Mothers Day Snowstorm?

[Hoosier]

It's interesting to look at the forecast soundings for this one.  Take the 18z RAP for example.  I was poking around the I-80 corridor and noticed that it's changing areas over to snow even with freezing level/wet bulb heights of like 3500 feet.  It is very difficult to get snow to the surface with a wet bulb height like that (unless in higher elevations) but I think the reason that the model is changing it to snow may be because most of the layer under that is literally only a few tenths of a degree C above 0C.  Regardless, to say this is a borderline setup is an understatement.  

[Hoosier]

Southward nudges continue. 

Obviously not focusing on amounts as much as the corridor in play.

[cyclone77]

First flakes this fall could be less than 5 months away. 

[madwx]

wagons definitely south on this one

[Hoosier]

They should've had Gino Izzi do the afd for this May snow, though that might have been cruel and unusual punishment for him.

 

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
247 PM CDT Sat May 8 2021

.SHORT TERM...
245 PM CDT

Through Sunday...

Mother`s Day will feature weather conditions more characteristic
to St. Patrick`s Day, with cloudy, blustery, and very wet
conditions for the morning. The main forecast messages are:

* Rain onset spreads from west-to-east this evening with possibly
  brief ice pellets mixing in at first

* Rain increases in intensity late this evening into overnight,
  with some embedded thunderstorms possible mainly south of I-80

* Potential for a mix with snow has increased for primarily a
  portion of north central Illinois and eastward toward the Fox
  River Valley part of northeast Illinois late tonight into early
  Sunday morning

* Rainfall of 1 to 2 inches for most locations along/south of
  I-88, with isolated over 2 inches possible, though flooding
  threat should remain low

* Gusty northeast winds keep temperatures down through Sunday,
  even as rain ends west to east late morning into afternoon

A lot to unpack for the rest of this weekend. Looking upstream on
GOES-16 water vapor imagery shows a well-defined, strong upper low
over Montana moving southeast bringing with it 100 meter 500 mb
height falls. In still a somewhat split flow pattern, a 100 kt
subtropical jet moving into the Central Plains ahead of this wave
will result in a deepening surface low below 1000 mb into
Missouri overnight. This should spread into an area of some
coupled jet divergence over our region overnight into Sunday
morning, resulting in the mid-latitude system overall maturing as
it heads over Illinois/Indiana. The synoptic pattern is such that
a rain shield should gradually blossom through the evening
followed by a steady moderate to more heavy rain with the stronger
upper forcing overnight into early Sunday.

Model guidance is in decent agreement with this synoptic
evolution, though some spread exists and given where we are
located within the baroclinic leaf, a subtle difference in low
track will alter the heavier QPF axis, the area where a few hour
wet snow mix is favored, and the magnitude of the winds. Given a
hefty footprint of convection anticipated over the Central Plains
into Missouri River Valley tonight, this could result in a more
south track within the model solution envelope, such as the RAP
has been advertising and the 12Z ECMWF depicts. The HRRR has also
trended ever so slightly south from its earlier solutions today.
This is the more favored route, but a more north solution such as
the 12Z NAM cannot be fully discounted yet.

All model guidance agree on the strong mid-level baroclinic zone
to our west (18C difference from LBF to MPX on 12Z RAOBs)
tightening over the area tonight and a sharpened frontogenetic
vertical circulation. This is a longer duration zone of such
forcing and this is the zone most favored to see the heaviest rain
rates on strong moisture convergence and ascent. It`s also along
this where enough wet bulb cooling may occur to support snow.
Given marginal low-level melting profiles (<10 J/kg of positive
energy using a local revised Bourgouin technique) and upright
instability predicted on an area of steeper 650-500 mb lapse
rates, there likely will be an area that does change over. As
mentioned earlier, there certainly is some wobble room where this
is, but a consensus/middle ground solution is toward I-88. Warm
surface temperatures will result in quite a bit of immediate
melting, but if a band of instability-driven heavier rates
persists for 2-3 hours as mainly snow, then could certainly see
accumulation on at least grassy and elevated surfaces. While a
tail of the solution envelope, f-gen magnitude events such as this
can provide a mesoscale-level (multi-county scale) quick several
inches. There have been a few CAMs run that have shown something
like this, though seem to be much too robust in their efficiency
of turning 100% QPF to snow, and at too high of ratio.

