Severe weather part ii the synoptic scale sets the table
Download
1 / 21

Severe Weather Part II: The Synoptic Scale Sets the Table - PowerPoint PPT Presentation


  • 137 Views
  • Uploaded on

Severe Weather Part II: The Synoptic Scale Sets the Table. Lab 11 Anthony R. Lupo Atms 4310 / 7310. Severe Weather Part II: The Synoptic Scale Sets the Table. Severe Weather Part II: The Synoptic Scale Sets the Table -or- A Synoptic Cookbook Approach

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Severe Weather Part II: The Synoptic Scale Sets the Table' - lola


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Severe weather part ii the synoptic scale sets the table

Severe Weather Part II: The Synoptic Scale Sets the Table

Lab 11

Anthony R. Lupo

Atms 4310 / 7310


Severe weather part ii the synoptic scale sets the table1
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Severe Weather Part II: The Synoptic Scale Sets the Table

  • -or-

  • A Synoptic Cookbook Approach

  • First let’s review stability – the atmospheric resistivity to lift.


Severe weather part ii the synoptic scale sets the table2
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Red – Ge (unstable) purple – Ge (conditional) blue – Ge (stable) Black - Gd and green Gm

  • Profiles:


Severe weather part ii the synoptic scale sets the table3
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Static Stability: S = Gd – Ge =

  • Hydrostatic:

  • when r’ greater (smaller) than r, air parcels will descend (ascend).


Severe weather part ii the synoptic scale sets the table4
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Stability:

  • We also have examined SI, LI, and CAPE.

  •  Now we’ll look at more empirical information.

  •  These indicies were drawn up by looking at many case studies and stating something general about the stability conditions.


Severe weather part ii the synoptic scale sets the table5
Severe Weather Part II: The Synoptic Scale Sets the Table

  •  Usually we look at the 500 hPa 850 hPa lapse rate. Some of these take moisture conditions, or attempt to include moisture empirically also.

  • Some indicies used:

  • 1) Vertical Totals (VT): T850 – T500

  •  this is based on the 850 hPa 500 hPa lapse rate, or stability. We are looking for values in excess of 26 as a good indicator of severe weather.


Severe weather part ii the synoptic scale sets the table6
Severe Weather Part II: The Synoptic Scale Sets the Table

  • 2) Cross Totals (CT): Td 850 – T 500

  •  cross totals because we are mixing dewpoint temperatures with ambient temperatures. This is a crude measure of bouyancy.

  • 3) Total Totals (TT) = CT + VT = T850 + Td 850 – (2T500)

  •  This is an index that is very popular to use. It’s very simple to calculate.

  •  Empirically includes stability and bouyancy. This index was popularized by the Air Force.


Severe weather part ii the synoptic scale sets the table7
Severe Weather Part II: The Synoptic Scale Sets the Table

  • The “K” index:

  •  In 1971 The K index was incorporated into the NMC’s (now NCEP’s) regular data stream.

  • George’s K Index (J.J. George) “Weather Forecasting for Aeronautics’ (1960).


Severe weather part ii the synoptic scale sets the table8
Severe Weather Part II: The Synoptic Scale Sets the Table

  • The K-Index appears in the NCEP composite moisture chart (Upper Left-hand corner under the lifted Index). They were impressed enough with the index’s performance to include it.

  • K = (T850 – T500) + Td850 – (T700 – Td700)

  • K = (T850 – T500) + Td850 – DD700


Severe weather part ii the synoptic scale sets the table9
Severe Weather Part II: The Synoptic Scale Sets the Table

  •  Takes into account stability, moisture content of lower troposphere. The DD700 tries to account for “deep layer” moisture assuming that a deeper moisture layer means more fuel for the fire.

  •  The K-Index turns out to be a better indicator of airmass type-thunderstorms as opposed to baroclinic type severe weather.


Severe weather part ii the synoptic scale sets the table10
Severe Weather Part II: The Synoptic Scale Sets the Table

  • The “K” index also forecasts thunderstorm probability

  • Advantages to all these indicies:

  • 1) Quick, one only need look at two maps and have a pen and paper handy, (or calculator)

  • 2. Rooted in thermodynamic principles


Severe weather part ii the synoptic scale sets the table11
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Disadvantages:

  • 1) can differ in differing regions, seasons, and situations.

  • 2) Not “coverall” indicies

  • 3) We look at lower troposphere only.

  • 4) excludes upper air dynamics


Severe weather part ii the synoptic scale sets the table12
Severe Weather Part II: The Synoptic Scale Sets the Table

  • The SweaT (Severe Weather Threat ) Index

  • SW = 12 * D + 20 (TT – 49) + 2f8 + f5 + 125(S + 0.2)

  • This index tries to take into account everything we learn in “cookbook” approaches.

  • Plenty of Lowlevel moisture:

  • D = 850 hPa dewpoint (Use 0 if Td < = 0 C)


Severe weather part ii the synoptic scale sets the table13
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Stability and bouyancy:

  • TT – 49 : Total Totals index – 49.

  • The higher, the better!

  • TT – 49 = 0 if TT < = 49, there are negative numbers used here.


Severe weather part ii the synoptic scale sets the table14
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Strong moist, low level winds:

  • 2*f8 = twice the 850 hPa wind speed.

  • Strong vertical speed shear (strong jet stream):

  • F5 = wind speed at 500 hPa


Severe weather part ii the synoptic scale sets the table15
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Strong baroclinicity or Directional shear

  • S = sine of the (500 hPa – 850 hPa) wind direction.

  • Set S equal to zero if the following are not met:

  • a) 850  wind direction 130 – 250

  • b) 500  wind direction 210 – 310

  • c) 500dir – 850dir  < = 0


Severe weather part ii the synoptic scale sets the table16
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Advantanges:

  • 1) includes upper air dynamics as well as thermodynamics.

  • 2) empirical number


Severe weather part ii the synoptic scale sets the table17
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Disadvantages:

  • 1) Not a coverall index.

  • 2) more complex, cannot calculate relatively quickly.


Severe weather part ii the synoptic scale sets the table18
Severe Weather Part II: The Synoptic Scale Sets the Table

  • Interpretation

  • Studied 189 tornado cases

  • Studied 402 severe thunderstorm cases

  • Summary:

  • SW > 400 necessary for severe weather, Severe weather not a threat untill SW > 500, tonadoes not a threat until SW > 600.




ad