Category: Met 101/Weather History

December: An Introduction To Winter

| December 1, 2016 @ 10:00 am

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Welcome to the month of December, considered the start of “meteorological Winter,” even though on the calendar the Winter Solstice is at 4:44 AM CST on December 21st. Its hard to believe that we are already on the 12th month of the year, and before you know it, 2017 will be here.

On average for the city of Birmingham, December ranks as the second coolest month. Average daytime highs start off at 60 degrees at the beginning of the month, and drops down to 54 degrees by New Years Eve. Average lows start the month off at 39 degrees, and finishes the month off at 34 degrees.

As far as all-time record temperatures for the month of December for the city of Birmingham, the warmest December high occurred on December 7, 1951, when the mercury reached an amazing 80 degrees in the Magic City. The coolest low ever for Birmingham was at 1 degree, and that occurred twice (12/13/1962 & 12/23/1989).

December ranks comes in at number 2 as the month that has the least amount of sunshine. The month’s 46% possible sunshine average is only beaten by January, whose average possible sunshine is at 42%. It normally rains on 10.4 days in the month, with 1 inch or more on 1.4 of those days. Snowfall average for the month is 1/10th of an inch, but one of the most memorable snowfall events in Birmingham occurred on New Years Eve in 1963, when 8 inches blanketed the city… the most ever for December.

December ranks as the seventh wettest month with an average rainfall amount of 4.47 inches for the month. The wettest December ever recorded for Birmingham was back in 1961 when 13.98 inches of rain fell. The wettest single December day on record for the Magic City was December 27, 1942, when an amazing 7.7 inches of rain drenched the city.

As you know in Central Alabama, our primary severe weather season is in the Spring during the months of March, April, and May. Most people do not realize that we also have a secondary severe weather season in the Fall, which typically runs during the months of November and December. Sometimes we are fortunate to experience a quiet season where there is little to no severe activity, but we may also see our fair share of destructive tornadoes and other severe events. During the last 66 years (from 1950 to 2015), the state of Alabama had at least one documented tornado in the month of November or December in 46 of those years, which equates to 70%.

Just within the last 14 years (not including data from November 2016), 21% (175) of all documented tornadoes (822) occurred during November and December. In that same period, 6% (18) of the tornado-related fatalities (283), and 10% (262) of the tornado-related injuries (2730) occurred in November and December. If you remove the number of fatalities from just April 27, 2011, the percentage of deaths that occurred during November and December is around 40%.

Welcome to November

| November 1, 2016 @ 10:00 am

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November is considered a “transition month” between fall and winter across much of the country, and Central Alabama is no different. The heat budget is becoming more negative as the days are becoming shorter, and that makes the average temperatures drop like a rock.

At the start of the month, the average high in Birmingham is 69 degrees, while the average low is 46 degrees. By the time we reach the end of the month, the average high in Birmingham is 60 degrees, while the average low has fallen to 38 degrees. The warmest high ever recorded in November in Birmingham was at 85 degrees, and this happened on three different occasions (1998, 2000, 2003). The coolest low of 5 degrees was recorded on November 25, 1950.

The month of November rates second, just behind October, in percentage of clear skies in the Magic City. The sky is cloudy only 33% of the month. Rainfall is observed usually on 9.1 days throughout the month, with only 1.9 of those involving thunderstorms.

November is also known as the sixth wettest month of the year, so maybe the 2016 version can live up to that and help us out with the drought situation. Average rainfall for November in Birmingham is 4.85 inches. The wettest November on record for Birmingham occurred in 1948, when 15.25 inches fell in the official rain gauge. There is no average for snowfall for November, but it can happen. 1.4 inches of the white stuff fell in the city back in 1950.

Finally, November is also the start to Fall Severe Weather Season. The storm track becomes more active and precipitation totals begin to increase. Back on November 10th, 2002, during an unusually strong outbreak, 12 people were killed on a day that saw 10 tornadoes across North Alabama, with two of those rated F3. I posted an infographic along with information on Fall Severe Weather Season in Alabama. Click here to visit that post.

