033
FXUS63 KDMX 011134
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
534 AM CST SUN DEC 1 2024
...UPDATED FOR THE 12Z AVIATION DISCUSSION...
KEY MESSAGES
- LIGHT SNOW ARRIVING THIS AFTERNOON AND TONIGHT WITH CHANCES
>60% OVER THE SOUTHWEST HALF. ACCUMULATIONS TO ONE INCH ARE
POSSIBLE WITH THE POTENTIAL FOR HIGHER IN THAT SOUTHWEST AREA.
- THE MONDAY MORNING COMMUTE MAY BE IMPACTED BY THE SNOW.
- GUSTY TO POTENTIALLY STRONG WINDS WEDNESDAY.
DISCUSSION
ISSUED AT 405 AM CST SUN DEC 1 2024
WELCOME TO METEOROLOGICAL WINTER! WHAT BETTER WAY TO START
METEOROLOGICAL WINTER THAN TO HAVE SOME WINTER WEATHER? FOR THOSE OF
YOU THAT DO NOT LIKE THE FIRST TWO SENTENCES, THE THREE MONTH TIMER
HAS OFFICIALLY STARTED FOR METEOROLOGICAL SPRING.
WE BEGIN DECEMBER WITH COLD HIGH PRESSURE STILL RIDGED ACROSS THE
STATE. DESPITE THE VERY LOW SURFACE DEW POINTS WHICH ARE IN THE
SINGLE DIGITS TO TO LOW TEENS, THIS IS CONSIDERED A "DIRTY" HIGH
WITH A FAIR AMOUNT OF STRATUS CLOUDS THROUGH THE REGION. A QUICK
FACT CHECK, HEY THOSE DEW POINTS ARE ACTUALLY SLIGHTLY HIGHER THAN
24 HRS AGO, SO THERE YOU GO. THE STRATUS OVER THE REGION HAS CLOUD
BASES NEAR 2500 FT OVER THE SOUTH TO 3500-5000 FT NORTH. IT IS
ACTUALLY THE HIGHER BASED STRATUS ACROSS THE NORTH THAT A FEW
FLURRIES HAVE BEEN OCCURRING AS A WEAK SHORT WAVE PASSES ACROSS THE
STATE.
A MORE SIGNIFICANT SHORT WAVE IS UPSTREAM OVER ALBERTA CURRENTLY.
THAT SYSTEM IS WHAT WE HAVE BEEN MONITORING FOR POTENTIAL LIGHT SNOW
LATER TODAY AND TONIGHT. MENTIONED LAST NIGHT THAT THIS SYSTEM MAY
END UP BEING A HIGH POP/LOW QPF TYPE EVENT AND THAT SNOW CHANCES MAY
NEED TO BE GREATLY INCREASED. THE SATURDAY DAY SHIFT BEGAN THAT
INCREASE AND WILL BE DOING ANOTHER BIG INCREASE THIS MORNING AS THIS
SYSTEM WILL BE ARRIVING WITH A BIT MORE FORCING THAN PREVIOUSLY
PROGGED WHILE HAVING AMPLE MOISTURE. THE MAJORITY OF THIS FORCING
WILL BE OCCURRING WITHIN A RATHER DEEP DENDRITIC GROWTH ZONE (DGZ)
AND THIS DGZ WILL COMPRISE THE BULK OF THE CLOUD LAYER DEPTH. WHAT
THIS MEANS IN SNOW MICROPHYSICS LAND IS THE POTENTIAL FOR DENDRITES
IS HIGH AND SNOW ACCUMULATIONS OF ONE HALF TO ONE INCH WILL BE
COMMON BY MONDAY MORNING. THE HIGHER SNOW TOTALS SHOULD BE LOCATED
OVER THE SOUTHWEST HALF OF THE FORECAST AREA AND THERE IS SOME
POTENTIAL TO EXCEED 1 INCH ESPECIALLY IF THE PREDOMINANT SNOW
CRYSTAL TYPE DOES INDEED BECOME HIGHER SNOW RATIO (>15:1) DENDRITES.
THE SNOW SHOULD BEGIN TO END AROUND MIDNIGHT NORTHWEST AND BY 6 AM
SOUTHEAST AS THE SUBSIDENCE AND DRIER AIR ARRIVE BEHIND THE UPPER
SHORT WAVE PASSAGE. THE MAIN MESSAGE HERE IS THE POTENTIAL FOR SLICK
SNOW COVERED ROADS FOR THE MONDAY MORNING COMMUTE AND UNLESS SOME OF
YOU HAVE BEEN OFF VISITING ELSEWHERE WITH SNOW, THIS WILL BE THE
FIRST TIME DRIVING ON SNOW IN ABOUT 9 MONTHS SO BE CAREFUL OUT THERE.
MONDAY WILL REMAIN COLD WITH HIGHS IN THE 20S AS THE MAIN HIGH
PRESSURE CENTER SETTLES INTO THE STATE. THAT HIGH WILL BE OVER IOWA
MONDAY NIGHT WHICH MAY WHICH MAY LEAD TO RADIATIONAL COOLING OVER
PARTS OF THE AREA PENDING CLOUD COVER. THE CURRENT FORECAST LOWS ARE
IN THE SINGLE DIGITS TO LOW TEENS. THOSE VALUES MAY NEED TO BE
STEPPED DOWN IF SKIES DO CLEAR. NOTE THAT RETURN FLOW WARM ADVECTION
MAY COMMENCE OVER THE WEST LATE MONDAY NIGHT. TUESDAY WILL BE A BIT
WARMER AND BREEZY WITH HIGHS ACTUALLY GETTING BACK ABOVE FREEZING
OVER THE CENTRAL AND SOUTH BUT NORTHERN IOWA MAY LINGER IN THE UPPER
20S TO NEAR 30.
