Steve Horstmeyer's

90-Day Outlook - April, May and June

2012-03-20T18:30:00.003-07:00

Long term forecasts, actually called outlooks to emphasize that these predictions target average conditions over longer periods of time and a fairly wide areas, have come a long way since I was a young TV meteorologist.

Because we now know about El Niño/La Niña, a big sloshing of pressure systems spanning the tropical and subtropical Pacific Ocean and other oscillations of atmospheric pressure medium to long term forecasting has become more of a science and much less of a guess.

Other such sloshings are the Madden-Julian Oscillation, a tropical rain system pattern, Antarctic Oscillation, the Arctic oscillation, the North Atlantic Oscillation and the pacific-North America Pattern
along with a knowledge of blocking, patterns that persist for a long time have enabled the meteorological/climatological community to develop better long-term outlooks.

Remember that these outlooks talk about average conditions and not specific events so a period with an outlook for a dry, hot summer there can be a cool, wet week or two.

The video covers the latest outlook.

Tornadoes Without Hook Echoes

2012-03-08T15:14:00.001-08:00

Take a look at the first 5 radar images below. They are from the EF3 tornadoes that struck the FOX19 viewing area 2 March 2012. The top image is from the Crittenden-Piner-Fiskburg-Morning View tornado, the second is from the Peach Grove-Moscow-Hamersville tornado and the third and fourth are from the Holton, IN tornado.

Crittenden-Piner-Fiskburg-Morning View Tornado Hook Echo and debris ball 4:26:57 PM Friday March 2, 2012

Peach Grove, KY-Moscow, OH-Hamersville, OH Tornado Hook Echo 4:37 PM Friday March 2, 22012

Notice how well defined the hooks are, indicating a rotating updraft and a mesocyclone in the top two images. Oh the other hand a hook appears to be absent for the Holton, In tornado. The fourth image is for approximately the same time but with the radar dish tilted up to the next higher angle. The hook echo is obvious but not as well defined as the hooks for the "Piner" and "Moscow" tornadoes.

Holton, IN Tornado KIND radar reflectivity, lowest scan with no apparent hook echo 3:52:50 PM EST March 2, 2012

Holton, IN Tornado KIND radar reflectivity, 2nd scan up scan with a small hook echo 3:52:50 PM EST March 2, 2012

Holton, IN Tornado KIND spectrum width, lowest scan, a well defined area of large spectrum width, i.e. a large variation of target direction and speed, indicating the EF3 Tornado, 3:52:50 PM EST March 2, 2012

With a "marginal" hook in the Holton super it would be nice to have additional evidence of a tornado and the fifth image provides it. Spectrum width is a measure of the magnitude of the variation of movement of the targets. Lots of variation means high wind speeds, turbulence and big changes of wind direction and speed in a small space just like you find in a tornado.

The tornado stands out in the spectrum width image.

The lesson is that here 3 EF3s touched down. The evidence for a tornado was not obvious in the Holton, IN tornado with the lack of a visible or well defined hook. At a higher antenna elevation the hook is visible and using spectrum width the tornado can be easily seen. .

Now take a look at the Berlin, KY EF0 radar images. The black dot northwest of Brooksville is Berlin.

Radar reflectivity of flanking line thunderstorms entering and moving through northwest Bracken Co. KY at
5:05:15 PM March 2, 2012. the black dot west of Brooksville is Berlin, KY and the approximate location
of the brief touchdown of an EF0 tornado.

Not a hint of a hook echo and below where the red and green come together in a line a typical signature of outflow or the leading edge of a line of thunderstorms. In this case a flanking line off the super cell to the north.

Same time as the image above but this is radial velocity. Green represents air flowing towards the KILN
Nexrad Radar to the north. Green is flowing into the thunderstorm. Red represents air flowing out of the
thunderstorm and heading away from the radar. The dark green patch around Berlin indicates higher wind speeds there.

