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Warm Season Frontogenesis Forcing Applications and
Implications for Convective Initiation (or Failure)
Warm Season Frontogenesis Forcing Applications and
Implications for Convective Initiation (or Failure)
Dan MillerScience and Operations OfficerNWS/WFO Duluth, Minnesota
Dan MillerScience and Operations OfficerNWS/WFO Duluth, Minnesota
NWS Duluth Minnesota
Great Lakes Operational Meteorology Workshop – Toronto, Ontario 22 March 2010
Phil SchumacherScience and Operations OfficerNWS/WFO Sioux Falls, South
Dakota
Phil SchumacherScience and Operations OfficerNWS/WFO Sioux Falls, South
Dakota
Greg Mann, PhDScience and Operations Officer
NWS/WFO White Lake, Michigan
Greg Mann, PhDScience and Operations Officer
NWS/WFO White Lake, Michigan
ObjectivesObjectives
1) Review frontogenesis conceptual models
1) Review frontogenesis conceptual models
2) Review cold season frontogenesis applications
2) Review cold season frontogenesis applications
3) Establish a need for FGEN application during the warm season
3) Establish a need for FGEN application during the warm season
4) Develop a warm season frontogenesis conceptual model
4) Develop a warm season frontogenesis conceptual model
5) Warm season case example5) Warm season case example
6) A few thoughts about warm season “parameter space”
6) A few thoughts about warm season “parameter space”
Synoptic Cyclone Frontogenesis RegionsSynoptic Cyclone Frontogenesis Regions
LLLLF > 0
F > 0
AA
BB
CC
Frontogenesis Conceptual ModelsFrontogenesis Conceptual Models
Cold Frontal MovementCold Frontal Movement Dryline MovementDryline
MovementWarm Frontal MovementWarm Frontal Movement
The ascending branch of the ageostrophic circulation resides to the warm side of the FGEN maximum (in the max F vector convergence)
The ascending branch of the ageostrophic circulation resides to the warm side of the FGEN maximum (in the max F vector convergence)
Remember: By convention, we draw the front at the leading edge of the gradient - so FGEN > 0 on the cool side of the front. BUT…
Remember: By convention, we draw the front at the leading edge of the gradient - so FGEN > 0 on the cool side of the front. BUT…
F > 0F > 0
F > 0F > 0
F > 0F > 0
Cross Section A
Cross Section A
Cross Section B
Cross Section B
Cross Section C
Cross Section C
Frontogenesis Conceptual ModelsFrontogenesis Conceptual Models
LLLLF > 0
F > 0
We will focus on this area where “warm” frontogenesis is occurring
Review of Frontogenesis ConceptsReview of Frontogenesis Concepts
LLow Level
Jet
Low Level
Jet
FrontogenesisFrontogenesis Thermal Gradient
Thermal Gradient
Low Level Jet
Low Level Jet
QPF on Cool Side
QPF on Cool Side
Weak Stability or Instability needed for Heavy Precipitation
Weak Stability or Instability needed for Heavy Precipitation
Banded PrecipBanded Precip
Cold Season FGEN Conceptual ModelCold Season FGEN Conceptual Model
Sfc Pres/
QPF
Sfc Pres/
QPF
850 mbT/Wind/Isotach
s
850 mbT/Wind/Isotach
s
800 mb/FGEN
800 mb/FGEN
Sfc Pres/
Temp
Sfc Pres/
Temp
Cold Season FGEN Conceptual ModelCold Season FGEN Conceptual Model
700 mb700 mb
925 mb925 mb
500 mb500 mb
850 mb850 mb
FGEN (image), Isotherms and Wind
FGEN (image), Isotherms and Wind
Cold Season FGEN Conceptual ModelCold Season FGEN Conceptual Model
FGEN/Theta-
E
FGEN/Theta-
E
EPV*/Theta
EPV*/Theta
RHRH
T/Omega
T/Omega
X-Section Across Frontal ZoneX-Section Across Frontal Zonesouthsouth northnorth
FGEN in the Warm Season?FGEN in the Warm Season?
