Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250536
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1136 PM CST WED DEC 24 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 306 PM CST WED DEC 24 2014

SATELLITE IMAGERY INDICATES THAT THE BACK EDGE OF THE LARGE STRATUS
SHIELD PLAGUING THE REGION HAS GRADUALLY PROGRESSED EASTWARD
TODAY...AND NOW STRETCHES FROM AROUND LINCOLN NE TO MITCHELL SD TO
OUR WEST. STRAIGHT EXTRAPOLATION BRINGS IT ACROSS OUR FORECAST AREA
TONIGHT...HOWEVER...FORECAST SOUNDINGS MAINTAIN THE NEAR SURFACE
SATURATED LAYER THROUGH MUCH OF THE NIGHT AND CLIMATOLOGY AND RECENT
PERSISTENCE WOULD FAVOR CLOUDY SKIES THROUGH SUNRISE CHRISTMAS
DAY...SO HAVE TRENDED THE FORECAST IN THAT DIRECTION. THIS WILL ALSO
KEEP TEMPERATURES A BIT WARMER OVERNIGHT BENEATH THE CLOUDS. NO
PRECIPITATION IS FORECAST AS THE VERY LIGHT FLURRIES AND SPRINKLES
PEPPERING THE AREA AT THE CURRENT TIME SHOULD DISSIPATE BY AROUND
SUNSET. ALL IN ALL QUIET WEATHER FOR CHRISTMAS EVE WITH THE ONLY
POTENTIAL IMPACTS BEING TO AVIATION INTERESTS AS OUTLINED BELOW.

