985
FXUS63 KDMX 011958
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
158 PM CST SAT MAR 1 2025
KEY MESSAGES
- WARMER SUNDAY INTO MONDAY.
- SHOWERS AND STORMS MONDAY NIGHT INTO TUESDAY WITH
PRECIPITATION CHANCES > 80% AREA WIDE TUESDAY AFTERNOON.
- RAIN SWITCHING TO SNOW TUESDAY NIGHT INTO WEDNESDAY. STRONG
WINDS DEVELOPING DURING THIS TIME FRAME. WIND GUSTS OVER 50
MPH MAY OCCUR.
DISCUSSION
ISSUED AT 153 PM CST SAT MAR 1 2025
PRONOUNCED NORTHWEST FLOW IS STREAMING FROM CENTRAL CANADA
(MANITOBA/SASKATCHEWAN) AND INTO IOWA TODAY. THIS HAS RESULTED IN
MUCH COLDER CONDITIONS TODAY WITH TEMPERATURES IN THE 20S TO LOW 30S
EARLY THIS AFTERNOON. DEW POINTS ARE MUCH LOWER AND NEAR ZERO NORTH
TO AROUND 10 ABOVE SOUTH AS HIGH PRESSURE IS SETTLING SOUTH FROM THE
EASTERN DAKOTAS AND MINNESOTA. A REVIEW OF THE NORTH AMERICAN SCALE
500 MB MAP THIS AFTERNOON SHOWS ALL THE PLAYERS FOR THIS WEEK'S
WEATHER ARE NOW ON THE BOARD. A RIDGE OF HIGH PRESSURE ENCOMPASSES
MUCH OF THE WESTERN CONUS. A POTENT CLOSED LOW PRESSURE SYSTEM IS
MOVING INTO SOUTHWEST ARIZONA AND LAST BUT CERTAINLY NOT LEAST IS A
VERY STRONG SYSTEM APPROACHING THE PACIFIC NORTHWEST. A BIT OF A
SPOILER ALERT BUT THAT SYSTEM APPROACHING THE PACIFIC NORTHWEST MAY
BRING SIGNIFICANT IMPACTS TO IOWA, TUESDAY INTO WEDNESDAY.
OVER THE NEXT 24 HOURS, THE HIGH PRESSURE RIDGE AND THE SOUTHWEST
ARIZONA UPPER LOW WILL MOVE EAST WITH THE UPPER LOW REACHING THE
TEXAS PANHANDLE TOMORROW AFTERNOON. THE PACIFIC NORTHWEST UPPER LOW
WILL BEGIN TO DIG SOUTHEAST INTO CALIFORNIA BEHIND THE UPPER RIDGE.
FROM SUNDAY AFTERNOON INTO MONDAY AFTERNOON, THE UPPER RIDGE WILL BE
FURTHER WEST AND OVER IOWA. THE SOUTHERN SYSTEM WILL HAVE SHEARED
OUT WITH ANY REMNANT SHORTWAVE ENERGY MOVING QUICKLY TO THE EAST AND
THE WESTERN SYSTEM WILL BE MOVING EAST INTO THE INTER-MOUNTAIN WEST
WITH SURFACE CYCLOGENESIS COMMENCING OVER SOUTHEAST COLORADO.
PUTTING THIS TOGETHER OVER THE NEXT TWO DAYS WILL RESULT IN SEVERAL
ROUNDS OF THETA-E ADVECTION ALOFT ACROSS IOWA AS THE SURFACE HIGH
DEPARTS TO THE EAST AND THE UPPER RIDGE APPROACHES FROM THE WEST.
SURFACE WARM ADVECTION WILL ALSO BE ONGOING SO EXPECT SUNDAY TO BE
WARMER THOUGH DID BACK OFF HIGH TEMPERATURES A DEGREE OR TOO. MID-
LEVEL CLOUD COVER MAY INCREASE LATE SUNDAY AND SUNDAY NIGHT. DID
SLOW THE ARRIVAL OF HIGHER DEW POINTS SUNDAY NIGHT INTO EARLY
TUESDAY AND THIS WILL HAVE SOME IMPACT TO OVERNIGHT LOW TEMPERATURES
FOR THEN, PENDING CLOUD COVER TIMING. THE NBM HIGH TEMPERATURES FOR
MONDAY SEEM AGGRESSIVE IN THE MID 50S TO LOW 60S, AGAIN DUE TO
POTENTIAL CLOUD COVER AND IF THE STRATUS BIASED NAM IS PARTIALLY
CORRECT, THIS MAY BE MUCH TOO WARM. NOTE THE SLOWER DEW POINT
ARRIVAL ABOVE AND CLOUDY SKIES SHUTS DOWN WARMING OUTSIDE THAT DEW
POINT PUSH THIS TIME OF YEAR.