However… Instability is typically MUCH greater!
…and strong low level jet interaction with a low level baroclinic zone (front or outflow boundary) is quite common
However… Instability is typically MUCH greater!
…and strong low level jet interaction with a low level baroclinic zone (front or outflow boundary) is quite common
So, why are FGEN processes de-emphasized during the warm season?
So, why are FGEN processes de-emphasized during the warm season?
Presumably because…Presumably because…
1) Thermal gradients are weaker in the warm season
1) Thermal gradients are weaker in the warm season
2) Frontal zones are shallower in the warm season
2) Frontal zones are shallower in the warm season
3) Synoptic waves are generally weaker during the warm season (weaker dynamic forcing)
3) Synoptic waves are generally weaker during the warm season (weaker dynamic forcing)
Frequency of FGEN in Warm Season?Frequency of FGEN in Warm Season?
From Bettwy/Donofrio/Lonka, et al for 2006 warm seasonFrom Bettwy/Donofrio/Lonka, et al for 2006 warm season
MUCH more common that previously acknowledged!
MUCH more common that previously acknowledged!
FGEN processes need additional scrutiny in the warm season as well
FGEN processes need additional scrutiny in the warm season as well
Warm Season FGEN Conceptual ModelWarm Season FGEN Conceptual Model
Sfc Pres/
QPF
Sfc Pres/
QPF
850 mbT/Wind/FGEN
850 mbT/Wind/FGEN
MUCAPE
MUCAPE
Sfc Pres/Sfc CAPE
Sfc Pres/Sfc CAPE
Warm Season FGEN Conceptual ModelWarm Season FGEN Conceptual Model
700 mb
925 mb
500 mb
850 mb
FGEN (image), Isotherms and Wind
Warm Season FGEN Conceptual ModelWarm Season FGEN Conceptual Model
FGEN/Theta
FGEN/Theta
CAPE/Omega
CAPE/Omega
RHRH
Theta-E/
Ageo Circ
Theta-E/
Ageo Circ
X-Section Across Frontal ZoneX-Section Across Frontal Zonesouthwe
stsouthwe
stnorthea
stnorthea
st
Case Example: 13 August 2007Case Example: 13 August 2007
1630 UTC Hail Outlook
1630 UTC Hail Outlook
1630 UTC Wind Outlook
1630 UTC Wind Outlook
1630 UTC Tornado Outlook
1630 UTC Tornado Outlook
1630 UTC Categorical Outlook
1630 UTC Categorical Outlook
Case Example: 13 August 2007Case Example: 13 August 2007
2030 UTC Categorical Outlook
2030 UTC Categorical Outlook
2030 UTC Tornado Outlook
2030 UTC Tornado Outlook
2030 UTC Hail Outlook
2030 UTC Hail Outlook
2030 UTC Wind Outlook
2030 UTC Wind Outlook
13 August 2007: Convective Initiation13 August 2007: Convective Initiation
KDLH Reflectivity Loop 2159-2341 UTC
KDLH Reflectivity Loop 2159-2341 UTC
13 August 2007: Objective Analysis13 August 2007: Objective Analysis
Surface CAPE 21ZSurface CAPE 21Z
Most Unstable CAPE 21Z
Most Unstable CAPE 21Z
13 August 2007: Objective Analysis13 August 2007: Objective Analysis
Surface CAPE 23ZSurface CAPE 23Z
Most Unstable CAPE 23Z
Most Unstable CAPE 23Z
13 August 2007: Volumetric Reflectivity13 August 2007: Volumetric Reflectivity
KDLH Reflectivity 4-panel 2353 UTC
KDLH Reflectivity 4-panel 2353 UTC
~12,000ft agl
~12,000ft agl
~33,000ft agl
~33,000ft agl
~41,000ft agl
~41,000ft agl
~21,000ft agl
~21,000ft agl
Is the Frontal Zone Active?Is the Frontal Zone Active?
