963
FXUS63 KDMX 212030
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
230 PM CST TUE JAN 21 2025
KEY MESSAGES
- 40 TO 70% CHANCE OF LIGHT SNOW AND FLURRIES AFTER MIDNIGHT TONIGHT
INTO WEDNESDAY
- DRY CONDITIONS WITH TEMPERATURES SEESAWING BACK AND FORTH
AROUND TYPICAL LATE JANUARY LEVELS THURSDAY THROUGH THE
WEEKEND.
DISCUSSION
ISSUED AT 230 PM CST TUE JAN 21 2025
AFTER A VERY COLD MORNING WITH WIND CHILLS AS LOW AS 28 TO 38
DEGREES BELOW ZERO ACROSS CENTRAL IOWA, THIS AFTERNOON IS FEELING
MUCH BETTER WITH TEMPERATURES IN THE SINGLE DIGITS ABOVE ZERO. NOT
SURPRISINGLY, OBSERVATIONS AND RAP ANALYSIS SHOWS THAT WE HAVE
STRONG WARM AIR ADVECTION ONGOING IN THE LOW LEVELS AND THAT
WILL CONTINUE INTO TONIGHT WITH BREEZY WINDS AT THE SURFACE AND
IN THE LOW LEVELS. THIS SHOULD RESULT IN TEMPERATURES THAT ARE
NEARLY STEADY AND LIKELY WILL RISE OVERNIGHT TONIGHT. BEYOND
TEMPERATURES, OUR ATTENTION TURNS TO THE NORTHWEST AS GOES-EAST
DAY SNOW FOG RGB SHOWS FILAMENTS OF HIGH CLOUDS APPROACHING THE
STATE THIS AFTERNOON WITH MORE SUBSTANTIAL CLOUD COVER OVER THE
DAKOTAS. THESE CLOUDS ARE ASSOCIATED WITH A SHORTWAVE TROUGH
AND SURFACE LOW THAT ARE DROPPING OUT OF CANADA AND WILL BRING
THE CHANCE FOR LIGHT SNOW AFTER MIDNIGHT TONIGHT INTO THE DAY
WEDNESDAY. CROSS SECTIONS SHOW THAT SOME LEVEL OF SATURATION IS
FIRST ACHIEVED IN THE MID-LEVELS, WHICH PROPAGATES DOWN INTO THE
LOW LEVEL. FORECAST SOUNDINGS CONFIRM THIS IDEA AND ALSO SHOW
THAT MOISTURE IS SOMEWHAT LIMITED, BUT WITH WEAK LIFT/OMEGA AND
NO DOUBT ABOUT ICE INTRODUCTION, FLURRIES OR LIGHT SNOW SHOULD
FALL FOR UP TO AROUND 12 HOURS AT SOME LOCATIONS. TIMING SHOULD
BE AFTER MIDNIGHT OVER NORTHERN IOWA WITH SNOWFALL SLOW TO CREEP
SOUTHWARD REACHING THE I-80 CORRIDOR LIKELY AFTER SUNRISE
WEDNESDAY. TRENDS OVER THE LAST 24 HOURS HAVE BEEN UPWARD
SLIGHTLY IN QPF AND RESULTANT SNOWFALL OVER A PORTION OF
NORTHERN IOWA, THOUGH ENSEMBLE MEANS FOR MORE THAN AN INCH OF
SNOWFALL REMAIN AROUND OR LESS THAN 30%. LATEST 12Z
DETERMINISTIC GUIDANCE SHOWS 0.10 TO NEAR 0.15 INCHES OF LIQUID
ALONG AND JUST NORTH OF HIGHWAY 20. WITH SNOW RATIOS MAINLY OF
13-16:1, AN INCH TO AN INCH AND A HALF OF SNOWFALL IS EXPECTED
FROM AROUND HIGHWAY 20 TO AROUND HIGHWAY 3 WITH LESSER AMOUNTS
ON EITHER SIDE OF THE 'HEAVIER' SNOWFALL AREA. LATEST HREF
PROBABILITY MATCHED MEAN LARGELY AGREES WITH THIS AREA, THOUGH
HAS A SLIGHTLY LARGER FOOTPRINT IN THE 1 INCH AREA.
MUCH OF THE SNOWFALL WILL TAPER OFF WEDNESDAY EVENING AS THIS
SHORTWAVE TROUGH MOVES OFF TO THE SOUTHEAST WEDNESDAY NIGHT. COLD
AIR ADVECTION WILL FOLLOW IT WITH HIGH TEMPERATURES FALLING BACK
INTO THE TEENS AND LOW TEMPERATURES STAYING IN THE SINGLE DIGITS
ABOVE ZERO. OUR UPPER LEVEL PATTERN OF NORTHWEST FLOW WILL EVOLVE
WITH PASSING WEAK RIDGING AND THEN FLATTENING OUT TO MORE ZONAL
FLOW INTO THIS WEEKEND. THIS WILL KEEP THE BACK AND FORTH ABOVE
AND BELOW NORMAL TEMPERATURES GOING THROUGH ANOTHER CYCLE
FRIDAY/SATURDAY AND SUNDAY WITH MILDER TEMPERATURES INTO EARLY
NEXT WEEK. NO SIGNIFICANT WINTER PRECIPITATION SYSTEMS ARE ON
THE HORIZON WITH CONDITIONS DRY IN THE EXTENDED FORECAST.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1148 AM CST TUE JAN 21 2025
VFR CONDITIONS WILL PREVAIL THIS AFTERNOON, BUT CLOUDS WILL
INCREASE FROM NORTHWEST TO SOUTHEAST WITH A BAND OF SNOW
EXPECTED TO DROP INTO THE STATE LATE TONIGHT INTO WEDNESDAY. FOR
MOST SITES, THIS RESULTED IN PROB30 GROUPS WITH THE EXCEPTION
OF FOD WHERE CONFIDENCE IS HIGHER THAT SOME LEVEL OF
RESTRICTIONS WILL PREVAIL WEDNESDAY MORNING. FURTHER, CEILINGS
OVER NORTHERN IOWA ARE THE MOST LIKELY TO FALL INTO MVFR
WEDNESDAY MORNING. A PERIOD OF LOW LEVEL WIND SHEAR MAY DEVELOP
OVER SOUTHERN INTO CENTRAL IOWA, THOUGH IT IS BORDERLINE SO
HAVE HELD OFF MENTION.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...ANSORGE
AVIATION...ANSORGE
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