Notice the dark green around Berlin and indication of stronger winds. but green colors indicate winds heading towards the radar to the north or air flowing into the thunderstorm. Red indicates outflow from the line of thunderstorms. Neither the reflectivity or the velocity display have an easily detectable indicator of a tornado. Look below.

Same as the two images above but this is the display of spectrum width or the range of variation of wind
speed and direction. Notice the black spot near Berlin indicating a great deal of wind variation and the leading edge tornado.

The spectrum width display, similar to a display of turbulence but indicating variation in wind speed and direction along the line. Just north of Berlin a black spot indication too much variation to measure and the location of a small tornado.

The Berlin, KY tornado, an EF0, was a different type of tornado than the EF3s which were mesocyclone tornadoes.

Berlin, KY was a leading edge tornado. Leading edge tornadoes are difficult to detect because almost all leading edge vorticies are weak, small and are usually around for only a minute or two, maybe less. They form from air that gains spin outside the thunderstorm. The rotating air is pulled into the thunderstorm and tilted to nearly vertical and can cause a small tornado.

There is mounting evidence from Doppler on Wheels investigations that many large tornadoes may be caused by continual importation of rotation which is tilted to the vertical and stretched by the updraft. Stretching a rotating "tube" of air has the same effect as an ice skater pulling his or her arms towards the body, the rotation is concentrated in a smaller area and the rotation rate increases. When the tube is stretched the diameter shrinks and the rotation rate increases.

Take a look at the images I have produced to explain the importation of rotation:

Development of horizontal rotation from vertical wind shear

Rotation caused by vertical wind shear increases as air streams towards the thunderstorm through the
environment with large vertical shear values.

Large view of rotation being imported into a thunderstorm. Rotation can be imported over a large area.

An additional source of rotation involves the cold pool that develops under a
thunderstorm. As air is lifted up and over the cold pool horizontal rotation is
converted to rotation around a vertical axis.

When the rotating tubes of air are tilted to the vertical by the thunderstorm updraft and stretched vertically they can spin up enough to cause a leading edge tornado.

Leading edge tornadoes only live a very short time and the radar signatures are weak so they are much harder to warn for than a mesocyclone tornado.

These rotation elements can become an significant source to maintain large tornadoes as the super cell travels across the landscape.

It Has Been A While

2012-03-07T18:44:00.000-08:00

The chaos that ensues with the touchdown of a major tornado or three of them in the case of March 2, 2012 is a heartbreaking testament to the power of Nature. Chaos pretty much says it all, nearly total disorder and the end of daily routines until lives and homes can be rebuilt.

That chaos ripples down to the weather office. Unlike the victims of the storms, for us of course, it is a matter of a minor inconvenience and catching up with tasks put off for storm coverage. This is one of those tasks.

EF3, 4 and 5 tornadoes are classified as major tornadoes. There were three EF3s in the Cincinnati tristate region, 2 - EF2s, 2 - EF1s and 5 - EF0s for a total of 12.

High resolution Doppler radars like the TDWR (Terminal Doppler Weather Radar) often incorrectly called - Turbulence Detecting Doppler Radar - were located near major airports to detect wind shear, wind shifts and turbulence so aircraft can avoid the dangers associated with these on takeoff and landing. There is a TDWR in Kenton County south of CVG.

Here is what TCVG (the TDWR for CVG) saw at 4:29 PM Friday 2March2012.

The well defined hook echo is attenuated by heavy rain at the radar site (big black dot north of Piner) so instead of showing up as a bright yellow and red hook it curls around in shades of green to a distinct yellow "ball" we call a debris ball. Just what is a debris ball? It is parts of houses, trees, peoples memories and prized possesions abducted and pirated away by the 160 mph winds of the EF3 Crittenden-Piner-Fiskburg-Morning View tornado.

More On Severe Weather

2012-03-01T18:39:00.001-08:00

What you see is the Day 2 Convective Outlook issued by NOAA's Storm Prediction Center. It states that the FOX19 viewing area is under a moderate risk of severe weather for Friday (03.02.2012). This means severe weather will likely be widespread and some of the storms could be quite strong with a chance for a major tornado or two.

