Will the Streak Survive?

So far the number is 13. After a high today of 95° this could be the last consecutive day with a high temperature of 90° or hotter in this streak. If Saturday hits the 90° mark then it is liikely that we will end up with a record setting streak of 19 or 20 days becasue the forecast has the hot stuff here all next week.

Is a Streak Buster in the Near Future?

A streak buster is anything that stops the high @ CVG from getting to 90°F or higher. 

Today that could be thunderstorms or just the cloud cover that is associated with thunderstorms several miles away. Saturday a front passes southward and the cloud cover with it could block enough sun to stop the high from reaching 90°F. Both could be streak busters.  

Right now the odds are in favor of the streak continuing into Wednesday and setting a record for the greatest number of consecutive days with high temperatures 90°F or hotter. In 2007 the streak extended to 15 days but the longest streak was 17 days set in 1868 (before official records but recorded by reliable Smithsonian observers) and in 1901.

If high temperatures >=90° continue through Wednesday the new record will be 18 days.

Streakin' In the Queen City

Of course if you are a person of high weather interest  who lives in the vicinity of Cincinnati, OH, USA you know immediately I am not talking about that 70s fad of running across the landscape sans clothing.

The "Queen City" part of the title dates back to  May 4, 1819 when a B. Cooke wrote in the local newspaper that,  "The City is, indeed, justly styled the fair Queen of the West: distinguished for order, enterprise, public spirit, and liberality, she stands the wonder of an admiring world."

Henry Wadsworth Longfellow wrote this in his poem Catawba Wine (1854),

"And this Song of the Vine,
This greeting of mine,
The winds and the birds shall deliver,
To the Queen of the West,
In her garlands dressed,
On the banks of the Beautiful River."

Next time I will write a title that I do not have to explain.

The video below explains the streak we are building each day as of  Thursday morning July 28, 2011.  We could see a longer period with consecutive days having high temperatures 90°F or warmer than any time in Cincinnati history.

Consecutive Days Having

High Temperatures >=90°F

Cincinnati, Ohio, USA

Length

Days      Years

17 (2)     1868 – before official data, this is Smithsonian Inst. data
               1901

16 (0)     none

15 (3)     1933, 1966, 2007

14 (2)     1881, 1953

13 (2)     1934, 1946

12 (2)     1918, 1930

11 (5)     1887, 1890, 1964, 1995, 2011 (through Wed 7.27.2011)

10 (5)     1897, 1941, 1949, 1952, 2002

Postscript - On August 2, 2011 Cincinnati tied the 17 day streak set in 1868 and 1901. On August 3, morning thunderstorms left behind enough cloud cover to hold the high temperature to 89° and the streak ended  leaving behind a 3-way tie.

Hot But Not Bad Today! What About the Start of Next Month?

A trajectory is the path a parcel of air follows. It is not always simple and frankly until computerization and advances in forecast models it has only been possible for a bout a decade.

When I started my career in the late 1970's models were a brand new tool and frankly very unreliable.  Back then we were lucky to be close to accurate three days out but in today's world with reasonable accuracy we can look half-a-month ahead.  Reasonable accuracy means I cannot tell you what time it will start to rain on Day 15, in fact it may start on the 14th or even the 16th.

By following changes day-to-day, knowing model weaknesses and biases an attentive meteorologist can guide you so there are no surprises.

For example if a model starts to hint that the heat wave will not break down as early as previous model runs and does this consistently it may very well point to a trend that is developing and behind the scenes in the weather office we say that "the trend is your friend".

Holy Hot Stuff, Will It Ever End?

You know it has been hot when a high temperature of  91°, a dew point temperature of 71° and a heat index of 98°, like today,  feels like relief.  Tomorrow and Wednesday will be hot but without the oppressive humidity of last week so it will not be quite that bad. 

Late this week we are in for heat indices over the 100° mark.  But as the video below tells you early August should bring relief.

Heat, Heat Go Away, Smack Me Down Some Other Day

The heat is here through the weekend but it will ease a bit as we head into Monday.  Relief will get here for a couple days, not so much in the form of cooler air but in the form of less humid air.

