Tornado Forecasting

An overview of how I do forecasting before a storm chase.

A Source of Lift

Usually, thunderstorms won't initiate without some type of lift. Lift is usually produced by jet stream dynamics, surface boundaries, and sometimes topography (orographic lift). When the flow aloft is diffluent, it tends to produce lift underneath it. Frontal boundaries, drylines and outflow boundaries are sources of lift as airmasses with different densities converge. Lift can also be produced by upslope flow.

Convective Available Potential Energy (CAPE)

A measure of instability. When air near the Earth's surface is lifted, it expands and cools. Eventually condensation can occur, which releases latent heat and further increases buoyancy. This is what drives thunderstorm development. CAPE measures how much buoyancy is available. Usually I'm looking for CAPE of least 1,000 J/KG.

Convective Inhibition (CINH)

Convective Inhibition measures how much warm air aloft is inhibiting thunderstorm initiation (negative buoyancy). Usually this needs to be less than 50 J/KG to allow thunderstorms to initiate, but it varies depending on the strength of the lifting.

Deep Layer Shear

In order to sustain thunderstorm updrafts, precipitation needs to moved away from the updraft by sufficient vertical wind shear (change in wind speed or direction with height). Usually I look at the effective bulk wind difference (EBWD). It should be 25 knots at a minimum, and preferably higher than 40 knots.

Low Level Shear

Shear in the lowest 1 KM is important for tornado formation. 0-1 KM storm relative helicity (SRH) should be at least 100 M2/S2, and preferably higher then 200 M2/S2.

Veering With Height

Discrete supercells are the most favorable storm mode for tornadoes. Supercells are more favored when the wind veers with height (turns clockwise). Ideally, winds at the surface will be from the east, and as you go up from the south, then from the west.

Lifted Condensation Level (LCL)

The lifted condensation level determines the height of the cloud base. When rain falls below the cloud base, evaporative cooling occurs. If the cloud base is too high, storms tend to produce too much cold outflow for tornadoes to form. Generally, I want LCL heights to be below 1.5 KM.

Storm Motion Vectors

Discrete supercells are most likely when the storm motion takes it away from the boundary that initiated the convection. If storms are moving parallel to a boundary, they tend to merge into a line. If storm motion is perpendicular to the boundary, supercells will be favored. Storms should also be moving faster than the boundary or they may be forced into a line or even be undercut by the boundary. For storm chasing purposes, a storm motion to the east if preferred because it is more aligned with the road network. Slower moving storms are also preferred. It can be difficult to keep up with a storm moving to the northeast at 40+ mph if the roads are all east-west and north-south.

Huricane Dorian likely to hit Florida

The HMON, HWRF, GFS, GDPS, ECMWF, GEFS, CMCE and EPS all indicate Hurricane Dorian will landfall somewhere in central or southern Florida. Landfall is most likely Monday night of Tuesday morning (Sept 2nd or 3rd). Dorian may slow as it approaches Florida, which could prolong the impact of wind and storm surge, and increase the risk of flooding. Though it's still early, the models are now generally putting Dorian's track near West Palm Beach or Port St. Lucie.

Dorain is currently a category 2 hurricane with wind estimated at 105 mph. Dorian will be entering an area with light shear and water temperatures in the mid 80s. This should allow Dorian to strengthen to category 4.

April Snowstorm

A very late season snowstorm produced up to 33" of snow in central Wisconsin from April 13-15.

Some snow totals:

14.3" Sioux Falls, SD
15.8" Minneapolis - St Paul
24.2" Green Bay, WI
21.2" Appleton, WI
28.0" Stevens Point, WI
31.6" Carlsville, WI (Door County)
33.0" Amherst, WI (Portage County)

At Green Bay, the 24.2" that they received was the largest April snowstorm on record. The previous record was only 11.0" on April 4 - 5 in 1977. Incredibly, it was the 2nd largest snowstorm on record. The largest had been 29.0" on March 1 -2 1888. There have been numerous roof collapses in the Green Bay Area. Green Bay has had 36.7" of snow in just April alone. The previous snowiest April was just 15.1" in 1907.

