250
FXUS63 KDMX 211103
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
503 AM CST SUN DEC 21 2025
...UPDATED FOR THE 12Z AVIATION DISCUSSION...
KEY MESSAGES
- HIGH CONFIDENCE IN ABOVE NORMAL TEMPERATURES FOR THIS UPCOMING
WEEK.
- CLOUDY, DRIZZLE OR LIGHT PRECIPITATION POSSIBLE WEDNESDAY,
WHICH MAY LIMIT THE DEGREE OF WARMING THAT DAY.
- CONTINUING TO MONITOR FOR POSSIBLE FOG DEVELOPMENT THIS WEEK
OVER AREAS THAT HAVE MELTING SNOWPACK.
DISCUSSION
ISSUED AT 219 AM CST SUN DEC 21 2025
EARLY MORNING OBSERVATIONS SHOW HIGH PRESSURE TRACKING OVER THE
STATE WITH NORTHERLY FLOW OVER THE EASTERN HALF OF IOWA, BUT
ALREADY STARTING TO SEEING SOUTHERLY WINDS PUSHING INTO WESTERN
IOWA. THE NORTHERLY WINDS HAVE ALLOWED TEMPERATURES TO FALL
INTO THE UPPER SINGLE DIGITS OR TEENS OVER NORTHERN AND EASTERN
IOWA. WITH THE HIGH PRESSURE DEPARTING THROUGH THE DAY, THAT
SOUTHERLY SURFACE FLOW WILL BE JOINED BY STRONG LOW LEVEL
THETA-E ADVECTION. AS MENTIONED IN THE PREVIOUS DISCUSSION, HAVE
RAISED HIGH TEMPERATURES FROM THE INITIAL NATIONAL BLEND OF
MODELS (NBM) TO THE 75TH PERCENTILE OVER AREAS THAT ARE SNOWPACK
FREE (E.G. SOUTHERN INTO WESTERN IOWA). THE FORECAST YESTERDAY,
LARGELY DRIVEN BY THE NBM, PERFORMED WELL OVER THE SNOWPACK
AREAS, BUT THE 75TH PERCENTILE SHOULD OFFER A CORRECTION FACTOR
TO WHERE THE FORECAST UNDERPERFORMED YESTERDAY. WINDS AND WIND
GUSTS WERE ALSO BOOSTED, BUT NOT GREATLY AS FORECAST SOUNDINGS
SHOW THAT THE LOW LEVEL PART OF THE ATMOSPHERE WILL BE LIMITED
IN ITS MIXING DEPTH POTENTIAL. AS WE MOVE INTO TONIGHT, THE
THETA-E ADVECTION SHOULD BE SUFFICIENT TO DEVELOP LIGHT
PRECIPITATION TO THE NORTH AND NORTHEAST OF OUR FORECAST AREA.
DESPITE A FEW OF THE HIGH RESOLUTION MODELS SHOWING MODEL
REFLECTIVITY OVER NORTHERN IOWA, THESE SAME MODELS HAVE NO QPF
OVER IOWA. THIS IS LIKELY DUE TO THE AMOUNT OF DRY AIR RESIDING
BENEATH THE SATURATION AROUND AND ABOVE 700MB. SO, HAVE KEPT
OUR FORECAST DRY.
HEIGHTS WILL BE RISING INTO NEXT WEEK AS THE RIDGE SLOWLY AMPLIFIES
POLEWARD AND THIS WILL BRING WARMER CONDITIONS WITH TEMPERATURES
ABOVE NORMAL ALONG WITH LIMITED PRECIPITATION CHANCES. THOSE
WITH HOLIDAY TRAVEL PLANS IN IOWA THIS UPCOMING WEEK SHOULD HAVE
FAVORABLE WEATHER CONDITIONS FOR SURFACE TRANSPORTATION WITH
TWO POSSIBLE EXCEPTIONS: 1) FOG DEVELOPMENT DUE TO MELTING OF
THE LINGERING SNOWPACK OVER NORTHERN IOWA AS CONDITIONS TURN
WARMER AND 2) ROAD FROST AS DEWPOINTS RISE ABOVE THE ROAD
SURFACE TEMPERATURES. THE WARMER CONDITIONS WILL BE MOVING IN
ON MONDAY AS 850MB TEMPERATURES WILL RANGE FROM 8 TO 15C FROM
NORTHEAST TO SOUTHWEST OVER THE FORECAST AREA WITH HIGHS RANGING
FROM THE UPPER 30S (NORTHEAST) TO THE 50S (SOUTHWEST). A
SHORTWAVE TROUGH TREKKING ALONG THE US/CANADA BORDER WILL SEND A
COLD FRONT THROUGH THE STATE TUESDAY, WHICH WILL RESULT IN
HIGHS SEVERAL DEGREES LOWER THAN MONDAY, BUT STILL ABOVE NORMAL.
850MB TEMPERATURES SURGE BACK UPWARD ON CHRISTMAS EVE, BUT FORECAST
SOUNDINGS SHOW AN INCREASE IN LOW LEVEL SATURATION UP TO NEAR 1KM.
AT A MINIMUM, STRATUS CLOUDS ARE LIKELY ON WEDNESDAY AND WITH WEAK
OMEGA AND SOME DIRECTIONAL SHEAR IN THIS SATURATED LAYER, DRIZZLE
POTENTIAL SEEMS TO ALSO BE INCREASING. THE NAM, ECMWF, AND CANADIAN
ALL HAVE THE COMMON DRIZZLE QPF SIGNAL AS A RIBBON OF VORTICITY
MOVES OVER THE STATE. WILL ALSO HAVE TO WATCH TIMING AS ANY
DRIZZLE OR LIGHT PRECIPITATION OVERNIGHT COULD FALL WITH
TEMPERATURES BELOW FREEZING. THE STRATUS AND POTENTIAL DRIZZLE
COULD SPELL A FAILURE MODE FOR HIGHS ON WEDNESDAY. THE CURRENT
FORECAST OF HIGHS IN THE 40S TO NEAR 60 DEGREES FROM NORTH TO
SOUTH OVER THE STATE COULD END UP - REASONABLE WORST CASE - IN
THE UPPER 30S OVER NORTHERN IOWA TO AROUND 50 DEGREES IN
SOUTHERN IOWA. CONCERNS ABOUT HIGH TEMPERATURES MAY LINGER INTO
CHRISTMAS DAY AS GFS AND ECMWF ENSEMBLE SOUNDINGS SHOW LOW LEVEL
SATURATION PERSISTING, THOUGH THE DEPTH IS LESS SO DRIZZLE MAY
NOT BE A CONCERN. IF WE CLEAR OUT EARLY ENOUGH IN THE DAY,
RECORD HIGHS MAY BE CHALLENGED OVER SOUTHERN IOWA. IF MUCH OF
THE DAY IS CLOUDY, TEMPERATURES MAY NEED TO BE LOWERED IN A
SIMILAR MANNER TO CHRISTMAS EVE/WEDNESDAY.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 503 AM CST SUN DEC 21 2025
HIGH CONFIDENCE IN VFR CONDITIONS PREVAILING THROUGH THE PERIOD
AT ALL TERMINALS. A BRIEF PERIOD OF MARGINAL LOW LEVEL WIND
SHEAR IS FORECAST AT MCW THIS MORNING. IT LOOKS LIKE ANOTHER
ROUND OF MARGINAL LLWS MAY MOVE IN TONIGHT, BUT HAVE ONLY
INCLUDED AT A FEW SITES THAT SURPASS 30 KNOTS.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...ANSORGE
AVIATION...ANSORGE
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