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April 18th-19th Winter Storm

MNstorms

By MNstorms,
in Lakes/Ohio Valley

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beavis1729

beavis1729

Posted
Posted

NWS Des Moines: 

Area Forecast Discussion
National Weather Service Des Moines IA
649 AM CDT Tue Apr 17 2018

.SHORT TERM.../Today through Wednesday Night/
Issued at 332 AM CDT Tue Apr 17 2018

Confidence: Medium

Today will be pleasant compared to later tonight into Wednesday.
Clouds will be on the increase today ahead of the storm with
cloudy skies tonight. Highs today will recover to the mid to
upper 30s north and the upper 40s to lower 50s over the south.
Tonight with the low passing southeast of the region temperatures
will fall into the upper 20s north and in the mid 30s across the
south. The freezing line will be near the US 30 corridor.

Storm still on track to reach Iowa later tonight and bring a quick
hit of snow/freezing rain/and wind.  Models tonight are tracking
farther south and colder than earlier runs.  The GFS/Euro/NAM all
suggest abundant moisture available for snow production across the
north. Deep lift in the H700-H600 layer with potential for
elevated instability over the east may lead to more widespread
heavy snow farther south. H850 inflow into the storm of 40 to 45
kts from 09z through 17z will aid in 1 inch snowfall rates per
hour across the north during that time. Though saturation may take
until about 07z across the northwest...went ahead and began
warnings/adv over the northwest. Once the precip begins it will
quickly cause some impacts with some light icing/sleet and a quick
changeover to all snow by 09z as rates pick up over the northwest
for the remainder of the day. Over the northeast rain/freezing
rain will being initially with a changeover taking place nearer
09z to 12z. None the less...morning commutes will be impacted over
most of the north. Farther south a mixture of light icing and
light snow will be possible. Though road temperatures may limit
any road icing along the US Highway corridor north toward US
20...decided to add a row of counties to for chance that some
bridges/overpasses may become slick or briefly ice up in the
morning hours. If impacts lessen during the day Wednesday...this
portion of the advisory may end earlier. 

This storm has a lot going for it...possible convection along with strong forcing. 
Some uncertainty still remains regarding the amount of qpf and how far south the storm may still trend which will affect snowfall
amounts. Generally looking for a 6 to 8 inch area of snow north in
the warning areas with 2 to 5 inches in the advisory areas along
with a glazing of ice there. Day shift will need to carefully
evaluate trends and again later tonight. Highs tomorrow will warm
into the mid to upper 30s south of US 30 - at best with
temperatures holding in the lower 30s over the north. With the
snowfall rates quite high...this event will support snow below 35
degrees and likely some compaction will take place but with high
snow:water ratios up to 15 to 17 due to tremendous forcing...
should be able to see more than 6 inches in the warning areas.
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Luftfeuchtigkeit

Luftfeuchtigkeit

Posted
Posted
1 hour ago, beavis1729 said:

NWS Des Moines: 


Area Forecast Discussion
National Weather Service Des Moines IA
649 AM CDT Tue Apr 17 2018

.SHORT TERM.../Today through Wednesday Night/
Issued at 332 AM CDT Tue Apr 17 2018

Confidence: Medium

Today will be pleasant compared to later tonight into Wednesday.
Clouds will be on the increase today ahead of the storm with
cloudy skies tonight. Highs today will recover to the mid to
upper 30s north and the upper 40s to lower 50s over the south.
Tonight with the low passing southeast of the region temperatures
will fall into the upper 20s north and in the mid 30s across the
south. The freezing line will be near the US 30 corridor.

Storm still on track to reach Iowa later tonight and bring a quick
hit of snow/freezing rain/and wind.  Models tonight are tracking
farther south and colder than earlier runs.  The GFS/Euro/NAM all
suggest abundant moisture available for snow production across the
north. Deep lift in the H700-H600 layer with potential for
elevated instability over the east may lead to more widespread
heavy snow farther south. H850 inflow into the storm of 40 to 45
kts from 09z through 17z will aid in 1 inch snowfall rates per
hour across the north during that time. Though saturation may take
until about 07z across the northwest...went ahead and began
warnings/adv over the northwest. Once the precip begins it will
quickly cause some impacts with some light icing/sleet and a quick
changeover to all snow by 09z as rates pick up over the northwest
for the remainder of the day. Over the northeast rain/freezing
rain will being initially with a changeover taking place nearer
09z to 12z. None the less...morning commutes will be impacted over
most of the north. Farther south a mixture of light icing and
light snow will be possible. Though road temperatures may limit
any road icing along the US Highway corridor north toward US
20...decided to add a row of counties to for chance that some
bridges/overpasses may become slick or briefly ice up in the
morning hours. If impacts lessen during the day Wednesday...this
portion of the advisory may end earlier. 

This storm has a lot going for it...possible convection along with strong forcing. 
Some uncertainty still remains regarding the amount of qpf and how far south the storm may still trend which will affect snowfall
amounts. Generally looking for a 6 to 8 inch area of snow north in
the warning areas with 2 to 5 inches in the advisory areas along
with a glazing of ice there. Day shift will need to carefully
evaluate trends and again later tonight. Highs tomorrow will warm
into the mid to upper 30s south of US 30 - at best with
temperatures holding in the lower 30s over the north. With the
snowfall rates quite high...this event will support snow below 35
degrees and likely some compaction will take place but with high
snow:water ratios up to 15 to 17 due to tremendous forcing...
should be able to see more than 6 inches in the warning areas.

