000
FXUS63 KDMX 071756
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1156 AM CST SAT DEC 7 2013

.SHORT TERM /TODAY/...
ISSUED AT 354 AM CST SAT DEC 7 2013

MAIN CONCERN TODAY REMAINS TEMP AND WIND CHILL TRENDS.  ANY INITIAL
EFFECTS OF ADVANCING WRN CONUS TROUGH WILL NOT REACH IA UNTIL VERY
LATE IN THE PERIOD...AND THAT WOULD BE NOTHING MORE THAN INCREASING
MID CLOUDINESS.  RAW GFS TEMPS ARE STILL TOO WARM SO TEMPS WILL BE
BASED MORE ON NAM...MOS...RAP AND OTHER HIGH RES RUNS.  THERE IS
STILL SOME SPREAD IN THESE VALUES HOWEVER AND SOMEWHAT LOWER
CONFIDENCE THAN YESTERDAY.  LESS SUNSHINE AND MIXING WITH INCREASING
CLOUDS AND DIMINISHING WINDS MAY NOT ALLOW AS GREAT OF A REBOUND SO
FOLLOWED A BLEND MORE THAN ANYTHING.  WIND CHILL ADVISORY IS
SOMEWHAT MARGINAL AT THE MOMENT...BUT WITH TEMPS CONTINUING TO FALL
AND WINDS NOT DIMINISHING UNTIL LATER THIS MORNING CHANGES MAKE
LITTLE SENSE BASED ON PUBLIC PERCEPTION OF SENSIBLE WEATHER.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 354 AM CST SAT DEC 7 2013

FORECAST CONCERN WAS FOCUSED ON THE LONG DURATION SNOW EVENT
BEGINNING LATE TONIGHT AND LASTING INTO THE EVENING HOURS ON
SUNDAY. MODELS ARE IN GOOD AGREEMENT WITH TIMING AND TRACK
LOCATION OF MID-LEVEL SHORTWAVE TO PUSH ACROSS THE STATE SUNDAY
AND LEANED TOWARD A BLEND OF THE SREF/NAM12 POPS AND TEMPS.

TONIGHT THROUGH MONDAY...BROAD ISENTROPIC LIFT AND WEAK MOISTURE
TRANSPORT DEVELOPED TONIGHT PAST 03Z SUNDAY OVER THE WESTERN TO
CENTRAL PORTIONS OF THE STATE...THEN SPREADS EAST BY 06Z. NAM
SOUNDING AT CRL COMPLETELY SATURATES BY AROUND 09Z SUNDAY...WHILE
THE GFS AND SREF ROUGHLY AN HOUR OR TWO SLOWER. HOWEVER...SHOULD
SEE SOME LIGHT SNOW B/T 06-09Z TIME FRAME AS ISENTROPIC LIFT LOOKS
TO BE ENOUGH TO HELP THE COLUMN SATURATE A LITTLE QUICKER THAN
WHEN THE MODELS ARE ANTICIPATING. SO KEPT MENTION OF LIKELY POPS
ACROSS THE WEST B/T 06-09Z BUT WITH LITTLE ACCUMULATION. DSM TO
MCW BECOME COMPLETELY SATURATED CLOSE TO 12Z...WHILE ALO TO OTM
SHOULD SEE SNOW BY 15Z.

ALL SOUNDINGS DURING THE EVENT HAVE A DEEP DENDRITIC
LAYER...BASICALLY FROM THE SURFACE TO NEAR 600MB BUT LIFT WITHIN
THIS SGZ IS VERY WEAK AS OMEGA ONLY RANGES FROM 2 TO 4 UBAR/S.
06.21Z SREF PROB DENDRITE GROWTH ZONE GREATER THAN 100MB IS 100
PERCENT OVER MUCH OF THE FORECAST AREA BUT THE PROB OF 1 INCH/HOUR
SNOWFALL RATE IS LESS THAN 10 PERCENT...AND THAT IS LOCATED OVER
FAR NORTHWEST IOWA. THE SNOW RATIOS INCREASE TO 20 TO 22:1 AND
POSSIBLY A LITTLE HIGHER ACROSS THE NORTH DURING THE BULK OF THE
EVENT. EXPECTING LIGHT FLUFFY SNOW FLAKES WITH LITTLE WATER
CONTENT AS PRECIPITABLE WATER IS AT OR LESS THAN 0.25 INCHES FROM
12Z SUNDAY TO 00Z MONDAY.

NO MAJOR CHANGES WITH ONGOING SNOW FORECAST AND STILL
ANTICIPATING A WIDESPREAD 2 TO 4 INCHES CENTRAL TO NORTH...WITH
GENERALLY 2 INCHES OR LESS IN THE SOUTH TO SOUTHEAST. CERTAINLY
CANNOT RULE OUT A FEW ISOLATED LOCATIONS RECEIVING 5 INCHES WITH
THE LIGHT FLUFFY SNOW. IN ADDITION...WINDS WILL NOT BE MUCH OF A
FACTOR SO FELT CONFIDENT TO HOLD OFF ON ISSUING ANY HEADLINES
ATTM. ISENTROPIC LIFT AND DEEP MOISTURE MOVE EAST SUNDAY
NIGHT...AND DECREASED POPS SLIGHTLY ACROSS THE WEST. WENT
COMPLETELY DRY AFTER MIDNIGHT SUNDAY NIGHT.

TUESDAY THROUGH FRIDAY...A REINFORCED SHOT OF COLD AIR FILTERS INTO
THE STATE ON TUESDAY RESULTING IN A VERY COLD NIGHT AGAIN FOR TUESDAY
NIGHT. WITH THE FRESH SNOWPACK OVER THE AREA...TWEAKED LOWS DOWN
A DEGREE OR TWO. OTHERWISE...THE FORECAST WILL BE CONTINUED COLD
AND DRY THROUGH THE REMAINDER OF THE FORECAST PERIOD WITH HIGH
PRESSURE PERSISTING OVER THE REGION.

&&

.AVIATION...07/18Z
ISSUED AT 1151 AM CST SAT DEC 7 2013

MAIN CONCERN THIS PERIOD WILL BE LOWERING CONDITIONS THROUGH THE
PERIOD AFT 09Z AND THROUGH END OF PERIOD. HAVE MODIFIED TIMING A
BIT AS LIFT MAY ARRIVE A BIT SLOWER...BY A FEW HOURS AT MOST...
BUT THEN CONDITIONS DETERIORATE RAPIDLY AS CIGS DROP FROM VFR TO
IFR VERY QUICKLY OVER A 1 TO 2 HOUR PERIOD. LIGHT SNOW WILL THEN
CONTINUE WITH LOWERING VSBYS FOR THE REMAINDER OF THE PERIOD.
THOUGH WINDS WILL NOT BE A MAJOR CONCERN...SOME INCREASE IN SFC
WINDS AND GUSTS SHOULD ARRIVE ABOUT THE SAME TIME AS SNOW BEGINS
WITH ESE WINDS OF 10-16KTS FOR A PERIOD FROM WEST/EAST SUNDAY.

&&

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

$$

SHORT TERM...SMALL
LONG TERM...PODRAZIK
AVIATION...REV