THE OTHER MAIN SYSTEM TO MONITOR IN THE FORECAST ARRIVES WEDNESDAY
AND WEDNESDAY NIGHT. WE CONTINUE TO HIGHLIGHT WEDNESDAY AS THE
"WARM" DAY IN THE FORECAST WITH HIGHS IN THE UPPER 30S TO MID 40S
HOWEVER, THERE IS A BUT ATTACHED ATTACHED TO WEDNESDAY. THE THERMAL
RIDGE WILL BE MOVING ACROSS IOWA TUESDAY NIGHT. CURRENTLY HAVE LOWS
WEDNESDAY MORNING IN THE LOW TO MID 20S. THESE LOWS ARE ON THE LOW
END OF POTENTIAL EXPECTED VALUES AND MAY NEED TO INCREASE THEM
FURTHER. THIS WILL LEAD TO A WARMER START ON WEDNESDAY. THE
DETERMINISTIC ECMWF/GFS/NAM ARE ALL TRENDING FASTER WITH THE 850 MB
COLD ADVECTION ARRIVING OVER NORTHERN IOWA BY MID-MORNING AND INTO
SOUTHERN IOWA BY THE AFTERNOON. NOTE, THE MINIMUM 850 MB
TEMPERATURES WITH THIS SYSTEM ARE CURRENTLY PROGGED TO BE -20C OR
BELOW OVER PARTS OF NORTHEAST IOWA AND WISCONSIN. THIS WILL LEAD TO
INITIAL MIXING WITH STEADY TO SLIGHTLY RISING SURFACE TEMPERATURES
BEFORE THE SURFACE COLD ADVECTION ARRIVES AND LEADS TO FALLING
TEMPERATURES. ONCE THE MIXING OCCURS, GUSTY NORTHWEST WINDS ARE
EXPECTED WITH PEAK MIXED LAYER WINDS IN THE UPPER 30S TO MID 40S KT
RANGE AND THE PRESSURE GRADIENT INCREASES. THIS SYSTEM LOOKS TO
FEATURE THE STRONG COLD ADVECTION, GOOD PRESSURE HEIGHT RISES POST
BOUNDARY PASSAGE AND STRONG SUBSIDENCE IN THE WAKE OF THE UPPER SHORT
WAVE. THESE WILL PROMOTE NEAR MAX MASS TRANSPORT OF THE PEAK MIXED
LAYER WINDS TO THE SURFACE. AT THIS TIME, THESE WINDS ARE TRENDING
TOWARDS WIND ADVISORY CRITERIA WINDS. THE SYSTEM ITSELF IS MOISTURE
STARVED AND THERE WILL BE AN INVERSION AROUND 5 KFT OR BELOW THAT
WILL PUT THE LID ON ANY CONVECTIVE CHANCES. REGARDLESS, THIS IS NOT
LOOKING LIKE A PLEASANT DAY DESPITE THE "WARMER TEMPERATURES". WILL
CONTINUE TO MONITOR THE BOUNDARY TIMING AS THAT WILL HAVE AN IMPACT
ON THESE HIGHS.
THURSDAY WILL HAVE A RETURN TO COLD WITH HIGHS IN THE TEENS AND 20S
WHILE ANOTHER LARGE HIGH PRESSURE MOVES ACROSS THE REGION.
ANOTHER SHORT WAVE PASSAGE IS ON TARGET FOR LATE FRIDAY AND FRIDAY
NIGHT. DETAILS FOR THIS SYSTEM ARE STILL A BIT SKETCHY PENDING
MOISTURE AVAILABILITY. THE THURSDAY HIGH PRESSURE SYSTEM WILL MOVE
EAST/SOUTHEAST AND EVENTUALLY GULF OF MEXICO MOISTURE WILL BEGIN TO
WRAP AROUND THE WESTERN PERIPHERY OF THE SYSTEM. WHETHER ANY OF THAT
MOISTURE REACHES THE STATE IS STILL UNCERTAIN. THE WEEKEND IS
TRENDING A BIT WARMER AS UPPER WESTERLY/SOUTHWEST FLOW DEVELOPS
AHEAD OF ANOTHER DEEPENING TROUGH THAT COULD HAVE IMPACTS IN THE
REGION LATE NEXT WEEKEND.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 530 AM CST SUN DEC 1 2024
PRIMARILY VFR STRATUS IS IN THE REGION THIS MORNING. THAT SHOULD
BREAK UP FOR AWHILE LATER THIS MORNING AND EARLY AFTERNOON.
CLOUDS WILL INCREASE BY MID AFTERNOON AND INTO TONIGHT AND
EXPECT WIDESPREAD LIGHT SNOW TO DEVELOP. CIGS ARE EXPECT TO
BECOME MVFR WITH MVFR TO IFR VSBYS IN LIGHT SNOW. THE WIND WILL
BE FROM THE NORTHWEST BUT MAY BECOME LIGHT AND VARIABLE AT TIMES
TONIGHT.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...DONAVON
AVIATION...DONAVON
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page