Archive for September, 2010

Coldest Air of Season Near
September 30, 2010

***Watch WISN 12 News for the latest on the cold weather ahead!***

Thank you for stopping by the Weather Watch 12 Blog!  The first full month of Fall is upon us as October is here!  Just as October arrives, weather more typical of November is about to settle in.  If you remember back to last October, a very cold one, the first 18 days of the month had highs in the 40s or 50s!

The first 32 degree or lower reading in Milwaukee last Fall was on October 10 when it was 32 degrees.  Just one day later it was 29 degrees on the 11th.

This weekend’s cold push will give many furnaces and heaters their first workout of the Fall.  Not only will it be cold, but showers and frost are possible at times.  Let’s look in-depth at the changes ahead.

The best part of the day on Friday will be the morning and early afternoon.  That is when highs will top out in the upper 60s and some sunshine will be enjoyed.  By late in the day a strong cold front will drop south of the area.  This will bring clouds and a chance of rain showers. 

Below is a forecast map valid at 7:00 p.m. Friday, right when high school football games are kicking off!  Notice the green, this represents rain showers.  So expect a few showers near the cold front late Friday and Friday evening.  Notice the blue over southern Canada…that is snow! 

The showers should end over inland locations Friday Night, but with cold air spilling over Lake Michigan, lake effect rain showers could form.  The wind direction will play a major role in how far inland the lake effect showers move.  A north wind will keep showers right by the shore, a slight north-northeast wind will move the showers farther inland.  While a northeast wind could mean a few showers for areas well inland.  The wind direction will play a huge role in who see’s the showers on Saturday.

Another focus for the weekend forecast is the chance of frost.  Temperatures will be coldest inland, but even near the lakeshore temperatures could flirt with the 30s.

Below is the forecast temperature map at 7 a.m. Sunday from our in-house high resolution computer model.  It’s a little tough to see, but you can click on the image.  The isotherm in southwest Wisconsin is labeled 32 degrees.  As you move closer to Milwaukee, temperatures climb into the mid 30s, and then closer to the lakeshore the low 40s.

This means frost is possible well inland Sunday morning, but widespread frost is possible Monday morning with mostly clear skies and lighter winds!  So cover or bring in any plants that you want to save.  We will make sure to show detailed overnight low temperature maps on WISN 12 News on Friday and Saturday. 

Have a great day!

Jeremy Nelson

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Series of Cold Fronts Ahead
September 29, 2010

***Watch WISN 12 News for the latest weather information!***

Thank you for stopping by the Weather Watch 12 Blog!  If you follow the blog you know that I believe that a new weather pattern begins to form each Fall, that pattern then repeats and carries through the next year.  The formation of the new pattern typically occurs in October and November.

With a new pattern forming, the track of storms, position of troughs and ridges, and precipitation trends will be monitored closely to see what it may mean for our winter forecast.

So does the series of cold fronts about to move through hold a key to our overall weather pattern?  The quick answer is it is hard to tell since we are so early in the new pattern, but one thing is certain, the new pattern will be unique!

The first cold front to pass through our area will arrive later this evening and tonight.  It will be moisture starved, so outside of an increase in clouds and a wind shift, the front should pass with little fanfare. 

Below is a surface map valid at 7 p.m. this evening(Wednesday).  The cold front is on our doorstep, and a few light showers are near Madison.  Most/all of the moisture should dry up before reaching Milwaukee.  A few sprinkles or a brief shower can’t be ruled out in our northern counties.  Just click to enlarge.

Lurking over southern Canada is another, stronger, cold front.  This is the front that will barrel toward southeast Wisconsin and push in the coldest air so far this season.  The second cold front will slip by late Friday, and when you wake up on Saturday you will feel a big change!   The map below is valid at 7 a.m. Saturday.

Along with the colder air, winds will swing to the northeast.  With the cold air riding over Lake Michigan relatively warm waters clouds and lake effect rain showers will be possible.  Right now a few showers have been included in the Saturday forecast, along with highs in the low 50s!

