547
FXUS63 KDMX 020908
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
308 AM CST SUN NOV 2 2025
KEY MESSAGES
- DENSE FOG AND FREEZING FOG CAUSING VISIBILITIES OF A QUARTER
MILE OR LESS THIS MORNING. ISOLATED SLICK SPOTS POSSIBLE PRIOR
TO SUNRISE.
- BREEZY TO WINDY CONDITIONS DEVELOP TODAY, WITH WIND GUSTS OF
25 TO 35 MPH POSSIBLE. STRONGEST WINDS WILL BE OVER
NORTHWESTERN IOWA.
- WARMER AND DRIER WEATHER TO START THE WORK WEEK.
UPDATE
ISSUED AT 257 AM CST SUN NOV 2 2025
SKIES HAVE CLEARED OUT OVERNIGHT AND ALLOWED FOG TO DEVELOP OVER
MUCH OF EAST CENTRAL IOWA EARLY THIS MORNING. THIS FOG IS QUITE
EVIDENT ON THE NIGHTTIME MICROPHYSICS AND NIGHT FOG SATELLITE
IMAGERY, IMPACTING AREAS ROUGHLY ALONG AND EAST OF INTERSTATE 35.
VISIBILITIES LESS THAN 2 MILES ARE COMMON, WITH MANY SURFACE
OBSERVATIONS NOW SHOWING VISIBILITIES DOWN TO A QUARTER MILE OR
LESS. FOR THIS REASON, A DENSE FOG ADVISORY IS IN EFFECT FOR
MUCH OF EAST CENTRAL IOWA UNTIL 8 AM SUNDAY MORNING. A NORTH
AND/OR WESTWARD EXPANSION OF THE ADVISORY MAY BE NEEDED THROUGH
THE MORNING, BUT INCREASING WINDS IN WESTERN IOWA SHOULD HELP
TO MITIGATE DENSE FOG CONCERNS FARTHER WEST OF THE CURRENT
ADVISORY AREA.
IN ADDITION TO THE FOG, CLEAR SKIES HAVE ALLOWED TEMPERATURES TO
DROP INTO THE UPPER 20S TO NEAR 30. A FEW AREAS NEAR WATERLOO
ARE EVEN REPORTING TEMPERATURES DOWN INTO THE MID 20S. WITH
THESE SUB-FREEZING TEMPERATURES COMES THE RISK FOR FREEZING FOG,
CAUSING LIQUID DROPLETS IN THE AIR FREEZING ONTO SUB-FREEZING
SURFACES. FORTUNATELY, WHILE AIR TEMPERATURES ARE DROPPING
QUICKLY, GROUND/ROAD TEMPERATURES ARE STILL MOSTLY IN THE MID
30S TO LOW 40S, WHICH SHOULD HELP TO PREVENT ICE DEVELOPING ON
ROADWAYS. THAT SAID, THERE ARE A FEW ISOLATED AREAS WITH ROADS
NEAR FREEZING. LIKEWISE, BRIDGES AND OVERPASSES TEND TO COOL
MORE RAPIDLY THAN STANDARD ROADS, MAKING THEM MORE LIKELY TO
COLLECT ICE AND PRODUCE SLICK SPOTS. THEREFORE, WHILE WIDESPREAD
TRAVEL IMPACTS AREN'T ANTICIPATED, ISOLATED SLICK SPOTS ARE
POSSIBLE PRIOR TO SUNRISE.
THE CLEAR SKIES AND LIGHT WINDS RESPONSIBLE FOR FOG DEVELOPMENT
EARLY THIS MORNING ARE THANKS TO A BRIEF PERIOD OF HIGH PRESSURE ON
THE BACKSIDE OF THE UPPER LEVEL LOW THAT PASSED THROUGH ON SATURDAY.
HOWEVER, THIS SURFACE HIGH PRESSURE WILL DEPART WITH THE UPPER WAVE
THROUGH THE MORNING AND SURFACE LOW PRESSURE FILLS IN BEHIND.
