Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 291737
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1237 PM CDT MON SEP 29 2014

.SHORT TERM /TODAY/...
ISSUED AT 347 AM CDT MON SEP 29 2014

WEAK PRESSURE GRADIENT OVER IA WITH WEAK FORCING. ISOLATED SHOWERS
OVER NWRN IA WILL NOT LIKELY MOVE MUCH FURTHER SOUTHEAST. SPEED
CONVERGENCE AT THE H8 LEVEL IS AIDING THE DEVELOPMENT AS THE
MOISTURE AXIS ADVANCES NEWD. WOULD EXPECT TO SEE THIS WEAKEN WITH
SUNRISE INTO THE DAY. COLD FRONT NERN WI INTO NORTH CENTRAL
NEBRASKA WILL MOVE SOUTH DURING THE DAY TODAY...REACHING CENTRAL
IA BY THE END OF THE DAY. THIS MAKES FOR A TRICKY FORECAST OVER
THE NORTH. CENTRAL AND SOUTH WILL SEE TEMPS SIMILAR TO THE PAST
COUPLE DAYS LAYER OF COOL AIR IN THE LOWER LEVELS IN COMBINATION
WITH MORE CLOUDS WILL KEEP TEMPS FROM RISING A GREAT DEAL IN THE
NORTH AND HAVE LOWERED HIGHS IN THOSE AREAS ABOUT 10 DEGREES FROM
PREVIOUS PACKAGE WITH A COOL NELY FLOW OF AIR OUT OF THE POLAR
HIGH TO THE NORTHEAST.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
ISSUED AT 347 AM CDT MON SEP 29 2014

BIG CHANGES COMING MID TO LATE WEEK WITH A DEEP TROUGH DIGGING
INTO THE WESTERN AND CENTRAL SECTIONS OF THE COUNTRY AND A COUPLE
OF SHORTWAVES EMBEDDED IN THE UPPER FLOW LOOK TO PROVIDE PERIODIC
RAIN CHANCES TUESDAY NIGHT INTO THURSDAY. MODELS CONTINUE TO BE IN
GOOD AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN BEFORE THE MINOR
DISCREPANCIES SHOW UP WITHIN THE MESOSCALE FEATURES BY EARLY
WEDNESDAY. UTILIZED A BLEND THROUGH WEDNESDAY THEN LEANED CLOSER
TO THE ECMWF LATE IN THE WEEK INTO THE WEEKEND.

TONIGHT THROUGH WEDNESDAY...A WELL ADVERTISED 500MB LOW PRESSURE
LOOKS TO EJECT OUT OF THE CENTRAL ROCKIES INTO THE CENTRAL PLAINS
AND PUSHES NORTH INTO THE DAKOTAS/NORTHERN MINNESOTA FROM TUESDAY
INTO WEDNESDAY. PRECIP CHANCES FROM THIS SYSTEM LOOK TO STAY
ACROSS THE WEST TUESDAY EVENING BEFORE SLOWLY SPREADING EAST
DURING THE OVERNIGHT HOURS INTO WEDNESDAY MORNING AS FRONT DRAGS
THROUGH THE STATE. TEMPERATURES WILL BE COOLER ON WEDNESDAY THAN
PREVIOUSLY FORECAST WITH MUCH MORE CLOUD COVER AND LIKELY PRECIP
THROUGHOUT THE DAY. THERE IS SOME WEAK INSTABILITY PRESENT ON
WEDNESDAY TO KEEP THUNDERSTORMS GOING...BUT SEVERE PARAMETERS LOOK
BLEAK FOR ANYTHING SIGNIFICANT. HEAVIEST RAIN POTENTIAL WILL BE
06Z TO 18Z WEDNESDAY AS BEST MOISTURE TRANSPORT...STRONGEST
FORCING...AND GREATEST PRECIPITABLE WATER OF 1 TO 1.5 INCHES IS
FORECAST.

THURSDAY AND FRIDAY...ANOTHER UPPER LEVEL SHORTWAVE QUICKLY EJECTS
OUT OF THE SOUTHERN ROCKIES AND BEGINS TO PHASE WITH UPPER LOW
PUSHING OUT OF SASKATCHEWAN RESULTING IN DEEPENING OF LARGE 500MB
TROUGH BY THURSDAY INTO FRIDAY. THE BETTER FORCING AND MOISTURE
WILL BE ASSOCIATED WITH THE SOUTHERN VORT MAX THAT IS PROGGED TO
MOVE THROUGH THE OZARKS INTO THE TENNESSEE VALLEY BY EARLY FRIDAY.
WITH THE QUICKER EASTWARD MOVEMENT AND SLIGHTLY FURTHER SOUTH
TRACK LOCATION...LOWERED POPS ACROSS THE NORTHWEST THURSDAY AND
ENDED POPS SOONER THURSDAY NIGHT INTO FRIDAY FROM WEST TO EAST.
THE SECONDARY LOW BRINGS THE COLD AIR MASS INTO THE REGION ON
FRIDAY AND THE MAIN ISSUE WITH THIS SYSTEM LOOKS TO BE WINDS
DURING THE DAY FRIDAY. ACCORDING TO THE ECMWF...850MB TEMPS BEHIND
THE UPPER LOW DROP TO 0C TO -2C BY 18Z FRIDAY WITH THE STRONG CAA
AND COLDEST NIGHT LOOKS TO BE FRIDAY NIGHT WITH SEVERAL LOWS IN
THE NORTH DIPPING INTO THE MIDDLE 30S.

SATURDAY AND SUNDAY...NORTHWEST FLOW ALOFT AND SURFACE HIGH PRESSURE
BUILD INTO THE REGION OVER THE WEEKEND AND PROVIDES SOME DRY AND
MUCH COOLER WEATHER.

&&

.AVIATION...29/18Z
ISSUED AT 1231 PM CDT MON SEP 29 2014

BOUNDARY DRAPED ACROSS THE STATE WILL CONTINUE TO SETTLE TO THE
SOUTH THROUGH THIS EVENING AS HIGH PRESSURE MOVES ACROSS THE GREAT
LAKES. LOW STRATUS ON THE BACKSIDE OF THE BOUNDARY HAS GENERALLY
HALTED ITS ADVANCE ACROSS THE FAR NORTH WITH MVFR TO IFR CONFINED
THERE. ELSEWHERE...WIDESPREAD VFR CONDITIONS WILL CONTINUE THIS
AFTERNOON INTO THE EVENING HOURS WITH LIGHT SURFACE WINDS. LIKELY
TO SEE SOME LOWER CEILINGS DEVELOP ON THE BACKSIDE OF THE FRONT
LATE TONIGHT AS WARM ADVECTION AND LIFT INCREASE OVER THE FRONT
OVERNIGHT. HAVE GONE WITH MVFR TO IFR CEILINGS AND VSBYS OVERNIGHT
WITH SOME IMPROVEMENT ON TUESDAY MORNING ALTHOUGH THIS MAY BE A
BIT ROBUST GIVEN THE TIME OF YEAR AND LATER SHIFTS MAY HAVE TO
ADJUST TIMING BACK EVEN MORE.


&&

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

&&

$$

SHORT TERM...MS SEP 14
LONG TERM...PODRAZIK
AVIATION...COGIL


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