Further east with increasing easterly winds off the warmer waters
of Lake Michigan, the potential for snow drops into the heart of
the Chicago metro as well as far northwest Indiana. South of I-80,
more melting energy exists thanks to the proximity of the 850 and
700 mb lows passing closely by to the south.

It is always a true challenge with predicting snow during these
tail end of season events, as thermal profiles are marginal and
present one striking failure mode. Also there could be enough
moisture transport robbing from the south by daybreak to start
reducing the precipitation rates by early Sunday morning to the
point where overcoming the marginal low-level temperatures becomes
quite iffy.

[Brian D]

This something you normally see in NE MN this time of year, not N IL/IN. Enjoy the chill.

 

[Cary67]

54 minutes ago, Hoosier said:

Southward nudges continue. 

Obviously not focusing on amounts as much as the corridor in play.

Another miss with heavier precip for northern tier counties. Rain gauge hasn't been useful yet this spring

[madwx]

the real disappointment is that the clouds from this system are going to ruin my Chinese rocket debris views tonight

[Hoosier]

22 minutes ago, madwx said:

the real disappointment is that the clouds from this system are going to ruin my Chinese rocket debris views tonight

Do you know how much of a heads up there will be for possible impact area after it enters the atmosphere?

On the subject of this thread, I admit I am rooting for the snow at this point.  I missed out on the recent May snows and haven't seen snow in May since I was a little kid.  Would prefer a spring/summer like pattern for sure, but in this instance the alternative is a cold rain with temps in the 30s so why not cheer on the snow.  If anything falls it will be gone soon enough.

[madwx]

5 minutes ago, Hoosier said:

Do you know how much of a heads up there will be for possible impact area after it enters the atmosphere?

On the subject of this thread, I admit I am rooting for the snow at this point.  I missed out on the recent May snows and haven't seen snow in May since I was a little kid.  Would prefer a spring/summer like pattern for sure, but in this instance the alternative is a cold rain with temps in the 30s so why not cheer on the snow.  If anything falls it will be gone soon enough.

 

https://twitter.com/AerospaceCorp

 

I've been using this site to track the predicted landing spot.  Obviously there are many dynamics at play that we can't measure and being off by 30 mins means it could reenter about 1/4 of the globe away.  but it will most like be somewhere along the yellow or blue lines in this image around 10 pm Central tonight, with the best guess of the N Atlantic right now

[hawkeye_wx]

A spotter is currently reporting big snow flakes up near Mason City.

[cyclone77]

4 minutes ago, hawkeye_wx said:

A spotter is currently reporting big snow flakes up near Mason City.

This time last week that same area had temps in the low to mid 90s lol.  Several ob sites in the 37-39 degree range in that area.

Rain just started here.

[Hoosier]

8 minutes ago, hawkeye_wx said:

A spotter is currently reporting big snow flakes up near Mason City.

Don't think any model had flakes that early.

[Hoosier]

Thinking back on really fringe season anomalous snows that I have witnessed, the one that comes to mind on the other end of the spectrum is 10/7/2000.  That was a couple inches of extremely wet snow that did a number on the branches since leaf drop really hadn't begun in earnest yet.  

If this just ends up being some snow mixed in, then there's obviously no comparison.  But if we can somehow manage to pull out some accumulation, then it becomes an interesting thought as to which one stretches climo more.