THE RESULT AT THE SURFACE WILL BE BREEZY SOUTHERLY FLOW BRINGING
WARM AIR ADVECTION UP INTO THE STATE, BOOSTING HIGHS BACK INTO
THE 50S. WHILE WAA REGIMES DON'T TYPICALLY FAVOR DOWNWARD
MOMENTUM TRANSFER, STRONG PRESSURE GRADIENTS AT THE SURFACE AND
DIURNAL MIXING WILL STILL ALLOW WIND GUSTS OF 25 TO 35 MPH
TODAY, WITH A FEW POTENTIALLY HIGHER GUSTS IN NORTHWESTERN IOWA.
WINDS WILL THEN DIMINISH INTO THE EVENING.
DISCUSSION
ISSUED AT 235 PM CDT SAT NOV 1 2025
IOWA RESIDED ON THE EXITING SIDE OF AN UPPER-LEVEL DISTURBANCE THIS
AFTERNOON WITH CAA AND DRY NORTHWEST FLOW HELPING MIX OUT SOME OF
THE STRATUS. AS A RESULT, SOME SUNSHINE HAS BEEN ALLOWED TO POP
THROUGH. THE MIXING EXTENDS INTO THE SATURATED LAYER, SO CONVECTIVE
INSTABILITY WILL KEEP SCATTERED SHOWERS GOING FOR THE REST OF THE
DAY, MAINLY CLOSE TO THE LOW IN SOUTHEAST IOWA. IN FACT, THE LFC
EXTENDS INTO THE DGZ, SO IT'S CONCEIVABLE THAT "-UP" METAR REPORTS
AND MPINGS OF GRAUPEL ARE LEGITIMATE. WITH THE ABOVE FREEZING
SURFACE TEMPERATURES, NO ACCUMULATIONS ARE EXPECTED. RAINFALL
AMOUNTS WILL BE UNDER FIVE HUNDREDTHS. HIGHS WILL BE IN THE 40S
FOR MOST OF THE AREA. SOME 20MPH GUSTS HAVE BEEN ABLE TO MIX
DOWN AND THE OCCURRENCE OF THIS WILL REMAIN SPORADIC TODAY.
A TRICKY FORECAST IS IN STORE FOR TONIGHT, MAINLY DUE TO THE
FORECAST FOR CLOUD COVER. RETURN FLOW IN RESPONSE TO A DEEPENING
CANADIAN LOW WILL BEGIN TO AFFECT NORTHWEST AND WESTERN IOWA
TONIGHT. WIND WILL BE ENHANCED BY A SURFACE HIGH OVER CENTRAL AND
EASTERN IOWA. BENEATH THE HIGH PRESSURE, WHATEVER CLOUDS REMAIN WILL
STALL FOR THE NIGHT. WHERE CLEAR SKIES PERSIST, RADIATIVE COOLING
WILL DROP TEMPERATURES BELOW FREEZING AND DENSE FOG WILL BE
POSSIBLE. HIGHEST CONFIDENCE FOR NOW IS IN SOUTHEAST IOWA, AS FAR
WEST AS TAMA AND DOWN TO OTTUMWA. THE HREF ENSEMBLE BRINGS <0.5 MILE
VISIBILITIES AS FAR WEST AS DES MOINES, BUT DUE TO THE TENDENCY FOR
CAMS TO ERODE CLOUDS PREMATURELY (NOTICE IT ISN'T HANDLING THE
STRATUS OVER SOUTH DAKOTA WELL), THE FORECAST HEDGES TOWARDS MORE
CLOUD COVER, MAINLY ACROSS NORTHERN IOWA. MOST OF THE CLOUDS WILL BE
ASSOCIATED WITH THE REMNANT DEFORMATION ZONE THAT IS WRAPPING AROUND
THE UPPER LOW WHICH LOOKS TO BE ALONG AND EAST OF I-35. WEST OF THE
CLOUDS, WINDS AND WAA WILL SPARE THE TEMPERATURES FROM FALLING MUCH
BELOW THE FREEZING MARK. BENEATH THE CLOUDS, TEMPERATURES WILL
REMAIN ABOVE FREEZING. HAVE ADJUSTED TEMPERATURE FORECASTS TONIGHT
WITH THESE ZONES IN MIND, ADDING IN FOG MENTIONS FOR SOUTHEAST IOWA.
