD TEMPERATURES COULD SEE FREEZING
ON SURFACES AND WILL LEAVE REMAINDER OF ADVISORY AS IS. INCREASING
MOISTURE WILL ALLOW FOR FOG DEVELOPMENT ACROSS AREA AND MAY NEED
DENSE FOG ADVISORY IN THE WEST IN EARLY MORNING HOURS...THOUGH
WILL CONTINUE TO MONITOR ATTM GIVEN CURRENT VISIBILITIES REMAIN
WELL ABOVE ONE MILE ACROSS MOST OF AREA.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 355 PM CST FRI NOV 21 2014

LARGE FETCH OF THETA-E ADVECTION ENTERING SOUTHERN IOWA
WILL CONTINUE TO SURGE NORTHWARD THROUGH THE EVENING. FORECAST
SOUNDINGS STILL INDICATE FZDZ/FZRA POTENTIAL OVER THE EASTERN
SECTIONS OF THE FORECAST AREA...MAINLY EAST OF I35. THE HIRES MODELS
IN GREAT AGREEMENT WITH TIMING AND LOCATION OF LIGHT PRECIP TONIGHT
INTO EARLY SATURDAY MORNING AND LEANED TOWARD A BLEND OF THE
HRRR/HOPWRF/ARW FOR POPS.

LOOKS TO BE A VERY BRIEF PERIOD EARLY THIS EVENING FOR SOME FZDZ
OVER THE FAR SOUTH...BUT LATEST ROAD SURFACE TEMPS WELL INTO THE 30S
TO AROUND 40 AND EXPECTING THE WAA TO PERSIST INTO SATURDAY
MORNING...THERE IS A LOWER CONFIDENCE WITH THE MUCH...IF ANY...ICE
ACCRUAL SOUTH OF HIGHWAY 34 TOWARDS THE MISSOURI BORDER. MOST LIKELY
COULD CANCEL THE ADVISORY BY AROUND 03Z TIME FRAME.

FURTHER NORTH HOWEVER...ROAD TEMPS ALONG THE I80 CORRIDOR TOWARD
HIGHWAY 20 RANGE IN THE LOWER TO MIDDLE 30S AND FURTHER NORTH REMAIN
IN THE 20S. PLUS THE GROUND/SOIL TEMPS STILL BELOW FREEZING IN THIS
AREA DUE TO THE EXTENDED COLD PERIOD OVER THE PAST 10 DAYS. THERE IS
A HIGHER CONFIDENCE WITH A LIGHT GLAZE IN THE AFOREMENTIONED AREA
EVEN THOUGH TEMPS FROM AMES TO DES MOINES HAVE WARMED INTO THE
MIDDLE 30S. THINK THE GROUND IS COLD ENOUGH TO QUICKLY FREEZE ANY
PRECIP THIS EVENING. THE CURRENT TRAJECTORY OF PRECIP PLACES IT IN
THE DES MOINES METRO BETWEEN 02Z AND 04Z TONIGHT. HAVE THE GREATER
FZDZ/FZRA CHANCES FROM 02Z-08Z SOUTH TO NORTHEAST TONIGHT. WAA AND
GOOD SURGE OF SURFACE DEW POINTS IN THE MIDDLE 30S...EXPECTING THE
FREEZING RAIN/DRIZZLE POTENTIAL TO CEASE BY AROUND 06Z ALONG THE I80
CORRIDOR AND FURTHER NORTHEAST BY AROUND 09Z. HAVE MENTION OF THE
FOG OVERNIGHT AS WELL WITH THE LARGE AREA OF MOISTURE MOVING INTO
CENTRAL IOWA.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 355 PM CST FRI NOV 21 2014