If skies clear out Saturday night frost is possible Sunday morning mainly away from Lake Michigan.  Another frosty morning could occur on Monday.

While the weekend will be cold, another warm-up into the 60s and 70s looks likely by the middle of next week.  Enjoy the next two days before a real taste of Fall arrives!

Have a great day!

Jeremy Nelson

The West Sizzles & Our Mild Weather About To Fizzle
September 28, 2010

***Watch WISN 12 News for the latest weather information!***

Thank you for stopping by the Weather Watch 12 Blog!  This is Milwaukee’s top source for the inside scoop on the weather, and best of all you can interact with the weather team at any time!  In today’s entry we will look at the extreme heat in the West, and the cold weather headed toward the Midwest.

Let’s start with the heat out West.  High temperatures well above 100 degrees smashed daily and all-time records in southern California on Monday.  Below are just a few of the records broken.  The most significant being the all-time record high in Los Angeles, a scorching 113 degrees!  

                                                                 HIGH        RECORD               ALL 
                                                                TODAY      FOR THE             TIME
                                                                                   DATE (YEAR)    RECORD (DATE)
                                                                       —–   ———–    —————-

DOWNTOWN LOS ANGELES     113**   106 (1963)     112  ( 6/26/1990)    
LONG BEACH AIRPORT               111**   109 (1963)     111  (10/15/1961)
BURBANK AIRPORT                       110*    104 (1963)      113  ( 9/12/1971)
WOODLAND HILLS                         111*    107 (1993)       119  ( 7/22/2006)
LOS ANGELES AIRPORT             105*    105 (1963)     110  ( 9/26/1963)

In order for temperatures to get this hot in southern California in non-desert locations, the weather conditions at the surface and aloft must be perfect.  The ingredients needed to achieve this type of warmth include an offshore wind, an upper level ridge, and compressional warming.

The map below is a 500mb map from Monday at 1 p.m.  Notice the ‘H’ over the Great Basin?  This is an upper level ridge of high pressure.  With a clockwise flow around the ridge the winds will blowing from from east to west.  This meant an offshore wind was present over southern California.  The wind barbs clearly show this wind flow.  Just click on the map to enlarge.

With the flow around the ridge moving the air from east to west, the air flow ascends the mountains just east of Los Angeles, and then flows down the mountainside.  This downsloping wind causes compressional warming.  A warming wind is known as a Chinook Wind.

The diagram shows the upper level wind, and also the warming that is taking place as the air flows down the hillside.  For our sake, just pretend that Los Angeles is located where it says clear and dry.

As the air decends down the slope it warms at about 5.4F per 1,000ft.  So the net result of all factors coming together in L.A. on Monday was a record breaking hot day!

While the West is sizzling, our weather was cool this past weekend and on Monday.  A couple of seasonal days are in store before a big push of cool/cold air moves in the for the weekend.  Below is a forecast temperature map for Saturday at 7 p.m.  Notice that this has Milwaukee in the 50-55 degree range, but some inland locations will be in the 40s! 

A widespread frost/freeze is likely by Sunday morning.  Even lakeshore locations could be in the 30s.  Inland locations could even drop into the upper 20s IF skies are clear and winds are light.  This is something we will watch very closely over the next several days. 

Make sure to watch WISN 12 News for special graphics on the cold weather headed our way, and we will update the 7 day forecast when the latest data rolls in.  So who’s ready for the cold?

Have a great day!

Jeremy Nelson

Frosty Start to Monday
September 27, 2010

It was chilly this morning. Many areas away from Lake Michigan had some patchy frost. Check out the lows from across the area.

Click on the image to enlarge it.

Many areas dropped down to the middle 30s. It stayed warmer near Lake Michigan thanks to the relatively warm waters acting like a heater. Away from the lake, many of you woke up to this:

A big thank you to Jake Stehli for the picture from Hartford this morning.