A severe thunderstorm must have at least one of: hail >= 1" in diameter, winds of 58 mph or higher and a tornado.

The tables below summarize the categories Slight Risk, Moderate Risk and High Risk as defined by the Storm Prediction Center and are courtesy of SPC.

As you can see the Day 2 Convective Outlook defines a Moderate Risk as a 45% - 59% chance of of Tornadoes, Wind or Hail, any or all could occur.

The video has more on the forecast for Friday March 2, 2012.

Severe Weather Possible Again

2012-02-29T18:21:00.001-08:00

It is Déjà vu all over again. Warm moist air will again surge northward Friday and invade the tristate. At this point it looks like we have two chances for severe storms. The first chance is about midday with the warm front and the second is late evening with the cold front.

The video explains it.

Thinking About Severe Weather

2012-02-28T18:36:00.000-08:00

A strong velocity max (aka upper level disturbance) embedded in the jet stream with wind speeds approaching NASCAR velocity, 200 mph, is powering a strong surface low towards the Great Lakes.

North of the storm Winter Storm Watches and Warnings have been issued along with a large area under Blizzard Warning (in white) over parts of South and North Dakota.

Along the cold front from Oklahoma to Nebraska Tornado Watches have been issued. This is a typical late winter storm and severe weather is likely from the plains to the East Coast as the storm advances over the next several days.

The video has more on forecasting severe storms with this and similar systems.

Getting Stormier

2012-02-27T19:29:00.001-08:00

This is the time of the year that the cold air draped across the north pole begins to noticeably shrink back towards the pole as the late winter solar radiation gets stronger by the day.

The result is that the unstable tropical air that has stayed south through the dead of winter begins to be seen more and more frequently pushing northward deep into the continent.

The northward withdrawl of the cold air of winter is often slower than the invasion of tropical air from the south and in spring, more often than at any other time of the year, the two clash in the vicinity of The Ohio River Valley.

Moist tropical air gives birth to thunderstorms as the heat used to evaporate water molecules is released back to the thunderstorm environment when the molecules condense forming the torrential rains that fall from the storms.

If you throw in additional lift from a front, the dynamics of a jet streak (aka upper level disturbance) and the energy of the sun you may conjure up severe thunderstorms.

The video has more.

The Wettest 12 Months Ever for Cincinnati

2012-02-22T18:37:00.002-08:00

This post departs from my regular routine and does not coincide with my Inside The Forecast segment for the day.

We all know that Cincinnati had the wettest year ever in 2011 recording 73.28" of rain. Included in the total of course is melted snow and ice.

But if you think about it a year is an artificial division of time relative to weather. In fact so are weeks months and 24 hour days. It is not a difficult concept weather events are not confined to time intervals humans define.

But .... we have to organize the information some way so we talk about wettest days, months and years.

The reality is that by looking at rain totals over intervals of 12 consecutive months we can gain better insight.

That is just what I did. Reliable monthly rainfall data goes back to November 1834 and official monthly data back to November 1870. The earlier data set was observed by teachers at Woodward College (later High School) in Over The Rhine, Downtown Cincinnati. The official data was less than half-mile away also in Downtown Cincinnati. The Woodward data later moved to near the entrance of Eden Park about one mile into Walnut Hills from Downtown.

The data sets overlap from November 1870 through December 1902. I mention this because it allows us to compare the two and judge the accuracy of the unofficial data. The two are comparable.

For 12-consecutive month periods the wettest is 77.09" from Feb 2011 through the end of Jan 2012 almost 4" greater than the wettest year in history at 73.28".

The Table below lists the 20 wettest 12 month periods in Cincinnati history. The columns are year, ending month, total rainfall and departure from the normal annual rainfall for the 1981-2010 normal period.

