Wednesday, January 02, 2013

2012 Low Number of Tornadoes

The start of 2012 could not have been any busier for the numbers of tornadoes that were reported. So why couldn't the rest of the season keep up? Lack of shear and the drought are just 2 of the clues why the 2012 tornado season was so mundane.
Tornadoes cannot exist without the clouds and moisture to help build them.
(Picture from this summer in the  Midwest)
The jet stream during the most of the summer and fall took the storm systems well to north and west away from any available moisture. Similar patterns existed during the late 1970s and 1980s. The weather patterns helped create a preliminary count of only 1,116 tornadoes.

Many of the storm systems in late half of 2012 affected Canada thanks to a ridge of high pressure. 
This year's 1,116 tornadoes is well below the 6-year-average tornado count. The yearly tornado average is right around 1,530. During 2008, the tornado count hit 2,194- a record. And even though two tropical systems affected North Florida during 2012, tornadoes did not accompany what are usually tornadic producing systems.  
The 2012 year ranks in the bottom 25th percentile for tornado production.
The closest tornado to Jacksonville formed near Brunswick, GA, in 2012. It only was on the ground for short time before coming a waterspout. No damage from this tornado producing storm was reported.
Closest confirmed tornado to Jacksonville.

Thursday, December 27, 2012

Storm system on the way for the weekend

Yet another storm system is on its way for the eastern third of the country for the last weekend of 2012. This winter storm will likely produce somewhat similar affects to that of the last storm.

Forecast of Fronts/Pressure valid Sat 00Z
Synoptic scenario going into weekend.
Overall snow accumulations will be less and reports of severe will be minimal compared to this week's earlier storm. With the NAO positive and the PNA positive, a more zonal pattern will prevail which will tend to keep the lid on significant storm development.

yesterday Reports Graphic
Storm Reports from the Christmas Day storm.
North Florida will be closer to the center of the low pressure and should get a decent amount of rain from the storm system. Rainfall accumulations of an average of 1 or 2 inches will fall across much of the area. All of which will occur before Saturday afternoon. Severe parameters, at this point, do not seem too impressive for the northern part of the state. 
Forecast Rainfall
Parameters needed for severe weather will lack and pressures will be high. Instability values are forecast to be on the low side. Craven Brooks, which details severe parameters, are also not looking too impressive at this point. Conditions for severe weather will improve as you head down further down the peninsula.  

Craven Brooks Significant Parameter

Thursday, December 06, 2012

Hurricane Center Proposes New Hurricane Warning Criteria

One day systems, such as Sandy, that make landfall without having a hurricane status may be given hurricane watches and warnings. The new definition of hurricane watch and warning is reported to soon include any storm system that has winds of 74 mph or higher. Before now, only areas affected by hurricanes were warned through hurricane warnings. 
Another change is that the warning will remain in effect longer until dangerous conditions along the coast have deteriorated. 

The National Weather Service Statement:
“A proposal was raised during the NOAA Hurricane Conference last week for NWS to have the option to issue hurricane and tropical storm watches and warnings for post-tropical cyclones that threaten life and property. This is one step in the process required before any proposed change to operational products becomes final. As part of our review of the 2012 hurricane season, including the Sandy service assessment, we will review all policies and changes through the existing and established process.”

Current Hurricane / Tropical Storm Alerts

  • Tropical Storm Watch: An announcement that tropical-storm conditions are possible within the specified area.
  • Hurricane Watch: An announcement that hurricane conditions are possible within the specified area.
  • Because outside preparedness activities become difficult once winds reach tropical storm force,watches are issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.
    Action: During a watch, prepare your home and review your plan for evacuation in case a Hurricane or Tropical Storm Warning is issued. Listen closely to instructions from local officials.
  • Tropical Storm Warning: An announcement that tropical-storm conditions are expected within the specified area.
  • Hurricane Warning: An announcement that hurricane conditions are expected within the specified area.
  • Because outside preparedness activities become difficult once winds reach tropical storm force,warnings are issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.
    Action: During a warning, complete storm preparations and immediately leave the threatened area if directed by local officials.

Sunday, March 25, 2012

Minor Changes Coming To Saffir-Simpson Hurricane Wind Scale

The Saffir-Simpson Hurricane Wind Scale (SSHWS) is undergoing a minor modification
for 2012 in order to resolve awkwardness associated with conversions among the various
units used for wind speed in advisory products. The change broadens the Category 4
wind speed range by one mile per hour (mph) at each end of the range, yielding a new
range of 130-156 mph. This change does not alter the category assignments of any
storms in the historical record, nor will it change the category assignments for future
storms. The reasoning behind this change and a tabulation of the old and new scales is
given below.