So if no temperatures dropped to freezing, how did we have a frost? Keep in mind, official temperature readings are taken 5.5 feet off the ground. Here is what an official weather instrument shelter looks like. Note the white color and holes for ventilation. Most bank clock thermometers are wrong because the instrument is placed in the sun without the proper shelter.

 On a clear and calm night like last night, the temperatures can actually cool below freezing near the surface and on other surrounding objects…such as the roof in the picture above. To get frost, you still must have a temperature dropping to freezing or below. Frost is not frozen dew, but water vapor changing directly to ice. This is called deposition. Usually temperatures get coldest at night in low-lying areas as the cold air pools at the bottom of a valley.

No frost expected tonight, but it will still be chilly. Nice weather in Chicago for a Packers victory. Game time temperatures will be in the middle 50s with light winds.

In the extended forecast, I have dropped the temperatures for the weekend. It is looking like a pretty good blast of cold will move in. Our first freeze is possible.

Thanks for reading and have a great night. Go Pack Go!

Mark

Geese Flying South…As seen on radar
September 26, 2010

**UPDATE** FROST ADVISORY FOR WASHINGTON, SHEBOYGAN, FOND DU LAC, AND DODGE COUNTIES UNTIL 7AM. PATCHY FROST LIKELY AS TEMPS FALL INTO 30S.

The above image is from Sunday morning from the National Weather Service radar in Sullivan, Wisconsin. To make the image animate, touch the radar image. There was no rain in Green Lake or Dodge counties so what in the world is that weird-looking stuff on the radar screen. Here is a quick tutorial on how doppler radar works.

NEXRAD (Next Generation Radar) obtains weather information (precipitation and wind) based upon returned energy. The radar emits a burst of energy (green in the animated image). If the energy strikes an object (rain drop, snowflake, hail, bug, bird, etc), the energy is scattered in all directions (blue). Note: it’s a small fraction of the emitted energy that is scattered directly back toward the radar.

Learn about the Radar Beam here

radar animationThis reflected signal is then received by the radar during its listening period. Computers analyze the strength of the returned pulse, time it took to travel to the object and back, and phase, or doppler shift of the pulse. This process of emitting a signal, listening for any returned signal, then emitting the next signal, takes place very fast, up to around 1300 times each second!

NEXRAD spends the vast amount of time “listening” for returning signals it sent. When the time of all the pulses each hour are totaled (the time the radar is actually transmitting), the radar is “on” for about 7 seconds each hour. The remaining 59 minutes and 53 seconds are spent listening for any returned signals.

I want to thank the National Weather Service for the above images.

The radar does not know whether it is hitting rain, snow, hail, or birds. The radar signal is scattered and part of the signal returns to the radar. That is how we know where it is raining or snowing. The same can happen when birds are migrating. The most likely migratory bird from Green Lake and Fox Lake right now would be canada geese.  These birds rest on area lakes as they move south from Canada to their wintering areas in the south. You can actually see the birds take off and then go fly in a group to the south. I have not seen this too much from Green Lake and Fox Lake, but more often from the Horicon Marsh. This is the time of year to head to the marsh to see dozens of different types of migratory birds.

As for our weather, get ready for a very quiet week. The only item of interest tonight is the cold temperatures. A frost advisory is in effect for much of the state. It does not include any counties in our viewing area, but Green Lake and Marquette counties are included. Lows in Milwaukee will be in the middle 40s, but inland temperatures will drop into the upper 30s. Remember that temperatures are officially taken at 5.5 feet above the ground so you can still get a frost even if the official temperature is above freezing. Dry weather the rest of the week with highs in the 60s on Monday and Tuesday and near 70 on Wednesday and Thursday.

Thanks for reading and enjoy the dry fall weather this week.

Mark

Weird Weather Alert
September 25, 2010

***Watch WISN 12 News for the latest weather information!***

Thank you for stopping by the Weather Watch 12 Blog!  A sure sign that the seasons have changed is when we begin discussing lake effect rain and snow showers.  While no snow is in the forecast, we do have some lake effect rain showers to discuss.

