April 15-17 Snow

[sbnwx85]

What's the record for most Winter Weather Advisories in a season? 

[SchaumburgStormer]

Just hedge south and weaker and  you will be fine. 

[Hoosier]

Was looking back at the storm from the middle of last April

 

 

More of a sw-ne oriented band than this will be

[Chicago Storm]

1 hour ago, SchaumburgStormer said:

Just hedge south and weaker and  you will be fine. 

That trend died.

Last few events were north/snowier.

[Baum]

1 hour ago, Hoosier said:

Was looking back at the storm from the middle of last April

 

 

More of a sw-ne oriented band than this will be

and there was another event after that.

[sbnwx85]

Winter doesn't start until around mid-April anymore. In all seriousness, if trends continue it wouldn't be a surprise to see a relatively narrow swath pick up 6 to 8 inches of snow out of this. Should be plenty of moisture to work with. The snow falling at night/morning will help with accumulations, too. 

[Hoosier]

Looking good for about 1-1.5" overnight/tomorrow morning.

[AWMT30]

NAM looks north at 39 

[Chicago Storm]

8 minutes ago, Hoosier said:

Looking good for about 1-1.5" overnight/tomorrow morning.

Should come in close to 1" here.

Looks like a solid DAB-2" for a good portion of N/C IL.

[Chicago Storm]

2 minutes ago, AWMT30 said:

NAM looks north at 39 

Bigly changes.

Wave is more consolidated, digs a bit more and has more ridging ahead of it.

[AWMT30]

1 minute ago, Chicago Storm said:

Bigly changes.

Wave is more consolidated, digs a bit more and has more ridging ahead of it.

I knew I wasn't tripping when I saw that! Only problem here is it will fall during the day! For the Chicago folks you guys should get it overnight! 

[Hoosier]

Yeah, barring a curveball, this should be a pretty good run either side of I-80 and northward into Chicago. 

[Winter Man]

Oh man...

[cyclone77]

It's happening!  (Sorry too lazy to go look up the gif)

[ILSNOW]

[AWMT30]

What a run from Chicago to Detroit LOL 

[Hoosier]

3 minutes ago, cyclone77 said:

It's happening!  (Sorry too lazy to go look up the gif)

The special appearance by Bernie that I posted yesterday

[hawkeye_wx]

3k NAM isn't quite as far north.

[Cary67]

1 hour ago, ILSNOW said:

Three days of model runs left is an eternity to have this disappear. Remember February 

[HillsdaleMIWeather]

0Z GFS is a smidge northeast

[cyclone77]

4 minutes ago, Cary67 said:

Three days of model runs left is an eternity to have this disappear. Remember February 

That Vince one literally makes me lol every time I see it.

[SchaumburgStormer]

13 minutes ago, Cary67 said:

Three days of model runs left is an eternity to have this disappear. Remember February 

That knife... stop twisting it. 

[Hoosier]

Think there is a possibility we could already see some winter storm watches with the overnight package, especially in the western part of the sub.  Not a slam dunk warning event but a band in excess of 6" looks like a reasonable possibility at this point.

The Halloween snow seems like so long ago.  I guess it would be a fitting bookend to the season to have this fulfilled.

[MIstorm97]

The GFS, GEM, and UKMET all took steps north with their 00z runs. So stoked for a second half of April CHI-DET snow.

[hawkeye_wx]

The 00z Euro is, once again, stronger and farther north compared to its previous run.

[RCNYILWX]

Having looked at things a little bit, some thoughts:

The model guidance is overall in good agreement conceptually that there will be a fairly narrow band of higher QPF and snow. This will be driven at the mesoscale by response to a strong f-gen circulation amidst high moisture for a snow event (PWATs up to 3/4"). It's too far out to be a lock still and we know how things went at this time range during the winter. However, we can be reasonably confident that the above scenario will play out in some fashion. That said, while models are good at indicating f-gen response, actual placement can vary substantially at go time.

 

Temperatures, while chilly for April, will warm to 45 to 50 Thursday PM. With late August equivalent sun, road and near surface soil temps will be quite warm going into the evening. Evaporative cooling will quickly cool air temps, but it's possible they only get down to freezing, or even stay above freezing, as shown on 00z Euro. Ground and especially road temps will lag. This will cut into accumulation efficiency and the ratios despite the otherwise very favorable timing to get sig. accums in a late season event.

 

Going back to the placement of strongest mesoscale forcing from the f-gen, another thing we know is that in intense mesoscale banded setups, there is subsidence outside that band. Considering the marginal surface temps and antecedent warm ground temps, accumulations could struggle outside the heaviest banding. Inside that banding, rates could be 1-2"+/hr. But even there, road impacts might be mitigated some like the March 22-23 event. The snowfall gradient *may* end up tighter than modeled due to the above factors.

