151
FXUS63 KDMX 281146
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
646 AM CDT MON SEP 28 2026
...UPDATED FOR THE 12Z AVIATION DISCUSSION...
KEY MESSAGES
- AREAS OF FOG THIS MORNING, SOME OF WHICH WILL BE DENSE.
- MOSTLY CLOUDY TO OVERCAST CONDITIONS TODAY. HIGHS NEAR 70
DEGREES.
- PATCHY FOG POSSIBLE EAST TONIGHT.
- CONFIDENCE REMAINS HIGH IN A PROLONGED, WIDESPREAD RAINFALL
EVENT LATE TUESDAY THROUGH LATE THIS WEEK, WHICH RAISES
CONCERNS FOR POTENTIAL FLASH FLOODING AND RIVER RISES.
SHORT TERM /THROUGH TUESDAY/
ISSUED AT 248 AM CDT MON SEP 28 2026
DEEP LOW-LEVEL SATURATION CREATED A BLANKET OF THICK STRATUS
OVERNIGHT. THE SATURATED LAYER HAD ESSENTIALLY NO LIFT OR FLOW, SO
THE SURFACE SAW FOG AS OPPOSED TO DRIZZLE. FOG WILL BE LOCALLY DENSE
NEAR THE IOWA-MINNESOTA STATE LINE. THIS IS BECAUSE OF CLEARING
STRATUS, ALLOWING FOR THE SURFACE TO COOL MORE. THE DEEP SATURATION
MENTIONED ABOVE WILL MAKE THE FOG DIFFICULT TO BURN OFF AND IT MAY
WELL LAST PAST 9AM. SOUTHEAST WINDS WILL TRY AND ADVECT IN MORE DRY
AIR TODAY, WHICH MAY ALLOW FOR PEAKS OF SUNSHINE IN SOUTHEAST IOWA
BY THE AFTERNOON. THIS IS ALSO WHERE TEMPERATURES HAVE THE BEST
CHANCE TO REACH 70 DEGREES. FOR TONIGHT, WINDS WILL INCREASE IN THE
WEST. THIS IS IN RESPONSE TO THE INCREASED INFLUENCE OF WESTERN
CONUS TROUGHING. TROUGHING AT H85 ARRIVES IN THE PLAINS WHICH
WILL INCREASE THE LLJ AND MOISTURE TRANSPORT IN WESTERN IOWA.
MIDLEVEL CLOUDS WILL FORM IN RESPONSE. IN EASTERN IOWA, FLOW
WILL REMAIN WEAKER DUE TO THE INFLUENCE OF HIGH PRESSURE. FOG
WILL BE POSSIBLE IN THIS REGION, BUT WILL BE MORE PATCHY IN
NATURE DUE TO LESS LOW-LEVEL MOISTURE.
LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/
ISSUED AT 130 PM CDT SUN SEP 27 2026
GOES-EAST UPPER LEVEL WATER VAPOR IMAGERY SHOWS THE KEY
FEATURES THAT WILL BE IMPORTANT FOR THE LONGER TERM FORECAST. A
BROAD CYCLONIC SPIN IS ALONG THE CENTRAL WEST COAST ASSOCIATED
WITH A LONGWAVE TROUGH. AHEAD OF THIS IS REMNANT MOISTURE FROM
ODALYS, WHICH IS BEING DRAWN NORTHEASTWARD OVER THE FOUR CORNERS
REGION ALREADY. AND FINALLY, HURRICANE POLO IS READILY APPARENT
OFF THE SOUTHERN PORTION OF BAJA CALIFORNIA AS IT BEGINS ITS
NORTH AND LATER NORTHEASTWARD TRACK AND WEAKENS. BY TUESDAY
MORNING, THIS TROUGH WILL BE OVER THE SOUTHWEST WITH THE
WEAKENING POLO CRESTING THE SIERRA MADRE OCCIDENTAL. THERE WILL
ALREADY BE PIECES OF ENERGY SPILLING NORTHEASTWARD INTO OUR
REGION ALONG WITH SURGES OF LOW LEVEL THERMAL LIFT AND MODEST QG
CONVERGENCE TO SUPPORT SHOWERS AND STORMS SPREADING INTO AT
LEAST SOME PORTIONS OF IOWA LATER TUESDAY IF NOT TUESDAY NIGHT.