THE REMAINDER OF THE DISCUSSION WILL BE FOCUSED ON THE MAIN STORM
SYSTEM AND ITS IMPACTS ON IOWA. STRONGER THETA-E ADVECTION WILL
INCREASE AGAIN MONDAY NIGHT AS THE UPPER AND SURFACE LOWS MOVE EAST
INTO KANSAS. A 50+ KT LOW LEVEL JET IS EXPECTED TO DEVELOP OVER
EASTERN KANSAS AND INTO MISSOURI AND THIS WILL LEAD TO STRONG GULF
MOISTURE TRANSPORT TOWARDS IOWA. CONVECTIVE INSTABILITY SHOULD
DEVELOP OVER IOWA, ESPECIALLY AFTER 06Z TUESDAY WITH MUCAPES OF
500+ J/KG AND MID-LEVEL LAPSE RATES APPROACHING 8C/KM. THERE IS
SOME UNCERTAINTY IF THE MID-LEVEL DRY AIR WILL SATURATE ENOUGH
FOR THIS CONVECTIVE INSTABILITY TO BE REALIZED BUT GIVEN THE
SET UP, FAVOR A MORE MOIST SOLUTION MEANING CONVECTIVE
DEVELOPMENT. SHOULD STORMS DEVELOP, TIS THE SEASON FOR GRAUPEL
AND SMALL HAIL. MORE CONFIDENCE IN THE MID-LEVEL SATURATION ON
TUESDAY AND EXPECT WIDESPREAD SHOWERS AND STORMS. ONE THING TO
MONITOR FOR TUESDAY IS THE SURFACE LOW WILL BE LIFTING INTO
NORTHERN MISSOURI AND INTO FAR SOUTH CENTRAL/SOUTHEAST IOWA LATE
TUESDAY AFTERNOON AND EVENING AND THE SURFACE INSTABILITY WILL
BE CLOSE TO THE IA/MO BORDER. AT THIS TIME, THERE SHOULD BE TOO
MUCH CLOUD DEBRIS FOR MUCH SURFACE INSTABILITY BUT SOMETHING TO
MONITOR IS ANYTHING CHANGES. THAT SAID, THE LOW LEVEL WIND
FIELDS ARE SEASONABLY WEAK AND NOT IMPRESSIVE AT ALL.
THE MAIN IMPACTS OF THIS STORM ARRIVE TUESDAY NIGHT INTO WEDNESDAY
AND THESE IMPACTS COULD BE SIGNIFICANT. THE SURFACE LOW WILL LIFT
NORTHEAST INTO WILL MOVE NORTHEAST INTO THE NORTHERN IL/SOUTHERN WI
VICINITY BY WEDNESDAY MORNING. A WELL DEFINED DEFORMATION ZONE WILL
DEVELOP TO THE WEST/SOUTHWEST OF SURFACE LOW PRESSURE. THAT
DEFORMATION ZONE WILL BE FUELED BY A PRONOUNCED WARM CONVEYOR BELT
AND ASSOCIATED TROWAL DEVELOPMENT AROUND THE 310K THETA SURFACE.
THIS WILL BE ONGOING AS COLDER AIR ARRIVES BEHIND THE LOW PRESSURE
SO A TRANSITION TO RAIN TO SNOW WILL LIKELY OCCUR. THE RESIDENCE
TIME OF THE SNOW IS STILL NOT WELL DEFINED AND MAKES ANY ESTIMATES
DIFFICULT AT THIS POINT. THE FINAL PUNCH WITH THIS STORM SYSTEM IS
THE STRONG WINDS THAT ARE EXPECTED TO DEVELOP. THE NBM BLENDS ARE
DAMPENING THE PEAK WIND POTENTIAL SO WILL USE THE 12Z GFS/ECMWF TO
OFFER SOME ANALYSIS. BOTH HAVE AN INCREASING SURFACE PRESSURE
GRADIENT OF 50-60 UBARS/KM, WHICH IS QUITE HIGH. BOTH HAVE STRONG
PRESSURE RISES OF 10 MB/6HR OR STRONGER. BOTH HAVE 925 MB WINDS OF
45 TO 50 KTS AND 850 MB WIND OF 50 TO 60 KTS. DIFFERENTIAL COLD
ADVECTION SHOULD RESULT IN MIXING SOMEWHERE BETWEEN 925-850 MB. NOTE
IT IS NOT STRONG COLD ADVECTION WITHIN THIS LAYER SO IT COULD
DIMINISH THE MIXING EFFICIENCY TO A DEGREE BUT AT THIS POINT, A HIGH
WIND EVENT LOOKS PLAUSIBLY AND WELL WITHIN THE REALM OF
POSSIBILITY. DID WE MENTION THERE MIGHT BE SNOW WITH THIS?
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1109 AM CST SAT MAR 1 2025
VFR CONDITIONS REMAIN IN THE FORECAST THROUGH THE PERIOD. THE
WIND WILL CONTINUE TO DIMINISH THROUGH THE AFTERNOON THEN BECOME
LIGHT AND VARIABLE AT TIMES TONIGHT. THE WIND WILL BECOME
SOUTH/SOUTHEAST BY MID SUNDAY MORNING. SCT CUMULUS WITH BASES
AROUND 3 KFT OVER SOUTHEAST IOWA IS ERODING AND NOT EXPECTED TO
IMPACT KOTM. OTHERWISE MID TO HIGH LEVEL CLOUDS THROUGH TONIGHT.
A FEW CLOUDS WITH BASES AROUND 5 KFT ARE POSSIBLE BY SUNDAY
MORNING.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...DONAVON
AVIATION...DONAVON
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