Blizzard and High Wind in Iowa, March 4 to 5, 2025

Area Forecast Discussion
National Weather Service Des Moines IA
545 PM CST Tue Mar 4 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Blizzard conditions with intense winds gusting to around or
  over 60-65 mph and snow tonight into Wednesday - Blizzard
  Warning and High Wind Warning in effect.

- Winter Weather Advisory in place southeast for lighter snow
  amounts and blowing snow.

- Rain with ~1-2" totals ends into tonight as rain changes to
  snow. At least low lying ponding and rises on area streams are
  expected. Ice jam flooding remains possible.

- Next band of snow across central Iowa Thursday night into
  Friday with snow amounts increasing.

&&

.DISCUSSION...
Issued at 402 PM CST Tue Mar 4 2025

Intensifying surface low continues to trek towards and into the area
today into tonight deepening to near or sub 980mb by late tonight as
it moves through northern Missouri into eastern Iowa into tomorrow
morning. Highly amplified winds and precipitation will be associated
with this system with high impact weather expected tonight through
much of the day Wednesday.

QG forcing has been on the increase through the day today with ample
moisture flowing into the area off the Gulf and as a result,
scattered showers this morning have become widespread rain into this
afternoon. Pwats this afternoon top 1" in much of the southeast half
of Iowa with the strongest rain rates persisting the rest of
the afternoon into evening over southern into central Iowa
initially and shifting north and west with time as the low
continues to move into the area. Total rain amounts continue to
look like 1-2" through much of the area with some lighter
amounts to the northwest which may still pose some hydro issues
given frost depths and lingering ice on area rivers. Details on
the hydro situation can be found in the hydro discussion below.

Even though much of the area has warmed into the 40s to 50s today,
colder air has already begun to wrap into the area this afternoon
with locations far northwest, like Estherville, having already
reached the high temperature earlier in the day and since falling
into the 30s. This colder air will continue to move in on the
backside of the low with profiles cooling quickly changing the rain
to snow starting this evening northwest. This rain/snow line will
continue to progress southeast through the later evening into
overnight hours with nearly all areas transitioning to snow prior to
the morning commute by 12/13Z (6-7a). This snow will continue
through the morning before gradually tapering off west to east
midday into early afternoon as the low occludes and forcing begins
to wane. Prior to that, the well pronounced TROWAL with significant
vertical ascent keeps moisture wrapping around the system and
helping to lead to several inches of snow with snow rates that
may reach towards 1" per hour at times, especially north. Snow
totals themselves have increased again with amounts of 2-8" over
the northwest half of the area, the highest amounts furthest
north where the snow rates look to be highest, but are still
1-3" in the southeast half of the area. It does need to continue
to be stressed that the snow amounts themselves will not be the
highest impacts with this event, so do not focus on the snow
totals themselves! The snow will be extremely hard to measure
and some may be blown downstream making it exceptionally
difficult to verify any snow total forecasts.

The reason for this is the other high impact aspect of this system -
the winds. Winds continue to increase this afternoon into tonight,
quickly becoming strong as the pressure gradient increases rapidly
and remains tight through much of the day Wednesday. Hi-res guidance
continues to remain in good agreement with deterministic, ensemble,
and MOS text products keeping high confidence in very strong winds
out of the northwest with sustained winds 30-45 mph and gusts up to
60-65 mph. These are the strongest gradient winds since the
12/15/2021 event. A High Wind Warning remains in effect from tonight
through Wednesday and only changes were to start the northwest a bit
sooner and extend the entire headline a few hours later to provide a
better buffer on when winds start to decrease. May need to
ultimately adjust the High Wind Warning down to a Wind Advisory
towards the later part of the event tomorrow with advisory level
winds extending longer than those in the High Wind Warning, but will
address that in real time. Impacts from the winds themselves could
cause tree or power line damage, but then we also have snow ongoing
during part of the time of these high winds.

As to be expected, when you combine very strong winds and falling
snow, significant visibility reductions are forecasted which may be
as low as 1/4 mile at times and thus meeting Blizzard Warning
criteria. Note that it does not matter the amount of snow for a
blizzard warning, just to have low visibility and strong winds
making for difficult and treacherous travel. The impacts of the snow
+ blowing snow will be felt the most in open and rural areas,
however, significant visibility reductions are still to be expected
while snow is falling even in more protected areas given the strong
winds. As noted previously, the character of the snow will be wet
initially but transition to a more "normal" snow, however, the
high winds will lead to further fracturing of the snowflakes
overall keeping snow ratios on the lower side and helping to
encourage compaction. With the warm and wet antecedent
conditions some snow may melt or adhere to surfaces and when
combined with the blowing snow, fracturing snow flakes, and snow
that may even blow down stream, not to mention the measuring
challenges, there remains some uncertainty in the snow totals
themselves. Regardless, impacts will be significant, especially
while snow is falling, and no changes were made to the
previously issued Blizzard Warning. Have added a Winter Weather
Advisory to the southeast of the Blizzard Warning, however, with
winter impacts still expected in our far east/southeast given
new snow and still the strong winds. Similar to the wind
headline, may need to transition the Blizzard headline in real
time once the snow stops falling, especially for more protected
areas, but as noted in the previous discussion, uncertainty with
the extent of blowable snow continuing after the end of falling
snow precludes us from making those decisions preemptively.

