Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 280533
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1133 PM CST SAT DEC 27 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 328 PM CST SAT DEC 27 2014

ONLY LINGERING EFFECTS OF CENTRAL CONUS LONG WAVE TROUGH WILL BE
DEPARTING STRATUS TRENDS. DEEP SUBSIDENCE IS IN PLACE BUT LOW
LEVEL MOISTURE IN BROAD CYCLONIC FLOW HAS CONTINUED TO PRODUCE LOW
CLOUDS AS FAR WEST AS A CLARINDA-DES MOINES-WATERLOO LINE BY 21Z.
ALTHOUGH VISIBLE IMAGERY HAS SHOWN STREETS MORE THAN CELLULAR
TRANSITION...MOST OF THE HIGH RES MODELS SUGGEST STRATUS WILL
EITHER DISSIPATE OR ADVECT SOUTH AND EAST OUT OF THE FORECAST AREA
THIS EVENING. FOLLOWED MODEL CONSENSUS FOR MINS...WHICH IS
TYPICALLY JUST ABOVE MOS. WINDS MAY NOT DROP SUFFICIENTLY FOR
GREAT RADIATIONAL COOLING AND WEAK WARM ADVECTION WILL RETURN LATE
AS WELL.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 328 PM CST SAT DEC 27 2014

COLDER TEMPERATURES WILL BE THE MAIN THEME FOR THE EXTENDED.
TEMPERATURES SUNDAY WILL WARM SLIGHTLY AS WEAKLY ZONAL FLOW. A WEAK
SYSTEM WILL PUSH SOUTH THROUGH THE UPPER PLAINS BEGINNING LATE
SUNDAY. SYSTEM IS NOT WELL DEFINED...AND MODELS ARE NOT IN GOOD
AGREEMENT WITH TIMING AND LOCATION OF SYSTEM...THOUGH HAVE SLOWED
SYSTEM. FORCING WILL BE RATHER WEAK...AND BEST FORCING WILL BE
FURTHER WEST. THEREFORE HAVE SLOWED ONSET OF SYSTEM...AND HAVE KEPT
PRECIPITATION CHANCES TO THE WEST. CURRENT TRENDS INDICATE BEST
CHANCES WILL BE ACROSS WESTERN/WEST CENTRAL CWA...WITH BEST FORCING.
HOWEVER...DO NOT HAVE HIGH CONFIDENCE IN TRACK OF SYSTEM. HAVE CUT
BACK ON EASTERN EXTENT OF PRECIPITATION WITH LIMITED MOISTURE...AND
MAY STILL BE TOO FAR EAST WITH PRECIPITATION CHANCES. PRECIPITATION
WILL COME AS SNOW...WITH GENERALLY LIGHT ACCUMULATIONS.

BEHIND SYSTEM...MUCH COLDER AIR WILL PUSH INTO REGION WITH HIGH
PRESSURE SETTLING SOUTH BEGINNING MONDAY NIGHT. TEMPERATURES ARE
EXPECTED TO BE 10 OR MORE DEGREE BELOW NORMAL MAIN CONCERN WITH
COLDER TEMPERATURES WILL BE WIND CHILL VALUES...ESPECIALLY IN THE
NORTH MONDAY NIGHT AND TUESDAY NIGHT WHEN TEMPERATURES ARE
EXPECTED TO FALL BELOW ZERO. WINDS WILL BE STRONGEST MONDAY
NIGHT...WITH WIND CHILL VALUES EXPECTED TO BE NEAR OR BELOW
ADVISORY CRITERIA...AND MAY NEAR WARNING CRITERIA. HIGH WILL PUSH
EAST BEGINNING WEDNESDAY...WITH SOUTHERLY SURFACE FLOW RETURNING
WHICH WILL HELP TO WARM TEMPERATURES FOR THURSDAY AND FRIDAY.

FOR END OF PERIOD...MODELS DIVERGE SIGNIFICANTLY...THOUGH INDICATE
PRECIPITATION CHANCES RETUNING FOR THE WEEKEND. ECMWF IS LESS
AGGRESSIVE WITH LARGE AREA OF LOW PRESSURE TRACK ACROSS
CANADA...DROPPING BOUNDARY INTO CENTRAL IOWA BEGINNING LATE FRIDAY.
GFS PULLS LARGE SURFACE LOW NORTH FROM FOUR CORNERS REGION. ECMWF
HINTS AT THIS AS WELL...THOUGH KEEPS LOW FURTHER SOUTH AND EAST
FROM IOWA GIVEN STRENGTH OF CANADIAN LOW. FOR NOW...HAVE KEPT
SLIGHT CHANCES AND CHANCES FOR FRIDAY GIVEN UNCERTAINTIES. SYSTEM
WILL NEED TO BE MONITORED CLOSELY.

&&

.AVIATION...28/06Z
ISSUED AT 1133 PM CST SAT DEC 27 2014

THE LAST OF THE LOW MVFR CIGS FROM SATURDAY WILL CLEAR OUT OF OTM
IN THE NEXT HOUR...AFTER WHICH VIRTUALLY SKC WILL PREVAIL
OVERNIGHT AND INTO SUNDAY WITH LIGHT WSW WINDS. TOWARD SUNDAY
EVENING LAYERED CLOUDS WILL DEVELOP FROM THE WEST AS WINDS SHIFT
AROUND TO NNE AHEAD OF THE NEXT SYSTEM...BUT PRECIP IS EXPECTED TO
HOLD OFF UNTIL NEAR OR AFTER THE END OF THE 06Z TAFS. ONLY OTHER
CONCERN IS THE PROSPECT OF MORE DIURNALLY DRIVEN STRATOCUMULUS
FORMING BY SUNDAY AFTERNOON ESPECIALLY OVER AREAS WITH SNOW COVER.
CONFIDENCE REMAINS TOO LOW TO INCLUDE CIGS IN THE TAFS ATTM...BUT
THERE IS THE POSSIBILITY OF CLOUDS AT FL010-018 THAT WILL NEED TO
BE MONITORED IN SUBSEQUENT ISSUANCES.

&&

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

&&

$$

SHORT TERM...SMALL
LONG TERM...AWB
AVIATION...LEE


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