20 Wettest 12-Month Periods

2012	1	77.09	34.57
2011	12	73.28	30.76
2011	11	68.53	26.01
2011	10	67.14	24.62
1847	10	66.59	24.07
1847	11	66.28	23.76
1880	6	65.46	22.94
1847	12	65.18	22.66
1880	7	65.17	22.65
1848	3	65.15	22.63
1848	1	65.05	22.53
2011	9	64.60	22.08
1848	5	64.41	21.89
1848	2	63.80	21.28
1848	4	63.58	21.06
1882	9	62.31	19.79
1882	8	61.25	18.73
1880	5	60.82	18.30
1847	7	60.74	18.22
1882	5	59.95	17.43

By the way the driest 12-month period in Cincinnati history enede November 1901 with only 15.63" of rain while the driest year in Cincinnati was 1901 with 17.99" of rain.

So you see consecutive 12-month periods tell a more extreme story than calendar year data.

Here are the 20 driest 12-month periods in Cincinnati history. The columns are the same as for wet periods.

20 Driest 12-Month Periods

1901	11	15.63	-26.89
1902	3	17.71	-24.81
1901	12	17.99	-24.53
1902	2	18.25	-24.27
1902	4	18.65	-23.87
1902	1	19.22	-23.30
1901	10	19.39	-23.13
1901	8	19.61	-22.91
1931	2	20.14	-22.38
1931	3	20.20	-22.32
1901	9	20.25	-22.27
1857	3	21.13	-21.39
1941	5	21.20	-21.32
1931	1	21.21	-21.31
1857	2	21.88	-20.64
1905	3	22.07	-20.45
1931	4	22.08	-20.44
1871	6	22.33	-20.19
1857	1	22.39	-20.13
1902	5	22.57	-19.95

The West to East Jet Stream Continues

2012-02-21T19:38:00.003-08:00

The fanatical relationship between humans and weather has been part of almost all cultures as far back as archaeologists have evidence.

About 5000 years ago the saying we know as, "Red sky at night, sailors delight ..." was inscribed on Babylonian stone tablets. Years later Aristotle repeated the saying in his treatise Meteorologica.

The saying also appears in the Bible, Matthew 16, 1-3, and William Shakespeare penned a version in his 1592 poem, Venus and Adonis.

The folkloric rhyme it seems has been with us since the beginning and that makes sense, because long before all of the above recalled the weather forecasting rhyme, nomadic tribes had to know weather patterns and seasonal changes to survive. The sacred oral traditions were passed from one generation to generation the next.

Fast forward to today and modern humans cyber-digital relationship with weather is as fanatical as our earliest ancestors.

All this is a long way to get to an outlook for the next 10 days and whether there will be a big snow.

When the 20th Century dawned we had no knowledge of fronts, highs and lows and the weather they cause. In the years before and after WWI in Bergen, Norway a group of meteorologists developed the next-to-last big block in the structure of modern meteorology.

They developed the concept of fronts as the battle ground between contrasting air masses. The horrid trench warfare of "The War to End All Wars" had left its mark on meteorology.

The only problem is that when tested with equations the Bergen School's approach could not account for how strong cyclones, those low pressure storms you see on weather maps, would become.

They were not wrong, they just did not have enough information. After WWII at the University of Chicago the role of the jet stream and those mysterious entities TV meteorologists call upper level disturbances was unraveled and the final building block was in place.

And the video below tells you why I am not encouraged about the possibity of a "big one", a snowstorm that is, before it is too late this season. It is not impossible just not likely.

ZONAL FLOW

2012-02-20T21:39:00.000-08:00

The next 7 days should be dominated by numerous small storms with a bit of precipitation possible each day but no big storms and no temperature extremes.

Why? Because the jet stream flow is mostly west to east or what meteorologists call zonal. West to east jet stream flow is approximately parallel to the climate zones determined by latitude. In zonal flow most of the very cold air stays way north and the most of the very warm air stays far south. Without the jusxtposition of the very cold and the very warm the thermal energy difference across the jet is insufficient to drive big storms.