For late Tuesday and all Wednesday then into the early part of Thursday somewhat cooler air and somewhat lower humidity will combine to give us a break.

How the remainder of the month stacks up is covered in the video below.

Wavering Weather Models

Ok it is hot .... very hot but not the hottest it has been in Cincinnati. That occurred on this date in 1934 as one of the official thermometers topped out at 109° for the city's all-time record high temperature.

The years 1934 and 1936 were dust bowl years and for Cincinnati hot years too. In 1934 the thermometer topped out at 90° or hotter 54 times and in 1936, 63 times. So this year's 17 times (so far) is not too bad.

That hot air mass will be sloshing back and forth across the country. As it sloshes westward early next week we will get a brief break then it sloshes right back into the tristate for the remainder of the month.

The latest models say another break, this time a bigger one will get here around the 3red or 4th of August.

The video shows how this will happen.

Dome Hot Dome - Where it the Light at the End of the Tunnel

I am officially weary of blogging about a hot dome of air  that will continue to dominate our weather until Monday.  That means we have  6 more days with that sultry air front and center on this blog and on all our weather broadcasts. Frankly it is getting hard to come up with new ways to talk about it.

But there is light at the end of the tunnel and it comes Tuesday in the form of air from our friends north of the border. A Canadian air mass will arrive bringing cooler, less humid weather.

Take a look at the video for more.

How Hot, How Long?

The hot air mass will dominate our weather this week and the video below tells you what to expect as we head through the week and into next weekend.

This is nothing like Cincinnati's greatest heat wave. Every afternoon from July 8, 1936 through July 15, 1936 the temperature peaked above 100° WITHOUT the heat index. During that time the Cincinnati Reds played 8 games (the won three of them) in those old-time wool uniforms.

Here are the high temps. for that 8 day stretch and the Reds results:

103°  No Game
103°  Lost
105°  Lost
104°  Lost
105°  Double Header - Split
102°  Won
106°  Lost
104°  Won

Hot, Hazy and Humid For A While

Weather models are in agreement that a big hot airmass will dominate our weather this weekend and right on into next week.

These hot airmasses are also called hot anticyclones and form mainly because air high in the atmosphere is forced to sink by the global pattern of high and low pressure. The sinking air traps pollutants, supresses rain, lowers the relative humidity upstiars and  in casual weather lingo the air bakes.

While humid air near the surface makes it sultry because of the sinking aloft allows little relief in the form of rain.

Day after day the air gets warmer, the heat index rises, haze thickens and air quality deteriorates.  It looks like that is what we get starting Saturday and lasting at least until next weekend.

Take a look at the video for more.

What the Upper Winds Tell Us About the Remainder of July

In yesterday's post and several others before that I have discussed the hot air air mass that will dominate most of the remainder of July.  That air mass is best depicted in 3D as a dome of hot air and while it can be oppressively humid at the surface up stairs the air is dry and warm. Those two factors suppress thunderstorm formation.

In today's post I just look at  the upper wind flow and as you will see while a location is near the margin of the hot air mass a few spotty thunderstorms are possible. When the air mass moves and a spot is closer to the center rainfall is shut off and the Dog Days commence. Popularly any period of warm sultry weather is concidered and episode of the dog days.

The term  Dog Days (dies caniculares to the Romans) were thought to be hot because the star named Sirius, the brightest star in the constellation Canis major (large dog) rose at the same time the sun rose during summer mornings between July 23/24 and August 23/24. They thought Sirius added to the heating the air and led to the sultry weather. Sirius no longer rises with the sun during this period because of a gradual change of earth's orbital geometry called precession of the equinoxes.

Now ... back to the upper level winds.  probably the biggest advance in meteorology in my lifetime was the discovery of how jet stream systems energize storms.  But it is not just the main branch of the jet stream that contains "disturbances" that can energize weather systems. 

While Cincinnati is at or near the eastern margin of the hot air mass the winds upstairs are out of the northwest.  Small disturbances can travel in these winds and cause spotty pop up showers, As the big air mass expands to the east coast we are closer to the center and the rain is shut off.

