Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 060936
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
336 AM CST FRI MAR 6 2015

.SHORT TERM /TODAY/...
ISSUED AT 336 AM CST FRI MAR 6 2015

A SHORTWAVE WILL BE EXITING THE STATE EARLY THIS MORNING.  SOME
RESIDUAL MID LEVEL CLOUD COVER WILL LINGER INTO THE MID MORNING BUT
THE BIGGER STORY FOR TODAY WILL BE THE START OF A WARM UP THAT WILL
PERSIST INTO NEXT WEEK.  SNOW COVER ACROSS NORTHERN IOWA WILL HINDER
THE WARM UP IN THOSE AREAS BUT ACROSS THE FAR SOUTHWEST WHERE SNOW
COVER IS LACKING WE SHOULD SEE TEMPS CLIMB INTO THE MID 50S.  FOR
MUCH OF CENTRAL IOWA TEMPS WILL BE IN THE MID 40S AND THIS MAY BE
TOO COOL...ESPECIALLY THE FURTHER SOUTHWEST YOU GO.  WINDS GO FROM
SOUTHERLY TO SOUTHWEST OR WEST AND ARE NOT TOO STRONG AND ALOFT THEY
ARE MORE WEST TO NORTHWEST SO WE DON`T HAVE THE GREATEST SET UP FOR
MIXING BUT IF WINDS STAY MORE SOUTHERLY THROUGH A LITTLE DEEPER
LAYER THEN WE COULD SEE BETTER MIXING AND TEMPS EASILY A FEW DEGREES
WARMER.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 336 AM CST FRI MAR 6 2015

LONGER TERM CONTINUES TO FOCUS ON TRANSITION IN UPPER PATTERN
WHICH WILL IMPACT TEMPERATURES INTO NEXT WEEK. WILL CONTINUE TO
SEE NORTHWEST UPPER FLOW INTO THE WEEKEND ALTHOUGH WITH A
TRANSITION IN THE JET STREAM FARTHER NORTHEAST THAN HAS BEEN THE
CASE THIS PAST MONTH. THIS WILL ALLOW FOR THE MODERATION OF
TEMPERATURES TO MORE NORMAL LEVELS FOR THE WEEKEND. THERE WILL BE
A SERIES OF SHORTWAVES THAT WILL PASS THROUGH THE FLOW...ONE LATE
TONIGHT AND ANOTHER LATE SATURDAY NIGHT INTO SUNDAY MORNING. WHILE
BOTH ARE NOT OVERLY IMPRESSIVE...THE SECOND SYSTEM PRODUCES
SUFFICIENT LIFT IN THE STATE FOR DEEPER SATURATION AND THE THREAT
OF SNOW ACROSS NORTHERN IOWA OVERNIGHT ON SATURDAY INTO SUNDAY
MORNING. SOME LIGHT ACCUMULATION WILL BE POSSIBLE BUT NOTHING MORE
THAN AN INCH AT THIS POINT.

AFTER THIS SHORTWAVE...THE JET WILL LIFT FARTHER NORTH AND EAST
WITH UPPER RIDGING BUILDING INTO THE CENTRAL UNITED STATES BY MID
TO LATE IN THE WORK WEEK. LOW TO MID LEVEL FLOW WILL BECOME WSW
AND PERSIST THROUGH MUCH OF THE WEEK WHICH WILL BRING WARMER
CONTINENTAL AIR FROM THE SOUTHWEST INTO THE REGION. THERE ARE SOME
DIFFERENCES BETWEEN THE GFS AND EURO ON HOW STUBBORN THE COOLER
AIR DEPARTS NORTHEAST IOWA...OTHERWISE BOTH HAVE A VERY MILD
AIRMASS IN PLACE BY MIDWEEK WITH LITTLE THREAT OF PRECIPITATION.

&&

.AVIATION...06/06Z
ISSUED AT 1125 PM CST THU MAR 5 2015

VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD AND HAD NO
MAJOR CHANGES.

&&

.HYDROLOGY...
ISSUED AT 305 PM CST THU MAR 5 2015

THE SECOND /AND FINAL/ SPRING FLOOD OUTLOOK OF THE SEASON WAS
RELEASED EARLIER TODAY...AND CALLS FOR A NEAR NORMAL RISK OF
FLOODING THROUGH EARLY JUNE. THAT OUTLOOK DOES NOT GIVE FULL
CONSIDERATION TO ICE JAMS...HOWEVER...AS ICE JAMS TEND TO BE HIGHLY
LOCALIZED EVENTS. THERE HAS BEEN INTEREST IN ICE JAM POTENTIAL NEXT
WEEK GIVEN THE FORECAST WARMUP.

ALTHOUGH THE ICE IS THICK ON AREA RIVERS...AND IS THUS PRIMED FOR AN
ICE JAM EVENT...TYPICALLY A FORCING ELEMENT SUCH AS MODERATE TO
HEAVY RAINFALL AND/OR SIGNIFICANT SNOWMELT IS NEEDED TO START THE
ICE JAM PROCESS. ABSENT EITHER OF THOSE...THEN THERMAL BREAK-UP OF
THE ICE IS THE MOST LIKELY ROUTE WHICH DOES NOT NORMALLY CAUSE
SIGNIFICANT FLOODING ISSUES. THE GOING FORECAST IS NOT SHOWING HIGH
CONFIDENCE OF HEAVY RAINFALL LAST WEEK...AND THE EXISTING SNOWPACK
IS NOT SIGNIFICANT ENOUGH TO YIELD SIGNIFICANT SNOWMELT. THUS...THE
ICE JAM THREAT IS RATHER MINIMAL. ALTHOUGH SOME LOCALIZED MINOR
ISSUES MAY OCCUR...SIGNIFICANT FLOODING IS NOT EXPECTED. HAVING SAID
THAT...SINCE MARCH IS OUR CLIMATOLOGICAL PEAK FOR ICE JAMMING...WE
WILL CONTINUE MONITORING.

AS AN ASIDE...IF THERE WAS A SIGNIFICANT SNOWPACK...THEN FOR ICE
JAMS DRIVEN PRIMARILY BY SNOWMELT...3 TO 5 CONSECUTIVE DAYS WITH
DAILY MAX TEMPERATURES AT LEAST IN THE 40S WOULD BE NEEDED TO START
THE ICE JAM PROCESS. OVERNIGHT LOWS WOULD NOT MATTER MUCH.
ALSO...BASED ON PAST EXPERIENCE...WHENEVER THE DAILY AVERAGE
TEMPERATURE IS 42F OR HIGHER...THEN ICE JAMS ALMOST ALWAYS OCCURRED
WITHIN 1 TO 2 DAYS. FOR ICE JAMS DRIVEN BY THE COMBINATION OF
SNOWMELT AND RUNOFF...3 TO 5 CONSECUTIVE DAYS WITH DAILY MAX
TEMPERATURES AT LEAST IN THE MIDDLE 30S WOULD BE NEEDED TO START THE
ICE JAM PROCESS.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...FAB
LONG TERM...COGIL
AVIATION...PODRAZIK
HYDROLOGY...ZOGG


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