878
FXUS63 KDMX 010432
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1032 PM CST SAT NOV 30 2024
...UPDATED FOR THE 06Z AVIATION DISCUSSION...
KEY MESSAGES
- FLURRIES MAY FLY OVER WESTERN INTO PARTS OF CENTRAL IOWA THROUGH
THIS EVENING.
- A 20 TO 30% INCREASE IN LIGHT SNOW AND FLURRY CHANCES FROM PREVIOUS
FORECAST FOR SUNDAY AFTERNOON INTO SUNDAY NIGHT OVER
NORTHWEST INTO CENTRAL IOWA. CHANCES ARE NOW 30 TO 50% IN
THESE AREAS. ACCUMULATIONS UNDER AN INCH CURRENTLY FORECAST.
- BELOW NORMAL TEMPERATURES MUCH OF THE PERIOD.
DISCUSSION
ISSUED AT 150 PM CST SAT NOV 30 2024
THE OVERALL SYNOPTIC PATTERN FEATURES A BROAD TROUGH OVER
EASTERN NORTH AMERICA WITH A RIDGE OVER THE WEST COAST OF THE
SAME CONTINENT. WHILE THIS PATTERN WILL SHIFT A LITTLE THROUGH
THE WEEK, IOWA WILL REMAIN BENEATH LARGELY NORTHWESTERLY FLOW
KEEPING SHORTWAVE TROUGHS PASSING OVERHEAD OR NEARBY WITH
GENERALLY LIMITED MOISTURE FOR ANY SIGNIFICANT QPF. TEMPERATURES
WILL BE BELOW NORMAL WITH THE ONLY DAY THAT MAY BE AROUND OUR
EARLY DECEMBER NORMALS ON WEDNESDAY.
AT PRESENT, THE WINTER FRIENDLY DAY SNOW FOG RGB SHOWS A LARGE AREA
OF STRATUS MOVING IN FROM NORTHEASTERN NEBRASKA AND SOUTH DAKOTA
WITH SURFACE OBSERVATIONS REPORTING LIGHT SNOW OR FLURRIES BENEATH
THESE CLOUDS IN SOME AREAS. FORECAST SOUNDINGS SHOW THAT MUCH OF THE
SATURATION WITHIN THESE STRATUS CLOUDS IS NEAR OR RESIDES WITHIN THE
DENDRITIC GROWTH ZONE (DGZ). THESE SNOWFLAKES ARE OVERCOMING VERY
DRY SUBCLOUD LAYER AIR IN THE LOWEST 2000 TO 3000 FEET WITH RECENT
MPING REPORTS OVER WESTERN IOWA NORTH OF SUX AND NEAR CBF SHOWING
DEWPOINT DEPRESSIONS OF 15F. HAVE MAINTAINED AND SLIGHTLY EXPANDED
THE FLURRY MENTION ABOUT A COUNTY NORTH AND EAST FROM PREVIOUS
FORECAST THROUGH MID-EVENING. THESE CLOUDS WILL DEPART, BUT LATEST
HREF CONTINUES TO ADVERTISE A 20% CHANCE OR LESS THAT LOW STRATUS
WILL ARRIVE FROM THE NORTH TOWARD SUNRISE SUNDAY MORNING. THESE
CLOUDS COULD MAKE IT AS FAR SOUTH AS A GRINNELL TO AMES TO FORT
DODGE LINE. FURTHER, THESE CLOUDS MAY HAVE ENOUGH MOISTURE FOR
FLURRIES GIVEN THEIR MOISTURE RESIDES IN THE DGZ, BUT GIVEN THE
CHANCE OF OCCURRENCE HAVE NOT ADVERTISED THAT IN THE OFFICIAL
FORECAST.