The calendar shows spotty showers will return to the tristate late this month as the big hot air mass shrinks and sloshes back to the west.

Plenty of Humidity But Little Rain. Why?

Hot air like we have had this week does not seem to obey the rules.  After all TV meteorologists constantly say that the humid air will fuel thunderstorms, but little if any rain is in the forecast.  So... what's up?

Remember that weather is 3-dimensional and while the sultry air at the surface is conducive to thunderstorm formation the air above it is dry and warm in situations like this. Dry, warm air aloft inhibits thunderstorm formation.

Humid weather is in my forecast from late Friday into the end of the next work week.  We may see 10 hot and humid days before this streak is over but little rain because when rain does form in these hot high pressure situations it is usually around the margin of the hot air and associated with a jet stream.

If not the full fledged jet it is a small upper-level disturbance that kicks in the extra energy to set off spotty thunderstorms. The video below explains it.

Almost until August this air mass will dominate our weather and when we find ourselves on the margin of it and an upper-level disturbance passes over spotty thunderstorms could develop.

The animation below shows these disturbances.  Red represents positive spin in the atmosphere which is counter clockwise the same way Earth rotates on its axis.  Blue represents negative spin.  Meteorologists call positive spin "positive vorticity" and negative spin "negative vorticity".  Used together we can accurately place jet streams and see areas of upward motion that can spawn thunderstorms. 

Roughly red indicates upward motion and air is sinking where it is blue.  Watch how small to large patches of red pass over the tristate.  Each upper-level disturbance could set off an isolated thunderstorm.

Because of the dry air aloft thunderstorm formation often needs more than just the heat of the day to get going and these upper-level disturbances can provide the extra energy.

That is why I am saying rain will be scant but each day into Wednesday next week there is the chance of a pop-up thunderstorm.

Click for a Larger Animated Version
then click <back> to return.

 



How We know It Will Be Humid

Most of the rain that Cincinnati gets starts as moisture evaporated from the Gulf of Mexico and Caribbean Sea. But that is not the only source. Sometimes it is humid because of the recent past.  Today was an example.  Extreme rainfall in the spring saturated the soil. Remember that the 31-day period ending May 3rd was the wettest 31-day period in Cincinnati history.

Much of that rain just drains into rivers and streams and heads back to the Gulf.  But a certain amount is stored in the soil and when the air warms it is evaporated becoming part of the humidity you feel.  In addition all plants transpire moisture which also adds to the amount of humidity in the air.

So tomorrow will be humid because of moisture from the Gulf of Mexico and Carribbean and because there is already moisture here.

The video below explains it more.

Holy Heat Index!

The hot air mass out west will invade the east for a couple days and bring heat index values to 100° or more Sunday and Monday. It will continue to be very humid Tuesday but a comfortable and welcome break is on the way for mid week.

The heat index  is an effective or apparent temperature and just like the wind chill tells you how cold it feels, heat index tells you how hot it feels. What they really measure is how fast your body looses heat or how fast heat will build up in your body.

Wind removes heat quickly from the human body when the air temperature is less than skin temperature, approximately 90°. Any cooler than skin temperature and wind cools the body faster than in air of the same temperature without the wind. This is a topic I will cover again in winter.

High humidity slows evaporation of sweat, the primary way our bodies cool.  When heat removal is slowed body temperature rises because heat is accumulating. If enough heat accumulates the body it goes from heat stress to heat exhaustion to heat stroke.

Every concept has to have a starting point and with the heat index it is a temperature of  77°F and a dew point temperature of 57°F which yield a relative humidity of 50%. As the amount of moisture in the air (water vapor) increases the heat index rises more and more above the air temperature.

Depending on a person's physical condition when the heat index is around 100°F there can be a rapid onset of  heat stress and heat exhaustion. To avoid this take frequent breaks and drink plenty of non-alcoholic fluids.

