Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 280031
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
631 PM CST THU NOV 27 2014

.UPDATE...
ISSUED AT 628 PM CST THU NOV 27 2014

LOWERED MINS AND HOURLY TEMPS ACROSS THE EAST WHERE THE STRATUS IS
ABSENT. TEMPS ARE FALLING FAST IN CLEAR SKIES. ACROSS THE WEST
WHERE THE STRATUS RESIDES TEMPS HAVE STALLED. WE SHOULD SEE RISING
TEMPS OVERNIGHT. OTHERWISE NO MAJOR CHANGES TO THE GOING FORECAST.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 350 PM CST THU NOV 27 2014

HIGH PRESSURE CENTERED OVER IOWA WILL DRIFT OFF WITH STRONG WAA
SETTING IN OVERNIGHT. PRESSURE FALL ALREADY INDICATING THE WARM
AIR RETURN. BAND OF SC WILL CONTINUE TO SPREAD ACROSS THE STATE
TONIGHT. HAVE INTRODUCED FLURRIES ACROSS THE CWA TONIGHT. THOUGH
THE LOW LEVELS ARE DRY...WOULD EXPECT TO SEE A LOT OF 9SM -SN
TYPE STUFF...CERTAINLY NO MEASURABLE. VERY LOW POPS ALONG THE MN
BORDER HOWEVER WHERE THERE IS A BETTER CHANCE OF SATURATION AND
DEEPER MOISTURE. IN ANY CASE...DECENT LIFT IS PRESENT THROUGH THE
DGZ. TEMPS NON-DIURNAL TONIGHT WITH RISING TEMPS THROUGH THE NIGHT
AS THE COLD AIR RETREATS EAST.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
ISSUED AT 350 PM CST THU NOV 27 2014

IOWA WEATHER WILL BE INFLUENCED BY FAIRLY PROGRESSIVE PATTERN
THROUGH THE PERIOD WITH MAIN CONCERNS FLUCTUATING TEMPS AND FOG
INTO THE WEEKEND. LITTLE IN THE WAY OF PRECIPITATION. PERIOD WILL
BEGIN WITH WARM AIR ADVECTION /WAA/ WELL UNDERWAY WITH H85/H7
THETA-E ADVECTION THROUGH THE MS VALLEY AND SLY LOW LEVEL WINDS.
ANY PRECIPITATION IN THE THERMODYNAMIC FORCING SHOULD REMAIN JUST
NORTH AND EAST OF THE FORECAST AREA HOWEVER. FRI WILL START A TWO
DAY PERIOD WITH LOW TEMP CONFIDENCE DUE TO WAA OVER THE EVOLVING
SNOW PACK WITH APPRECIABLE ERRORS POSSIBLE ALONG THE GRADIENT. THE
STRENGTH OF THE WAA SHOULD BE ABLE TO BOOST TEMPS INTO THE 30S
NE/40S SW FRI. THIS PERSISTENT SLY FLOW WILL ALSO BOOST DEWPOINTS
INTO THE 25-35F RANGE BY FRI NIGHT WITH ADVECTION FOG/STRATUS
BECOMING A CONCERN...ESPECIALLY OVER WHAT IS LEFT OF THE SNOW. 20-
30KT 500M WINDS MAY HOLD THINGS BACK SLIGHTLY...BUT MOST MODEL
SIGNALS INCLUDING WRF NMM/ARW AND SREF SUGGEST LOW VISIBILITIES
AND CIGS INTO FRI NIGHT AND EARLY SAT MORNING...ESPECIALLY NE
HALF. DEWPOINTS AT AND ABOVE FREEZING WILL CONTINUE TO EAT
SNOWPACK SAT WITH TEMPS CONTINUING TO BE PROBLEMATIC. MODELS ARE
TOO AGGRESSIVELY HOLDING ONTO THE SNOWPACK SOUTH AND WEST SO MOS
WILL LIKELY NOT PERFORM TOO WELL EXCEPT N CENTRAL IN MOST
APPRECIABLE SNOW DEPTH. THUS HAVE USED PAST EXPERIENCE AND
SOUNDING EXAMINATION TO MIX TEMPS OUT HALFWAY BETWEEN RAW SURFACE
TEMPS AND TOP OF INVERSION WHICH ENDS UP VERY CLOSE TO PREVIOUS
FORECAST...50S CENTRAL/SOUTH AND 40S HOLDING ON NORTH BUT STILL
ABOVE MOS.

THE FOG/STRATUS/TEMP BATTLE WILL COME TO AN ABRUPT END SUN HOWEVER
WITH A STRONG COLD FRONTAL PASSAGE SUN AS ARCTIC HIGH SETTLES INTO
THE HIGH PLAINS. HIGHS SUN SHOULD BE VERY EARLY WITH FALLING OR
STEADY TEMPS THROUGHOUT THE DAY. A RIBBON OF MID LEVEL FORCING WILL
PASS THROUGH IA SUN NIGHT BUT WITH LITTLE SUPPORT OR MOISTURE BELOW
3KM SO FORECAST STAYS DRY. RETURN FLOW AND WAA WILL BEGIN AGAIN MON
NIGHT. THERE COULD BE SOME VERY LIGHT PRECIP WITH THIS FEATURE
AND LONG WAVE TROUGH PASSAGE TUE...ESPECIALLY IF THE ECMWF IS
CORRECT...BUT CHANCES NOT GREAT ENOUGH TO MENTION AT THE MOMENT.
MODEL CONFIDENCE THEN DIMINISHES TOWARD THE END OF THE PERIOD WITH
GFS MORE AGGRESSIVE PUSHING PIECES OF TROUGH OFF THE CA COAST INTO
AND THROUGH THE ROCKIES INTO THE MO VALLEY. GFS AND ECMWF HAVE
BOTH BEEN STEADFAST WITH THEIR RESPECTIVE WET/DRY SOLUTIONS
RESPECTIVELY SO HAVE LEANED TOWARD THE /IF IN DOUBT GO WITH THE
ECMWF / SOLUTION AND KEPT DAYS 6/7 DRY FOR THE TIME BEING.

&&

.AVIATION...28/00Z
ISSUED AT 555 PM CST THU NOV 27 2014

HIGH PRESSURE OVER IOWA WILL MOVE TO THE EAST WITH FLOW BECOMING
SOUTHEASTERLY AT 10KTS ALLOWING WARMER AIR TO RETURN. MOISTURE
ASSOCIATED WITH THE WARM ADVECTION WILL BRING VFR STRATUS INTO THE
TAF LOCATIONS WITH SOME SOME LIGHT SNOW OR FLURRIES POSSIBLE.  CIGS
SHOULD LIFT AFT 12Z TO AROUND 6KFT.


&&

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

$$

UPDATE...FAB
SHORT TERM...MS NOV 14
LONG TERM...SMALL
AVIATION...FAB


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