Friday, July 29, 2016

How Much Rainfall in July?

If you think July has been abnormally wet, especially over the last week or so, you are absolutely correct. The month wasn't too terribly wet early on, but the last several days have featured rounds of rain and storms that dumped inches of rainfall in many locations throughout Illinois and Wisconsin. In fact, Friday's rainfall totaled 4.65" in Morrison, which is located in Whiteside County. An area just southeast of Rockford reported 2.62" of rain in just two short hours. These are two locations that saw storms for a few hours. There simply were no upper-level winds in place to steer the storms. As a result, they didn't move much at all. That, along with high moisture levels, led to heavy rain producing thunderstorms sitting over the same areas for an extended period of time Friday afternoon.
From the 21st of the month through Friday the 29th, Rockford has recorded 4.96" of rainfall. The month of July as a whole has featured a whopping 6.93" of rainfall. That puts the city at a 3.39" surplus in the rain department this month. This comes after June ended more than 2.00" below normal. Essentially, July has been the polar opposite of June in terms of rain and thunderstorm activity. That trend will continue on Saturday, but drier weather looks likely for the last day of the month on Sunday!

Another Wave of Heat

We get a bit of a break from the heat this weekend with temperatures actually below average in the upper 70's and low 80's. A trough in the atmosphere is keeping the cooler temperatures around along with periodic showers and storms. More storms in the forecast for Friday, though mainly we will see shower activity. The coverage in any rain however will be less than Thursday, though could still see areas of heavy rain. Showers will continue this evening but will begin to diminish with just a few showers possible into Saturday. Temperatures then warm to 83° with a little more sunshine.

A ridge builds to the west over the weekend and then once again spreads east bringing the heat with it. Temperatures make it into the mid 80's on Monday and then highs in the 90's possible through midweek. However, models have been indicating that we will be on the eastern edge of the ridge. This means a couple of things for us, the first is that we won't be under the 'core' of the heat. Meaning the hottest conditions will be centered over the center of the country and we will be on the outer fringe. It will still be hot though with highs in the low 90's possible.

Also, disturbances in the atmosphere like to ride along the edge of the heat - the ridge. This will allow for daily rain and storm chances, but it also plays a roll on temperatures. The less rain we see, the hotter it will get.  If we end up seeing more rain, temperatures will be limited to the upper 80's.

This will be what we're watching for next week as we kick off the start of August. This won't be the last of the heat, with a healthy corn crop still around, muggy and warm weather will be with us too.

Thursday, July 28, 2016

Funnel Clouds and Storm Pictures!

Crystal Prince
Sandy Hollow & Alpine
Brenda Feathers Nesbitt
Linden & Perryville
Bobby Young
August Rundle
Mark Pellini
NE of Polo
Paul Hackerson
Penelope J. Fosse
Cherry Valley
Sharon Creamean
Tiffany O'Neill
Tom Long
Pecatonica Corners
A BIG Thank You to everyone who submitted storm cloud pictures from Thursday.  If you have any pictures you would like to send, please email them to:

Amanda Breedlove
Dixon, IL
Funnel Cloud
Location/Name Unknown

Isolated Severe Weather and Funnel Clouds Over Northern Illinois.

What a messy, messy afternoon it's been for many over Northern Illinois and Southern Wisconsin.  Sunshine early in the day really charged up our atmosphere for thunderstorms, some of which turned severe.

The biggest story, however, were the reports of multiple funnel clouds over Northwest Illinois early this afternoon.  Thankfully there were no confirmed reports of tornadoes or damage, but it was enough to probably rattle some nerves.  There was even enough of a strong storm to prompt a Tornado Warning for Northwest Stephenson and Northeast Jo Daviess counties a little before 3pm.

The atmosphere was not conducive for supercell thunderstorms or large tornadoes today, but there was just enough spin to generate the funnels many of you reported.

Low pressure over Northwest Illinois and a stationary boundary with a cold front near the Wisconsin/Illinois border was the focal point for thunderstorms this afternoon.  As the low got closer to Illinois late this morning, it caused the air ahead of it to rise.  Because we had sunshine to start the day, there was enough instability to allow the rising air to turn into towering cumulus clouds and eventually thunderstorms.  And since the storms were forming so close to a frontal boundary with shifting winds from south to north (south winds south of the boundary and northeast winds north of the boundary) it caused the air to spin - aided by the air already spinning around low pressure.

