Winter Storms: Mid Latitude Cyclones and Moisture-Robbing Thunderstorms

[Jeff Miller]

Over the years, I have observed many winter-type systems traverse the country. I have observed many of these with explosive tornadic thunderstorm development (i.e. March 8, 2002) that have not impeded winter storm development to the north.

At the other extreme, I have seen severe thunderstorms develop and shut off the winter storm to the north faster than a cat can grab a chew toy. My question is as follows:

What are the paramaters to look for when predicting if convective development will impede/hinder a winter storm event in the cold sector? Or if it will have little effect on the cold sector as is often the case? This can make or break winter storm warnings/advisories...and almost certainly is the "fizzler" that causes a winter storm to "fizzle" as my folks so often said.

The only thing I can figure is that the system has to tap into another source of moisture to continue dendretic growth to winter storm potential. Hope I am close here and looking for some input on this.

 

[Tom Stefanac]

Not sure if I can pin point a case where thunderstorms have shut down precip to the north. I find enhanced thunderstorm activity usually leads to more moisture feeding into the snow zone of the storm. The thunderstorms create a seeder feeder effect by saturating the mid levels and providing a nice cirrus deck which may not exist otherwise.

Most of the cases I can recall where precipitation to the north has been killed or over forecasted relate to evaporative cooling and dry air intrusion, especially between the ground and 700mb level. The models have usually saturated the polar air mass too quickly and not accounted for enhanced CAA and sometimes even factor in and over quantify things like CSI (conditional symmetric instability).

The fact of the matter I would argue is that synoptic storms are simply outside the realm of the mesoscale. If anything the synoptic environment would directly hinder or support the mesoscale stuff but the reverse is not exactly true. The amount of moisture advection is copious as usually noted by the 700mb maps, so even if the thunderstorms did not form along the front/trof/waves, the snow storm would still materialize.

This is best seen with storms which are almost purely snow in nature. You will get a cut off low every so often in Idaho/Nevada that entrains purely polar air which at one point in time was completely arctic. Once the low wanders east of the rockies and gets caught by the jet stream the precipitation shield will develop quickly (especially with good PVA/NVA) as moisture is pulled in from any number of possible sources. Usually snow rates will approach 1 inch per hour without the aid of thunderstorms or visible moisture coming out of the Gulf, in fact there may or may not be clouds in the advection field south of the storm.

So with that, I would say thunderstorms are actually a by-product of the synoptic snow storm and not the other way around.

 

[Jordan Hartley]

The only thing I can figure is that the system has to tap into another source of moisture to continue dendretic growth to winter storm potential.

The last 4 storm systems have got a little help from the Pacific Ocean which I dont know if that is an effect of El Nino or not but I've watched the water vapor loop on the last 4 and they all tapped into that "other" source.

 

[Joel Wright]

I've seen many snowstorms "robbed" of moisture in the past several years. From my observations, it seems to happen most when there's a band of intense rain/thunderstorms aligned southwest/northeast along a stalled coldfront. This usually happens when there are a series of weak surface lows riding up the boundary, instead of one big/organized surface cyclone.

As this is happening, the snowbands in the cold sector are usually fairly narrow and in between them the snow is very light, and sometimes non-existent.

 

[Robert Dewey]

It all depends on the parcel trajectory. There are times where the parcels are actually coming from the region east of the convection and wrapping around into the system - you really need to look at isentropic charts to know for sure.

I know the Blizzard of '99 featured quite an outbreak of severe weather to the south, but never really robbed the system of moisture.

Check out the radar (it's in QuickTime FLI format):

http://speedy.meteor.wisc.edu/cgi-bin/displayCaseT2?date=2jan99

 

[Tom Stefanac]

Well, does anyone have a solid case(s) or date where the storms have seemingly killed off the moisture feed?

This is a very interesting topic which definately needs futher exploration.

I think a case study would be great!

 

[Mike Hollingshead]

I guess I'm not sure why it wouldn't disrupt things. The last storm might be a decent case. The day I talk about is the severe day in TX while nw KS had that permanent area of heavy precip. TX storms blew up and the nw KS area survived, but not for long. You could almost tell how long it would take before the nw KS snow/sleet area was affected by bad air. Sure enough, a couple hours after TX erupts all the radar returns up north take a big dump. It seems to be rather common if one watches. You can't have a wide area of several supercells, and an area of general heavy rain, and not have it affect where that moisture was headed. You can look at the radar and half visualize almost every possible gap being closed off from a storm in some location(if to the south there is really no east-west hole for gulf moisture to move north through).

That last one it just looked like a switch was thrown a few hours after all of TX blew up(there was still good air north of the TX storms for a width of a most of KS and OK, so it was doing well till that moved on north..then it began to get the stable air). The abrubt wind down to it seems to lean towards it having been directly affected by convection down south, especially considering the time after convection exploded and the distance. I'd think in most cases, if there isn't already good moisture in place(most of the winter), the majority of useable moisture will come from the western gulf. Yeah some locations may have an easterly component, but just south of there was likely more southerly. I don't know, it just seems like it happens often.

 

[Tom Stefanac]

Here is a good example of a storm drawing in extra moisture thanks to convection, and you will actually see the moisture feed start to die with the convection to the south shrinking.

http://www.vaughanweather.com/winter/cases/01_26_04/radar_big_loop.gif

http://www.vaughanweather.com/winter/cases/01_26_04/radar_big_loop_2.gif

So in this particular case, convection was key in keeping the moisture feed flowing rather than detrimental. I have a whole archive filled with different storms so I will post them all at the URL below.

http://www.vaughanweather.com/winter/cases/