Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdmx 221657 
afddmx

Area forecast discussion
National Weather Service Des Moines Iowa
1057 am CST Mon Jan 22 2018

Update...
issued at 1055 am CST Mon Jan 22 2018

Ongoing blizzard over portions of west-central to northwest Iowa.
Current precipitation band extending from Storm Lake through
Algona eastward through Mason City will produce some significant
heavy snow through the late morning into the early afternoon
hours. This band looks to pivot over the northwest (roughly around
the Estherville area) and become more oriented southwest to
northeast this afternoon. Expecting the blizzard conditions to
persist for much of the day in the far northwest. Further south,
looks to be brief break in the heavy snow from Carroll to Denison
before the heavy snow band moves back into this location by around
21z this afternoon. Still the potential for convectively enhance
precipitation with the upright convection and negative epv over
western to northwest Iowa. Already had a brief period of
lightning, mainly thunder sleet, in the Pocahontas area earlier.
Thus, snowfall rates of 1-2 inches per hour are likely at times
within the headline areas into the afternoon. We continue to
receive sleet/freezing rain reports within the transition zone on
the southeast edge heavy snow band, and this is likely to
continue with the dry slot punching in from the south-southeast.
Also with the dry slot, lowered pops in the southeast before the
cold air advection later this afternoon and evening brings the snow.

&&

Short term.../today through tonight/
issued at 346 am CST Mon Jan 22 2018

The well advertised blizzard/winter storm/rain/thunder event has
arrived in Iowa. Models have cinched up on a track for the low...
placing it over southeast Iowa at 12z Mon, and east of Iowa by 06z Tue.
Important to note that latest trends have been to push the track
of the low, and thus the warm air sector ever so slightly further
to the west-northwest. The ramifications of this trend have been to lower
snow amounts in our northeastern County Warning Area. Left the Winter Storm
Warning going in Worth County, but it may struggle to verify. If
this trend continues through the day shift, Worth and Cerro Gordo
counties may struggle to get out of the tr. To 2 inch range for
snow.

Winds will be a major factor in impacts across
northern/northwestern Iowa. At 09z, Storm Lake had winds of 31
mph, gusting to 40 mph. Confidence is very high in strong winds
across Iowa today, with the strongest winds west of I-35, right
over the area running with a Blizzard Warning. All ingredients for
high winds present as low passes through Iowa and pressure
gradient spreads eastward. 3-hr pressure change nears +6mb over southeast
Iowa, so have amplified winds from Carroll to Cass County vs
previous forecast. Will be a somewhat fascinating wind gradient
today... placement of low over Iowa mitigates pressure gradient.
Winds from Des Moines to Ottumwa may struggle to reach 10 to 15
mph, whereas winds in Estherville will likely reach 30 mph, with
a gust of 50 mph looking very plausible for a brief time today.

Cannot emphasize hazardous travel conditions expected in Blizzard
Warning area. With high confidence of widespread winds sustained
in the 25 to 35 mph range, with gusts of 40 to 50 mph possible,
moderate to heavy snow will fall in the form of blowing snow,
reducing visibility to near zero at times and causing blowing and
drifting snow onto roadways. "Stucco" type snow also possible, as
snow will likley initially be of the wet and heavy variety.

By 12z Tue, system should be east of Iowa. Pressure gradient will
also to relax through the overnight tonight, meaning winds should
start to gradually diminish to the 10 to 20 mph range, beginning
around 00z Tue.

Long term.../Tuesday through Sunday/
issued at 346 am CST Mon Jan 22 2018

The area of low pressure will be over lower Michigan by Tuesday
morning with the precipitation having ended across the forecast
area with drier air arriving. Cyclonic flow will be over the state
to begin the day before weak ridging arrives in the afternoon.
This will lead to gradual diminishing northwest winds. A few
patches of stratus will likely linger part of the day though due
to the cyclonic flow. Another short wave will arrive Tuesday night
and will bring modest kinematic forcing and saturating profiles
and may result in a few flurries or brief light snow. Snow mention
for Tuesday night is currently not in the forecast but may need
to be added. At this point, it appears to be little to no impact.
Surface high pressure ridge will move across Iowa on Wednesday.
This will be followed by the upper flow transitioning to southwest
flow toward the end of the week as a large trough develops to the
west. This will bring warm advection back to the state and
temperatures back into the 40s and 50s over the snow free areas.
The next system will arrive Friday night and will bring the next
chance for precipitation.

Temperatures through much of the forecast period will be dependent
on snow cover. High temperatures over the northwest will be
dampened due to the new snow while warmer temperatures will occur
across the remainder of the area. High temperatures for Tuesday
will range from the mid 20s north to mid 30s south. Better melting
potential will arrive over the northwest with the end of the week
warmer temperatures.

&&

Aviation.../for the 12z tafs through 12z Tuesday morning/
issued at 540 am CST Mon Jan 22 2018

Tafs will likely be a mess throughout today and into tonight.
Kfod will be dealing with light to moderate impact mixed precip
today, and kmcw and Kalo will be dealing with very low impact
mixed precip tonight.

Throughout today, confidence is high there will be cigs and vsbys
that bounce around LIFR to IFR. Have stuck with general trends
versus trying to pinpoint a specific hour and location in a
specific category. Amendments likely throughout the day.

Confidence high that precip should be east of kmcw and Kalo by 12z
Tue... though winds will still likely be up in the 15 to 25 kt
range.



&&

Dmx watches/warnings/advisories...
Winter Weather Advisory until midnight CST tonight for iaz017-
025-035-045-046-057.

Blizzard Warning until midnight CST tonight for iaz004>006-015-
023-033-044.

Winter Storm Warning until midnight CST tonight for iaz007-016-
024-034.

&&

$$

National Weather Service Glossary of Abbreviations