Tuesday, May 20, 2014

Warm and Summer-like Temperatures Through the Next 10 Days

Well above normal temperatures are on the way for all of the Midwest this week and into next week as the jet stream lifts north into Canada for much of the next two weeks. A small cold pocket of air will rotate on through parts of the western Great Lakes on Thursday, but will be short lived as winds kick over to a more southerly direction yet again on Friday.

Memorial Day Weekend will be nice across all of the Midwest, temperature-wise with highs in the 80s for much of the area. A few strong to severe thunderstorms are possible across the entire area on Sunday and Monday as a disturbance passes through, stay tuned for severe weather updates for the Memorial weekend.

On the right is a snapshot of 850mb temperatures Memorial Day morning. It is a good example of the general pattern that will shape the Midwest over the next couple weeks...A strong area of high pressure to the east allowing for a southerly wind around the clockwise rotation of a high pressure. This wind direction will usher in warm Gulf air as a continuous fetch of wind will set up from the Gulf all the way into southern Canada. A summer pattern indeed.

Severe Weather Threat Rapidly Increasing Tonight

A brand new severe thunderstorm watch has just been posted for much of Iowa and Northern Illinois. Strong to severe clusters of thunderstorms are developing behind a strong warm front and an area of strong convergence. With a hot and humid air mass in place, the atmosphere is primed for further development this evening and into the overnight. The severe thunderstorm watch is in effect until 11:00pm CDT.

Below are the current CAPE values, basically a general telling of the amount of energy a T-storm has to work with at the given time. It can be increased by surface warming and environmental factors.

Below is current (5:00CDT) Bulk-Richardson number across the Midwest, a basic composite value for severe weather.

Below is the Craven-Brooks severe weather composite value.
It is the product of 100mb MLCAPE and 0-6km magnitude of the vector difference (m/s; often referred to as "deep layer shear") accounts for the compensation between instability and shear magnitude. Using a database of about 60,000 soundings, the majority of significant severe events (2+ inch hail, 65+ knot winds, F2+ tornadoes) occur when the product exceeds 20,000 m3/s3.

Monday, May 12, 2014

Low Pressure System to Pose Severe Weather Threat

The severe threat will continue late afternoon through the overnight hours and a slow moving are of low pressure passes through. Strong Gulf moisture and southerly winds are creating ideal conditions of thunderstorm development. Once the cold front passes, the threat will rapidly diminish from west to east tonight and into Tuesday. Behind the cold front temperatures will run 10-20 degrees below average, this weather will last into the weekend before we see moderating temperatures yet again.

Saturday, May 3, 2014

Summer Weather on the Way for Many!

After a prolonged area of low pressure separate from the jet stream controlled the cool and active weather for the eastern half of the country, called a cut off low, a change is on the way. Temperatures will run above average by the middle of the next week, if not earlier. The jet stream will bump north allowing for warm southern air to filter in all week. An area of low pressure will develop and sift out of the Rockies and push towards the Midwest. Exactly where the track of the system falls will be a major factor for the weather in the Midwest next week.
The map on the above is showing the current model consensus of where this system will be near on Thursday.
The warm sector (to the east of the
cold front and to the south of the
warm front) will see highs in the 70s and 80s area wide. This will likely be the first 80 for many in the Midwest. With dew points on the rise and ample surface heating, the atmosphere will become prime for severe weather, with CAPE values approaching 3000 J/KG from Wisconsin on south. A severe weather outbreak is certainly possible on Thursday in the warm sector and ahead of the cold front. We will have to see just where and when this system sets up. The 00z GFS (below) is firing up some thunderstorms for Thursday evening along the cold front. While the front will not bring much in the way of colder air, it will create necessary lift and convergence to develop strong to severe thunderstorms with heavy rains. Back to the temperatures, the chart above is forecasted high temperatures for late next week off the 00z GFS model run. Another temperature map is attached below coming off the European weather model, showing a major range of temperature across the Midwest. The barrier between warm and cool with depend solely on the track of the system mentioned above, either way warmer weather and a kick start to severe weather is on the way for the first full week of May.