Once we get through this high impact system Wednesday night, there
is only a short break prior to the next system which moves in
Thursday night into Friday. Warm air advection increases through the
night Thursday with snow, or rain mixing with snow initially
later Thursday afternoon, becoming all snow into Thursday night,
the highest snow amounts occurring through the overnight and
into Friday morning. Snow amounts with the system continue to
increase with a band of 2-4 inches currently forecasted around
the Highway 30-20 corridors, but with snow extending through
much of central Iowa. Although most attention has been on the
high impact system tonight into tomorrow, do know that there is
additional snow to end the week keeping an active forecast in
place with additional details to come.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 541 PM CST Tue Mar 4 2025

Widespread rain with IFR/LIFR conditions across the entire area
to being the period. The wind will increase from west to east
overnight as a boundary moves across Iowa and will switch from
southeast to northwest. The wind will peak during the day
Wednesday before slowly diminishing. Peak winds will reach
50kts at most locations. Rain will transition to snow with the
boundary passage and expect significant snow and blowing snow at
most locations though conditions may be slightly better at
KALO/KOTM. The snow will end during the morning Wed but blowing
snow may continue.

&&

.HYDROLOGY...
Issued at 402 PM CST Tue Mar 4 2025

There are no significant changes to thinking regarding hydrologic
concerns from the previous forecast. In the short term, isolated
flash flooding will remain a risk mainly from this evening through
tonight. National Water Model (NWM) rapid onset flooding (ROF) data
suggests the area of most concern is mainly along and south of the I-
80 corridor, west of U.S. Hwy 63, north of IA Hwy 2 and east of IA
Hwy 25. In other words, roughly the southwest 1/4 of the CWA.
Residence time for the moderate to heavy rain will be greatest in
this area. Even though we have no snow on the ground as of Tue
afternoon, the frost still in the ground will reduce infiltration
capacity and thus increase runoff potential. Our office is reporting
a 24 inch frost depth with 3 inches of thaw at the top. Toledo is
reporting a 16 inch frost depth with 5 inches of thaw at the top. So
while some infiltration can occur, ponding of water in low lying
areas is expected along with increased runoff. The main concerns for
the potential isolated flash flooding would primarily be driven by
rainfall over urban areas.

Isolated river flooding remains a concern primarily from Wednesday
into Thursday. Current USGS streamflow data shows values are near to
much below normal meaning there is some extra capacity for runoff.
National Water Model (NWM) medium-range output suggests that
moderate to significant within-bank rises are expected along many
streams mainly across the southeast third to half of the CWA. A
couple locations may reach flood stage with minor flooding being
possible. Our ensemble QPF river forecasts are conservative for this
event. They show a few places in southern Iowa reaching minor flood
stage if we receive about another 1.5 inches more rain than
currently forecast. Similarly, our Hydrologic Ensemble Forecast
System (HEFS) output is conservative for this event as well. Its
reasonable worst case scenario only shows a few points to action
stage. Farther north, ice remains on rivers and this is where the
rainfall could lead to potential isolated ice jams and resultant ice
jam flooding along with rapid local fluctuations in river stages.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 PM CST Wednesday for IAZ004-005-015-
023-024-033-034-044-045.
Blizzard Warning from 9 PM this evening to 3 PM CST Wednesday
for IAZ004>007-015-016-023>025-033>035-044>046-057-058-070.
High Wind Warning from 9 PM this evening to 6 PM CST Wednesday
for IAZ006-007-016-017-025-026-035-036-046-047-057>059-070-071-
081-092.
Blizzard Warning from midnight tonight to 3 PM CST Wednesday
for IAZ017-026>028-036>039-047>049-059>061-071>074-081>084-
092>094.
High Wind Warning from midnight tonight to 6 PM CST Wednesday
for IAZ027-028-037>039-048>050-060>062-072>075-082>086-093>097.
Winter Weather Advisory from 3 AM to 3 PM CST Wednesday for
IAZ050-062-075-085-086-095>097.

&&

DISCUSSION...KCM
AVIATION...Donavon
HYDROLOGY...Zogg

Hazardous Weather Outlook
National Weather Service Des Moines IA
323 PM CST Tue Mar 4 2025

IAZ004>007-015>017-023>028-033>039-044>049-057>061-070>074-
081>084-092>094-051300-
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-Audubon-Guthrie-Dallas-Polk-Jasper-Cass-
Adair-Madison-Warren-Marion-Adams-Union-Clarke-Lucas-Taylor-
Ringgold-Decatur-
323 PM CST Tue Mar 4 2025

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

A Blizzard Warning and a High Wind Warning is in effect for the
area tonight. Please refer to the National Weather Service
website at weather.gov/desmoines for further details.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

A Blizzard Warning and a High Wind Warning are in effect for the
area Wednesday. Please refer to the National Weather Service
website at weather.gov/desmoines for further details.

A band of snow is forecast Thursday night into Friday over some
portion of central Iowa.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated, however reports of rain,
snow and any wind damage are always appreciated.

IAZ050-062-075-085-086-095>097-051300-
Tama-Poweshiek-Mahaska-Monroe-Wapello-Wayne-Appanoose-Davis-
323 PM CST Tue Mar 4 2025

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

A High Wind Warning and a Winter Weather Advisory is in effect
for the area later tonight. Please refer to the National Weather
Service website at weather.gov/desmoines for further details.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

A High Wind Warning and a Winter Weather Advisory is in effect
for the area Wednesday. Please refer to the National Weather
Service website at weather.gov/desmoines for further details.

A band of snow is forecast Thursday night into Friday over some
portion of central Iowa.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated, however reports of rain,
snow and any wind damage are always appreciated.