Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 232113
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
313 PM CST FRI JAN 23 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 312 PM CST FRI JAN 23 2015

HIGH CLOUDS MOVING ACROSS THE AREA THIS AFTERNOON WILL DEPART TO THE
SOUTHEAST LATER THIS EVENING AS A WEAK SURFACE TROUGH MOVES
THROUGH...SHIFTING WINDS AROUND TO NORTHWEST. DESPITE THE CHANGE IN
DIRECTION THERE DOES NOT APPEAR TO BE ANY COLD AIR ADVECTION
ASSOCIATED WITH THE BOUNDARY AND IN FACT IT IS JUST THE
OPPOSITE...AS TEMPERATURES BEHIND IT ARE PROGRESSIVELY WARMER THAN
AHEAD OF IT DUE TO THE DOWNSLOPING EFFECT. MEANWHILE...A BIG PATCH
OF LOW STRATUS CLOUDS ACROSS NORTHERN MINNESOTA IS MOVING SOUTHEAST
TOWARD WISCONSIN.

THE PRIMARY FORECAST ISSUE FOR TONIGHT IS CLOUD COVER. NEARLY ALL
MODELS...ESPECIALLY THE HIGH RESOLUTION NAM/RAP/HRRR
SOLUTIONS...ATTEMPT TO BLOW UP A LARGE AREA OF VERY LOW STRATUS OVER
THE SNOW COVER AREAS OF WESTERN MINNESOTA AND EASTERN SOUTH DAKOTA
THEN SPREAD AND GROW THESE CLOUDS OVER OUR ENTIRE FORECAST AREA
OVERNIGHT. HOWEVER...SKIES OVER THE ENTIRE GENERATION REGION REMAIN
CLEAR AS A BELL AT THIS HOUR AND THE HIGH RES MODELS WERE EARLIER
DEVELOPING THE CLOUDS EVEN BY THIS TIME. IT APPEARS THAT THEY ARE
VASTLY OVERFORECASTING NEAR SURFACE MOISTURE FIELDS. GIVEN
APPARENTLY DRIER PROFILES...THE LACK OF ANY CLOUD GENERATION SO
FAR...AND THE EFFECTIVE WARM AIR ADVECTION OCCURRING BEHIND THE
BOUNDARY...IT APPEARS UNLIKELY THAT CLOUDS WILL DEVELOP IN THIS
AREA. THE STRATUS SHIELD OVER NORTHERN MINNESOTA MAY DROP A BIT MORE
SOUTHWARD AND CLIP OUR NORTHEASTER COUNTIES OVERNIGHT AND HAVE
MAINTAINED CLOUDS IN THAT AREA...BUT CLEARED THEM FURTHER SOUTHWEST
TOWARD CENTRAL IOWA AND BEYOND. OBVIOUSLY CLOUD COVER WILL HAVE A
DRAMATIC EFFECT ON OVERNIGHT LOW TEMPERATURES...BUT EVEN IF SKIES
ARE CLEAR ANY COOLING WILL BE MITIGATED BY THE AFOREMENTIONED
DOWNSLOPING AS WELL AS ORGANIZED NORTHWEST WINDS OF AROUND 6 TO 10
KNOTS.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 312 PM CST FRI JAN 23 2015

NORTHWEST FLOW ALOFT WILL CONTINUE TO DOMINATE THE UPPER PATTERN
ACROSS THE STATE FOR THE REMAINDER OF THE FORECAST. WILL SEE WARM
ADVECTION RESUME ON SATURDAY AHEAD OF APPROACHING SHORTWAVE WITH
THERMAL RIDGE BUILDING INTO WESTERN IOWA. ANY MORNING CLOUDS
SHOULD GIVE WAY TO SUNSHINE BY LATE MORNING AND WITH WESTERLY
WINDS...ANOTHER DECENT WARMUP ACROSS ALL OF CENTRAL IOWA. CLOUDS
WILL MOVE BACK IN BY LATE AFTERNOON AS LIFT INCREASES AND EXPAND
ACROSS THE WHOLE AREA BY EVENING. BOTH MID LEVEL KINEMATIC
FORCING AND ISENTROPIC LIFT WILL BE IN PLACE DURING THE EVENING
WITH KINEMATICS TAKING OVER THE DURING THE OVERNIGHT AS THE UPPER
SYSTEM SLIDES INTO THE STATE.  MODELS STILL TRYING TO NAIL DOWN THE TRACK
WITH GFS NOW FARTHEST SOUTHWEST...EURO IN THE MIDDLE AND NAM TO
THE NORTHEAST. WILL STICK WITH THE MOST CONSISTENT EURO WHICH
PLACES BEST THREAT OF PRECIPITATION AND HAVE GONE HIGH LIKELY IN
THOSE LOCATIONS. SHOULD GFS END UP VERIFYING...HIGHER POPS WILL
NEED TO BE EXPANDED TO THE SOUTHWEST ALONG WITH THE SNOW AREA.