THE COVERAGE OF FOG WILL EXPAND OR CONTRACT DEPENDING ON HOW THE
CLOUD FORECAST CHANGES IN THE NEXT 16 HOURS.
BREEZY CONDITIONS IN NORTHWEST AND WESTERN IOWA ARE EXPECTED SUNDAY
AND WILL BE INHIBITED BY THE WAA AND PRESSURE FALLS (NET RISING
MOTION) SO THE 45KTS AT 925MB AREN'T EXPECTED TO REACH THE SURFACE.
GUSTS ON THE ORDER OF 35MPH WILL BE POSSIBLE, ESPECIALLY FOR
LOCATIONS SUCH AS ESTHERVILLE (60% CONFIDENCE THERE). HIGHS RETURN
TO THE MID 50S. THE SAME SYSTEM SPLITS OFF A SEGMENT OF ENERGY WHICH
WILL MOVE ACROSS THE GREAT LAKES REGION. IT WILL PULL THE PEAK OF
THE THERMAL RIDGE AWAY, BUT WON'T HAVE ENOUGH MOISTURE FOR RAINFALL.
THE 850MB REFLECTION OF THE RIDGE APEXES OVER SOUTHWEST IOWA SUNDAY
NIGHT BEHIND THE FRONT. THERE COULD BE ENOUGH RADIATIVE COOLING FOR
ADDITIONAL FOG DEVELOPMENT.
WESTERLY UPPER-LEVEL FLOW SETS IN FOR THE WEEK AND AT LEAST FOR NOW,
MIDLEVEL CLOUDINESS STAYS NORTH OF THE STATE THROUGH TUESDAY. THERE
WILL BE A WAVE THAT WILL MAKE A DRY, BUT CLOUDY PASSAGE ON WEDNESDAY
WHICH WILL DROP HIGHS BACK INTO THE 50S MOMENTARILY. TEMPERATURES
WILL REBOUND BACK INTO THE 60S AND A COOLDOWN WILL ARRIVE SOMETIME
OVER NEXT WEEKEND.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1028 PM CDT SAT NOV 1 2025
CLOUDS HAVE CLEARED ACROSS THE EASTERN HALF OF THE FORECAST
AREA, SO CONFIDENCE IN SIGNIFICANT FOG/FREEZING FOG DEVELOPMENT
AT KOTM AND KALO HAS INCREASED AS A RESULT. HREF PROBABILITIES
OF VISIBILITIES UNDER 1/2 MILE ARE IN THE 40-60% RANGE AT THOSE
SITES, AND THE HRRR HAS CONSISTENTLY SHOWN A STRONG SIGNAL FOR
DENSE FOG AFFECTING THOSE SITES AS WELL. WILL FOLLOW THESE
TRENDS AND FORECAST LIFR CONDITIONS FOR A FEW HOURS LATE
TONIGHT AND EARLY SUNDAY MORNING AT KOTM AND KALO. FARTHER
WEST, VFR CONDITIONS ARE FORECAST THROUGH THE PERIOD, BUT THERE
REMAINS A LOW CHANCE (20-30%) FOR SOME FOG DEVELOPMENT AT
KMCW/KDSM AS WELL. RESIDUAL CLOUD COVER AND LIGHT SOUTHERLY
RETURN FLOW WILL BE INHIBITING FACTORS FOR ANY FOG AT THOSE
SITES. FOG WILL BURN OFF QUICKLY AROUND MID MORNING SUNDAY AS
GUSTY SOUTH WINDS DEVELOP. GUSTS IN THE 20 TO 30 KNOT RANGE WILL
BE COMMON DURING THE DAY SUNDAY. LLWS WILL BE FORECAST AT KALO
SUNDAY EVENING AS SURFACE WINDS DECOUPLE SOMEWHAT AFTER SUNSET.
DMX WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL 8 AM CST THIS MORNING FOR IAZ026>028-
037>039-049-050-061-062-074-075-085-086-096-097.
UPDATE...DODSON
DISCUSSION...JIMENEZ
AVIATION...MEP
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