Blizzard and Winter Storm in Iowa, January 11 to 13, 2024

Area Forecast Discussion
National Weather Service Des Moines IA
932 PM CST Thu Jan 11 2024

.UPDATE...
Issued at 931 PM CST Thu Jan 11 2024

Previous expectations for an impactful blizzard still appear on
track this evening. Recent RAP analysis continue to show
tremendous thermodynamic support upstream with deep warm and moist
advection advancing northward from MO. This should eventually
result in extreme snowfall rates during the early morning hours
with low static stabilities and frontogenetic contributions
phased. Thundersnow is not out of the question, with thunder
already occurring between St. Louis and Quincy.

00Z HREF progs still align with this thinking and suggest 1"+/hr
snowfall rates moving northward from southern into central IA
06-09z with only a minor decrease heading toward sunrise.
Confidence is high that this will be followed by blizzard
conditions later Friday considering the heavy snow, cold
temperatures, and wind gusts to 45 mph by afternoon.

&&

.DISCUSSION.../This afternoon through Wednesday/
Issued at 224 PM CST Thu Jan 11 2024

Key Messages:

- Another heavy snow event will occur tonight into Saturday
  morning, with a wide swath of 5-7 inches or more across nearly
  the entire area.
- Strong winds, continuing light snow, and deep snow on the ground
  will combine to produce blizzard conditions and make travel very
  dangerous from around midday Friday through Friday night.
- Dangerously cold temperatures and wind chills will dominate the
  region from later Saturday into Tuesday.

Obviously the primary focus of the forecast is the significant
winter storm and Arctic cold outbreak slated to impact Iowa over
the next several days. Currently a large 500 mb low is centered
over western Canada, while a rather energetic southern stream
trough moving eastward across the Rocky Mountain region of the
U.S. As this trough emerges into the High Plains tonight it will
sharpen and deepen quickly, then become positively tilted and
close off as it moves northeastward over the Midwest on Friday and
into the Great Lakes region by Friday night. This will induce
rapid surface cyclogenesis, with a large low tracking from
Oklahoma into Missouri tonight, then bombing out over Illinois on
Friday. The large precipitation shield developing around the
northwest hemisphere of this gyre will fall smack dab over Iowa,
spreading in from the south and southwest tonight and out of our
northeastern counties on Friday morning. Within this initial surge
of precipitation, strong forcing and deep saturation through the
dendritic growth layer will promote significant QPF and snowfall
amounts, with snow accumulation rates exceeding an inch per hour
for several hours overnight. This will make travel very hazardous
overnight, with accumulations of around 5-7 inches on top of the
existing snow pack and remaining snow on roadways from the storm
earlier this week. No significant changes were made to total
snowfall amounts with the forecast update and the Winter Storm
Warning remains in effect overnight. It is worth noting that the
forecast snowfall totals from the upcoming storm combined with
those from the storm earlier this week will raise five-day
snowfall amounts from Monday through Friday of this week to near
all-time records, making this one of the snowiest weeks in history
for portions of the area.

During the day on Friday as the surface cyclone deepens rapidly
and passes just to our southeast, winds will increase
significantly from the northwest with cold air advection kicking
in. Most model guidance indicates gusts to around 35 KT from
around midday or early afternoon into Friday night, and
soundings/cross-sections show that while overall moisture will be
lower/shallower, it will be deeper within the DGZ as the column
cools, and weak but persistent lift will promote lingering light
snowfall through the day and into the night. While accumulations
during that time will be lighter than with the initial heavier
snow event tonight, it will be falling on top of a very deep snow
pack with the fresh heavier snow from tonight and the pre-
existing snow from earlier this week. This has rendered most
ditches full and surfaces slick, and the additional falling snow
combined with what is lofted off the deep existing snow pack will
promote significant blowing snow and very low
visibility/dangerous travel conditions through Friday afternoon
and night. HREF and other high-resolution guidance shows positive
probabilities for blizzard conditions, supported by the
persistently strong forecast winds, and given the enhancing
factors of the existing snow pack and increased impacts on a
weekday afternoon/evening, have issued a Blizzard Warning from
late Friday morning through Friday night. The strong winds will
actually persist or re-surge during the day Saturday when blowing
snow will continue to be a problem, however, with falling snow
having ended by that time confidence in visibilities and impacts
that would support a Blizzard Warning is lower, and a later
transition to another winter weather hazard type is likely.

Aside from the forecast considerations and hazards associated with
the prolonged snowfall and strong winds, extremely cold air will
also surge into the region behind this storm system and persist
for several days. High temperatures will only be generally in the
single digits above zero on Saturday, then on Sunday and Monday
remain below zero through the day, and on Tuesday only barely peek
above again. Combined with the strong winds, especially during the
earlier part of this period, the result will be multiple days of
nearly continuous wind chill values below -30, and below -40 at
times, making for one of the most prolonged dangerously cold
periods in recent memory across central Iowa. A Wind Chill Watch
has been issued from Saturday night through Tuesday morning, and
this will likely be upgraded to a Warning sometime tomorrow. All
time outdoors should be limited during this Arctic cold outbreak,
and any appropriate precautions taken when venturing out.

From Tuesday through the remainder of the forecast period no
significant storm systems, precipitation chances, or hazardous
weather events are foreseen at this time. However, temperatures
will remain generally cold and the deep snow pack in place, so
minor blowing snow and slick travel spots may persist for quite
some time.

&&

.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 603 PM CST Thu Jan 11 2024

Conditions varied from VFR in mid clouds northeast down to
MVFR/IFR farther south and west where lower ceilings were in
place. Much of the precipitation in central IA was still aloft
for the time being. Snow is expected to overspread central IA SW
to NE later this evening however, and last well into Friday.
Winds will increase tomorrow as well, with 30-40kt gusts possible.
Ceilings, falling snow, and blowing snow will all contribute to
widespread and prolonged IFR/LIFR conditions with blizzard
conditions anticipated tomorrow.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 10 AM CST Friday for IAZ004>007-
015>017-023>028-033>039-044>050-057>062-070>075-081>086-092>097.

Blizzard Warning from 10 AM Friday to 6 AM CST Saturday for
IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097.

Wind Chill Watch from Saturday evening through Tuesday morning
for IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097.

&&

UPDATE...Small
DISCUSSION...Lee
AVIATION...Small

Hazardous Weather Outlook
National Weather Service Des Moines IA
319 PM CST Thu Jan 11 2024

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-122130-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
319 PM CST Thu Jan 11 2024

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

A Winter Storm Warning is in effect for the area starting tonight.
Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

A Blizzard Warning is in effect from late Friday morning through
Friday night. A Wind Chill Watch is in effect for the area from
Saturday Evening though Tuesday morning. Please refer to the
National Weather Service website at weather.gov/desmoines for
further details.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed. However, snowfall amounts
are always appreciated.