Let’s start with the cool weather first.  Daytime highs were stuck in the 50s on Saturday across all of southeast Wisconsin.  In Milwaukee, the high at Mitchell Airport was 58 degrees.  This was the coolest high temperature since May 17.  So in the past 2 days, the high temperature has gone from 89 to 58 degrees in Milwaukee!

As the title of the blog indicates, I’m issuing a ‘Weird Weather Alert’.  Tonight into Sunday morning there will be a wide range of weather conditions across our viewing area.  With clearing skies and winds easing up well inland, lows could drop into the upper 30s in places like Fond du Lac, Watertown, Oconomowoc, Lake Geneva, and Beaver Dam.

While the temperatures will be dropping, the winds will gradually shift to the northeast.  As the winds begin to blow in from Lake Michigan.  As the cold air flows over the ‘warm’ lake water(lake temps still in the 60s), the cold air will pick up moisture and clouds will form.  Those clouds will build and could produce a few lake effect rain showers after midnight and continuing into Sunday morning.

The diagram below shows how lake effect rain showers form.  Remember, the greater the temperature difference between the air and the water, the greater the chance of lake effect rain or snow. 

As the clouds begin to move into the lake shore counties in our area, temperatures may begin to rise.  So lows near the lake will be in the 40s, and then rise back to around or above 50 degrees.  Any rain showers should be light.

Below is an image from our high resolution computer model…the RPM.  This shows the surface winds out of a north to northeast direction, this type of wind flow is ideal for lake effect in Milwaukee.  The model also shows some light green, which represents rain showers.  This image is valid at 3 a.m. Sunday.

As temperatures warm on Sunday through the 50s to around 60…the temperature difference will not be great enough between the air and water to sustain any lake clouds or lake effect showers.  So expect increasing sunshine by afternoon!

Right now the cool temperatures with highs around or just above 60 will likely hang around through Tuesday, with most nights in the 40s for lows. 

Have a great weekend and make sure to stop by our comments section and say hi!  We love to hear from our viewers and bloggers!

Jeremy Nelson

Peak Wind Gusts & Chilly Days Ahead
September 24, 2010

***Watch WISN 12 News at 5, 6, & 10 p.m. for Milwaukee’s most accurate forecast!***

Thank you for stopping by the Weather Watch 12 Blog!  Weather conditions have been all over the place in the past 36 hours.  From daytime highs near 90 on Thursday, to wind gusts of 50+ mph, and now overnight lows tumbling through the 40s.  As I like to say, welcome to Wisconsin!

The gusty winds that occurred across the region Thursday Night and Friday did knock out power in some areas, and also damaged the huge inflatable pumpkin at State Fair Park.  This is a picture of the, well, deflated pumpkin Friday afternoon.

Here is a look at the peak wind gusts(mph) across southeast Wisconsin.

  • Milwaukee  54
  • Racine  46
  • Kenosha  46
  • Waukesha  46
  • Sheboygan  45
  • West Bend  43
  • Fond du Lac  39

 

The intense low pressure center that brought the wild weather to the Midwest and Great Lakes took on the classic ‘comma’ shape on the visible satellite today.  The low pressure center is located in the comma head, while the clouds in the tail are along the cold front.  Below is the visible satellite image from around 2:15 p.m. Friday.  Pretty cool!

With a counter-clockwise flow around the low, northwest winds will pull in cooler air for the weekend.  It will be a drastic change after seeing highs near 90 on Thursday!  So how cool?

High temperatures will likely be around 60 degrees both Saturday and Sunday.  Now if those are the highs, you know that morning lows will be chilly…in the 40s here in Milwaukee!  With clear skies and light winds to start Sunday morning, a few spots well inland could start off in the 30s! 