Wind(green barbs)/Wind Isotachs (peach lines) and Divergence (image)
Wind(green barbs)/Wind Isotachs (peach lines) and Divergence (image)
Active Part of Frontal ZoneActive Part of Frontal Zone
Frontolysis/Frontogenesis couplet indicates active part of the frontal zone (Sawyer-Eliassen Equation)
Frontolysis/Frontogenesis couplet indicates active part of the frontal zone (Sawyer-Eliassen Equation)
Cold Season Warm Season
Ageostrophic ResponseAgeostrophic Response
Active Frontogenetic/Frontolytic circulations develop
Active Frontogenetic/Frontolytic circulations develop
Cold SeasonCold Season Warm SeasonWarm Season
Impact on Parcel TrajectoriesImpact on Parcel Trajectories
Parcels hit a “speed bump” and weak subsidence just before entering the ascending branch of the frontogenetic circulation resulting in further dynamic strengthening of an already strong cap
Parcels hit a “speed bump” and weak subsidence just before entering the ascending branch of the frontogenetic circulation resulting in further dynamic strengthening of an already strong cap
Cold SeasonCold Season Warm SeasonWarm Season
Layer Lifting ProcessesLayer Lifting Processes
Significant limitation of Parcel Theory:
Layer Lifting Processes
Significant limitation of Parcel Theory:
Layer Lifting ProcessesParcel Computed CAPE can
underestimate Actual Realized CAPE by 2 to 4 times!!
Parcel Computed CAPE can underestimate Actual Realized CAPE by 2 to 4 times!!
From: Bryan et al
CI: 13 August 2007 Case - 21 UTCCI: 13 August 2007 Case - 21 UTC
Surface Warm Front
Surface Warm Front
Location of Initiation
Location of Initiation
CI: 13 August 2007 Case - 22 UTCCI: 13 August 2007 Case - 22 UTC
CI: 13 August 2007 Case - 23 UTCCI: 13 August 2007 Case - 23 UTC
CI: 13 August 2007 Case - 24 UTCCI: 13 August 2007 Case - 24 UTC
Thermodynamics North of BoundaryThermodynamics North of Boundary
**
Location of Initiation
Location of Initiation
North of Boundary: Initial ProfileNorth of Boundary: Initial Profile
MU layer: ~860-830 mb
MU layer: ~860-830 mb
2100 UTCCAPE: 491CIN: 455LFC: ~16000
ft/agl ~570 mb
2100 UTCCAPE: 491CIN: 455LFC: ~16000
ft/agl ~570 mb2100 UTC
Sustained Layer Forced Ascent due to frontogenesis
Sustained Layer Forced Ascent due to frontogenesis
North of Boundary: Profile ChangesNorth of Boundary: Profile Changes
2200 UTC
Sustained Layer Forced Ascent due to frontogenesis
Sustained Layer Forced Ascent due to frontogenesis
2200 UTCCAPE: 980CIN: 276 LFC: ~14400
ft/agl ~602 mb
2200 UTCCAPE: 980CIN: 276 LFC: ~14400
ft/agl ~602 mb
MU layer: ~850-830 mb
MU layer: ~850-830 mb
North of Boundary: Profile ChangesNorth of Boundary: Profile Changes
2300 UTC
Sustained Layer Forced Ascent due to frontogenesis
Sustained Layer Forced Ascent due to frontogenesis
2300 UTCCAPE: 1320CIN: 130LFC: ~13800
ft/agl ~616 mb
2300 UTCCAPE: 1320CIN: 130LFC: ~13800
ft/agl ~616 mb
MU layer: ~820-780 mb
MU layer: ~820-780 mb
North of Boundary: Profile ChangesNorth of Boundary: Profile Changes
Sustained Layer Forced Ascent due to frontogenesis
Sustained Layer Forced Ascent due to frontogenesis
2400 UTC2400 UTC
2400 UTCCAPE: 1737CIN: 72LFC: ~13205
ft/agl ~630 mb
2400 UTCCAPE: 1737CIN: 72LFC: ~13205
ft/agl ~630 mb
MU layer: ~810-790 mb
MU layer: ~810-790 mb
North of Boundary: Forcing ModificationsNorth of Boundary: Forcing Modifications
MU Parcel Layer
MU Parcel Layer
3 Hour ChangeCAPE: 1737
(+1247)CIN: 72 (-383)
3 Hour ChangeCAPE: 1737
(+1247)CIN: 72 (-383)LCL/LFC
heights lower by ~3000 feet!