This week will be dominated by zonal flow.

High amplitude jet stream flow or flow where the jet pushs way to the north and way to the south in big ridges and trofs (meteorologists' shorthand) is called meridional flow. In this type of regime warm air pushes way north and cold air pushes into the deep south. The difference in temperature across the jet helps power big storms.

In addition meridional flow and help bring Gulf of Mexico moisture northward to produce precipitation and release heat as the water vapor condenses to liquid or directly to frozen precipitation. Theis "latent heat" that condensing moisture releases also helps drive storms.

The video has more.

Looking 90 Days Ahead

2012-02-16T18:24:00.001-08:00

Around the middle of each month NOAA's Climate Prediction Center (CPC) issues seasonal outlooks for a variety of time periods in the future.

Producing these outlooks is very different from forecasting. Forecasting weather is basically the application of physics and math to the atmosphere through the tool of numerical models.

Seasonal outlooks like the ones for March, April and May can use a number of tools including historical analogues and statistical methodologies, and the persistance of typical flow patterns.

Also important are patterns of atmosphere-ocean interaction. To the public the most recognizable pattern is El Niño/La Niña.

There are others like the Madden-Julian Oscillation of the tropics, the Arctic Oscillation, the Antarctic Oscillation, the North Atlantic Oscillation and the Pacific North American Pattern. Essentially these all describe and quantify atmospheric flow patterns and their persistence in different geographic regions of the globe.

For example La Niña interacting with the North Atlantic Oscillation is blamed for the relatively harsh winter of 2010-2011 in Cincinnati. For the winter of 2011-2012 La Niña interacted differently with the North Atlantic Oscillation, because the NAO had changed, and though both winters were La Niña winters they were very different.

If a blocking pattern is expected to persist only slow changes to the jet stream flow may occur and as a result changes in the weather will be forecast to be slight or very slow.

Using all these tools the CPC issues extended outlooks from 5 days to 1 year in the future.

Here is what March, April and May are expected to bring:

The top map, precipitation outlook shows the La Niña "bullseye" of precipitation (as I call it) will continue over the Tristate. It is smaller and weaker as the La Niña. pattern starts to ease.

Temperatures here are expected to be warmer than average.

So at this point a repeat of the record-setting wet weather of Spring 2011 seems unlikely.

By the way CPC thinks Cincinnati will have about normal precipitation and warmer than normal temperatures for Summer 2012.

A Look At The Weekend

2012-02-15T18:39:00.000-08:00

Each Wednesday I look ahead to, what in my opinion, is the best part of a week - The Weekend! It is not that I do not like my job, truthfully after nearly 35 years in TV I still like each and every day. It is that weekends are the time to kick back and enjoy the parts of life we do not have time for the other 5 days.

The coming weekend is a bit of a question mark. The GFS (global forecast system) or what I often call on the air the "American Model" to distinguish it from the European Model and the Canadian Model.

The American Model from this morning (12z or 7am EST run) had the FOX19 viewing area on the northern edge of precipitation from a storm that will cross Georgia into the Carolinas Sunday. The European and the Canadian both had the storm farther south and the precipitation shield smaller resulting in a dry weekend.

The midday run of the American Model (18z or 1PM EST) pushed the rain shield to Lake Erie Saturday and had it moving out of the tristate early Sunday.

In my experience the European and Canadian models often play "catch up" with the American, not always but much of the time. So even though the score is 2 dry models to 1 wet model I am leaning towards some light rain or sprinkles for Saturday. Also we have a saying that "the trend is your friend", meaning as the day gets closer the models begin to zero in on what will really happen. The trend in the American model is for wet weather over the weekend.

Before I am convinced I want to see a few more runs but right now (Wednesday evening) I am leaning towards some rain.

The video has more.

The Next Storm Brings Rain

2012-02-14T18:35:00.000-08:00

Extended range forecasting has come a long way since I started in the weather business. In 2012 we are easily more accurate 7 days out than we were 3 days out in 1977.