THE BIGGEST CHANGE TO THE FORECAST IS SUNDAY AFTERNOON AND EVENING
WITH THE FORECAST NOW ADVERTISING LIGHT SNOW AND FLURRIES OVER MUCH
OF CENTRAL IOWA. AS THE PREVIOUS DISCUSSION NOTED AND THIS MORNING'S
DETERMINISTIC MODELS SHOWED, THERE REMAINS A LOW QPF EVENT IN THIS
TIME FRAME. THIS LIGHT SNOW EVENT IS DUE TO A STRONGER SHORTWAVE
TROUGH THAT DIVES SOUTHEASTWARD WITH FAVORABLE LARGE SCALE ASCENT
FROM UPPER LEVEL JET STREAKS AND LOW LEVEL QG CONVERGENCE. WHILE IT
IS MODEL DEPENDENT, HRRR RUNS SHOW A VERY DEEP LAYER (8000 FEET) OF
SATURATION WITHIN THE DGZ WITH THE NAM AND GFS NOT QUITE AS DEEP
(5000-6000 FEET). THIS DEPTH OF SATURATION COUPLED WITH WEAK OMEGA
SHOULD RESULT IN SNOW PRODUCTION. THE INITIAL NATIONAL BLEND OF
MODELS HAD LESS THAN 15% CHANCE POPS, BUT GIVEN THE THERMODYNAMIC
AND KINEMATIC FIELDS AT PLAY, FEEL CONFIDENT IN THE INCREASE IN
POPS. WHILE QPF WILL ONLY BE A FEW HUNDREDTHS AND RESULTING SNOWFALL
IS FORECAST TO BE UNDER AN INCH, ANY UNTREATED ROADWAYS MAY RESULT
IN SLICK ROADS, PARTICULARLY AS HOLIDAY TRAVEL WINDS DOWN AND WORK
WEEK TRAFFIC PICKS UP MONDAY MORNING.
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE UPCOMING WEEK
EXCEPT FOR WEDNESDAY. AS HIGH PRESSURE SLIDES INTO THE TENNESSEE
RIVER VALLEY, OUR SURFACE FLOW BECOMES MORE SOUTHWESTERLY AND OUR
UPPER LEVEL NORTHWESTERLY FLOW BECOMES A BIT MORE WESTERLY. THIS
WILL ALLOW FOR TEMPERATURES TO PEAK IN THE UPPER 30S TO LOW TO
MIDDLE 40S ON WEDNESDAY - THE WARMEST OF THE WEEK! HOWEVER, MORE
COLD AIR ARRIVES LATE THIS WEEK BEHIND A COLD FRONT. LARGE SCALE
PRECIPITATION CHANCES ARE MUTED BELOW 20% THROUGH THE END OF THE
WEEK IN THE CLUSTER ANALYSIS AND OUR OFFICIAL FORECAST SHOWS A DRY
FORECAST AS WELL.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1032 PM CST SAT NOV 30 2024
MID-LEVEL CLOUD COVER REMAINS ACROSS SOUTHERN IOWA, THOUGH
ANOTHER BAND IS ENTERING NORTHERN IOWA AND WILL CONTINUE TO PASS
SOUTHEAST THROUGH THE STATE INTO SUNDAY MORNING, IMPACTING ALL
SITES BUT REMAINING VFR. LIFTING CEILINGS ARE EXPECTED TO FOLLOW
MID TO LATE MORNING AND REMAIN THROUGH THE AFTERNOON, BEFORE A
SYSTEM ARRIVING AROUND 00Z WILL BRING THE CHANCE FOR LIGHT SNOW.
OVERALL CONFIDENCE IS LOW ON EXACT TIMING AND LOCATION, THOUGH
BEST CHANCES SUNDAY AFTERNOON ARE EXPECTED OVER KFOD AND KDSM,
SO HAVE INCLUDED AT LEAST PROB30 MENTIONS AT THIS TIME. LOW
STRATUS WITH THIS SYSTEM IS EXPECTED TO RESULT IN MVFR CEILINGS
TO SPREAD ACROSS MUCH OF WESTERN IOWA AFTER 00Z AS WELL. WINDS
REMAIN LIGHT OUT OF THE NORTHWEST THROUGHOUT THE PERIOD.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...ANSORGE
AVIATION...BURY
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