WILL SEE FIRST SURGE OF THETA-E AND WARM ADVECTION DEPARTING ON
SATURDAY MORNING. SOME RESIDUAL DRIZZLE/VERY LIGHT RAIN REMAIN
POSSIBLE IN THE FAR SOUTHEAST FORECAST AREA ALONG WITH SOME FOG
AREAWIDE AS HIGHER DEWPOINTS MOVE INTO THE STATE. MUCH OF SATURDAY
APPEARS RELATIVELY DRY BEFORE NEXT SURGE OF MOISTURE AND LIFT
ARRIVE AS MAIN UPPER SYSTEM LIFTS NORTHEAST SATURDAY NIGHT INTO
SUNDAY. THIS NEXT SURGE BEGINS SATURDAY EVENING WITH DRIZZLE/VERY
LIGHT RAIN SPREADING NORTHWARD ACROSS THE FORECAST AREA AS
ISENTROPIC LIFT INCREASES. MOISTURE ADVECTION WILL ALSO CONTINUE
AND AS THIS CONTINUES OVER THE COLD GROUND...FOG SEEMS AS IF IT
SHOULD THICKEN OVERNIGHT SATURDAY. TEMPERATURES WILL LIKELY FALL
LITTLE IF ANY AND MAY ACTUALLY RISE INTO SUNDAY MORNING AHEAD OF
APPROACHING BOUNDARY. PRECIPITATION WILL BEGIN TO CONSOLIDATE ON
SUNDAY MORNING WITH MAIN WAVE LIFTING NORTHEAST INTO ILLINOIS WITH
DEFORMATION PRECIPITATION ALONG AND EAST OF I35 BY AFTERNOON. COLD
ADVECTION WILL ALSO INCREASE DURING THE AFTERNOON AS FRONT SLIDES
EASTWARD. DRY SLOT WILL OVERSPREAD MUCH OF THE FORECAST AREA BY
SUNDAY EVENING WITH ONLY THREAT OF PRECIPITATION REMAINING IN THE
FAR EAST ON BACKSIDE OF DEFORMATION AXIS. AS COLD AIR SURGES INTO
CENTRAL IOWA...A BRIEF TRANSITION TO SNOW IS POSSIBLE HOWEVER ANY
AMOUNTS APPEAR LIGHT AT THIS POINT.

MONDAY AND TUESDAY APPEAR WINDY AND COLD WITH BROAD CYCLONIC FLOW
ACROSS THE UPPER MIDWEST. SNOW SHOWERS AND SOME LIMITED BLOWING
SNOW WILL BE POSSIBLE ON MONDAY WITH SOUNDINGS IN DENDRITIC GROWTH
ZONE HELPING TO PROMOTE SNOW DEVELOPMENT. AT THIS POINT...THERE
APPEARS ONLY LIMITED THREAT OF PRECIPITATION LATE TUESDAY NIGHT
INTO WEDNESDAY MORNING AS ANOTHER WAVE DROPS INTO BROAD EASTERN
TROF...HOWEVER THANKSGIVING APPEARS DRY AT THIS POINT ALBEIT COLD.

&&

.AVIATION...22/06Z
ISSUED AT 1159 PM CST FRI NOV 21 2014

LOW MVFR AND IFR CEILINGS AND VISIBILITIES WILL IMPACT SITES
THROUGH MUCH OF PERIOD AS BAND OF DZ CONTINUES TO PUSH EASTWARD.
LOWEST CEILINGS AND VISIBILITIES WILL COME NEAR 12Z BEFORE
SUNRISE...AND MAY SEE LIFR CONDITIONS AT TIMES...ESPECIALLY AT
NORTHERN SITES KMCW/KALO. MAY SEE CEILINGS RISE TO LOW VFR
BRIEFLY BEYOND 18Z...THOUGH ANTICIPATE MVFR CONDITIONS TO RETURN
ONCE AGAIN NEAR 00Z. WINDS WILL BE FROM THE SOUTH AROUND 12KTS
WITH HIGHER GUSTS POSSIBLE THROUGH PERIOD.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FREEZING RAIN ADVISORY UNTIL 6 AM CST SATURDAY FOR BLACK HAWK-
BREMER-BUTLER-CERRO GORDO-FRANKLIN-GRUNDY-HAMILTON-HARDIN-JASPER-
MAHASKA-MARION-MARSHALL-POWESHIEK-STORY-TAMA-WORTH-WRIGHT.

FREEZING RAIN ADVISORY UNTIL 3 AM CST SATURDAY FOR APPANOOSE-
DAVIS-MONROE-WAPELLO.

&&

$$

UPDATE...AWB
SHORT TERM...PODRAZIK
LONG TERM...COGIL
AVIATION...AWB


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