Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 221138
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
538 AM CST Wed Jan 22 2020

...Aviation Update...

.DISCUSSION.../Today through Tuesday/
Issued at 355 AM CST Wed Jan 22 2020

Summary...

Precipitation has moved into western and northern Iowa overnight,
initially falling as a wintry mix initially before changing over to
snow. Snow will overtake the remainder of the state through the
morning and daytime hours, slowly moving eastward. Beyond today,
messy forecast remains over the next couple of days with snow,
rain/snow mixes, and rain chances through Friday night. Weekend and
early next week continues to remain dry and seasonable, with the
best opportunity for precipitation appearing Tuesday night into
Wednesday, though details remain hazy and uncertain.

Today through Friday...

Low to mid level warm air and moisture advection, combined with the
upper level shortwave overtaking the area have worked to spread
precipitation into large portions of western and northern Iowa early
this morning. Given the phasing of the moisture return and mid-upper
level forcing, very little doubt in widespread precipitation
traversing the state through the day. There remains some degree of
uncertainty as to the prevailing precipitation type at times today
with temperatures forecast a couple degrees above freezing. Given
relative shallow depth of the warm air, it is most likely that
"heavy/wet" snow will prevail much of the time, especially as the
900-800 mb warm nose erodes this morning. Fortunately,
GEFS/HRRR/HREF all in agreement that snow should prevail across
much of the state. While a number of areas in central and eastern
Nebraska did reach to around 35-36 degrees F overnight, causing
widespread rain and wintry mixes initially. Do not suspect we will
have the same issue as strong WAA will not persist, especially as
one looks upstream. Toward the evening, a period of freezing
drizzle may occur as drier air intrudes, but confidence not great
enough to introduce into the forecast at this time. Snow
today/tonight may yield 2 to 4 inches of snow in total. Winter
weather advisory will remain in affect through Wednesday evening,
and have opted not to extend or alter the headline at this time.
It is possible it may need to be extended into the evening as
heaviest precipitation moves eastward, but given the relatively
light snowfall amounts, mild temperatures helping limit road
accumulations, and past the evening commute, will leave for future
assessment.

Second round Thursday into Friday remains on track as a pair of
waves slide off the Rockies and down the Plains. Recent runs have
suggested a delayed phasing of the waves, however the precipitation
consequences generally remain the same as the initial wave deepens
and closes off as it slides through eastern Kansas and into
Missouri. Once again, with persistent deep lift and a saturated air
mass, periods of prolonged precipitation are likely. While near
surface temperatures will remain around and just above freezing,
snow ratios are likely to be a bit greater than the Wednesday
snowfall due to an overall cooler thermodynamic profile. Snowfall
amounts could once again yield 2 to 4 inches in some areas,
especially west as recent runs suggest a move westward of heaviest
axis. Additionally, as the upper level low exits east, there may be
a brief period of freezing drizzle as ice introduction and deeper
moisture dissipates. Another round of winter weather advisory
headlines may be necessary, but will be evaluated over the next 12
to 24 hours and as the current headlines play out.

Lastly, as previous discussions have mentioned, while total snowfall
through Friday night may be around 6 inches in some locations, it
will experience some degree of melting each day as well as extra
compaction due to its heavy/wet nature. Regardless, travel may be
hazardous at times during the snowfall, especially outside of
daylight hours.

Saturday through Tuesday...

Weekend and early next week continues to appear dry with the only
wave of note continuing to be progged to pass south of the region.
Otherwise, surface high pressure and quieter upper level flow will
prevail. Temperatures will continue to be mild with highs topping
out in the 30s. Best precipitation chances continue to look like mid-
week next, however details in timing and track remain in flux.

&&

.AVIATION.../For the 12Z TAFS through 12Z Thursday morning/
Issued at 534 AM CST Wed Jan 22 2020

Overall aviation message remains the same with impactful
reductions to IFR/LIFR expected from ceiling and visibility
reductions as snow moves across all TAF sites. KFOD/KMCW already
beginning to see -SN, with KDSM/KALO likely to see by around 14z
and KOTM 17z. Even as precipitation dissipates, ceilings likely to
remain well below 1kft as well as BR/FG development across all
sites likely.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM CST this evening for IAZ028-
039-049-050-060>062-073>075-083>086-094>097.

Winter Weather Advisory until 6 PM CST this evening for
IAZ004>007-015>017-023>027-033>038-044>048-057>059-070>072-081-
082-092-093.

&&

$$

DISCUSSION...Curtis
AVIATION...Curtis



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