Mid-Latitude Cyclone Development BFB: 10/20/2015 Zach Hiris & Phil Pascerelli

Purpose of Mid-Latitude Cyclones What is the role of mid-latitude cyclones in the atmosphere? Balance the temperature gradient Gradient forms because heating is never equal in the atmosphere If it was, we’d never see the weather we have each day! Strong gradients can produce very strong mid-latitude cyclones!

Characteristics Cold Core Lows Strengthen with height Warm Air Advection prevalent near most precipitation Creates lift needed for precip Heaviest Snow “Always to the left of the low” -Dr. Ballentine. Why? Deformation! Winds converge on one axis and diverge on another- creates lift!

2 3 1 1 Formation Where do these cyclones tend to form in the CONUS? Eastern Seaboard/Gulf of Mexico Heating effects of diabatic and latent heating (Gulf Stream interaction) Lee side of the Rockies Due to stretching effects Alberta Canada region Known for “Alberta Clippers” and Miller B storms- more on this later! 3 2 1 1

Ingredients Needed Divergence! Vorticity Baroclinic Zones Where upper level winds are diffluent (spreading apart) Leads to low level convergence Vorticity “Spin” in the atmosphere Part of the reason the Lee side of the Rockies sees cyclogenesis Baroclinic Zones Heating differences- think frontal zones, strong temperature boundaries (Gulf Stream)

Upper Level Troughs Mid-latitude cyclones are often associated with 500mb “troughs”, or areas of lower heights Depending on the orientation of the trough, this can indicate strengthening, weakening, etc. Also indicate diffluence/confluence, among other things (i.e. upper level lift)

Positive Tilt vs. Negative Tilt Positive tilted troughs indicate that a low pressure system has not yet reached maturity or is weakening Typically don’t produce significant weather Negatively tilted troughs Most commonly produce sigificant weather Indicates low pressure has reached maturity Also is a sign of differential advection- low level WAA below mid/upper level CAA Increasing instability!

Positive vs. Negative Tilt

Common Storm Tracks Rockies Cyclones Gulf of Mexico/East Coast Panhandle Hook Tracks through Ohio Valley or further south Great Lakes Cutter Cuts west of the Great Lakes- commonly produce severe weather East of the Mississippi Gulf of Mexico/East Coast Miller A Classic winter storm track for I-95 corridor Miller B Technically different versions - depending on the definition these storms also originate from Alberta, Canada

L L L Cyclone Tracks Great Lakes Cutter Panhandle Hook Miller B “Transfers” Miller A “Nor’Easter” L

Winter Storms Storms from Fall to Spring are typically stronger than in the summer. Why? The temperature gradient/jet stream is stronger! Stronger thermal gradient- more rapid cyclogenesis Stronger storms = Stronger lift = Heavy snow! Must know what to look for for where a storm is tracking! Where will the snow develop?

Winter Storm Forecasting Tips to producing a successful winter storm forecast (rain/snow/ice) Know the track of the low Use Dr. B’s rule for determining where snow is most likely to occur Keep in mind what’s happening in the upper levels- where’s the baroclinic zone, PVA? Thermal Profiles Must know the thermal profiles of every level- let BUFKIT/Skew-T’s be your friend! Identify less obvious features- Warm Air Advection, Cold Air Damming, etc. Magic temperatures for Dendritic growth (DGZ): -16 to -12C Deeper DGZ- better snow rates and heavier snow

Cyclone Forecasting- Archive (GHD 2011) Things to look for… 500mb Heights/Vorticity Look at the trough and its orientation- where it’s tracking Where is the PVA? 700mb Humidity & 850mb Temps/Humidity Where is the moisture? Thermal gradient (aka baroclinic zone?)- Where is the low going? Surface Maps Where does the actual low track in relation to these?

Cyclone Forecasting- Archived Case (GHD 2011)

Example of Cyclone Forecasting- GFS Look for lower 500mb heights- where is the upper level low developing? Is there confluence ahead of the storm track? Confluence- Upper Level air coming together- convergence in the upper atmosphere tends to deflect cyclones away Where are the areas of vorticity- where is it heading? Positive Vorticity Advection (PVA)- where the PVA is, the surface low usually follows Where is the best place diffluence (divergence)? Important to know the features above the surface Knowing where the storm tracks in relation to these gives you the storm track!

GFS Example- Images

Famous Mid-Latitude Cyclones (March 1993) One of the strongest mid-latitude cyclone observed in the United States The low rapidly intensified at a rate of 17 hPa in 12 hours in the Gulf of Mexico A pressure of 961 hPa recorded in White Plains, New York Weather models forecast the storm accurately five days out. One inch of snow was observed along the Gulf Coast, 42.9 inches of snow recorded in Syracuse, New York Birmingham, Alabama recorded 13 inches of snow and a low temperature of -16.7°C (2°F)

March 1993- Triple Phaser Can be referred to as a “Triple Phaser” All 3 portions of the jet stream (Arctic, Polar, Subtropical) combined over the eastern U.S. coast Led to massive strengthening

Famous Mid-Latitude Cyclones (March 1993)

Famous Mid-Latitude Cyclones (Oct. 2010) Also known as the “Octo-bomb” Known as the most intense extratropical cyclone in U.S. history (beats out Blizzard of 1978) with a recorded pressure of 952mb The low rapidly intensified (bombed out) over the Northern Plains Wind gusts of up to 70mph were recorded from the strong pressure gradient Produced significant severe weather One of only 3 days in October the SPC highlighted a “High Risk” Oct. 26th produced 57 tornado reports, 339 wind reports

Famous Mid-Latitude Cyclones (oct. 2010)