The thunderstorms that moved through were not supercellular (which is where tornadoes come from).  But the spinning air within these thunderstorms was enough to generate rotation, which then formed into funnel clouds.  Funnel clouds like what occurred today rarely touch down.  They usually come about half way down, spin like a top for a few minutes and then lift back into the cloud.  There just wasn't enough large scale spin in the atmosphere to sustain the funnels.  Scary to see, but most of the time harmless.

With an almost same atmosphere tomorrow, we could see a repeat of thunderstorms but less in coverage.  And with very little wind movement aloft, any storms that do develop will be heavy rain producers.

Thursday Afternoon Severe Weather

The Severe Thunderstorm Warning for Ogle and Lee counties has been allowed to expire.  The storm that had the warning has weakened below severe limits.

A Severe Thunderstorm Warning has been issued for Lee and Ogle counties until 6pm.  Outflow boundaries from earlier thunderstorms have allowed storms over Lee and Ogle counties to maintain their strength, if not strengthen just a little more.

Biggest threat with this storm will be the locally heavy rainfall, but also large hail.  There has been very weak rotation noted with this storm and given what's occurred this afternoon, we can't completely rule out funnel clouds.

This storm is moving to the southeast at 20mph.  Lost Nation and Dixon are included in the warning.

Along with the Severe Thunderstorm Warning, a Flood Advisory has been issued for Ogle and Lee counties until 8:30pm.  Shortly before 5:30pm, radar indicated very heavy rainfall with the slow movement of previous storms and this storm.  Isolated rainfall amounts of 2 to 3 inches is possible in the Advisory area.  Localized flooding is possible and there was a report of ditches full and water over the road just west of the intersection of Rt 52 and US 30.

Wednesday, July 27, 2016

Slow Winds Aloft Keep Threat for Heavy Rain Looming

Very slow moving showers and isolated thunderstorms developed Wednesday late afternoon.  So slow that they prompted a Flood Advisory for Boone and Winnebago counties with nearly two inches of rain falling.  This likely isn't going to produce flash flooding, but areas that typically have poor drainage and low lying areas could experience minor flooding until late tonight.

To understand why these storms are moving so slow, we have to look up above our heads - at the jet stream.  Winds within the jet stream during the summer months typically are not that strong.  And that's why during July and August our focus shifts from the big, robust thunderstorms to heavy rain producing storms and flooding.

Without much wind in the atmosphere to push these storms through, they will just sit over one area for a while and continue to produce heavy rainfall.  We've actually seen this occur a few times over the past couple of weeks. 

While instability won't be the greatest, thunderstorms are expected to develop Thursday.  And with continued weak winds aloft those, too, could be heavy rain producing storms.  So heads up for Thursday.

Wednesday Evening Showers

9:40pm Update: The Flood Advisory for Boone and Winnebago counties has been canceled.  The heavy rain has ended in those counties and flooding is no longer a threat.  There are additional showers that have developed south of Rockford and could see heavy rainfall with those.

Flood Advisory now issued for Boone County until 10:15pm.  The storm that developed over Winnebago County has now slowly shifted east into Boone County, likely producing between one to two inches of rainfall. 

8pm Update: The Urban and Small Stream Flood Advisory has been extended until 11:15pm.  The heaviest rain core has shifted into Boone County with heavy rain occurring along IL 173 from Caledonia and Poplar Grove.

An Urban and Small Stream Flood Advisory has been issued for East-Central Winnebago County until 8:15pm.  A nearly stationary rain shower near Machesney Park has produced close to one inch of rain within the past hour.  Due to very light winds in the atmosphere, the heavy rain shower hasn't moved much within the past hour causing some minor flooding.

Additional rainfall of up to half an inch to an inch is possible under the heaviest core.  An outflow boundary from thunderstorms earlier this afternoon in Wisconsin has been slowly migrating southwest into southern Wisconsin and could help focus additional isolated showers through sunset.  Then our attention will turn to the north and northwest with an advancing cold front.  This will be the trigger for showers/storms Thursday afternoon and Friday.

We actually caught a nice view of the rain with our MercyHealth Weather Camera in Beloit looking south.  You can definitely see the tall towering cumulus cloud and heavy rainfall.  This shower will continue to slowly sink south/southeast through the evening.