Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 290448
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1148 PM CDT TUE OCT 28 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 345 PM CDT TUE OCT 28 2014

MAIN FORECAST CHALLENGE WILL BE CLOUD TRENDS. BKN CONDITIONS HAVE
MADE IT AS FAR SOUTH AS THE I-80/US 30 CORRIDOR. EXPECT THE STRATOCU
TO GRADUALLY LIFT NORTHEAST. TIMING IS THE QUESTION. EXPECT
NOTICEABLE IMPROVEMENT AFTER 00Z ESPECIALLY SOUTH OF US 20...HOWEVER
CLOUDS WILL BE SLOWER TO GO FROM THE US 20 CORRIDOR NORTHWARD
ESPECIALLY EAST OF US 169. MODELS KEEP ELEVATED RH AROUND FOR MUCH
OF THE NIGHT ACROSS THE NORTHEASTERN CWA...WITH MOST OF THE STRATOCU
TO THE NORTHEAST OF THE CWA BY 12Z WED.

LOW TEMPS ACROSS THE NORTHEASTERN CWA WILL ALSO DEPEND ON CLOUD
COVER. IF CLOUDS DISSIPATE EARLIER THAN EXPECTED THEN TEMPS THERE
MAY BE LOWER THEN INDICATED IN THE FCST. WINDS WILL NOT FULLY
DECOUPLE THERE OVERNIGHT...HOWEVER...SO IF THE CLOUD COVER DOES
DISSIPATE EARLIER THAN FCST THE TEMPERATURE DROPS WOULD BE
RELATIVELY MINOR.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 345 PM CDT TUE OCT 28 2014

FORECAST CONCERNS IN THE EXTENDED CENTER AROUND PRECIP CHANCES
WEDNESDAY NIGHT/THURSDAY THEN AGAIN EARLY NEXT WEEK ALONG WITH A
COLD SNAP FRIDAY/SATURDAY WHICH WILL BRING SOME OF THE COLDEST AIR
YET THIS SEASON TO CENTRAL IOWA.

HIGH PRESSURE MOVES ACROSS THE AREA THROUGH WEDNESDAY EVENING
BRINGING A DRY PERIOD WITH SEASONAL TEMPERATURES TO THE FORECAST
AREA.

MODELS ARE VERY CONSISTENT WITH THE SHORT WAVE DROPPING OUT OF
THE NORTHERN PLAINS AND ACROSS IOWA AND MINNESOTA LATE WEDNESDAY
NIGH  AND THURSDAY.  ALL THE MODELS ARE EVEN A TOUCH SLOWER WITH
THIS FEATURE BRINING IT INTO NW IA BETWEEN 06Z AND 09Z THEN DROPPING
IT THROUGH IOWA BY 21Z THURSDAY.  THE MODELS DO DIFFER ON THE
EVOLUTION OF SURFACE FEATURES HOWEVER.  THE NAM AND GFS DEVELOP A
DOUBLE BARRELED LOW WITH THE SOUTHERN LOW BECOMING THE DOMINANT
SURFACE FEATURE AS IT DRIFTS SE ACROSS IA/MO.  OTHER MODELS EITHER
DON`T HAVE MUCH OF A SURFACE REFLECTION OR THEY DEVELOP A SURFACE
LOW IN THE SOUTHERN STREAM OF THE SHORT WAVE.  IN ANY EVENT THE
FORCING...SUCH THAT IT IS...GETS SPLIT BETWEEN SOUTHERN MN/NE IA AND
SOUTHERN IA/NORTHERN MO.  LOW LEVEL MOISTURE IS SPARSE TO NON-
EXISTENT WITH THIS WAVE BUT THERE IS DECENT MID LEVEL MOISTURE.  SO
THE QUESTION IS HOW MUCH WILL THE LOW LEVELS SATURATE  AND HOW MUCH
PRECIP WILL WE GET FROM THIS.  AT THIS POINT IT APPEARS NORTHERN/NE
IA WILL NOT SEE MUCH...SPRINKLES TO A HUNDRETH OR TWO.  SOUTHERN/SE
IOWA MAY SEE A BIT MORE BUT STILL ON THE ORDER OF HUNDREDTHS.  THE
BETTER FORCING AND HENCE THE BETTER QPF CHANCES REMAIN IN NORTHERN
MO AND MAY EXTEND INTO FAR SE IA.  I DON`T HAVE ANYTHING MORE THAN
SLIGHT CHANCES GOING ACROSS IA FOR THIS ENTIRE EVENT.

