711
FXUS63 KDMX 210529
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1129 PM CST MON JAN 20 2025
...UPDATED FOR THE 06Z AVIATION DISCUSSION...
KEY MESSAGES
- DANGEROUSLY LOW WIND CHILLS INTO TUESDAY MORNING WITH CONDITIONS
IMPROVING LATE MORNING INTO THE AFTERNOON
- TEMPERATURES QUICKLY BEGIN TO 'WARM UP' AND ARE NEAR IF NOT A BIT
ABOVE NORMAL WEDNESDAY THROUGH THE WEEKEND
- NO SIGNIFICANT WINTER STORMS ON THE HORIZON. HOWEVER, SEVERAL CHANCES
TO SEE SNOWFLAKES FLY, INCLUDING THIS AFTERNOON INTO THIS
EVENING, TUESDAY NIGHT AND WEDNESDAY, AND THURSDAY WITH LITTLE
IF ANY ACCUMULATION EXPECTED.
UPDATE
ISSUED AT 906 PM CST MON JAN 20 2025
BASED ON SHORT-TERM OBSERVATIONAL TRENDS, AND PRIMARILY DUE TO
WINDS BEING SLOWER TO DIMINISH THAN ANTICIPATED THIS EVENING,
FOUR COUNTIES (DALLAS, POLK, JASPER, AND POWESHIEK) WERE
UPGRADED FROM THE COLD WEATHER ADVISORY TO THE EXTREME COLD
WARNING. NO OTHER CHANGES HAVE BEEN MADE AT THIS TIME.
DISCUSSION
ISSUED AT 243 AM CST MON JAN 20 2025
THE MAIN WEATHER THEMES IS A FINAL FRIGID NIGHT FOLLOWED BY
TEMPERATURES MODERATING TO NEAR NORMAL FOR THIS TIME OF JANUARY BY
WEDNESDAY WITH NO SIGNIFICANT WINTER PRECIPITATION SYSTEMS OVER THE
NEXT 7 DAYS. AT THE MOMENT, A BROAD, LARGE SCALE TROUGH COVERS MUCH
OF THE UNITED STATES WITH THIS RATHER EVIDENT ON GOES-EAST UPPER
LEVEL WATER VAPOR IMAGERY. OUR NEXT AND FINAL WAVE OF ARCTIC AIR HAS
ALREADY PUSHED INTO THE STATE WITH THIS SUBTLY VIEWABLE ON THE SAME
IMAGERY WITH 925MB OR 850MB LEVEL COLD AIR ADVECTION MAPS MORE
TELLING OF THIS PUSH. WITH THIS COLD AIR, ADDITIONAL STREAKS OF LOW
CLOUDS, OR HORIZONTAL CONVECTIVE ROLL (HCR) CLOUDS, ARE PUSHING INTO
THE STATE. AS HAS BEEN THE CASE THE LAST FEW DAYS AND DESPITE
LIMITED MOISTURE, THESE HCR CLOUDS HAVE BEEN ABLE TO GENERATE BRIEF
BOUTS OF FLURRIES AND SNOW SHOWERS. CROSS SECTIONS SHOW THE MARGINAL
FULL SATURATION WITH WEAK OMEGA AND FURTHER THE SOUNDINGS SHOW THAT
THE TEMPERATURE FALLS BELOW THE FROST POINT. THESE FLURRIES WILL
CONTINUE TO FLY ENDING FROM NORTHWEST TO SOUTHEAST VERY LATE THIS
AFTERNOON UNTIL ABOUT MIDNIGHT. THE QUESTION THEN TURNS TO HOW
QUICKLY DO THE CLOUDS DEPART AND ALLOW FOR EFFICIENT RADIATIONAL
COOLING OVERNIGHT. BULK OF GUIDANCE HAS CLOUDS DEPARTING WESTERN
IOWA BY MIDNIGHT, CENTRAL IOWA BY 3AM OR SO, AND EASTERN IOWA TOWARD
SUNRISE. THUS, WE SHOULD SEE TEMPERATURES FALL OFF QUICKLY AS THE
CLOUDS DEPART AND HAVE LOWERED LOWS A FEW DEGREES FROM THE INITIAL
NATIONAL BLEND OF MODELS (NBM). THIS PUTS THE LOWEST TEMPERATURES
OVER NORTHERN INTO WESTERN IOWA. ALTERNATIVE SCENARIOS WOULD BE A)
