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Using Frontogenesis in Winter Weather Forecasting. Greg Patrick WFO FWD Nov 13, 2008 Parts of this presentation derived from presentations by Dr. David Schultz (NSSL) and Pete Banacos (formerly SPC ). Topics. Motivation Frontogenesis Review Definition Interpretation

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using frontogenesis in winter weather forecasting

Using Frontogenesis in Winter Weather Forecasting

Greg Patrick

WFO FWD

Nov 13, 2008

Parts of this presentation derived from presentations by

Dr. David Schultz (NSSL) and Pete Banacos(formerly SPC)

topics
Topics
  • Motivation
  • Frontogenesis Review
    • Definition
    • Interpretation
  • Diagnosing Frontogenesis
    • Conceptual Models
    • Example
motivation
Motivation
  • Frontogenesis was a significant contribution to forcing during two of the most significant winter events across north TX in the past ~ 5 years (2/24/03 & 3/6/08)
  • Winter weather events with large geographic variations in impacts can result from events where Fgen forcing is dominant
motivation4
Motivation

Frontogenesis produced

Banded pcpn

Mar 6, 2008

Feb 24-25, 2003

frontogenesis review
Frontogenesis Review
  • Conceptually, F is the local change in horizontal temperature gradient near an existing front, baroclinic zone, or feature as it moves.
  • When we talk about frontogenesis forcing, it’s the resulting ageostrophic circulation we are most interested in for precipitation forecasting
frontogenesis review6
Frontogenesis Review
  • Frontogenesis is an intensification of a temperature gradient at the surface or aloft
  • Frontolysis is a weakening of the temperature gradient at the surface or aloft
  • The 2-D scalar frontogenesis function (F ) – quantifies the change in horizontal (potential) temperature gradient following air parcel motion :

F > 0 frontogenesis, F < 0 frontolysis

petterssen 1936 frontogenesis
Petterssen (1936) Frontogenesis

F = d/dt |Ñq|

F = 1/2 |Ñq| ( E cos2b - D)

q = potential temperature

E = resultant deformation

b = angle between the isentrope and the axis of dilatation

D = divergence

frontogenesis review9
Frontogenesis Review

• Diagnosis of frontogenesis results in a diagnosis of the

forcing for vertical motion on the frontal scale.

• Ascent occurs on the warm side of a maximum of

frontogenesis and on the cold side of a region of

frontolysis

horizontal deformation
Horizontal Deformation

Flow fields involving deformation acting frontogenetically are prominent in the majority of banded precipitation cases.

F>0

displaying fgen fields
Displaying Fgen Fields
  • WFO only : AWIPS workstation
  • Web: HPC Model Diagnostics pagehttp://www.hpc.ncep.noaa.gov/mdd/mddoutput/
  • Web: SPC SREF page http://www.spc.ncep.noaa.gov/exper/sref/
  • Web: Others?
example feb 24 2003
Example – Feb 24, 2003
  • Convection developed in a zone of strong frontogenetical forcing across western and northern parts of north TX, resulting in a mixture of moderate-heavy sleet and snow in some areas.
  • Models (particularly Eta) focused UVM and QPF across southern parts of the FWD CWA, closer to surface front and stronger elevated instability
slide23

Eta 3 pm Monday - Cross section taken across front – frontal circulation

highlighted

10,000 Feet

5000 Feet

Cold Air

KSPS

Warm Air

KGLS

operational forecasting summary
Operational Forecasting Summary
  • Frontogenesis fields should be assessed anytime a strong frontal zone affects north TX
  • Look for banded QPF in numerical model output or large values of +VV in bands parallel to front as clues that Frontogenesis may be a factor
  • Look for sloped continuity of Frontogenesis
  • Must also assess moisture and instability parameters along with vertical temp profile
references
References

Dr. David Schultz

NSSL http://www.cimms.ou.edu/~schultz/

Pete Banacos

SPC Link to his banding/Fgenconference paper

http://spc.noaa.gov/publications/banacos/F_conf_030415b.pdf

Reference to dynamic explanations of F and UVM

H. B. Bluestein, Vol II, Synoptic-Dynamic Meteorology

In Midlatitudes. Pages 297-304