AFTER THIS SYSTEM PASSES HIGH PRESSURE BUILDS IN BOTH AT THE SURFACE
AND ALOFT.  THE SURFACE HIGH IS ANCHORED RIGHT OVER IOWA FRIDAY
NIGHT.  WITH LIGHT WINDS AND CLEAR SKIES TEMPS SHOULD REALLY TUMBLE.
THE ONLY SAVING GRACE WOULD BE THAT THE RIDGE AXIS DURING THE
OVERNIGHT WILL SHIFT OVER THE FAR EAST CWA OR EASTERN IA SO SURFACE
WINDS...ALBEIT LIGHT...WILL BECOME EAST TO SOUTHEAST.  THE MODELS
DID PICK UP ON THIS AND DID LOWER TEMPS FOR FRIDAY NIGHT.  I HAVE
DROPPED THEM A DEGREE OR TWO MORE IN FAVORED LOCATIONS LIKE FAR
EASTERN PORTIONS OF THE CWA AND THE NISH VALLEY.  SATURDAY WILL
START OUT VERY COLD AND RECOVERY IS SOMEWHAT QUESTIONABLE DESPITE
THE STRONG RETURN FLOW IN THE LOWEST LAYERS.  FOR NOW I HAVE KEPT
THE HIGHS IN THE 40S BUT THIS MAY BE TOO COOL.  THE UPPER LEVEL
RIDGE IS STILL IN PLACE ACROSS IOWA SO WE WILL HAVE TO SEE HOW MUCH
INFLUENCE THAT WILL HAVE ON ALLOWING THINGS TO WARM UP.

BY LATE SUNDAY/SUNDAY NIGHT  THE UPPER RIDGE IS EAST OF IA SO WE ARE
IN A DEEPER SOUTHERLY FLOW AND TEMPS SHOULD DEFINITELY
RESPOND...ESPECIALLY ACROSS THE WEST AND SOUTHWEST.  HIGHS MAY STILL
BE IN THE UPPER 40S OR SO NORTHEAST BUT WE MAY TOUCH 60 IN THE FAR
SOUTHWEST.

SUNDAY NIGHT AND MONDAY A LONGWAVE TROUGH WILL SWEEP OUT OF THE
INTERMOUNTAIN WEST AND HIGH PLAINS.  A LOW WILL DEVELOP IN THE
TROUGH AND DEEPEN OVER THE NORTHERN PLAINS WHILE SOME ENERGY EJECTS
OUT OF THE TROUGH OVER THE PLAINS.  MOISTURE WILL BE ON THE INCREASE
SUNDAY EVENING AND WE SHOULD SEE SOME PRECIP DEVELOP LATE SUNDAY
NIGHT AND OVERSPREAD THE CWA THROUGH MONDAY.  THE SYSTEM WILL BE
PROGRESSIVE THOUGH AND PRECIP SHOULD PUSH OFF TO THE EAST BY
EVENING.  THE BASE OF THE UPPER TROUGH WILL COME THROUGH OVERNIGHT
MONDAY AND WE SHOULD SEE CLEARING OVERNIGHT.  THERE ISN`T ANY COLD
AIR BEHIND THIS SYSTEM SO TEMPS SHOULD BE IN THE 50S FOR TUESDAY
WITH CLEARING SKIES.

&&

.AVIATION...29/06Z
ISSUED AT 1144 PM CDT TUE OCT 28 2014

NOT MUCH CHANGED SINCE LAST TAF PACKAGE. ST DECK/SC FIELD ASSOC
WITH AREA OF LOW PRESSURE STILL MOVING VERY SLOWLY TO THE EAST SO
WILL LIKELY BE BKN TO OVC FOR NORTHERN TAF SITES THROUGH THE
OVERNIGHT. KMCW MAY BRIEFLY DROP TO MVFR CONDITIONS A TIME OR
TWO TONIGHT...BUT VFR EXPECTED TO BE MOST PREVALENT. EXPECT SKIES
TO BECOME SKC TO SCT AT AROUND THE 20Z TO 22Z WED TIME FRAME.

&&

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

$$

SHORT TERM...ZOGG
LONG TERM...FAB
AVIATION...KOTENBERG



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