783
FXUS63 KDMX 030931
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
331 AM CST MON MAR 3 2025
KEY MESSAGES
- STRONG STORM SYSTEM SET TO AFFECT THE REGION FROM TUESDAY INTO
WEDNESDAY. RAIN AND THUNDERSTORMS INITIALLY, WITH SMALL HAIL
POSSIBLE IN A FEW STORMS. THEREAFTER, VERY STRONG WINDS AND A
TRANSITION TO SNOW FROM TUESDAY NIGHT INTO WEDNESDAY, WITH
BLOWING SNOW AND SLICK TRAVEL CONDITIONS EXPECTED AND BLIZZARD
CONDITIONS POSSIBLE AT TIMES.
- A WINTER STORM WATCH FOR POTENTIAL BLIZZARD CONDITIONS HAS
BEEN ISSUED FOR MUCH FOR MUCH OF THE AREA.
- MORE CHANCES FOR MIXED PRECIPITATION OR SNOW THURSDAY NIGHT
AND FRIDAY, BUT CONFIDENCE IN DETAILS IS LOW.
DISCUSSION
ISSUED AT 331 AM CST MON MAR 3 2025
AS EXPECTED, MID-LEVEL CLOUDS AND A FEW RADAR RETURNS HAVE
BLOSSOMED OVERNIGHT IN THE FIRST WAVE OF WARM AIR ADVECTION
ALOFT, BUT SO FAR ECHOES HAVE BEEN CONFINED TO OUR NORTHEAST AND
PRECIPITATION HAS BEEN TOO LIGHT TO REACH THE GROUND. A FEW
SPRINKLES WILL REMAIN POSSIBLE IN OUR NORTHEASTERN AND EASTERN
COUNTIES EARLY THIS MORNING BEFORE MOVING OFF TO THE EAST, BUT
WILL HAVE NO IMPACT. MEANWHILE, UPSTREAM SATELLITE IMAGERY AND
FORECAST SOUNDINGS DO INDICATE THE POTENTIAL FOR A FEW HOURS OF
RELATIVE CLEARING TODAY BEFORE CLOUDS MOVE BACK IN THIS
AFTERNOON/EVENING, AND HAVE NUDGED HIGH TEMPERATURES UP JUST A
BIT IN ACCORDANCE WITH THE STEADILY INCREASING SOUTHERLY LOW-
LEVEL FLOW. A SECOND WAVE OF THETA-E ADVECTION ALOFT WILL THEN
GENERATE ADDITIONAL CLOUDS AND SHOWERS FROM THIS EVENING INTO
TONIGHT AND HAVE REFINED TIMING OF POPS TO ESTIMATE ITS
PROGRESSION ACROSS THE AREA.
ALL EYES ARE FIXED UPON THE LARGE WINTER STORM SYSTEM SET TO
IMPACT THE REGION FROM TUESDAY INTO WEDNESDAY. THE OVERALL
SCENARIO HAS NOT CHANGED TONIGHT, HOWEVER CONFIDENCE IN SOME
ASPECTS OF TIMING AND IMPACTS HAS INCREASED. VERY STRONG WINDS
REMAIN LIKELY, WITH GUSTS NEAR OR EXCEEDING 50 MPH AT TIMES LATE
TUESDAY NIGHT THROUGH WEDNESDAY MORNING. WIDESPREAD
PRECIPITATION IS ALSO A CERTAINTY, WITH SIGNIFICANT
ACCUMULATIONS AS QPF IS PEGGED AT 1.5-2.0" ACROSS MOST OF OUR
FORECAST AREA, EXCEPTING THE NORTHWEST WHERE IT IS CLOSER TO AN
INCH. MOST OF THE FORECAST CHALLENGES AND POTENTIAL IMPACTS STEM
FROM THE PRECIPITATION TRANSITION FROM RAIN TO SNOW AS
NORTHWEST WINDS AND COLDER AIR SURGE IN TUESDAY NIGHT, AND THE
RESULTING SNOWFALL ACCUMULATIONS, BLOWING SNOW/VISIBILITY
REDUCTIONS, AND ASSOCIATED TRAVEL IMPACTS.