 

At this time, there is a decent shot at wet snow accums of 6"+ within the heaviest banding. However, regarding headlines, unless we become confident in amounts well over 6", we might be able to get by with an advisory given overnight timing, less cars on road due to covid and possibility that marginal surface and road temps mitigate road accums and impacts. As an example, the 00z Euro increased QPF amounts vs 18z run but actually only has narrow areas of 6"+ within LOT and DVN CWAs due to the marginal 2m temps and low ratios.

 

 

 

 

 

 

 

 

[Hoosier]

22 minutes ago, RCNYILWX said:

Having looked at things a little bit, some thoughts:

The model guidance is overall in good agreement conceptually that there will be a fairly narrow band of higher QPF and snow. This will be driven at the mesoscale by response to a strong f-gen circulation amidst high moisture for a snow event (PWATs up to 3/4"). It's too far out to be a lock still and we know how things went at this time range during the winter. However, we can be reasonably confident that the above scenario will play out in some fashion. That said, while models are good at indicating f-gen response, actual placement can vary substantially at go time.

 

Temperatures, while chilly for April, will warm to 45 to 50 Thursday PM. With late August equivalent sun, road and near surface soil temps will be quite warm going into the evening. Evaporative cooling will quickly cool air temps, but it's possible they only get down to freezing, or even stay above freezing, as shown on 00z Euro. Ground and especially road temps will lag. This will cut into accumulation efficiency and the ratios despite the otherwise very favorable timing to get sig. accums in a late season event.

 

Going back to the placement of strongest mesoscale forcing from the f-gen, another thing we know is that in intense mesoscale banded setups, there is subsidence outside that band. Considering the marginal surface temps and antecedent warm ground temps, accumulations could struggle outside the heaviest banding. Inside that banding, rates could be 1-2"+/hr. But even there, road impacts might be mitigated some like the March 28th event. The snowfall gradient *may* end up tighter than modeled due to the above factors.

 

At this time, there is a decent shot at wet snow accums of 6"+ within the heaviest banding. However, regarding headlines, unless we become confident in amounts well over 6", we might be able to get by with an advisory given overnight timing, less cars on road due to covid and possibility that marginal surface and road temps mitigate road accums and impacts. As an example, the 00z Euro increased QPF amounts vs 18z run but actually only has narrow areas of 6"+ within LOT and DVN CWAs due to the marginal 2m temps and low ratios.

 

 

 

 

 

 

Thanks for your thoughts RC.

A couple things.  Did you check into the circumstances prior to the 4/14/2019 snow?  It actually looks like the lead up to this is colder.  The rates with that were very good, heavy enough that the roads were a debacle even in the daytime.  

The other thing... in your opinion, does it make sense for the Euro to have the 2m temps that it does?  I would think that we would be able to nudge them down a little more in areas with heavy precip and the nighttime timing.  Possible exception being in the city of Chicago due to urban effects and developing onshore flow.

[RCNYILWX]

Thanks for your thoughts RC. A couple things.  Did you check into the circumstances prior to the 4/14/2019 snow?  It actually looks like the lead up to this is colder.  The rates with that were very good, heavy enough that the roads were a debacle even in the daytime.  

 

The other thing... in your opinion, does it make sense for the Euro to have the 2m temps that it does?  I would think that we would be able to nudge them down a little more in areas with heavy precip and the nighttime timing.  Possible exception being in the city of Chicago due to urban effects and developing onshore flow.

 

 

Regarding this potential event and 4/14/19, I think that these are two different scenarios, though it's a fair point about the temperatures leading in. Aside from the NAM likely being overamped with a much stronger synoptic forcing and low level response (closed 850 mb low, 50+ kt southwesterlies at 850 mb, even tighter thermal gradient and f-gen response), the other guidance seems to be pointing toward this being driven heavily by narrower mesoscale banding. 4/14/19 was a stout synoptic system with a strong deformation axis with embedded f-gen circulation. I certainly think there will be road impacts with this event given the favorable timing and obviously as last year showed heavy enough rates overwhelm even April sun.  

 

But paradoxically, temps in this case will have to be driven downward solely by evaporative cooling, as well above freezing starting point won't be aided by radiational cooling since clouds will have been increasing by then. The guidance is showing dew points ending up around 31-33, so I do think it's plausible many areas outside the heaviest banding end up staying above freezing, while locations within heaviest banding are driven down to 31-32.

 

Euro may be overzealous in keeping even places within heaviest banding above 32F, though I can't completely discount it because it tends to perform quite well overall with 2m temps. In this event, I'm not sure yet that more than a narrow area and a good deal narrower than 4/14/19 gets the very heavy rates for reasons I mentioned earlier. I'm curious to see how roads behave since in the March 22-23 event, it was surprising how little impact the 3-6" amounts had overall.

 

 

 

 

 

[Stebo]

That is the one thing going for this potential locally, it is coming at night so unlike places to the west, don't have to deal with the sun. That being said I hope it doesn't materialize like shown.

[A-L-E-K]

SN right now

 

Looks like close to an inch already and ripping. A legit event.