"but with high snow:water ratios up to 15 to 17 due to tremendous forcing..."

High ratios on April 18th? This is nuts.  Not sure they will be right about that, but it will definitely be interesting to watch. 

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Hoosier

Hoosier

Posted
Posted
2 hours ago, Baum said:

Through all of this nightmare of a spring Chicago has pretty much missed every big snow while those north, south, east, and west have cashed in. Maybe this is what'll take to get to sunny and 75.

Yeah, not a great deal to show for it.  00z Euro had the potential for a couple inches as far south as us.

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Hoosier

Hoosier

Posted
Posted
2 hours ago, beavis1729 said:

Yep. While unlikely...ORD needs more than 1.3” with this storm to be among the Top 5 heaviest snowfalls so late in the season. 

3.1” on 4/23/1967

2.5” on 4/25/1910

2.0” on 4/19/1888

1.6” on 5/1/1940

1.3” on 5/3/1907

Also a 2.1" on 4/23/1910

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snowstormcanuck

snowstormcanuck

Posted
Posted
20 minutes ago, Hoosier said:

Kind of hard to figure why DVN went with a warning for some areas.  The amounts in the warning text don't fit with typical warning criteria.  I do think it is possible they are lowballing amounts a bit but that is a different issue.

Seasonality? I seem to remember NWS offices issuing warnings for snow amounts below warning criteria if they were unusually timed (either really early or really late in the season), because they may catch people off-guard. That being said, I'm thinking for that part of the Midwest appreciable accumulating snow is not that uncommon in mid-April.

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Hoosier

Hoosier

Posted
Posted
3 minutes ago, snowstormcanuck said:

Seasonality? I seem to remember NWS offices issuing warnings for snow amounts below warning criteria if they were unusually timed (either really early or really late in the season), because they may catch people off-guard. That being said, I'm thinking for that part of the Midwest appreciable accumulating snow is not that uncommon in mid-April.

"Out of season" could be a possible explanation in some circumstances, but they used advisories for relatively similar amounts for the storm from a couple days ago.

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Hoosier

Hoosier

Posted
Posted
2 minutes ago, cyclone77 said:

Looks like a kitchen sink kind of event for the QCA.  Probably gonna be a nice period of pingers and cold rain before shifting to a little light snow later in the afternoon.  DAB most likely.  Interesting little wave.  

Your last time lapse of melting snow is going to come in June at this rate lol. Maybe, just maybe, this will be the last one for our areas.

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cyclone77

cyclone77

Posted
Posted
10 minutes ago, Hoosier said:

Your last time lapse of melting snow is going to come in June at this rate lol. Maybe, just maybe, this will be the last one for our areas.

Haha.  I actually thought about doing another one yesterday morning, but it would have basically been exactly like the last one.  Maybe I'll do one tomorrow in case something sticks in the afternoon.  

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ams30721us

ams30721us

Posted
Posted

Man....I love this whole "Midwest Spring" weather! Ha

From DVN:

Quote 

Through sunset and this evening quiet and dry conditions will be
seen across the area. Attention then turns to late tonight.

As expected there has been a southward shift with the storm system.
Atmospheric profiles show considerable dry air being pulled into the
area which is slowing down the arrival of the precipiation a little.
The possibility does exist that the storm system may shift a bit
further south.

However, the forcing developing late tonight into Wednesday morning
is very impressive. Thus the dry air will quickly get overcome in
the far west in the pre-dawn hours.

The intense forcing combined with an unstable layer of air aloft
means that thunderstorms will be possible late tonight and Wednesday
morning.

The dry air will also allow the atmosphere to quickly cool Wednesday
morning forcing the precipitation over to all snow for some areas.

The sensible weather Wednesday will be quite interesting. The
potential is there for thundersleet, thundersnow, and potentially
thunder freezing rain.

Wednesday afternoon the strongest forcing moves east of the area
allowing the overall intensity of the precipitation to decrease.

The cooling of the atmosphere means that temperatures will likely
stay right around or just under freezing for much of the day. High
temperatures on Wednesday may not occur until mid to late Wednesday
afternoon.

 

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cyclone77

cyclone77

Posted
Posted

Big difference in precip types for this area between the HRRR and NAM.  NAMs are much more bullish in bringing in mixed/snow for precip vs mostly a rain event on the HRRR runs.  If HRRR ends up being correct we may not get any measurable snow, but if the NAMs are correct an inch of slushy accumulation is a possibility.  

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Hoosier

Hoosier

Posted
Posted
15 minutes ago, cyclone77 said:

Big difference in precip types for this area between the HRRR and NAM.  NAMs are much more bullish in bringing in mixed/snow for precip vs mostly a rain event on the HRRR runs.  If HRRR ends up being correct we may not get any measurable snow, but if the NAMs are correct an inch of slushy accumulation is a possibility.  

I'd lean a bit more on the cooler models personally.  It seems like another case of some of the models being like "hey, it's April, better warm the boundary layer excessively despite precip."  

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