THERE IS UNCERTAINTY ON WHERE THE HIGHEST RAINFALL OF THIS LONG
DURATION RAIN WILL SET UP OVER THE REGION. AI GUIDANCE HAS SHOWN
PROMISE FOR HIGHLIGHTING THE LOCATION OF THE BAND OF HEAVIEST
PRECIPITATION AND OVER THE LAST DAY, THE AIFS HAS STABILIZED IN THE
48 HOUR RAINFALL TOTAL AXIS THROUGH MIDDAY THURSDAY. MEANWHILE, THE
AIGFS CONTINUES TO TREND NORTHWARD IN ITS PLACEMENT. LOOKING AT
DETERMINISTIC AND ENSEMBLES, THESE HAVE GENERALLY TRENDED NORTHWARD
IN THE LAST SEVERAL RUNS AS WELL. THESE SHIFTS COMPARED TO 24 HOURS
AGO DO NOT LEND THEMSELVES TO FORECAST CONFIDENCE, BUT INVESTIGATING
SOME OF THE CAUSES FOR THESE SHIFTS DOES PROVIDE ELEMENTS OF THE
WEATHER PATTERN TO MONITOR THIS WEEK. FIRST, WHAT DEGREE OF
INTERACTION WILL THE APPROACHING TROUGH AND TROPICAL MOISTURE HAVE
WITH A NORTHERN STREAM WAVE OVER THE CANADIAN PRAIRIES. YESTERDAY'S
12Z SUITES HAD MINIMAL INTERACTION, WHICH RESULTED IN THE NORTHWARD
SURGING MOISTURE BEING MET WITH DRY AIR IN THE MID-LEVELS. OVERNIGHT
AND SO FAR TODAY, MODELS ARE SHOWING MORE PLAY WITH THE NORTHERN
STREAM AND THUS A CHANGE OF RAINFALL BEING FARTHER NORTHWARD AND
ORIENTED FROM SOUTHWEST TO NORTHEAST VS WEST TO EAST. SECOND, A ZONE
OF HIGH PRESSURE OVER THE UPPER MISSISSIPPI RIVER VALLEY AT THE
START OF THIS WEEK WILL SLIDE EASTWARD AND SPRAWL OVER THE EASTERN
SEABOARD. THIS MAY LEAVE SOME DEGREE OF MID-LEVEL DRY AIR OVER THE
REGION, THOUGH UNCERTAINTY IS WHERE AND HOW LONG THAT MAY LAST
AGAINST THE NORTHWARD PUSH OF MOISTURE. THIRD AND FINALLY, LAST
NIGHT'S AND TODAY'S GFS AND CMC HAVE A NORTHERN STREAM TROUGH
ADVANCING SLOWER THAN AT LEAST LAST NIGHT'S ECMWF, WHICH ALLOWS THE
GFS AND CMC TO PICK UP THE APPROACHING TROUGH AND TAKE IT THROUGH
THE STATE MORE QUICKLY. HOWEVER, THE ECMWF IS FASTER WITH THE
NORTHERN TROUGH, WHICH CAUSES THE APPROACHING TROUGH TO BREAK OFF
INTO A CLOSED LOW. THUS, THE RAINFALL DOES NOT PROGRESS THROUGH AS
FAST, BUT IN THE END THE CLOSED LOW DOES PULL IT AWAY FROM THE STATE
BY LATE WEEK. DEPENDING ON WHERE THIS RAIN FALLS WILL HAVE
IMPLICATIONS ON RIVER FLOODING AND POSSIBLE FLASH FLOODING, WHICH
ARE ALSO HIGHLIGHTED IN THIS MORNING'S NATIONAL WATER CENTER'S
HYDROLOGIC DISCUSSION (NMDNWC).
WHILE THE DETAILS ARE MORE MURKY BEYOND TUESDAY NIGHT IN LOCATION OF
HIGHEST RAINFALL, CONFIDENCE IS HIGH THAT IT WILL BE RAINING OVER
SOME PORTIONS OF IOWA FROM LATE TUESDAY THROUGH WEDNESDAY NIGHT. IN
ADDITION, THE RAIN THAT DOES FALL WILL BE IN AN ENVIRONMENT THAT
WILL SUPPORT EFFICIENT RAINFALL GIVEN THE ATYPICAL DEEP WARM CLOUD
DEPTHS AND ABOVE 90TH PERCENTILE PRECIPITABLE WATER VALUES. THIS
WILL LEAD TO AREAS OF RAINFALL OF 2 INCHES OR MORE SOMEWHERE IN IOWA
BY WEEK'S END. 7Z/13Z NBM PROBABILITIES OF 2"+ RAINFALL IN A 48 HOUR
PERIOD ENDING THURSDAY MORNING ARE ALREADY ABOVE 50% OVER MUCH OF
WESTERN AND CENTRAL IOWA WITH 4"/48 HOUR PROBABILITIES BETWEEN 20
AND 30% OVER PARTS OF WESTERN IOWA. AND ENDING ON A BIT OF GOOD
NEWS, THE WEAK LAPSE RATES WILL MINIMIZE ANY SEVERE WEATHER RISK
THIS WEEK.
AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 639 AM CDT MON SEP 28 2026
FOG IS COMMON IN TWO AREAS OF THE STATE THIS MORNING: LOCALLY
DENSE FOG IS COMMON IN NORTHERN IOWA AND IN SOUTHEAST IOWA. KMCW
AND KOTM ARE THE PRIMARY IMPACTED TERMINALS AT THIS TIME. LIFR
STRATUS IS COMMON ACROSS MOST OF THE AREA, MVFR CIGS MOVING IN
FROM THE EAST. KDSM POSES THE MOST UNCERTAINTY IN THE SHORT TERM
AS IT IS AT THE EDGE OF THE FOG AND STRATUS. HAVE KEPT A TEMPO
FOR CIGS AND VSBYS AS NEARBY OBS HAVE WORSENED. EXPECTING VSBY
IMPACTS TO BE TRANSIENT HERE.
FURTHER INTO THE PERIOD, HAVE DELAYED THE DEPARTURE OF IFR AND
MVFR CIGS IN THE NORTH. EVENTUALLY STRATUS WILL BREAK APART AND
MIDLEVEL CLOUDS WILL REPLACE THEM OVERNIGHT. WHILE NOT MENTIONED
IN THE PLANNING PERIOD, PATCHY FOG WILL BE POSSIBLE AT KALO AND
KOTM, BUT IS NOT EXPECTED TO BE AS IMPACTFUL AS THE FOG THIS
MORNING.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...JIMENEZ
LONG TERM...ANSORGE
AVIATION...JIMENEZ
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