Terry's winter storm blog

Apr 4, 11:51 AM

UPDATE 10:58pm
Alas, the storm is winding down and all the warnings and advisories have been dropped. For most of us it was a good reminder that spring in the Midwest has plenty of ups and downs. For the next 24-36 hours the forecast will resemble winter more than spring but each and every day gets us closer to May which I believe is the lushest month we have. So, take the snow, wind, and cold in stride and remember, not only is the best yet to come, it’s just a matter of a few short weeks.
Ride the wind….Terry

UPDATE 6:50pm
Well, the snow has started and the deformation band has begun to press across the area. There are pockets of heavier snow in the north but overall light to occasionally moderate snow is what we will see for several hours. Most of us will end up with 1” or less of accumulation. The exception would be the area near and north of HWY 30. Up to 2” may fall there with one or two isolated spots picking up 3”. Ordinarily this would not be much to sniff at but considering the time of year, this is a respectable event. Until later…..Terry

UPDATE 3:02pm

UPDATE 3:02pm
I did see the new 18z WRF and it still depicts the area under a deformation snow band this evening. It is a slow mover but pushing from west to east, this will reach the QCA around 7. QPF’s are generally less that 2/10’s of an inch so that works well with my 24hr thinking of 1-2” snowfall amounts. Thought that was worth passing along. Later.

UPDATE 2:10pm
So far, things seem to be progressing on schedule. The freezing line aloft is now near the Quad Cities and that is key in the sense that the cold air is progressing and growing deeper. That will allow the deformation band we are wating on to produce snow when it arrives.

Deformation band rotating around the 500mb low-that should eventually be our snow band as it moves southeast this evening

Precipitation is starting to blossom and I take that as a good sign the deformation band is going to remain intack as it works eastward late this afternoon and evening. THIS IS CRITICAL FOR ACCUMULATING SNOW. I would think widespread 1-2” amounts are still on track. Here and there a 3” total is a possibility. Winds will continue to crank into Monday and with falling temperatures and snow this evening will be less than ideal. Travel will also get a bit tricky as readings slip to and eventually fall below freezing.

I will continue to watch the development of our snow shield to see that it progresses as expected. I will also have the 18Z afternoon model runs to share so stick around. Things should get interesting in the next few hours.
Terry

UPDATE 11:30am
I see that the fine folks at the NWS are thinking along my lines. At 11:22 they cancelled the winter storm warning for Jackson, Jo Daviess, and Stephenson counties and downgraded to winter weather advisories. Dubuque is still in but I think they could be scaled back as well. Anyway, I commend the move from the NWS as it needed to be done. See my previous reasoning below. Now, let’s see what happens with that deformation band! Hang with me.

UPDATE 11:11am

We have been in an extensive dry slot for much of the morning and as expected precip has been showery and scattered, even in the far north(not so much anticipated there) Anyway, we a are playing the waiting game now as the storm reorganizes and kicks east into Illinois. As the afternoon wears on and this happens, colder air aloft at 850mb will get drawn into the region. This will then set the stage for snow when the deformation band wraps around the low pressure center. From west to east a band of snow is likely to develop and push through during the late afternoon and evening. Stress this, it will be several hours before this happens meaning our worst issues will be winds, cold, and showery conditions until at least mid or even late afternoon.

With the deformation band snow later on, things will go downhill for the evening. Most spots, even in the south it now appears have a chance of picking up an inch or 2 of snow. If things get going well a few locations may knock off 3”. This will taper off by midnight and that leaves us with snow showers and windy, cold weather into much of Monday.

As I stated last night at 10:50 in my blog, I was not overly excited about this event and you can see why. I suggested it would be tough to meet warning criteria and I still belive that. Maybe the winter storm warning will be dropped soon. That comes from the NWS. I personally think advisories would cover the event in all areas. So much for me….

Stay tuned through the afternoon as I will be watching the development and progression of the deformation band. If we are going to get accumulating snow that is CRITICAL.
Terry

UPDATE 5:30am

UPDATE 5:30am
The new runs of the 6Z package have arrived and our storm is on the move. It appears that some restructuring will take place later today as the upper air low wobbles east southeast. This process will be important to snow totals as it will determine the strength of the deformation band that wraps around the surface low. The deformation band is what is often called the comma head and it is where the heavier snow falls on the northwest quadrant of the storm.

That said, the two things I will be watching are the freezing line at 850mb. and the progression and development west to east of the deformation band. Outside of the far north where temperatures will be below 0C at 850, the rest of the area will not get there until sometime in the afternoon. (after 3:00pm in the QCA) That implies showery type precip in most areas that will be either rain or mixed rain, snow and sleet. In fact, many spots south of I-80 will see little in the way of action as a bit of a dry slot holds into the afternoon. Again, the more general area for continual precipitation will be up in the north where snow will get going early and be around much of the day.

As the storm rolls east into Illinois later today cold air will quickly collapse southeast cooling 850 temps below freezing so that snow will spread through all of the region by evening. This is when the deformation band snows will produce whatever accumulations most of us get. As the day wears on I will be watching this closely as the forecast snow totals hinge on the intensity of this band. It still appears that snow totals of 3-5” are likely far north, 1-3” central (QCA included), and 1” or less far south.

The bottom line here is that outside of the northern 1/4 of the region (Dubuque & Jo Daviess counties in particular), problems from snow or freezing precipitation are not likely until late afternoon or evening. It will be a crummy day with gusty winds and cold temperatures when rain or snow is not falling. Stay tuned for a mid morning update when the 12Z runs are in.
Ride the wind,
Terry

UPDATE 10:50pm
The new data is in and I am not overly excited. The 0Z WRF and GFS are weaker on upper air strength, precip output, and surface reflection. Most areas are not cold enough aloft to go over to snow until afternoon Sunday. By then, the deeper moisture is being shunted off to the east. While I do see periods of snow and some blustery winds in all locations by Sunday night, I think it will be marginal to warrant warnings. There is a chance the NWS will downgrade some of the warnings and advisories that are currently in effect when the new zone forecasts are issued around 4am. Knowing what I do now I think it could go either way. Based on what I have seen I would think total accumulations will average about 4 inches around Dubuque and Galena to an inch or two along the I-80 corridor. South of I-80, snow totals should typically be less than 1 inch. Unless something really drastic happens, I think this will be more of a nusiance storm than a high impact event. New runs around 4am will be telling. More to come.

UPDATE 8:01PM

New data will be coming in on the developing storm over the next 1-2 hours. I will be doing analysis and will have a major briefing on the latest trends and model guidance. This will be out between 10 and 11:00pm. My coverage will be significantly increased from now until the worst has passed. See you then.
Terry

A powerful spring snowstorm will develop over the next 24 hours bringing a wide variety of weather to the area. Initially rain and a few thunderstorms will overspread the area tonight. There is a chance of some sleet and snow in the far north. Sunday, colder air will spread from west to east changing the rain to sleet and eventually snow in all locations. This will happen during the morning north and west of the Quad Cities and during the afternoon from the Quad Cities south and east. Gusty winds up to 40mph and falling temperatures will be likely Sunday.

A winter storm warning has been posted for the area north of a line from Cedar Rapids, to Maquoketa, and then on to Freeport. Significant sleet and snow accumulations are likely here by Sunday night and on into Sunday. (potentially 3-6”) Further south amounts will be less due to a slower transition to snow. Even so, 1 to 3” totals are possible by Monday morning. Fluctuations in track or intensity could alter amounts so please check in often for revisions or refinements.
Terry

Mid-day satellite image of developing storm