Mid-Latitude Cyclones: -Formation and Forecasting- Jake Presented By: Jake Mulholland and Michael Vuotto

Mid-Latitude Cyclones: What’s their role … ???? Any guesses .. ?? Answer: these systems act to “mix-out” or decreases the north/south temperature gradient that forms due to differential heating of the earth’s surface, however, this “balanced-state” is NEVER achieved! Mike

Some Mid-Latitude Cyclone Climatology … #1 #2 Mike Two favored areas over the United States for cyclone-formation: guesses anyone .. ??? Any guesses also as to why .. ???

Answers … 1) Off the Eastern Seaboard (diabatic heating and latent heating effects – think of the Gulf Stream current) and … 2) on the Lee side of the Rocky Mtns. (vortex stretching effects – we’ll get to this later on) Jake

Cyclogenesis Regions of “pre-existing frontal boundaries” are hot-spots for mid-latitude cyclone development .. Why?? Answer: fronts have pre-existing areas of “cyclonic vorticity” (or in simple terms .. cyclonic rotation) along with enhanced low-level convergence! – SEE LINK BELOW! http://books.google.com/books?id=LSqIxGcFIoQC&pg=PA101&lpg=PA101&dq=gary+lackmann+figure+5.8&source=bl&ots=0-CYK5fG99&sig=pQA9bsRcaslbA-06H_6oneCq8WA&hl=en&sa=X&ei=kev-UcKGL7X94APZ74DADA&ved=0CDgQ6AEwAg#v=onepage&q=gary%20lackmann%20figure%205.8&f=false Jake

Cyclogenesis con’t What also is important is upper-level divergence! Upper-level divergence (where winds are diffluent on an upper-air map) leads to low-level convergence which is favorable for surface cyclones! (think Continuity eq.) See map on next page … Mike

Cyclogenesis: Upper-Level Pattern Mike Which area would favor surface cyclone development .. ??? .. Why .. ???

Mike

Sutcliffe-Petterssen “self-development” ideas An idea of continued self-development of cyclones Positive Feedback loop: **Begin with an upper-level trough-ridge pattern with a surface cyclone at the inflection point ..  .. CAA to west of sfc low, WAA to the east ..  .. Height rises to the west, falls to the east .. .. Stronger surface cyclone ..  .. Leads to a more amplified pattern ..  .. More advections, height falls/rises increases,etc. ..  .. A stronger surface cyclone ..  .. Repeats!!! Jake

Click the link for “self-development” image … http://books.google.com/books?id=LSqIxGcFIoQC&pg=PA106&lpg=PA106&dq=gary+lackmann+figure+5.13&source=bl&ots=0-CYK5mCd6&sig=HIfAqsyOVL8dEHaxurU3FnhVDUc&hl=en&sa=X&ei=fgX_UY-OCq2q4AOxnYCwAQ&ved=0CCoQ6AEwAA#v=onepage&q=gary%20lackmann%20figure%205.13&f=false Jake

… but … there is a “brake” we need to discuss! In a fairly complicated equation (See Lackmann Pgs. 105->108; Equation #5.6), there is a “braking term” on the S-P self development idea: any guesses … ??? … w(Γad - Γenv) The answer is adiabatic cooling!! Can this “brake” ever be shut-off .. ??? The answer = YES! How so .. ??? The answers are via latent heat release and boundary layer moistening! (basically make brake = 0) Jake – Temperature tendency equation

Explosive Cyclogenesis! Definition: a sfc-cyclone with a 24-mb decrease in central pressure within a 24-hr span Favored regions are ___________ ???? Answer = Off the east coast, above the Gulf Stream current! This region is favorable because: Pre-existing frontal zones (i.e. – coastal front) Lots of latent heat release and boundary layer heat/moisture fluxes Mike

Example: Presidents Day Nor'easter, 1979 Mike

Colorado Lows Sfc low’s tend to form downwind of the Rocky mtns. typically in eastern parts of Co. Why you may ask .. ??? Any guesses .. ??? The answer: the previous mentioned, “vortex stretching”! Viewpoint = Potential Vorticity! Mike

Colorado Lows con’t Potential Vorticity Framework for Co. Low formation is fairly simply … A conserved quantity!!! Jake

Where Co. Lows form!!! Jake

Colorado Lows con’t Where: COLORDAO! DUHHH! Typical path they take: ???? (Can anyone help me … ????) Mike

Correct Answer … “Colorado Hookers” Mike

Jake Any questions … ????