The first half of April has been up to 16F below normal for the Midwest:

NWS Des Moines reports that temperatures for the April 1 - 15 period have been 11.5 - 16.0F below normal, and the coldest since 1881:

Estherville, Mason City, Waterloo, Ottumwa and Lamoni currently 
rank as the coldest start to April on record /April 1-15/. Des 
Moines is currently 2nd coldest, behind 1881, as it is the only of
the sites with records dating back that far.

First Week of January

The first week of January was more than 20F below normal from Illinois to West Virginia.

Full Unedited Video of Greensburg Tornado

Tomorrow is the ten year anniversary of the F5 Greensburg tornado. On the night of May 4, 2007 a tornado grew to a width of 1.7 miles and destroyed most of Greensburg, KS, where 11 people were killed. It was the first F5 in 8 years.
 

Texas Snow and Tornadoes

On April 29th, six tornadoes hit eastern Texas, including an EF4, an EF3, an EF2, and three EF0s. Four fatalities were confirmed.

The April 29th 12Z (7 AM CDT) sounding for Fort Worth showed that there was already 2,500 CAPE:

As dew points rose into the mid 70s in the afternoon east of Dallas, CAPE values exceeded 5,000 by 21Z (4PM CDT) according to NAM:

There was strong low level wind - greater than 40 knots at the 1 km level - and a clockwise turning wind field with height, producing sufficient shear and helicity for tornadoes.

On April 29 and 30, heavy snow fell across the High Plains as far south as the Texas Panhandle. Amarillo received 3" and Dalhart had 9". There were over 50,000 power outages in the Texas Panhandle caused by high winds. At Amarillo, winds gusted to 54 mph and visibility dropped to 1/2 mile.

Garden City, KS had blizzard conditions on the 30th and 11" of snow, causing three structures to collapse. 14" fell in the southwest corner of Kansas at Elkhart. One farmer near Sublette estimated that he had lost 80% of his crop. At Wallace in northwest Kansas, 28" of snow fell, with drifts of 8-10 feet. 33" fell at Lander, WY and 39" fell at San Isabel, CO.

Flooding has killed 7 in Arkansas and 3 in Missouri. In southern Missouri, the town of Houston received 11.15" of rain.

Minimum Maintenance Road

Yesterday when we were storm chasing in southeastern Nebraska, we came across a "minimum maintenance road". We decided to take a different route.

Chicago's Winter

It's been a weird winter for Chicago. December had 17.7" of snow - all of which fell before the 18th. The 19th had low temperature of -13. But the day after Christmas had a high 54. Only 0.6" of snow fell in January. February had just a trace. The normal for January and February combined is 19.9". In mid-February, there were six days in a row with a high temp in the 66 - 70 range. Now on March 14th, Chicago just received 7.5" of snow. December had 9.5" above normal snowfall, January was 10.2" below normal, February was 9.1" below normal, and March will be 2.2" above normal even if there isn't any more snow for the rest of the month.

Hurricane Matthew

Hurricane Matthew has become a category 5 storm with 160 mph wind and a minimum central pressure of 941 mb. The wind speed doubled in 24 hours. At 11 PM EDT on September 29th, it was only an 80 mph storm. None of the models had indicated such a rapid strengthening.

Matthew is the first category 5 hurricane in the Atlantic in over 9 years. The last category 5 was Hurricane Felix in September of 2007. Felix made landfall in Nicaragua. The US hasn't been hit by a major hurricane since Wilma in 2005.

Matthew is located south of Haiti and moving westward. It will soon begin curving to the north as it moves toward an upper trough. Matthew will likely pass near Jamaica, and cross Cuba and move into the Bahamas. It's too early to tell if Matthew poses a threat to the US East Coast. It may depend in part on the behavior of a larger trough currently over the West Coast.

Big Tornado Season Next Year?

The number of tornadoes in the US has been below normal for the last 5 years:

El Nino is gone. Over the last two months, sea surface temperatures have been below normal in the central equatorial Pacific. Trade winds have been above normal across most of the Pacific for the last week. It is likely that La Nina will emerge sometime later this year.