Below is a forecast temperature map valid at 7 a.m. Sunday morning.  Notice the pockets of 30s that touches parts of our viewing area.  Just click on the map to enlarge. 

Quiet weather should prevail for the weekend, so enjoy any and all outdoor activities that you have planned.  Just remember to check in with WISN 12 News for the updates all weekend long!

Have a great weekend!

Jeremy Nelson

More Flooding & Cold Front Swings In
September 23, 2010

***Watch WISN 12 News at 5, 6, & 10 p.m. for the latest weather information!***

Thank you for stopping by the Weather Watch 12 Blog.  Parts of Wisconsin were slammed with heavy rain Wednesday Night and Thursday.  The result was another round of flooding, a scene that has been too common in 2010. 

Rain totals in the western part of the state were in the 5.00″ to 8.00″ range!  The town of Arcadia was flooded in many areas with over 7.00″ over rain!  Arcadia is labeled on the map below with a ‘*’.  Check out some of the NEXRAD estimated rainfall totals below!  Just click to enlarge.

The heavy rain lined up a long a warm front boundry that slowly lifted north Wednesday Night.  That front surged north of our area Thursday leading to a near record high for the first full day of Fall!  The high in Milwaukee on Thursday was 89, just shy of the record of 93 set back in 1937.

Look at the dynamic setup across the Midwest shortly after 2 p.m. on Thursday.  I drew in the low, cold front, and warm front.  While it was nearly 90 in Milwaukee, it was just in the low 60s in central Wisconsin!  Just click on the map to enlarge.

The cold front will push east into early Friday.  As the front nears southeast Wisconsin, showers and thunderstorms will be possible from late Thursday evening into early Friday.  A few showers could linger into the morning commute.

The timing for southeast Wisconsin will be good in the sense that the storms will weaken as they move in, and they should prevent any severe weather or heavy rain from occurring.  In fact, I think some areas will see little to no rain, and top end rain totals may only be around a half inch. 

Below is the rainfall forecast from our in-house high resolution computer model through early Friday.  Notice, the part of western Wisconsin that already saw heavy rain could see more! 

Behind the cold front cooler weather will settle in on Friday.  Most areas will see highs back into the upper 60s.  If the sun would poke through a few low 70s are possible.  The wind will again be gusty, with gusts topping 30 mph in the afternoon.

Cooler, but drier weather settles in for the weekend.  Morning lows on Saturday should be back into the 40s!  After a summery start to Fall, the typical late September weather is back!  Make sure to watch WISN 12 News for the latest on rain and the weekend forecast!

Remember, you can always add your thoughts to the comments section of the blog! 

Have a great day!

Jeremy Nelson

Hail Pictures & First Day of Fall
September 22, 2010

***Watch WISN 12 News for the latest weather information!***

Thank you for stopping by the Weather Watch 12 Blog!  Today marks the beginning of a new weather journey for our area…Fall.  If you follow the blog, you know that I believe this is the time of year that a brand new never before seen weather pattern begins to set-up.  Once the new weather pattern forms, it will then repeat for about the next 9 months.

In the coming days and weeks we will analize the new pattern, which will lead up to the winter forecast!  Look for the long range winter forecast right here in the blog coming in November

To start, let’s take a look back to yesterday’s severe storms that hit parts of Walworth and Racine counties.  Hail reports were numerous, and storm reports that I saw put hail sizes in the neighborhood of dime to golf ball.

The picture below is courtesy of Karen Heine of Delavan.  This hail measured 1.0″ in diameter, about the size of a quarter.

The next picture is from the U-Local section of WISN.com  This picture shows several hailstones from about dime to nearly quarter sized.  These hailstones fell near Delavan.  Remember, you can always share your pictures by posting them to the U-Local section!  Any pictures posted may be used on WISN 12 News and right here in the blog.

