820
FXUS63 KDMX 012054
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
254 PM CST SUN DEC 1 2024
KEY MESSAGES
- LIGHT SNOW ARRIVES LATE THIS AFTERNOON INTO TONIGHT WITH MINOR TRAVEL
IMPACTS POSSIBLE FOR RETURN THANKSGIVING TRAVELERS AND/OR
MONDAY MORNING COMMUTE. SNOW CHANCES ARE ABOVE 70% OVER AREAS
WEST OF I-35 IN THE STATE.
- TONIGHT'S SNOW ACCUMULATIONS MAINLY UNDER AN INCH, BUT THERE'S
A 20% CHANCE OF A NARROW CORRIDOR OF 1 INCH OR SLIGHTLY MORE
FROM NORTHWEST INTO PERHAPS SOUTH CENTRAL IOWA.
- MONDAY THROUGH FRIDAY FEATURES BELOW NORMAL TEMPERATURES EXCEPT ON
WEDNESDAY WITH NEAR NORMAL CONDITIONS FOR EARLY DECEMBER.
- INCREASING WINDS DURING THE DAY WEDNESDAY WITH GUSTS OVER 40
MPH POSSIBLE.
DISCUSSION
ISSUED AT 253 PM CST SUN DEC 1 2024
EARLY AFTERNOON SATELLITE IMAGERY OVER THE CONUS SHOWS LITTLE
IN THE WAY OF SIGNIFICANT CHANGE FROM THIS TIME YESTERDAY. A
BROAD TROUGH REMAINS OVER THE EASTERN HALF OF THE US WITH IOWA
RESIDING BENEATH NORTHWESTERLY FLOW WITH A DEVELOPING REX BLOCK
OFF THE WEST COAST. RAP ANALYSIS SHOWS A 100 KNOT JET STREAK OFF
TO THE WEST OF IOWA WITH A STRONG SHORTWAVE TROUGH MOVING INTO
NORTH DAKOTA THAT WILL BRING LIGHT SNOW INTO IOWA. AHEAD OF THIS
SHORTWAVE, THERE IS AN EXPANSIVE SHIELD OF CLOUDS OVER THE
DAKOTAS WITH MORE SCATTERED AND BROKEN CLOUDS FROM NEBRASKA DOWN
INTO NORTHWESTERN MISSOURI. RADAR RETURNS OVER THE DAKOTAS ARE
GENERATING ENOUGH SNOW FOR VISIBILITY AND SURFACE STATION
OBSERVATION. CLOSER TO IOWA, RADAR ECHOES OVER SOUTHWEST IOWA
AND SOUTHEASTERN NEBRASKA WITH COLLOCATED RECENT MPING REPORTS
ARE EITHER VERY LIGHT SNOW OR MORE LIKELY FLURRIES GIVEN NO
RECENT SURFACE OBSERVATIONS OR OBSERVATIONS ON IOWA DOT
STREAMING WEBCAMS. THE ARRIVAL OF THE CLOUDS AND LIGHT SNOW HAS
SLOWED DOWN A BIT SO HAVE ADJUSTED NEAR TERM FORECAST FOR THIS
DELAY, BUT EVENTUALLY THE UPSTREAM CLOUDS WILL SPILL INTO THE
STATE THROUGH TONIGHT. WITH THE THE STRONG THERMODYNAMIC AND
MODEST KINEMATIC FORCING ASSOCIATED WITH THE SHORTWAVE TROUGH,
LIGHT SNOW WILL DEVELOP. FORECAST SOUNDINGS SHOW THIS AS
SATURATION IN THE MID- LEVELS WORKING ITS WAY DOWN WITH MUCH OF
THIS SATURATION RESIDING JUST BELOW TO WITHIN THE DENDRITIC
GROWTH ZONE (DGZ). THE LIFT IS WEAK TO MODEST AND IS EXPECTED TO
PRODUCE SNOWFALL RATES UNDER A QUARTER OF AN INCH PER HOUR WITH
SNOW TOTALS GENERALLY UNDER AN INCH. HOWEVER, THERE DOES REMAIN
A LESS THAN 20% CHANCE OF 1 INCH OR SLIGHTLY MORE IN A NARROW
CORRIDOR (30ISH MILES WIDE) FROM SOMEWHERE IN NORTHWEST IOWA TO
NEAR IF NOT JUST WEST OF DES MOINES INTO PERHAPS SOUTH CENTRAL
IOWA PER DETERMINISTIC AND LATEST 12Z HREF GUIDANCE. THIS CHANCE
MAY INCREASE IF THE DEPTH OF SATURATION WITHIN THE DGZ IS
DEEPER THAN CURRENTLY SHOWN IN THE FORECAST SOUNDINGS SUCH AS
THE RAP, NAM, AND GFS. WHILE ALL OF THIS SNOW WILL FALL WITHIN
OR LESS THAN 6 HOURS AT ANY GIVEN LOCATION, SLICK SPOTS ON
UNTREATED ROADWAYS MAY BE ENCOUNTERED BY ANY RETURN THANKSGIVING
TRAVELERS AND/OR FOR THOSE HEADING OUT THE DOOR MONDAY MORNING
FOR WORK OR SCHOOL. FLURRIES MAY LINGER FOR A BRIEF BIT ON THE
BACKSIDE AS CLOUDS PERSIST LONGER THAN THE SNOWFALL INTO THE
DAYLIGHT HOURS OF MONDAY MORNING, BUT HAVE NOT ADVERTISED THAT
BEYOND THIS MENTION.