4 out of the last 5 years with tornado counts being more than 1 standard deviation above normal have been during or immediately following a transition from El Nino to La Nina (1998, 1999, 2008, 2011):

Three of these years (1999, 2008, 2011) had well above the normal number of strong tornadoes.

East Coast Blizzard

A major 983 mb East Coast storm (aka snowzilla) produced up to 42" of snow Friday and Saturday (Jan 23 and 24). Winter storm warnings (pink) were issued from Arkansas to South Carolina to Massachusetts. Blizzard warnings were issued from Washington DC to Long Island:

Here is a time lapse of the blizzard from Purcellville, VA:

Some snowfall totals:

Bowling Green, KY: 11"
Glengary, WV 1 ese: 42"
Dulles Airport, VA: 28.3"
BWI airport, MD: 29.2"
Rehouse, MD: 38"
Dover, DE 5.1 wsw: 18.2"
Philadelphia, PA: 22.4"
Atlantic City, NJ: 13.4"
Newark Airport, NJ: 28.1"
JFK Airport, NY: 30.5"
Nantucket, MA: 11.5"

The 29.2" for Baltimore is their largest on record. Winds gusted to 75 mph at Dewey Beach, DE and Langley AFB, VA. This storm caused 250,000 power outages, and over 12,000 flights were canceled.

Major coastal flooding occurred in New Jersey:

Jason Pellegrini shot this video of flooding in Sea Isle City, #NewJersey, on Saturday. #Snowzilla #blizzard https://t.co/f0cpQHz7DL

— Josh Berlinger (@j_berlingerCNN) January 24, 2016

Central US Winter Storm

Over the past several days (Dec 26 - Dec 28) a major winter storm hit the central US. Winter storm warnings stretched almost from the Canadian Border to the Mexican border:

Blizzard warnings were issued for west Texas, where up to two feet of snow fell (Queen). At Lubbock, 11" of snow fell, a state of emergency was declared, and a roof collapsed at a mall. Sleet accumulated to 3.4" at Rockford, IL and 4.8" at Springville, IA. 1" of freezing rain fell at Anthony Kansas and Kewanee, IL, but some areas had problems with just 0.25" of ice because of the strong winds: in the Peoria area 70,000 customers lost power, and a gas line was ruptured.

In Missouri, flooding closed parts of I-70 and I-44. 12.25" of rain fell at Union, MO, causing record flooding. At Springfield, MO the 6.03" that fell on December 26th was the second highest 24 hour total on record. The storm total there was exactly 10.00". At least 13 flood related fatalities occurred across Missouri.

On December 26th, tornadoes killed 11 in Texas. 8 of the fatalities were from an EF-4 that hit Garland, TX:

Hurricane Patricia Landfall

At 5 PM CDT, the eyewall of Patricia is over San Patricio. Current intensity is 900 mb, wind 165 knots (190 mph). Peak intensity was at 1 PM: pressure 879 mb, wind 175 knots (200 mph).

Update: NHC has indicated that at the time of landfall minimum pressure was 920 mb, and wind was 165 mph.

Hurricane Patricia

Hurricane Patricia has intensified at an incredible rate over the last 24 hours. At 4 AM CDT yesterday (Oct 22), Patricia was a 75 knot hurricane; by 4 AM today, based on data from the Hurricane Hunters, it was at 175 knots. This makes Patricia the strongest hurricane on record for the NHC's area of responsibility, which includes the East Pacific and Atlantic. The minimum central pressure was estimated at 880 mb, another record for the East Pacific/Atlantic. The previous record was Hurricane Wilma at 882 mb. The record lowest pressure globally was Typhoon Tip in the West Pacific.

Hurricane Patricia should make landfall near Puerto Vallarta tonight. In addition to catastrophic storm surge and wind damage, flash flooding and mudslides will be a major problem, because Patricia will be moving directly into mountainous terrain.

