Winter Storm in Iowa, April 8 to 9, 2018

Area Forecast Discussion
National Weather Service Des Moines IA
641 AM CDT Sun Apr 8 2018

.SHORT TERM.../Today through Tonight/
Issued at 315 AM CDT Sun Apr 8 2018

Shortwave currently passing across the Front Range of the Rockies
will continue to progress east today.  Warm advection across the
Plains ahead of the shortwave is increasing with isentropic lift
strengthening.  This has lead to the development of a broad swath of
snow from northeast/north central Nebraska northwest into Montana.
Models continue to indicate the isentropic lift moving into Iowa
this morning and persisting into tonight.  Pressure deficits will
drop rather quickly in west central and northwest areas initially
with precipitation moving into those areas by mid morning.  The
strongest lift remains across northern Iowa into this afternoon and
this will likely be the area of higher QPF.  Snow ratios may
initially be rather robust but may not be realized as much in
impacts with relatively quick compaction and increasing road
temperatures today.  Farther south, the RAP and HRRR remain dry into
southern Iowa but they seem to be keeping the low levels much too
dry.  Given the decent lift by midday into the afternoon, some light
precipitation seem likely in the south as well.  Precipitation types
in the south may waffle between rain and snow as temperatures will
be a bit higher. The higher precipitation rates in the south will
likely be associated with snow and lighter rates with sprinkles or
very light rain.

For tonight, the upper low will drift southeast toward the state
with relatively good forcing persisting across much of the forecast
area. However, the mid levels are drying at this point and there is
likely some threat of mixed precipitation on the western fringe of
the precipitation area where the dry will be most pronounced.
Farther to the north and east, deeper saturation will persist with
snow the likely precipitation type into tonight.  Precipitation will
be ending from west to east late tonight as the upper system and
forcing slowly progress through the state.  Total snow amounts
remain similar to previous forecast with highest amounts near the
Minnesota border.  Estherville will top out around 6 inches with 4
or more generally along and north of Highway 20 with up to 3-3.5"
along the Highway 30 corridor.  Therefore, have expanded the
advisory farther west along Highway 30 as amounts from Jefferson to
Ames are very similar to those in Marshalltown where the advisory
already exists.

.LONG TERM.../Monday through Saturday/
Issued at 310 AM CDT Sun Apr 8 2018

Long term period begins Monday morning with possibly some
lingering light snow or freezing rain, but precip chances cease
by 18z as deep layer subsidence increases behind the departing
wave. Northerly winds keep temperatures well below normal through
the day, but a long awaited warm up commences Tuesday as upper
level ridging finally starts to build east of the Rockies. We will
more typical spring like conditions by Wednesday as breezy
southwest winds help push temperatures into the 50s and 60s. A
shortwave trough quickly slides through the area Wednesday
evening, but dry mid- level air will limit most precip potential.

Persistent southerly flow in response to a deepening western
conus trough will support a few more warm days to end the work
week. The Des Moines area could see its first 70 degree day of
the year by Friday. All long range model guidance continues to
show a deep low emerging into the central or northern Plains by
the weekend. Gusty winds and a return to below normal temperatures
are likely, but the precipitation potential is much more nebulous
at this time due to significant model differences in the track
and evolution of this system. Slight to low chance PoPs from the
model blend are appropriate until the models begin to converge on
a unified solution.

&&

.AVIATION.../For the 12Z TAFS through 12Z Monday morning/
Issued at 641 AM CDT Sun Apr 8 2018

System will move into the state today with ceilings lowering with
precipitation becoming widespread by this afternoon. MVFR to IFR
conditions will be common after 18Z and these poor conditions will
persist into tonight with areas of snow and even brief fzra at
times. Visibilities will also be restricted due to falling
precipitation for much of the period. Surface winds will be modest
to strong from the southeast today but weaken into tonight.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 1 PM this afternoon to 7 AM CDT
Monday for IAZ004>007-015>017-023>028-033>039-046>050.

&&

SHORT TERM...Cogil
LONG TERM...Martin
AVIATION...Cogil

Hazardous Weather Outlook
National Weather Service Des Moines IA
333 AM CDT Sun Apr 8 2018

IAZ004>007-015>017-023>028-033>039-046>050-090845-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Greene-Boone-Story-
Marshall-Tama-
333 AM CDT Sun Apr 8 2018

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

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

.DAYS TWO THROUGH SEVEN...Monday through Saturday

A few thunderstorms are possible Thursday night into Friday. The
threat for severe weather is low at this time.

.SPOTTER INFORMATION STATEMENT...

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

IAZ044-045-057>062-070>075-081>086-092>097-090845-
Crawford-Carroll-Audubon-Guthrie-Dallas-Polk-Jasper-Poweshiek-
Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas-
Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis-
333 AM CDT Sun Apr 8 2018

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Light snowfall will overspread much of central and southern Iowa
this afternoon and evening, possibly continuing into Sunday night.
Temperatures hovering near freezing will limit most accumulation
to grassy or elevated surfaces, but a few slick roadways are
still possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

A few thunderstorms are possible Thursday night into Friday. The
threat for severe weather is low at this time.

.SPOTTER INFORMATION STATEMENT...

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