Significant Storm System: Blizzard, severe weather AND heavy rain?

If you haven't heard already, the storm system that has been predicted on the models since last Sunday and Monday has finally consummated, and occluded in the Midwest. It is currently weakening very slowly as we speak. But even so, it packed a pretty significant punch to the Midwest.

Just to recap the last few days of weather from this storm system:

1.) It produced feet of snow and impassable travel conditions Thursday night in parts of the Rocky mountains.

2.) It strengthened further Friday morning into the afternoon, producing high winds, extremely heavy snowfall, and cold air across South Dakota and Nebraska. Snow totals have exceeded 45 inches in some areas, with the vast majority of the region receiving well over a foot of snow. The heavy, wet nature of the snow has caused a lot of tree damage and quite a few power-outages.

3.) On the NW side of the storm, within the blizzard, high winds became so strong that it broke records across South Dakota. For instance, Rapid City, SD observed wind speeds exceeding 70 MPH during the highest part of the storm! This caused widespread whiteout conditions within the heavy snow-bands, as well as causing interstate highways to be nearly impassable.

4.) In the warm-sector, heavy rain, flash-flooding and severe weather has been prevalent from Iowa and Missouri into the upper Ohio Valley. Yesterday afternoon, parts of NW Ohio recorded several inches of rain due to training thunderstorms, and most areas saw at least a period of heavy rain. In Iowa and Missouri, large, violent tornadoes destroyed several towns and caused many injuries.

5.) The storm system is still expected to produce very heavy rain across a large part of the Midwest, even with the storm system weakening. This is because of its interaction with the moisture plume associated with Karen, and the fact that it is slowing down significantly.

Take a look at the latest visible satellite imagery:

Notice the spiral band shape of the entire cyclone. Clearly, this indicates that the entire system has already occluded, and is beginning to weaken. Also notice the prevalence of convection on the eastern flank. What this means is that we should see a strong increase in thunderstorm activity over the next hours, and days perhaps if computer models are right.

The strong, closed-low in the Midwest will continue to propagate slowly eastward, drawing rich, Gulf moisture from the south, and causing repeated rounds of showers and thunderstorms. Today, expect showers and thunderstorms to rapidly build-up due to the marginally unstable and humid air mass in place. These storms will move rather slowly, allowing for the possibility of heavy rains before the main events comes under way.

By later this weekend, expect the showers and thunderstorms to organize into more organized structures, and allowing for the possibility of repeated waves of heavy rain.  It will then become possible that we see several inches of rain through Monday.

WINTER OUTLOOK COMING IN MID-LATE OCTOBER

I'm currently planning on releasing my preliminary winter-outlook for the season towards the end of October, or possibly early-mid November. It will all depend upon how certain I am of the winter forecast. 

Storm System Potential: Model Consensus

After many consecutive runs of indicating some kind of "major" storm system later this week, models have finally reached general agreement on the track of the storm system itself. Other issues such as intensity, precipitation, and thunderstorms still need to be sorted out, but over all, we are reaching a model consensus on when and where this storm will form. The timing issues that need to be sorted out are related to the mesoscale movement of the cold front into the area, which will be discussed on Tuesday and Wednesday.

And now, on to the model run-down.

12z GFS takes a shift west and south with Saturday's system, while at the same time weakening its overall amplitude and anomalous structure [instead of having a 540-546 DM core at 500 MB, it has a 552-558 DM core]. It will be some time before the GFS quits shifting the intensity and track of the system, but I think I can get a general track and intensity of the system.

The storm will likely track from Western Kansas and Eastern Colorado into Eastern Minnesota and NW Wisconsin. From both the latest runs of the GFS and the ECMWF, it appears the storm will have a maximum strength at occlusion near 1000-996 MB [if the wave is as amplified as currently forecast; right now, there are only moderate differences on the issue of amplitude; all that needs to be watched now is differences in run to run consistency] in the Western Great Lakes region before translating eastward across the Great Lakes and into Ontario. 

I'll keep watching this, especially on WV imagery, as that will help determine how well the models are currently handling the wave.

More details coming later on this potential storm system.

POTENTIAL STORM SYSTEM LATER THIS WEEK AND WEEKEND

 While other people are going gung-ho on winter outlooks.. I decided I would post something on the upcoming storm system.

Take a look at the 12z GFS and 12z ECMWF: They are coming into agreement on a rather large trough pivoting into the Midwest and amplifying by late this week and early weekend. A strong cold front will plow through the Midwest [regardless of how amplified the surface reflection becomes], causing sharp temperature drops across the front. This could quite possibly be the first major storm system of the season if everything pans out correctly. So far, the strength of the upper level wave and the surface low has been increasing between runs, so I wouldn't doubt that we see at least a slight similar trend to continue. Even without an amplified surface trough, both models are still predicting a strong cold front to move through the Midwest and eventually the East.

The key to predicting this system will most likely be dependent upon which model is over-developing/under-developing the system. At this time, I would say that a consensus of both the 12z GFS and 12z ECMWF with some uncertainty is our best bet. I think we should keep an eye on this system.

12z GFS 850 TEMP map

12z GFS 500 REL. VORTICITY

12z ECMWF