.LONG TERM /THURSDAY THROUGH WEDNESDAY/...
ISSUED AT 306 PM CST WED DEC 24 2014

GENERAL TRENDS FOR THE EXTENDED REMAIN THE SAME...WITH MUCH COLDER
CONDITIONS NEXT WEEK. IN THE NEARER TERM...CHALLENGES INCLUDE EXTENT
OF CLEARING FOR CHRISTMAS DAY AS WELL AS TEMPERATURES...AND SNOWFALL
AMOUNTS FOR THE FRIDAY/SATURDAY SYSTEM. MODELS IN GENERAL AGREEMENT
IN PARTIAL CLEARING FOR TOMORROW...WITH WARM AIR ADVECTION AND
INCREASING SOUTHWEST FLOW ALOFT INTO THE MORNING HOURS CHRISTMAS DAY
WHICH WILL AID IN THE CLOUD DISSIPATION PROCESS. BUT DESPITE THE
RIDGE ALOFT BUILDING EAST...THE AMPLITUDE OF THE RIDGE LESSENS WITH
TIME AS THE NEXT UPSTREAM WAVE DEEPENS IN THE LEE OF THE ROCKIES.
CURRENT VISSAT SHOWS WESTERN EDGE OF CLOUD DECK NOT MOVING MUCH TO
THE EAST. WITH THE ABOVE FACTORS POSSIBLY KEEPING CLOUDS MORE
INTACT...WILL CONTINUE TREND OF PARTIAL CLEARING SOUTH AREAS WITH
MOSTLY CLOUDY CONDITIONS ACROSS THE NORTH TOMORROW. HIGHS TOMORROW
WILL BE SOMEWHAT HELD LOWER ACROSS THE NORTHWEST WHERE CLOUD COVER
WILL BE MOST PREVALENT. H850 TEMPS LOOK TO BE QUITE MILD WITH +4C OR
MORE OVER THE SOUTH...WHICH SHOULD LEAD TO HIGHS IN THE LOWER TO MID
40S BY AFTERNOON OVER THE SOUTH AND 30S NORTH. THE NEXT STORM SYSTEM
WILL BE WEAKENING AS IT EXITS THE ROCKIES AND SOUTHERN PLAINS...AND
MAINLY BECOME AN INVERTED TROUGH OVER IOWA. WITH THE FORCING
EXPECTED TO BE LIMITED UNTIL THE BOUNDARY ARRIVES LATE FRIDAY
AFTERNOON...CURRENT TRENDS OF LOW POP NORTHWEST LOOK ONTRACK. BY
FRIDAY EVENING...HAVE INCREASED SNOW CHANCES NORTHWEST WITH LIGHT
AMOUNTS OF PRECIPITATION EXPECTED AND SNOWFALL REMAINING ON THE
LIGHT SIDE...STILL GENERALLY AROUND AN INCH. THE MODELS ARE IN GOOD
AGREEMENT FOR LATE FRIDAY NIGHT INTO SATURDAY...WITH THE PREDOMINANT
SPLIT FLOW HOLDING ON AND THE SOUTHERN STREAM LOW TRACKING FAR
ENOUGH SOUTH TO KEEP SNOWFALL MAINLY ACROSS THE SOUTH. OTHER THAN
THE 12Z GEM...BOTH THE NAM AND GFS AND 00Z/12Z EURO HAVE CONTINUED
TRENDING THE STORM SOUTH OF THE REGION. FOR THE OVERNIGHT HOURS...
LIGHT SNOW WITH A DUSTING OF ACCUMULATION IS EXPECTED AS ISENTROPIC
LIFT AND FORCING REMAINS WEAK ACROSS THE AREA. BY EARLY SATURDAY THE
MAIN MOISTURE CHANNEL AND LIFT SHIFTS INTO SOUTHEAST IOWA AND AREAS
SOUTH AND EAST OF THE STATE...QUICKLY EXITING BY 18Z. THROUGH THE
REMAINDER OF THE WEEKEND A GRADUAL EXPANSION OF THE H500 TROUGH WILL
OCCUR ACROSS THE PLAINS. THIS WILL SLOWLY BRING COLDER AIR ACROSS
THE REGION THROUGH NEXT WEEK. A WAVE OVER THE PACNW SUNDAY WILL DIG
SOUTHEAST ACROSS THE ROCKIES AS THE UPPER LEVEL H500 LOW AMPLIFIES.
TODAY THE EURO/GFS KEEP THE COLDEST AIR TO THE WEST OF THE REGION
AND DIG THE WAVE INTO THE DEEP SOUTH EARLY NEXT WEEK. CONFIDENCE IN
THE EXTENDED SOLUTIONS LESSEN TODAY. OVERALL...THE COLDER TREND WILL
HOLD BUT TIMING OF ANY PRECIPITATION FROM THE PATTERN IS MORE
SUSPECT. THE PERIOD OF MORE LIKELY LIGHT SNOW FALLS BETWEEN LATE
MONDAY EVENING AND TUESDAY EVENING AS SEVERAL PIECES OF ENERGY TEAR
AWAY FROM THE MAIN UPPER LEVEL SYSTEM AND CROSS IOWA AS THEY WEAKEN.
OVERALL...EXPECT MORE CLOUDS AGAIN IN THE NEXT 7 DAYS WITH
CHRISTMAS...SUNDAY...AND POSSIBLY AGAIN NEW YEARS EVE DAY SHOWING
SIGNS OF SUNSHINE AT THIS POINT.  TEMPERATURES WILL TREND LOWER
THROUGH THE PERIOD WITH HIGHS/LOWS ENDING IN THE TEENS/20S AND LOWS
IN THE SINGLE DIGITS ABOVE/BELOW ZERO FOR THE LAST FEW DAYS OF THE
YEAR.

&&

.AVIATION...25/06Z
ISSUED AT 1133 PM CST WED DEC 24 2014

HIGH PRESSURE RIDGE OVER IA WILL MOVE TO THE EAST. IFR CONDITIONS
WILL IMPROVE FROM THE WEST AFTER RIDGE PASSAGE WITH CIGS LIFTING
TO VFR AFTER 12Z. VFR CONDITIONS WILL PREVAIL THROUGH CHRISTMAS
DAY INTO THE EVENING.

OUTLOOK...DETERIORATING CONDITIONS FROM THE NORTHWEST AS THE NEXT
FRONTAL SYSTEM APPROACHES FRIDAY. IFR AND MVFR WILL SPREAD INTO
NWRN IA DURING THE DAY...AND OVER THE TAF SITES FRIDAY NIGHT.

&&

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

$$

SHORT TERM...LEE
LONG TERM...REV
AVIATION...MS DEC 14



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