We still cannot accurately time the start of end of a snow event a week away. Commonly it may arrive a day earlier or a day later than a particular model run predicts.

The job of a meteorologist in extended forecasting is to let you in to our thought processes, let you know "something" may happen on a particular day then update the progress of the forecast as the storm gets closer. The goal is no surprises.

For example I was asked today by an elementary school child if there will be any snow days this year. Coincidentally the models are kicking out information on what could be a big storm in the U.S. Wednesday through Friday of next week, that is 8 to 10 days in the future. Only a fool would emphatically pronounce a prediction of a big snow storm starting any of those days. But i could tell her it would rain Thursday with no chance of a snow day and next week there is a chance. Stand by.

There are three things in general that determine if a storm will bring snow or if it will bring rain.

Now don't get me wrong it is much more complex than that once the storm is a few hours away but in general for the extended forecast three things dominate my thinking. I cover them in the video.

Wet Snow Friday - Slick Streets Saturday Morning

2012-02-09T17:59:00.000-08:00

A weak to moderate upper level disturbance will push a low eastward across Tennessee Friday into Saturday bringing the Cincinnati Tristate wet snow.

The good news is that there will be NO SNOW for the Friday morning commute and only wet snow (translated wet roads) for the homebound commute.

The bad news is that untreated roads will ice up for early Saturday morning as meltedsnow freezes when the temperature drops quickly before dawn Saturday morning.

The video explains it.

Impact Is More Important Than How Much Snow Falls

2012-02-07T18:31:00.000-08:00

Here in Cincinnati we are just far enough north to get disruptive snow events almost every winter and just far enough south that sometimes we are dealing with the icy stuff.

By icy stuff I mean the precipitation that is transitional between snow and rain. Because of the geometry of storm systems in the middle latitudes the cold air at the surface is sometimes overrun by warmer air. When snow falls through the warm layer it can melt into rain and then when it hits the colder-than-freezing surface splat and freeze into a glaze of ice. Glaze is the agreed upon international name for waht we call freezing rain.

If the cold air at the surface is deep and well below freezing the snowflakes that melted to raindrops can refreeze into small ice pellets, which is the internationally agreed upon name for them. We call it sleet.

Everyone knows the helpless feeling of hitting a patch of friction-free glaze ice on foot or worse in a car and that is almost always worse than several inches of snow.

Upper Level Disturbances

2012-02-06T20:44:00.000-08:00

This post covers what you have heard TV Meteorologists call "Upper Level Disturbances". These mysterious entities go by other names like "short wave", an "impulse", a "velocity maximum" or a "jet streak". I like to call them "bundles of energy" because the energy part of the name tells the viewer that these jet stream-level disturbances energize the low pressure systems you see on weather maps at the surface along with their companion cold fronts and warm fronts.

It is within the bundles of energy that the highest jet stream wind speeds are observed, thus one of the names, "velocity maximum". So you have a jet stream and these bundles of energy follow the jet. What makes the forecast sometimes difficult is that the upper disturbances also can modify the jet if they are strong enough.

To be sure there is no confusion the upper level disturbances do NOT power tropical systems. In the tropics storms are driven by the energy released when water vapor (humidity) condenses back to liquid.

The way these bundles of energy work is beyond the scope of this post but with each one comes some lift and the chance for precipitation is there is sufficient moisture. This week moisture is scarce so precipitation will be light or non-existent.

The video describes how this week looks.

Ground Hog Day Eve! And No Snow In Sight

2012-02-01T18:46:00.000-08:00

After two days in the 60s, high temperatures 20° and 22° warmer than normal, the weather will cool, but not too much. The La Niña pattern continues to dominate the global jet stream pattern. Basically brief intrusions of cold air push into the "Lower 48" and occasional surges of moist air bring episodes of rain. What is missing are big winter storms.

The coming weekend one of those surges of moisture will come our way and bring a period of rain lasting about 24 hours.

