767
FXUS63 KDMX 022037
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
237 PM CST SUN MAR 2 2025
KEY MESSAGES
- HIGH IMPACT AND SIGNIFICANT STORM SYSTEM EXPECTED WITH MAIN
STORM IMPACTS TUESDAY NIGHT AND WEDNESDAY. MONITORING FOR HIGH
WIND AND POTENTIALLY BLIZZARD CONDITIONS DURING THIS PERIOD.
- SHOWERS AND STORMS LIKELY MONDAY NIGHT INTO TUESDAY EVENING.
SMALL HAIL MAY OCCUR WITH THE STRONGER STORMS.
- ANOTHER CHANCE FOR SNOW ON FRIDAY.
DISCUSSION
ISSUED AT 235 PM CST SUN MAR 2 2025
A STRONG STORM SYSTEM IS STILL ON TARGET TO IMPACT MUCH OF IOWA
EARLY TO MID WEEK WITH THE GREATEST IMPACTS OCCURRING TUESDAY NIGHT
AND WEDNESDAY. AHEAD OF THE SYSTEM, WARM ADVECTION IS ONGOING OVER
IOWA WITH TEMPERATURES CLIMBING INTO THE UPPER 30S TO UPPER 40S. THE
MOISTURE ADVECTION IS LAGGING THOUGH WITH DEW POINT VALUES IN THE
SINGLE DIGITS AND TEENS. NEED TO GO TO SOUTHWEST KANSAS AND OKLAHOMA
TO FIND DEW POINT VALUES IN THE 30S. SURFACE CYCLOGENESIS IS ONGOING
OVER EASTERN COLORADO THIS AFTERNOON AHEAD OF THE POWERFUL UPPER
LEVEL LOW PRESSURE/PV ANOMALY CLUSTER THAT IS NOW OVER NORTHERN
CALIFORNIA AND NEVADA.
A COUPLE STRONG SURGES OF THETA-E ADVECTION WILL BE LIFTING INTO
IOWA TONIGHT INTO MONDAY MORNING AS THE WESTERN LOW LEVEL JET TURNS
MORE INTO THE STATE. A FEW LIGHT SHOWERS MAY DEVELOP FROM CENTRAL TO
NORTHEAST IOWA AS THIS OCCURS. THE REMAINDER OF MONDAY IS EXPECTED
TO BE MILD WITH HIGH TEMPERATURES IN THE 50S TO LOW 60S ASSUMING AT
LEAST SOME AFTERNOON SUNSHINE. THERE IS A CHANCE CLOUDS COULD
PREVAIL WHICH WOULD RESULT IN LOWER TEMPERATURES. A STRONGER LOW
LEVEL JET OF 55-60 KTS DEVELOPS MONDAY NIGHT INTO TUESDAY MORNING
AND THIS WILL BRING A MUCH STRONGER AND DEEPER SURGE OF MOISTURE
INTO THE STATE AS EVIDENCED BY 1 INCH PWATS REACHING CENTRAL IA.
EXPECT THUNDERSTORMS TO BE EMBEDDED WITHIN THE SHOWERS AND THERE
WILL BE A PERIOD WHERE THE MID-LEVEL LAPSE RATES AND MUCAPE BECOME
FAVORABLE FOR A FEW MODERATE UPDRAFTS THAT WOULD BE
CAPABLE/SUPPORTIVE OF SMALL HAIL, PERHAPS APPROACHING 0.75-1 IN.
NOTE THAT AS OF NOW, SURFACE BASED INSTABILITY MAY STILL REACH FAR
SOUTH CENTRAL AND INTO SOUTHEAST IOWA TUESDAY AFTERNOON AND EVENING
THOUGH PROJECTED LOW LEVEL SHEAR PROFILES REMAIN LESS THAN STELLAR.
AS THE SURFACE LOW LIFTS FROM NORTHERN MISSOURI INTO SOUTHEAST IOWA
TUESDAY NIGHT, THE PRECIPITATION WILL TRANSITION TO DEFORMATION
PRECIPITATION. SHOULD POINT OUT THAT LARGE CLOSED UPPER LEVEL
SYSTEMS TEND TO ARRIVE A BIT SLOWER THAN CURRENTLY PROGGED BY MODEL
GUIDANCE SO KEEP THAT IN MIND WITH THE DISCUSSION TO FOLLOW. THE
OVERALL TRACK OF THE SURFACE LOW IS A BIT MORE SOUTH WHICH WOULD
RESULT IN A LONGER RESIDENCE TIME OF ANY DEFORMATION. THAT IS
SUPPORTED BY THE DEVELOPMENT OF A WELL DEFINED TROWAL FUELED BY THE
WARM CONVEYOR MOISTURE BELT. THE TROWAL SLOWLY SHIFTS EAST WEDNESDAY
MORNING WITH PRECIPITATION DIMINISHING. THE KEY FACTOR DURING
THIS PERIOD IS TIMING OF THE TRANSITION FROM RAIN TO SNOW AS
COLDER AIR ARRIVES BEHIND THE SYSTEM AND HOW LONG OF RESIDENCE
TIME OF FALLING SNOW OCCUR. THE KEY WITH THE RAIN TO SNOW
TRANSITION IS GOING TO BE THE NEAR SURFACE WET BULB TEMPERATURES
AS COOLING WILL ALREADY BE GOING ON ALOFT FOR SNOW DEVELOPMENT.