INITIALLY, DURING THE DAY TUESDAY, RAIN/SHOWERS WILL SPREAD
NORTHWARD ACROSS IOWA WITH MODEST ELEVATED INSTABILITY RESULTING
IN A FEW THUNDERSTORMS MAINLY OVER THE SOUTHERN HALF OR SO OF
THE STATE. INITIALLY DECENT MID-LEVEL LAPSE RATES MAY SUPPORT A
BRIEF OPPORTUNITY FOR SOME HAIL, BUT THIS WILL DIMINISH AS THE
COLUMN SATURATES AND THE OVERALL SEVERE WEATHER THREAT REMAINS
LOW. THE HIGH QPF IS SUPPORTED BY ANOMALOUSLY HIGH PWAT VALUES
IN EXCESS OF THE 95TH PERCENTILE FOR THE DATE AS MOISTURE
STREAMS NORTHWARD FROM THE GULF IN ADVANCE OF THE APPROACHING
CYCLONE. THIS WILL MAKE FOR A SOGGY AND DREARY DAY TUESDAY WITH
OCCASIONAL RUMBLES OF THUNDER. BY AROUND SUNSET THE DEEPENING
LOW PRESSURE CENTER WILL BE LOCATED OVER NORTHWEST MISSOURI AND
A VERY TIGHT PRESSURE GRADIENT WILL STRETCH AROUND ITS
NORTHWESTERN FLANK AND NORTHWARD INTO MINNESOTA CONCURRENT WITH
THE ZONE OF STRONGEST WINDS. A LARGE SWATH OF FRONTOGENETICAL
FORCING COINCIDENT WITH A WARM CONVEYOR BELT WILL WRAP INTO THE
CYCLONE FROM THE SOUTHEAST AND AROUND TO ITS NORTHWESTERN AND
WESTERN SIDE, GENERATING RELATIVELY HEAVIER PRECIPITATION THAT
WILL MOVE SLOWLY ACROSS OUR AREA TUESDAY NIGHT AND THEN PUSH OFF
TO THE EAST WITH THE CYCLONE ON WEDNESDAY. RESULTING SNOWFALL
AMOUNTS REMAIN QUITE UNCERTAIN DUE TO THEIR RELIANCE ON THE
PRECISE TIMING OF THE RAIN/SNOW (FREEZING) LINE PROGRESSION AND
HOW THAT WILL BE OVERLAID WITH OR SLIGHTLY SEPARATED FROM THE
ZONE OF HEAVIEST PRECIPITATION AT ANY GIVEN TIME, AS WELL AS THE
DEGREE OF MELTING/COMPACTION WITHIN THIS ZONE GIVEN THE
TEMPERATURES NEAR FREEZING. AS COLDER AIR FLOWS IN SLR'S WILL
INCREASE, BUT THIS SHOULD MAINLY OCCUR BEHIND THE ZONE OF
HEAVIER PRECIPITATION/QPF AND LIMIT ACCUMULATIONS SOMEWHAT.
HOWEVER, IF THE PHASING OF THIS TIMING CHANGES SUCH THAT THE
RESIDENCE TIME OF THE BAND OF STRONGER FORCING IS FURTHER BACK
INTO THE COLDER AIR AND THUS MORE INTO THE ACCUMULATING SNOW
REALM, THEN AMOUNTS COULD CERTAINLY OVERACHIEVE.