[RCNYILWX]

You never know with these intense f-gen bands. I think if it snows heavy enough for long enough, a couple sloppy inches on colder surfaces certainly possible. The most likely outcome probably still is mostly white rain aside from a sloppy coating here and there (similar to what 3km NAM has been showing), but will be interesting to see what we wake up to.

Sent from my SM-G998U using Tapatalk

[Hoosier]

Can you tell we're deep into Spring with the pencil thin band of snow where cooling is maximized?

[LibertyBell]

4 hours ago, madwx said:

 

https://twitter.com/AerospaceCorp

 

I've been using this site to track the predicted landing spot.  Obviously there are many dynamics at play that we can't measure and being off by 30 mins means it could reenter about 1/4 of the globe away.  but it will most like be somewhere along the yellow or blue lines in this image around 10 pm Central tonight, with the best guess of the N Atlantic right now

wow the yellow line model has this flying right over NYC and Long Island on its way to the middle of the Atlantic, how much would that have to be off to actually hit the east coast here?

 

[madwx]

10 minutes ago, LibertyBell said:

wow the yellow line model has this flying right over NYC and Long Island on its way to the middle of the Atlantic, how much would that have to be off to actually hit the east coast here?

 

it changes very rapidly.   For example it's now expected to reenter about a half hour earlier which would mean it impacts in the pacific ocean.   Each horizontal dash on the yellow/blue line is five minutes in time

[Hoosier]

No chance of verifying, but the 00z NAM is insane.  Almost tempting to post the clown map to document the absurdity.

[Hoosier]

1 minute ago, madwx said:

it changes very rapidly.   For example it's now expected to reenter about a half hour earlier which would mean it impacts in the pacific ocean.   Each horizontal dash on the yellow/blue line is five minutes in time

Is the right way of interpreting that map being that if it were to strike in the US, it wouldn't be north of the yellow line?

[LibertyBell]

7 minutes ago, madwx said:

it changes very rapidly.   For example it's now expected to reenter about a half hour earlier which would mean it impacts in the pacific ocean.   Each horizontal dash on the yellow/blue line is five minutes in time

wow these are more variable than weather forecasts.

 

Could you imagine if an asteroid or comet were headed here, I wonder how well we can forecast those?

 

[LibertyBell]

6 minutes ago, Hoosier said:

Is the right way of interpreting that map being that if it were to strike in the US, it wouldn't be north of the yellow line?

wait, the three lines aren't three different model interpretations of its future path?

 

[madwx]

14 minutes ago, Hoosier said:

Is the right way of interpreting that map being that if it were to strike in the US, it wouldn't be north of the yellow line?

Correct, the maximum north latitude it will track is around 41.5 degrees north.

 

7 minutes ago, LibertyBell said:

wait, the three lines aren't three different model interpretations of its future path?

 

 

That is its path over the 3 hour period it is expected to reenter, with the best estimate reentry time in the middle where the satellite icon is.  The blue is the track before the expected reentry and the yellow is the track after the reentry time but still in the window

[madwx]

the aformentioned NAM run.  Kuchera totals

[Hoosier]

The NAM looks too generous with precip amounts on the northern edge.  Certainly the vast majority of evidence points against that.

[Hoosier]

Here's something you don't see a lot.  A snow (or at least snow-ish) forecast sounding with a pwat not far under an inch (0.89")

[Hoosier]

4-7 am seems like a good timeframe to start mixing with snow here.  Not sure if we'll be able to sustain a complete changeover then.  Then forget about anything sticking after mid morning as precip lightens and now that we are dealing with a sun angle that is equivalent to the first few days of August.

[Cary67]

1 hour ago, Hoosier said:

The NAM looks too generous with precip amounts on the northern edge.  Certainly the vast majority of evidence points against that.

Screwed again here for precip

[Hoosier]

Temp has slid down into the upper 30s

[cyclone77]

Cold moderate rain and 40 here.  Don't think we'll see any snow here.

Up to 0.63" for the event with quite a bit more on the way.