THE WEEK AHEAD WILL FEATURE BELOW NORMAL TEMPERATURES WITH THE
EXCEPTION OF WEDNESDAY. SURFACE HIGH PRESSURE WILL DROP OVER IOWA
MONDAY INTO MONDAY NIGHT. WITH HIGH PRESSURE OVERHEAD MONDAY NIGHT
AND WITH A CLEARING SKY AND FRESH SNOW EVEN AN INCH OR LESS, WE
COULD SEE TEMPERATURES OUTPERFORM AND DROP LOWER THAN CURRENT
FORECAST, WHICH DOES HAVE SOME SINGLE DIGITS ABOVE ZERO OVER WESTERN
AND NORTHERN IOWA. THE HIGH PRESSURE WILL MOVE OFF TO THE SOUTHEAST
ON TUESDAY WITH OUR SURFACE FLOW BECOMING MORE SOUTHWESTERLY. THIS
WILL ALLOW TEMPERATURES TO RISE TUESDAY AND WEDNESDAY WITH HIGHS
PEAKING IN THE MIDDLE 30S TO LOW 40S ON WEDNESDAY. HOWEVER, A
SURFACE COLD FRONT WILL ALREADY BE SLIDING THROUGH IOWA WEDNESDAY
AND WITH GUSTY WINDS DEVELOPING BEHIND THE FRONT, IT WON'T FEEL LIKE
THE MIDDLE 30S OR LOW 40S WITH WIND CHILLS RANGING FROM THE UPPER
TEENS TO LOW 30S. FORECAST SOUNDINGS SHOW DEEP BOUNDARY LAYER MIXING
WITHIN THE COLD AIR ADVECTION, SUBSIDENCE REGIME AND GUSTS OVER 40
MPH COULD OCCUR, PARTICULARLY OVER NORTHERN IOWA LATE MORNING INTO
THE AFTERNOON. A STRONGER SHORTWAVE TROUGH ASSOCIATED WITH THIS COLD
FRONT WILL DROP INTO THE WESTERN GREAT LAKES WITH MUCH OF ITS
PRECIPITATION LOOKING TO REMAIN NORTHEAST OF THE STATE. AS IOWA
FALLS BACK INTO THE NORTHWESTERLY FLOW LATE IN THE WEEK, OTHER
SHORTWAVES MAY PASS NEAR THE STATE, BUT MOISTURE AVAILABILITY
REMAINS IN QUESTION. AT THIS POINT, THE END OF THE WEEK LOOKS TO
HAVE BELOW NORMAL TEMPERATURES WITH NO OBVIOUS LARGE SCALE
PRECIPITATION CHANCES.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1148 AM CST SUN DEC 1 2024
OUTSIDE OF A FEW CLOUDS OVER SOUTH CENTRAL IOWA AT MIDDAY TODAY,
CENTRAL IOWA IS CLOUD FREE, BUT THAT WILL CHANGE AS CLOUDS
INCREASE THIS AFTERNOON INTO TONIGHT WITH MVFR CEILINGS
EXPECTED. LIGHT SNOW IS FORECAST TO DEVELOP WITH A NARROW BAND
ORIENTED NORTH-NORTHWEST TO SOUTH-SOUTHEAST MOVING OVER WESTERN
INTO CENTRAL IOWA. THIS BAND WILL BE LARGELY WEST OF FOD AND
DSM AND GIVEN CURRENT TRENDS, HAVE MOVED PREVAILING IFR
VISIBILITY AT DSM TO PROB30 AND RAISED VISIBILITY AT ALO FROM
PREVIOUS FORECAST. THIS SNOW WILL DEPART WITH PERHAPS SOME
LINGERING FLURRIES AT DAYBREAK MONDAY WITH MVFR CEILINGS
GRADUALLY BREAKING AND LIFTING INTO VFR BY THE END OF THE
PERIOD.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...ANSORGE
AVIATION...ANSORGE
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