With the storms behind us in the short term, let’s focus on Fall!  Fall begins today at 10:09 p.m.  The official name for the first day of Fall is the Autumnal Equinox.  Equinox is from the Latin for ‘equal night’.  While the days and nights are close to being equal on the first day of Fall, they are not.  Here is why…

During the equinox, the length of night and day across the world is nearly, but not entirely, equal. This is because the day is slightly longer in places that are further away from the equator, and because the sun takes longer to rise and set in these locations. Furthermore, the sun takes longer to rise and set farther from the equator because it does not set straight down – it moves in a horizontal direction.

Moreover, there is an atmospheric refraction that causes the sun’s disk to appear higher in the sky than it would if earth had no atmosphere. timeanddate.com has a more detailed explanation on this topic.

This is sort of complex, if you have questions just let me know.  On the first day of Fall, the sun’s direct rays pass over the equator, and begin to head over the southern hemisphere.

The Earth’s axis continues to tilt away from the sun, meaning our days continue to see less daylight, and our nights are longer.  This eventually sends us into winter! 

While Fall is here, another summery day is in store for Thursday.  Showers and t-storms will bookend a day with highs in the 80s.  Very slight chance of a strong storm or two on Thursday.  We’ll discuss the big change for Thursday more on WISN 12 News and also in Thursday’s blog! 

Have a great day and please leave a thought or question in the comments section of the blog!

Jeremy Nelson

Summer Sizzles To An End
September 21, 2010

****UPDATE****

Severe Thunderstorm Watch for Milwaukee, Waukesha, Racine, Kenosha, Jefferson, and Walworth Counties Until 9 pm. Damaging Winds will be greatest threat. Storms arriving in the metro between 5 and 7 pm. Stay with Weather Watch 12 and Interactive radar on wisn.com for the latest.

***Watch WISN 12 News for live radar updates!***

Thank you for stopping by the Weather Watch 12 Blog!  The official start of Fall is just hours away, but the last full day of Summer will feel more like mid-July!

Fall officially begins on Wednesday at 10:09 p.m.  Before we get there, a wild swing of weather is in store for the next 24 hours! 

As of this writing(Tuesday morning), a cold front was located from the western tip of the U.P. of Michigan back through western Wisconsin and into the Plains.  Ahead of the front winds were out of the southwest, temperatures were in the 70s, and dew points in the muggy 60s.

Below is the surface map from 7:33 a.m. Tuesday morning.  Just click to enlarge.

High temperatures today will soar well into the 80s.  The record high for September 21 in Milwaukee is 90 degrees set in 1893 and tied in 1920.  While I think we fall short of a record(I went 85), it will be a very warm end to summer.

The cold front will continue to slide east throughout the day, and by afternoon it will reach our viewing area.  With the front arriving during peak heating, increasing low level moisture(dew points), and lift courtesy of the front, thunderstorms are likely.

The 3 ingredients needed for severe weather are moisture, lift, and instability.  All of those ingredients should be in place today for a chance of strong to severe storms.  Below is the severe weather outlook from the Storm Prediction Center.  It has southern Wisconsin in the slight risk area.

Within that slight risk area the threat is further broken down into the probabilities for tornadoes, hail, and wind.  The biggest threat for today is damaging winds.  Below is the probability breakdown for wind.  The 30% area over far southeast Wisconsin means that there is a 30% chance of damaging winds within 25 miles of a point. 

Along with the threat for damaging winds, there could also be hail.  And as we have seen many times this summer season, a brief and isolated tornado can never be ruled out.  Anytime day or night you can track severe weather with our interactive radar.  Just click on the link below.  Give it a try!

www.wisn.com/irad

The threat for severe weather will be highest in the afternoon and evening hours.  If severe weather develops make sure to watch WISN 12, as we are always on Weather Watch!  You can also stayed up-to-date throughout the day here:

  • Facebook – WeatherWatch 12
  • Twitter – WISN12News
  • iPhone App – WISN12
  • WISN.com  – Interactive Radar & Futurecast

Have a great day and make sure to send us your storm related photos or post them to the U-Local section of WISN.com!

Jeremy Nelson