LCL/LFC heights lower by ~3000 feet!
Sustained Layer Forced Ascent
Sustained Layer Forced Ascent
Thermodynamics South of BoundaryThermodynamics South of Boundary
**
Warm Sector Profile
Warm Sector Profile
South of Boundary: Initial ProfileSouth of Boundary: Initial Profile
Sustained Layer Forced Weak Subsidence due to Frontolysis
Sustained Layer Forced Weak Subsidence due to Frontolysis
2100 UTCCAPE: 3605CIN: -125LFC: ~10745
ft/agl ~694 mb
2100 UTCCAPE: 3605CIN: -125LFC: ~10745
ft/agl ~694 mb2100 UTC
South of Boundary: Profile ChangesSouth of Boundary: Profile Changes
Sustained Layer Forced Weak Subsidence due to Frontolysis
Sustained Layer Forced Weak Subsidence due to Frontolysis
2200 UTCCAPE: 3717CIN: -129LFC: ~10745
ft/agl ~694 mb
2200 UTCCAPE: 3717CIN: -129LFC: ~10745
ft/agl ~694 mb2200 UTC
South of Boundary: Profile ChangesSouth of Boundary: Profile Changes
Sustained Layer Forced Weak Subsidence due to Frontolysis
Sustained Layer Forced Weak Subsidence due to Frontolysis
2300 UTCCAPE: 3756CIN: -133LFC: ~10745
ft/agl ~694 mb
2300 UTCCAPE: 3756CIN: -133LFC: ~10745
ft/agl ~694 mb2300 UTC
South of Boundary: Profile ChangesSouth of Boundary: Profile Changes
Sustained Layer Forced Weak Subsidence due to Frontolysis
Sustained Layer Forced Weak Subsidence due to Frontolysis
2400 UTCCAPE: 3919CIN: -147LFC: ~10700
ft/agl ~695 mb
2400 UTCCAPE: 3919CIN: -147LFC: ~10700
ft/agl ~695 mb2400 UTC
South of Boundary: Forcing ModificationsSouth of Boundary: Forcing Modifications
MU ParcelMU Parcel
2200 UTCCAPE: 3919
(+314)CIN: 147 (+22)
2200 UTCCAPE: 3919
(+314)CIN: 147 (+22)
LCL/LFC height nearly unchanged
LCL/LFC height nearly unchanged
Dynamic Cap Strengthening: CI FailureDynamic Cap Strengthening: CI Failure
Agrees well with Weisman/Wieseler Study (St. Cloud State University)Conv Vs. NonConv Lid Strength
0
2
4
6
8
10
12
14
16
18
20
22
Lid Strengths (°C)
Nu
mb
er o
f O
ccu
rren
ces
CI cases = redCI cases = red
CI failure cases = greenCI failure cases = green
Dynamic Cap Strengthening
Parameter Space vs. ProcessesParameter Space vs. Processes
Sharp precip/cloud cutoff on warm side of boundary
Sharp precip/cloud cutoff on warm side of boundary
Severe Weather Parameter Space is Maximized
Severe Weather Parameter Space is Maximized
Parameter “Sufficiency” + Maximized Processes
Parameter “Sufficiency” + Maximized Processes
Thanks For Your Attention
Thanks For Your Attention
Questions/Comments/Discussion?
Questions/Comments/Discussion?dan.j.miller@noaa
.govdan.j.miller@noaa
.gov