COLDER - LESS CLOUDS AND A FASTER CLOUD DEPARTURE ALLOWING
TEMPERATURES TO DROP ANOTHER 5 OR SO DEGREES ACROSS THE NORTH AND 1
TO 2 DEGREES ACROSS THE SOUTH FROM CURRENT FORECAST AND B) NOT AS
FRIGID - CLOUDS LINGER ABOUT 3 OR SO HOURS LONGER PER THE LATEST
HREF LOWEST LOW CLOUD PROBABILITIES, WHICH WOULD OFFER THE THE
HIGHEST LOW TEMPERATURE FORECAST. AS FOR COLD WEATHER HEADLINES,
EXPANDED THE WARNING SLIGHTLY OVER OUR WESTERN FORECAST AREA WHERE
WIND CHILLS ARE GOING TO BE A BIT LOWER THAN THE PREVIOUS FORECAST
AND TO EXTEND TO MIDDAY TUESDAY ALL COLD HEADLINES, WHICH WAS IN
PART DUE TO THE SLIGHTLY LOWER LOW TEMPERATURES LINGERING THE COLD A
BIT INTO TUESDAY MORNING AND MORE SO MATCHING UP WITH ALL OF THE
SURROUNDING OFFICES THAT WERE ALREADY ENDING AT MIDDAY. OVERALL,
TEMPERATURES AND WIND CHILLS WILL BE RISING QUICKLY THROUGH THE
MORNING HOURS SUCH THAT THE MOST DANGEROUS WIND CHILLS WILL BE PAST
BY AROUND MID-MORNING WITH MID-AFTERNOON WIND CHILLS ANYWHERE FROM -
5 TO -15 ACROSS THE CENTRAL PORTION OF THE STATE.
AS THE LOWEST HEIGHTS PUSH INTO SOUTHEASTERN CANADA AND SURFACE HIGH
PRESSURE PASSES SOUTH OF THE STATE ON TUESDAY, SURFACE WINDS FROM
THE SOUTHWEST AND SOUTH GUSTING 20 TO 30 MPH WILL BRING IN WARMER
AIR WITH HIGHS IN THE SINGLE DIGITS ABOVE ZERO OVER ROUGHLY EASTERN
IOWA AND TEENS OVER WESTERN IOWA. TEMPERATURES WILL STAY STEADY
TUESDAY EVENING AND PERHAPS RISE SLIGHTLY AS WARM AIR ADVECTION AND
BREEZY WINDS PERSISTS AND GO AGAINST THE TYPICAL DIURNAL TEMPERATURE
TREND. TEMPERATURES FROM WEDNESDAY INTO THE WEEKEND ARE IN THE 20S
AND 30S AND FOR MOST DAYS WILL BE NEAR TYPICAL VALUES FOR THIS TIME
OF YEAR.
AS OUR AREA REMAINS IN NORTHWESTERLY FLOW, A SHORTWAVE TROUGH WILL
DROP INTO THE STATE TUESDAY NIGHT INTO WEDNESDAY WITH CROSS SECTIONS
SHOWING SOME FRONTOGENETICAL FORCING AROUND 700MB FOR A BAND OF
LIGHT SNOW. ENSEMBLE MEANS FROM THE GLOBAL SUITES SHOW ANYWHERE FROM
A 30 TO 70% CHANCE OF MEASURABLE PRECIPITATION WITH THE PROBABILITY
FOR 1 INCH OF SNOW NO HIGHER THAN 10%, WHICH IS SPURIOUS SPATIALLY
AND TEMPORALLY AND JUST IN THE GEFS MEAN. DETERMINISTIC COBB OUTPUT
ALSO SHOWS AMOUNTS MAINLY UNDER AN INCH, WHICH MAKES SENSE WITH US
COMING OUT OF SUCH A DRY AIRMASS AND NO APPRECIABLE MOISTURE RETURN.
WHILE THE AMOUNTS ARE NOT GREAT, THIS COULD SPELL A FEW MINOR TRAVEL
TROUBLES ON WEDNESDAY. ANOTHER LOBE OF SHORTWAVE ENERGY ARRIVES
THURSDAY AND MIGHT BRING FLURRIES OR LIGHT SNOW, THOUGH
PROBABILITIES ARE UNDER 20% FOR ANY MEASURABLE PRECIPITATION. AS
THIS SHORTWAVE DEPARTS THURSDAY NIGHT, FLOW ALOFT TURNS FROM
NORTHWESTERLY TO SOMEWHAT ZONAL WITH DECREASING CONFIDENCE IN ANY
ADDITIONAL LIGHT PRECIPITATION CHANCES FRIDAY NIGHT INTO THIS
WEEKEND GIVEN THE FASTER FLOW OF LOW AMPLITUDE SHORTWAVES.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 1129 PM CST MON JAN 20 2025
VFR CONDITIONS ARE FORECAST THROUGH THE TAF PERIOD WITH NO
AVIATION IMPACTS ANTICIPATED.
DMX WATCHES/WARNINGS/ADVISORIES
EXTREME COLD WARNING UNTIL NOON CST TUESDAY FOR IAZ004>007-
015>017-023>028-033>039-044>050-057>062.
COLD WEATHER ADVISORY UNTIL NOON CST TUESDAY FOR IAZ070>075-
081>086-092>097.
UPDATE...LEE
DISCUSSION...ANSORGE
AVIATION...LEE
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