Dry Air Upstairs

In my last couple posts I have been talking about what the remainder of the month looks like.  Of course not I or anyone else can forecast a specific day a couple weeks out so we go for general trends. 

I have mentioned that it looks like fairly dry, hot and humid weather into August with rain fairly rare.

The video below extends yesterday's post where I looked at the different trajectories of air arriving in Cincinnati around the 21st of July. At the surface is flowing from the warm and humid source region over the Gulf of Mexico and Caribbean Sea. Air aloft is dry and moving in from the Northwest.

From Where Comes Our Air?

A trajectory is the path a parcel of air follows to arrive at a location. Everyone has an intuitive feel for what air arriving here brings. 

If I say that air from the north pole will arrive for the second week of January you know it will be very cold.  What you are more likely to hear is that arctic air is on the way.

On the other hand if I say our air for next week will arrive from the Caribbean you know you that means heat and humidity because tropical air will soon be here.

But it really is NOT that simple. Air at different heights in the atmosphere comes from different places and that is what this post is about.

We know that significant rain requires more than just a shallow layer of moist air. Big rains require deep moist layers in the air above.

The animation shows that the air upstairs, colored blue, that arrives here on July 20th, is off the Kamchatka Peninsula in eastern Russia today.  Air that today that is over the tropical South Atlantic will arrive via the Caribbean and Gulf of Mexico on July 20th.

What the animation also shows is that the air high in the atmosphere from eastern Russia will start out much lower then rise thousands of feet through a storm over the North Pacific.  When it rises much of the moisture falls out as rain over the north Pacific Ocean.

The moisture depleted air then heads east and around July 20th the air sinks over Cincinnati and warms. This means there are two reasons rain will be scarce through the remainder of the month:

1. Dry air upstairs prevents a deep layer of moisture
2. The dry air is also sinking which stops the upward motion required for rain to form

So my long-term out look into the first week of August is only spotty rains and generally hot and humid days.

As always things could change.



The Return (and Extended Stay) of the 3-Hs

The 3-Hs of course are haze, heat and humidity and it looks like we are in for an extended period of dry, hot and moderately humid weather. In fact except for a few scattered thunderstorms Thursday into early Friday this week then Tuesday next week we may be rain free until the beginning of August.

Extended periods of hot, dry weather are best explained using weather maps at jet stream level. Those long stretches almost always happen when the jet stream bulges northward and a hot air air mass stops moving and stays over top of us. The descending air within this hot high pressure system traps airborne dust, other particulates and pollutants so visibility drops, air pollutant levels increase and the combination of heat, humidity and air quality put quite a bit of stress on the human body.

The animation below shows the jet stream flow and the location of the hot air mass from today through July 21.  That's as far out in time the models go but there are indications that the hot air mass will persist as a factor in our weather until early August.

As upper level disturbances (aka jet max, wind max, velocity max, jet stream, impulse) push through the jet stream they cause the hot air mass to "slosh" back and forth bringing a chance of rain and potentially some relief.  That happens in the next few days and around  20-21 July.  The last frame shows a big low out west pushing south which should cause the hot air to slosh back to the east and keep us hot and dry through the beginning of August.

As always this could change. In case it doesn't get ready to water your plants and take it easy in the heat.

A Good Looking and Traditional (Weatherwise) 4th of July Weekend

When I think of the 4th of July I remember heat, humidity, sunshine and potato chips lacking that crisp snap and going almost limp.  Yes, humidity is the enemy of that Great American snack and I will cover that in another post in the future.

This discussion goes with the animated weather map below.

Yesterday I wrote that through the weekend we will lack a deep moist layer of air and that adds up to only scattered showers. That is still true and it looks like Saturday night into Sunday morning is when a few  thunderstorms will fire up over the area.

The forecast for Monday has changed ... for the better ... as a cooler, less humid air mass will push its leading edge (the cool front) to the deep south. That practically guarantees three things for the holiday:

1. Less humidity for Monday the 4th
2. No Rain and
3. Plenty of sunshine 

The nice weather will hold Tuesday but by the end of the week the humidity will return. Enjoy your holiday.