Because of the inherent uncertainty in estimating the strength of tropical cyclones, the
National Hurricane Center and the Central Pacific Hurricane Center assign tropical
cyclone intensities in 5-knot (kt) increments (e.g., 100, 105, 100, 115 kt, etc.). Some
advisory products, however, require intensity to be given in units of mph and kilometers
per hour (km/h). For these products, the intensity in knots is converted into mph and
km/h and then rounded to 5-mph and 5-km/h increments, so as not to suggest that the
intensity of the storm can be known to unrealistic precision (e.g., 127 mph!).

Unfortunately, this conversion and rounding process doesn’t work well at the Category 4
boundaries. Category 4 has historically been defined to be 131-155 mph (with
corresponding ranges in other units given as 114-135 kt, and 210-249 km/h). A hurricane
with an assigned intensity of 115 kt, therefore, is a Category 4 hurricane. However,
when 115 kt is converted to mph (132.3 mph) and then rounded to the nearest 5 mph (130
mph), the result falls in the Category 3 mph range. In order for the hurricane to appear
as Category 4 in both kt and mph, NHC is forced to incorrectly convert 115 kt to 135
mph in its advisory products. A similar problem occurs when the Category 4 intensity of
135 kt is converted to km/h.

To solve these rounding issues, the new SSHWS broadens the Category 4 wind speed
range by one mph at each end of the range, yielding a new range of 130-156 mph (113-
136 kt, 209-251 km/h). With this change, a 115-kt Category 4 hurricane can have its
intensity properly converted to mph and rounded to the nearest 5 mph (130 mph) – and
remain within the Category 4 mph range.

It’s important to reiterate that because NHC assigns intensity using 5-kt increments (and
will be doing so for the foreseeable future), neither storms in the historical record nor any
future storms would have their SSHWS category changed as a result of this adjustment.
Changing the Category 4 range to 130-156 mph, 113-136 kt, and 209-251 km/h simply
allows all unit conversions from knots to be done correctly and keep storms in the correct
category, regardless of the units used.
Summary of the changes (highlighted in yellow):
Category >>>Previous range>>>New range
1...74-95 mph....New: 74-95 mph
2...96-110 mph....New: 96-110 mph
3...111-130 mph....New: 111-129 mph
4...131-155 mph....New: 130-156 mph
5...156 mph or higher....New: 157 mph or higher

Monday, March 05, 2012

Drought To Continue

Officially, this year, less than 2 inches of rainfall has fallen over North Florida. Some locations have seen more than others. Last year, at this time, already some 10 inches of rainfall had occurred. We are certainly running behind last year's numbers.

The lack of rainfall has the area in an extreme drought. Not too far north of the Florida line parts of Georgia are experiencing exceptional drought levels. And there is no good news in the pipeline. Most of the energy the next couple of weeks will be far displaced from North Florida. Much of the rest of the month will be dry, and there is a chance that the area will finish the month with less than 2 inches of rainfall for the entire year.

Jet Stream

Sunday, January 15, 2012

Fire Danger Soars

High to extreme fire danger, across the entire State.
The state of the drought is about to turn ugly across a good portion of the Southeast, including Florida. Since December 1st around 1.5 inches of rain has fallen around the region. And since January 1st, only sprinkles have been recorded in the official rain gauge. The drought isn't a new topic; it has really been in the formation process for years. The years 2010 and 2011 produced a combined rainfall deficit of around 27 inches.
Precipitation over last 100 years for North Florida.
La Ninas and global weather pattern changes are mostly responsible, for the drier conditions. Over the past 100 years, there has been a gradual decline in precipitation observed. And the news continues to get worse- there are no changes to the forecast ahead. Drier than normal conditions look like they will dominate the next two weeks. January typically sees 3.69 inches of rain. So far, we are at zero inches of precip. for the month.
5 day precipitation forecast
Many areas of the State could finish the remaining 2 weeks, of the month, without any significant rainfall.  An amplified to zonal pattern will hold on for much if this time period. This type of pattern will tend to bring in warmer air, but it will also keep the majority of major systems, to the north.

Current Jet Stream Pattern

Sunday, January 08, 2012

Several Warm Days Ahead

Climatologically speaking, the area is entering what is usually the coldest week of winter. Typically the area struggles to reach the mid 60s, for our high, and plummets into the lower 40s, for the low. The week were are just now entering will be anything but typical.

For the majority of this week, temperatures will be some 10-15 degrees above average in many areas.  A lack of snow cover across the Continental 48 and the combination of a high pressure system, to our east-northeast, are responsible for the warm conditions. Temperatures could approach 80 degrees both on Monday and Tuesday.

High pressure helps pump southeasterly flow into Florida.

Only about 13% of the U.S. 48 has snow on the ground. This figure should be
between double or triple of where it is right now.
By the end of the week, a change in the warm/dry pattern could be in the making. But the verdict is still out on whether a temporary change or something more consequential. A good place to start looking for definitive answers is in the eastern Pacific. This is where water temperatures have been warming over the last couple of weeks. This warming could indicate that La Nina's control over the weather pattern could be lessening.