This discussion is specific to the weekend forecast, however it illustrates in general how "return flow" around an anticyclone, coming off the Gulf of Mexico transports moisture deep into the continent for rain.

The video below explains it.

The End of a La Niña January

2012-01-31T18:44:00.000-08:00

The preliminary numbers are in and lust like any well behaved La Niña january this one was warmer than normal and wet. The average high temp 5.4°F warmer than normal, the average low 3.5° warmer than normal and the month 4.9° warmer than normal.

It was also a wet month with 2.29" or rain more than normal and snowfall 4-9" less than normal.

As I write this the rain has started. Is this going to be a record setting deluge? No way. The video explains.

Just Another Southern Storm

2012-01-24T18:47:00.000-08:00

A storm this evening developing over Texas will once again bring Gulf of Mexico moisture northward, lift it up and over cold air at the surface and the resulting rain will fall through cold air at the surface. But this time the cold air is not as cold as the air was this past weekend. So the difference is this time we get chilly rain, last time it was ice.

The video below explains the forecast.

Active Weather Ahead

2012-01-18T18:47:00.000-08:00

There is plenty going on at jet stream level. The first effect on the Cincinnati Tristate will be some light snow tomorrow as an Alberta Clipper with little moisture comes our way. Temperatures during the afternoon will be at or above freezing and it looks like a wet system.

Behind this system will come a surge of moisture as a low develops over the southern Great Plains. With some cold air in place this could bring some ice to parts of the Tristate.

The video explains the forecast for this particular situation but also gives a general view of the conditions conducive to freezing rain and sleet.

The Weekend and Beyond Part 2.

2012-01-05T18:52:00.000-08:00

In my last post we looked at an upper level disturbance coming out of Asia that is crossing the north Pacific which will bring rain here on Wednesday 01.11.2012.

The most recent model runs now have a strong clipper type upper disturbance forming over western Alaska that will follow the first one and work with it. The result will be a quick shot of cold air after the main storm.

The video explains it.

The Weekend and Beyond

2012-01-04T20:36:00.000-08:00

Tweaking is by definition a fine adjustment. In forecasting we often have the large scale pattern and weather dead on but when you look at the small scale details, the distribution of rainfall from a storm for example, we have to adjust or tweak the forecast to allow for variations within the storm.

The video below explains how we forecast what will happen a week out. This was a forecast I made on 01.04.2012 for Wednesday 01.11.2012. Eventhough it was for a specific period of time it illustrates what a meteorologist looks at to forecast for a week in the future.

Lake Effect Snow

2012-01-02T20:17:00.000-08:00

Right in time for the New Year (2012 - for those of you reading this in the distant future) an arctic air outbreak brought snow showers to the Cincinnati Tristate area. The snow was not purely lake effect but often in winter Cincinnati receives snow courtesy of far away Lake Michigan.

The video explains it.

Secrets of Forecasting Snow

2011-12-26T17:56:00.000-08:00

Snow, just the mention of it in the forecast induces panic and a rush on grocery stores to grab the last bread and milk lest we get stranded by what has affectionately become known as "White Death".

The map image is the model forecast snow accumulation by 10PM Tuesday. The yellow temperature shows that in Cincinnati at least the temperature will remain at or above freezing white the wet snow falls, as it tapers to flurries the temperature drops but at the same time the roads dry out. So an isolated icy spot is possible Wednesday morning.

The video below explains more about snow forecasting.

A Tale of Three Models - Part Deux

2011-12-21T19:00:00.000-08:00

When working on the forecast yesterday for Christmas Day I was faced with three models and three different solutions. To a meteorologist the forecast that results from a run of a weather model run is called a solution.

The American Model (called the GFS for Global Forecast System) said Christmas Day would be dry. The Canadian Model said it would rain then change to light snow for the morning of Dec. 26th. while the European Model had an all-day light snow falling.

Today the models are converging on a common solution close to the original GFS run and that means dry weather and no snow for Christmas.

The video below shows latest runs available.