REGARDLESS OF HOW MUCH SNOW FALLS, VERY STRONG WINDS ARE
FORECAST FROM TUESDAY NIGHT INTO WEDNESDAY AS THE AFOREMENTIONED
TIGHT PRESSURE GRADIENT MOVES THROUGH IOWA WITH NAM AND GFS
SOUNDINGS INDICATING POTENTIAL FOR WIND GUSTS OF 50-55 KT. WHILE
HEAVIER SNOW IS FALLING, EVEN IF IT DOES NOT ACCUMULATE HEAVILY,
THE STRONG WINDS SHOULD BLOW THE FALLING SNOW SUFFICIENTLY TO
LOWER VISIBILITY SIGNIFICANTLY, WITH WHITEOUT CONDITIONS EVEN
POSSIBLE FOR A PERIOD, AND THIS COULD COINCIDE WITH THE
WEDNESDAY MORNING COMMUTE ACROSS PARTS OF CENTRAL IOWA. ALSO,
EVEN IF SNOW AMOUNTS DO REMAIN LIGHT THE SNOW CHARACTER, AT
LEAST, INITIALLY, SHOULD BE WET AND STICKY AND LEAD TO SLICK
DRIVING CONDITIONS THAT WILL BE EXACERBATED BY THE LOW
VISIBILITY AND STRONG WINDS. GIVEN THE LIKELIHOOD OF
SIGNIFICANT TRAVEL/BLOWING SNOW IMPACTS HAVE OPTED TO HOIST A
WINTER STORM WATCH FOR POSSIBLE BLIZZARD CONDITIONS, RATHER THAN
A HIGH WIND WATCH, TO HIGHLIGHT THE GREATER THREAT. ADJUSTMENTS
TO THIS WATCH IN LATER UPDATES MAY INCLUDE TRANSITIONS TO
BLIZZARD WARNING, OR HIGH WIND WARNING, OR WINTER WEATHER
ADVISORY, OR SOME COMBINATION AT VARIOUS LOCATIONS/TIMES IN OUR
SERVICE AREA. PLEASE MONITOR FORECAST UPDATES CLOSELY OVER THE
NEXT COUPLE OF DAYS.
AS LINGERING SNOW CLEARS OUT EASTWARD ON WEDNESDAY CONDITIONS
SHOULD STEADILY IMPROVE, AFTER WHICH WEDNESDAY NIGHT AND
THURSDAY WILL BE QUIET AS RIDGING MOVES QUICKLY THROUGH THE
REGION. ANOTHER STORM SYSTEM WILL THEN AFFECT US LATER IN THE
WEEK, WITH A SURFACE LOW PRESSURE SYSTEM TRACKING ACROSS KANSAS
ON THURSDAY NIGHT AND MISSOURI ON FRIDAY. A SWATH OF
PRECIPITATION WILL SPREAD NORTH OF THE LOW ACROSS IOWA DURING
THIS TIME BUT WINDS AND QPF ARE NOT AS HIGH AS WITH THE
TUESDAY/WEDNESDAY SYSTEM AS THE LOW IS NOT AS STRONG AND NOT AS
MUCH MOISTURE IS AVAILABLE. NEVERTHELESS, TEMPERATURES THURSDAY
NIGHT/FRIDAY MORNING MAY BE NEAR FREEZING SO WINTERY
PRECIPITATION AND IMPACTS MAY BE POSSIBLE, BUT CONFIDENCE IN
THOSE DETAILS IS LOW AT THIS RANGE.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 1141 PM CST SUN MAR 2 2025
VFR CONDITIONS ARE IN PLACE AT 06Z WITH VARIED MID AND HIGH
LEVEL CLOUDINESS, ALTHOUGH LLWS IS IN PROGRESS OVER CENTRAL AND
WESTERN SECTIONS AND AFFECTING KFOD AND KDSM EARLY THIS
MORNING. SOME STRATUS MAY DEVELOP INTO THE DAY MONDAY, BUT
EXPECTATIONS ARE TO REMAIN VFR THROUGH THE AFTERNOON WITH SOME
SOUTHERLY WIND GUSTS +/- 25 KTS. THE GUSTS SHOULD DIMINISH BY
EVENING, BUT THE POTENTIAL FOR MVFR STRATUS INCREASES WEST TO
EAST AS WELL.
DMX WATCHES/WARNINGS/ADVISORIES
WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
AFTERNOON FOR IAZ004>007-015>017-023>028-033>039-044>049-
057>060-070>073-081>083-092>094.
DISCUSSION...LEE
AVIATION...SMALL
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