THE NEAR SURFACE WARM LAYER WILL BE THE LAST MELTING LAYER TO
OVERCOME. THE BEST PROJECTION NOW IS A TRANSITION BETWEEN 00-06Z
OVER THE NORTHWEST THIRD OF IOWA AND BETWEEN 06-12Z FOR THE
REMAINDER OF THE FORECAST AREA OUTSIDE OF THE FAR
EAST/SOUTHEAST. THE SNOW MAY BEGIN AS WET AGGREGATE TYPE SNOW
BUT THE SNOWFLAKE MORPHOLOGY WILL CHANGE RELATIVELY QUICK INTO A
LESS WET AND MORE MOBILE TYPE SNOW. THAT WILL BE IMPORTANT WHEN
DISCUSSING THE BLOWING SNOW POTENTIAL BELOW. OVERALL, THE 50
PERCENT OR HIGHER PROBABILITY OF 2 INCHES OR MORE OF SNOW FROM
ROUGHLY DES MOINES AND NORTHWARD LOOKS REALISTIC AT THIS POINT.
THE WIND WITH THIS STORM SYSTEM IS A HIGH CONFIDENCE FORECAST
ESPECIALLY WHEN CONSIDERING THE POTENTIAL OF 50+ MPH WIND GUSTS. MIX
LAYER WINDS OF 50-55 KTS ARE COMMON AREA WIDE THOUGH THE COLD
ADVECTION IS NOT STRONG SO IT WILL LIMIT THE MIXING EFFICIENCY SOME.
THE BIG BOOST TO THESE WINDS REMAINS ON THE ISALLOBARIC SIDE OF
THINGS AS THE PRESSURE GRADIENT INCREASES TO AN IMPRESSIVE 55-65
UBARS/KM AND 10-13 MB/6 HR PRESSURE RISE EXPECTED. THOSE NUMBERS
HAVE INCREASED THE PAST 24 HRS. THIS SHOULD ALL SUPPORT 50-60 MPH
WIND GUSTS LATE TUESDAY NIGHT AND WEDNESDAY MORNING BEFORE GRADUALLY
DECREASING IN THE AFTERNOON. THE NUMBER ONE QUESTION OF THE DAY,
WITHOUT ANY PRE-EXISTING SNOW COVER, HOW MUCH SNOW WILL IT TAKE FOR
HIGH IMPACT BLOWING SNOW TO OCCUR? THE DEFINITION OF A BLIZZARD IS 3
HOURS OF WHITEOUT CONDITIONS. AT THIS POINT, FOCUSING ON THE HIGH
IMPACTS OF POTENTIAL WHITEOUT CONDITIONS FOR A SHORTER DURATION, SAY
1-3 HOURS. IN GENERAL AND WITH THE EXPECTED EVOLUTION OF THE SNOW
MICROPHYSICS AND MORPHOLOGY DISCUSSED ABOVE, 2 INCHES OF SNOWFALL IS
A GOOD START WHEN CONSIDERING POTENTIAL BLIZZARD VS HIGH WIND
HEADLINES. IT IS POSSIBLE TO HAVE A BUFFER BETWEEN THE TWO AND HAVE
A HIGH WIND WARNING WITH A WINTER WEATHER ADVISORY BUT THAT REGION
WITH LESS THAN 2 INCHES OF SNOW COULD HAVE SIGNIFICANT IMPACTS ALSO.
DUE TO SOME UNCERTAINTY IN THE SNOW AMOUNTS, THERE ARE NO HEADLINES
ON THIS SHIFT BUT IT WILL BE A MUCH BIGGER CONSIDERATION TONIGHT.
NOT MUCH FOCUS THIS SHIFT BEYOND WEDNESDAY BUT THERE COULD BE
ANOTHER ROUND OF ACCUMULATING SNOW AROUND FRIDAY BUT AT THIS
POINT, THE HIGH IMPACT STORM WILL REMAIN THE FOCUS.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1143 AM CST SUN MAR 2 2025
VFR CONDITIONS ARE EXPECTED THOUGH THIS EVENING. SOUTHEAST WINDS
MAY REACH 12KTS AT TIMES THIS AFTERNOON BEFORE DIMINISHING A BIT
TONIGHT. CLOUDS WILL INCREASE OVERNIGHT AND THERE MAY BE A FEW
PERIODS OF MVFR CIGS OVER NORTHERN IOWA. A FEW SHOWERS MAY
DEVELOP OVERNIGHT INTO MONDAY MORNING ALSO BUT CONFIDENCE
REMAINS LOW ENOUGH TO NOT INCLUDE IN THIS FORECAST.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...DONAVON
AVIATION...DONAVON
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