Today is Fall Severe Awareness Day

| October 19, 2016 @ 10:00 am

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As you know in Central Alabama, our primary severe weather season is in the Spring during the months of March, April, and May. Most people do not realize that we also have a secondary severe weather season in the Fall, which typically runs during the months of November and December. Sometimes we are fortunate to experience a quiet season where there is little to no severe activity, but we may also see our fair share of destructive tornadoes and other severe events. During the last 66 years (from 1950 to 2015), the state of Alabama had at least one documented tornado in the month of November or December in 46 of those years, which equates to 70%.

Just within the last 14 years, 21% (175) of all documented tornadoes (822) occurred during November and December. In that same period, 6% (18) of the tornado-related fatalities (283), and 10% (262) of the tornado-related injuries (2730) occurred in November and December. If you remove the number of fatalities from just April 27, 2011, the percentage of deaths that occurred during November and December is around 40%.

These statistics are not used to bring you fear, but does show the need to be prepared for the Fall Severe Weather Season. Your preparation can make a difference between life and death. Here are some important tips:

  • Now is the time to check your emergency supplies and to make sure your NOAA Weather Radio, other portable radio, and flashlights have fresh batteries.
  • Regardless of the strength, ALL tornadoes should be considered dangerous and capable of producing damage and injuries.
  • Treat a Severe Thunderstorm Warning the same as you would a Tornado Warning. Most storm-related damage occurs with severe thunderstorm winds.

For more information, the NWS Birmingham has a great page dedicated to Fall Severe Weather Awareness. You can find it by clicking here.

The Many Names of Tropical Systems and What They Mean

| October 1, 2016 @ 1:17 pm

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While I was attending the annual NWA Meeting in Norfolk, Virginia, back in September, one of the subjects that was brought up was the confusing names of tropical systems. No I am not talking about the human names that the systems are given, but the terms used in the different stages of the lifespan. Hermine had just recently dissipated before the trip, and that was the storm the focus was set on. During the lifespan of Hermine, it had seven different names…

Tropical Disturbance
Tropical Wave
Investigative Area (Invest 99L)
Tropical Depression
Tropical Storm
Hurricane
Post-Tropical Cyclone

There was a lot of confusion over what each name actually means. So here are those terms defined by the National Hurricane Center…

Tropical Disturbance:
A discrete tropical weather system of apparently organized convection, generally 100 to 300 nautical miles in diameter, originating in the tropics or subtropics, having a nonfrontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field.

Tropical Wave:
A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere.

Investigative Area (Invest):
A weather system for which a tropical cyclone forecast center (NHC, CPHC, or JTWC) is interested in collecting specialized data sets (e.g., microwave imagery) and/or running model guidance. Once a system has been designated as an invest, data collection and processing is initiated on a number of government and academic web sites, including the Naval Research Laboratory (NRL) and the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS). The designation of a system as an invest does not correspond to any particular likelihood of development of the system into a tropical cyclone; operational products such as the Tropical Weather Outlook or the JTWC/TCFA should be consulted for this purpose.

Tropical Cyclone:
A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere.

Tropical Depression:
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knots (38 mph or 62 km/hr) or less.

Tropical Storm:
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 knots (39 mph or 63 km/hr) to 63 knots (73 mph or 118 km/hr).

Hurricane:
A tropical cyclone in which the maximum sustained surface wind (using the U.S. 1-minute average) is 64 knots (74 mph or 119 km/hr) or more. The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north of the Equator west of the International Dateline.

Post-tropical Cyclone:
A former tropical cyclone. This generic term describes a cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Post-tropical cyclones can continue carrying heavy rains and high winds. Note that former tropical cyclones that have become fully extratropical…as well as remnant lows…are two classes of post-tropical cyclones.

Remnant Low:
A post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone…and has maximum sustained winds of less than 34 knots.

Dancing With the Stats: September’s 90s Drawing to a Close

| September 25, 2016 @ 12:01 pm

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Saturday was another extremely hot day across Central Alabama with all locations in the upper 90s and a couple of 100F readings. It was 100F at the Mercedes Plant in Vance and at Weedon Field in Eufaula. These readings are some 10-15 degrees above normal for late September.