INITIALLY...SURFACE TEMPERATURES WILL BE WARM ENOUGH FOR RAIN
ACROSS MOST OF CENTRAL IOWA EXCEPT FOR THE FAR NORTHEAST NEAR
KMCW. HOWEVER...AS THE NIGHT PROGRESSES...COLD SURFACE AIR WILL
SPREAD ACROSS THE NORTH WITH THE RAIN SNOW LINE SHIFTING SOUTHWARD
TO THE INTERSTATE 80 CORRIDOR BY MORNING. SNOW AMOUNTS OF 1 TO 3
INCHES WILL BE COMMON IN NORTH CENTRAL IOWA TOWARD THE BLACK
HAWK/TAMA COUNTY AREA. THE PRECIPITATION WILL QUICKLY DIE OFF ON
SUNDAY MORNING AS THE SYSTEM DEPARTS TO THE EAST WITH BRIEFLY
COOLER WEATHER ON SUNDAY. WARM ADVECTION KICK RIGHT BACK IN BY
LATE SUNDAY NIGHT INTO MONDAY WITH STRONG WARM ADVECTION AND
ISENTROPIC LIFT LEADING TO CLOUDS AND SOME LIGHT PRECIPITATION
OVER EASTERN IOWA BY LATE SUNDAY NIGHT INTO MONDAY MORNING ACROSS
THE NORTH AND EAST. ANY AMOUNTS LOOK QUITE LIMITED AT THIS TIME
WITH THE BULK OF FORCING REMAINING IN MINNESOTA AND WISCONSIN.
WARMER AIR WILL THEN OVERSPREAD THE MIDWEST INTO THE MIDDLE OF THE
WEEK WITH TEMPERATURES HOLDING WELL ABOVE NORMAL. IT DOES APPEAR
A MORE VIGOROUS TROF WILL DEVELOP ACROSS THE EASTERN UNITED
STATES BY LATE NEXT WEEK BRINGING TEMPERATURES CRASHING DOWN TO
REALITY ALONG WITH THE THREAT OF SOME SNOW AT THE END OF THE
PERIOD.

&&

.AVIATION...23/18Z
ISSUED AT 1132 AM CST FRI JAN 23 2015

OVERNIGHT A STRATUS DECK COULD DEVELOP AND MOVING INTO THE
AREA...BUT CONFIDENCE IS RELATIVELY LOW. SATELLITE IMAGERY DEPICTS
SUCH CLOUDS APPROACHING FROM NORTHERN MN BUT ON A TRAJECTORY TO
JUST CLIP NORTHEAST IA. ALL MODEL GUIDANCE INDICATES DEVELOPMENT
OF LOW CLOUDS OVER EASTERN SD AND WESTERN MN TODAY...APPARENTLY
THOSE THAT WOULD FOLLOW THE STEERING FLOW DOWN INTO CENTRAL IOWA
TONIGHT...BUT CURRENTLY SATELLITE AND OBSERVATIONS SHOW CLEAR
SKIES OVER THOSE AREAS. SUSPECT THAT THE MODELS POOR HANDLE ON
CURRENT SNOW COVER MAY BE LEADING TO OVERZEALOUS PREDICTIONS OF
NEAR SURFACE MOISTURE AND CLOUD DEVELOPMENT. HOWEVER...WITH MVFR
CIGS ALREADY IN THE TAFS HAVE MAINTAINED THEM AND WILL WATCH
OBSERVATIONAL TRENDS TO OUR NORTHWEST THIS AFTERNOON AND TONIGHT.


&&

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

&&

$$

SHORT TERM...LEE
LONG TERM...COGIL
AVIATION...LEE


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