Hurricane Joaquin Strengthens

At 12:00 PM EDT, data from a Hurricane Hunter plane prompted the NHC to increase the intensity of Joaquin to 135 knots (155 mph), and drop the minimum central pressure to 933 mb. Joaquin is expected to miss the US, but there is still some chance for it to pass close to Nova Scotia. Joaquin is moving north into areas with increasing shear and should not strengthen any further.

As tropical moisture, some of which is associated with Joaquin, has been forced into a front along the East Coast, over 14" was reported near Wilmington, NC over the last 2 days.

Hurricane Joaquin

Hurricane Joaquin has encountered water temperatures around 85F, and decreasing shear as it moves into the Bahamas. This has led to Joaquin strengthening from 70 knots to 110 knots over the last 24 hours. A trough over the southeast US should begin to turn Joaquin to the north within 24 hours. Ridging is forecast to develop over New England by Saturday, Oct 3. Although the models are still split, it is possible that the ridge will turn Joaquin westward and into the East Coast. This is a pattern similar to the one for Hurricane Sandy. Right now, models indicate that landfall may occur anywhere from South Carolina up to Newfoundland.

As Joaquin moves north, it will remain in water that is at least 80F until it moves north of Cape Hatteras. The depth of warm water will be sufficient to sustain a major hurricane as well:

Depth of the 26C isotherm

Even if Joaquin does not landfall, tropical moisture will be absorbed into the southeast US trough and produce flooding across the East Coast region:

Pacific Hurricanes

During El Ninos, the Atlantic hurricane season is usually quieter than normal, and the east and central Pacific is often more active than normal. In the image above, from left to right, we have Hurricane Kilo (winds 110 knots), Hurricane Ignacio (winds 120 knots), and Hurricane Jimena (winds 130 knots).

Strong El Nino 2015

A strong El Nino has developed with sea surface temperature anomalies reaching 3C. This El Nino should persist, and possibly strengthen even further because subsurface water temperature anomalies are 6C at the 50-100 meter depth in the Eastern Pacific:

Impacts from this El Nino could include reduced Atlantic hurricane activity, and much needed rain in California. El Ninos, particularly strong ones, are usually associated with warm winters in the northern US, but some cold outbreaks may be possible this time, because of a westerly QBO.

Theodor Landscheidt believed that ENSO events are correlated to solar subcycles which have enhanced x-ray flare activity. The Southern Oscillation Index (SOI) was used, because it changes before temperatures do. Significantly anomalous values in the SOI go back to August of 2014. It was only in July 2015 that the SOI indicated a strong El Nino, but trade winds were weaker than normal (westerly anomalies, shown in red below) for many months before that:

X-ray flares did increase in August 2014 right when SOI indicated the beginnings of El Nino:

Don Easterbrook has noticed that El Ninos correlate to spikes in the AP index (indicates geomagnetic activity). In March, the AP index reached the highest value since September 2005:

Boone County Supercell July 13

Yesterday, this storm in Boone County, IL damaged trees and power lines, and produced golf ball size hail near Poplar Grove, IL:

There was also a weaker cell to its south:

And this one to its southwest:

We were driving north on I-39 just north of US 34 at the beginning of the video below. At that time the storm was probably 50 miles away. The video runs from 8:46 - 9:12 PM CDT as we go through LaSalle, Lee and Ogle counties.

Here is the storm from up close. We are driving east on 173 between I-39 and 76 from 9:37-9:41 PM CDT.

June 20 2015 Storm Chase

Yesterday (June 20th), we were storm chasing eastern in Iowa. We saw a very well defined shelf cloud associated with a severe squall line which had horizontal rotation at Wayland, IA. This was from 7:00-7:05 PM CDT:

6 minutes later, and a little east of Wayland on highway 78:

A view from directly underneath the shelf cloud at the junction of 78 and US 218 at 7:14 PM:

While we were on our way home after the storm chase, we encountered a spectacular sunset near Muscatine, IA. We were able to see lightning from the storm to our east, a rainbow, crepuscular rays, and even anti-crepuscular rays. This was from 8:19-8:34 PM CDT.