For the second time this month, the Birmingham Shuttlesworth International Airport hit 98F, which was short of the record for September 24th (99F) set in 1931). Records were set for the second straight day at Anniston, Montgomery and Tuscaloosa with 97F, 98F and 99F respectively.

SUMMER WON’T QUIT: In an average year, we see 6.2 days of 90 degree heat in September in Birmingham. This year, there have been 21 and today will most certainly add another.

ABOVE NORMAL: The graphic shows the amounts average temperatures have been above “normal”, a statistical term used to smooth the jagged edges of “average” temperatures. You can see, we have certainly been above that normal curve, even on the “cooler’ days of September. In fact, we are running 6 degrees above average so far this month.

EYE OPENING STAT: In a typical June – September period, Birmingham will record 52.3 days of 90 degree heat. We will end 2016 with 91 days of 90+ degree heat. We only hit 100F this summer, so it was a season of extremes, but it was relentless.

ONE MORE DAY, ONE MORE DAY: Let me hear you: one more day… Everyone will be back into the middle and upper 90s today and many spots will hit 90F tomorrow. Will that be the last time this year? Probably not. We have registered a 90F reading as late at October 17th in Birmingham. Highs starting Tuesday will average around 80F into the weekend. Lows will be quite comfortable, with 50s each morning this week starting Wednesday.

ANY RAIN? Not much chance. The cold front that will deliver the cooler temperatures will bring scattered showers and storms tomorrow. But rainfall amounts will average one tenth of an inch.

EYE ON THE TROPICS: What will probably become Matthew is a tropical wave some 1350 miles east of the Lesser Antilles this afternoon. More on that and what might be its impact on the U.S. around 130 p.m.

Remembering Hurricane Agnes (1972)

| June 19, 2016 @ 10:00 am

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On this date in 1972, Hurricane Agnes moved ashore in the Florida panhandle as a weak Category 1 storm. The highest wind reported on the Gulf Coast was a gust to just 56 mph at Apalachicola, Florida. The $10 million in damage in the Florida Panhandle was just a drop in the bucket. Hurricane Agnes would be downgraded to a tropical depression as it moved northward through Georgia and the Carolinas after landfall.

Agnes’ main damage would come two days later as the remnants of the storm brought tremendous rains and flooding to parts of the Northeast. On the 21st, the storm system emerged over the warm waters of the Atlantic and gained strength.

The storm would make landfall again in southeastern New York on the 22nd and then stall over Pennsylvania on the 23rd. The first day of summer was a wet one in eastern Pennsylvania as rains overspread the area ahead of the northward moving remnants of Hurricane Agnes. The wet storm system was expected to move out into the Atlantic Ocean, but it made an unexpected turn the next day and dumped unprecedented amounts of rain over the Susquehanna Valley.

Agnes’ torrential rains deluged parts of Pennsylvania. The state capital of Harrisburg was inundated and the governor’s mansion flooded. Nineteen inches of rain deluged Wilkes-Baare, PA, forcing the Susquehanna River over its 38 foot high dikes.

By late evening on the 22nd, Civil Defense officials in Wilkes-Baare, PA watched the rapidly rising floodwaters of the Susquehanna River. Evacuation warnings were not sounded during the night because emergency officials thought that a nighttime evacuation would be confusing. By early morning, evacuations were ordered with the river already at 33 feet and major flooding occurring. By late morning, warnings were frantic as the area’s worst natural disaster in history was underway.

At 11:14 am, sirens sounded seven short blasts indicating that the waters were breaching the dike in Wilkes-Baare. Nearly 75,000 people would evacuate in the face of the rising waters. The raging waters would flood much of the city.

Hurricane Agnes’ five-day romp through the Atlantic seaboard made the storm the costliest natural disaster in the United States at that time. Damage was estimated at $3.5 billion and 134 deaths were reported from Florida to New York. Agnes would produce more damage than all tropical cyclones in the previous six years, including Camille.