Flow Channeling In The Mohawk & Hudson Valleys A Multiscale Case Study of Surface Flow Convergence...

Flow Channeling In The Flow Channeling In The Mohawk & Hudson ValleysMohawk & Hudson Valleys

A Multiscale Case Study of A Multiscale Case Study of Surface Flow ConvergenceSurface Flow Convergence

Ninth Annual Northeast Regional Operational Workshop/NWS/CESTM

7-8 November 2007

Michael E. Augustyniak

Lance F. BosartDepartment of Earth and Atmospheric

Sciences, University at Albany State University of New York, Albany, New York

Hugh W. Johnson IVNOAA/NWS, Weather Forecast Office, Albany,

New York

Flow Channeling In The Mohawk Flow Channeling In The Mohawk & Hudson Valleys& Hudson Valleys

Known locally as Known locally as Mohawk-Hudson Mohawk-Hudson convergenceconvergence, it occurs when surface air , it occurs when surface air parcels traveling down the upper Hudson parcels traveling down the upper Hudson Valley (from north to south) meet air Valley (from north to south) meet air parcels traveling down the Mohawk Valley parcels traveling down the Mohawk Valley (from west to east)(from west to east)

Flow Channeling In The Mohawk Flow Channeling In The Mohawk & Hudson Valleys& Hudson Valleys

Low-level convergence generates a resurgence Low-level convergence generates a resurgence of precipitation behind departing low pressure, of precipitation behind departing low pressure, which is unrelated to lake effectwhich is unrelated to lake effect

Why study it?Why study it? ““Mohawk-Hudson convergence” tends not to be Mohawk-Hudson convergence” tends not to be

forecast very well by today’s models, which poses a forecast very well by today’s models, which poses a problem for forecastersproblem for forecasters

It tends to occur over the region’s population centersIt tends to occur over the region’s population centers The effects of a poor forecast are amplified when The effects of a poor forecast are amplified when

snowfall is involved, or during peak travel timessnowfall is involved, or during peak travel times

Case StudiesCase Studies

Discussed today:Discussed today: 27 Nov. 200227 Nov. 2002 (The day before Thanksgiving) (The day before Thanksgiving)

Studied as part of M.S. Thesis research:Studied as part of M.S. Thesis research: 16-17 Dec. 200216-17 Dec. 2002 23-24 Jan. 200323-24 Jan. 2003 17 Jan. 200517 Jan. 2005 03 Mar. 200603 Mar. 2006 28-29 Jan. 200728-29 Jan. 2007

Geography of New York & New EnglandGeography of New York & New England

27 November 200227 November 2002Case StudyCase Study

(The day before Thanksgiving)(The day before Thanksgiving)

Surface FeaturesSurface Features

1200 UTC 27 Nov. 2002

Albany, NY (ENX) Radar ImageryAlbany, NY (ENX) Radar Imagery

0958 UTC 27 Nov. 2002


1202 UTC 27 Nov. 2002


1400 UTC 27 Nov. 2002


1558 UTC 27 Nov. 2002


1803 UTC 27 Nov. 2002


2001 UTC 27 Nov. 2002


2229 UTC 27 Nov. 2002

Synoptic Overview (GFS)Synoptic Overview (GFS)

Synoptic Overview (GFS)Synoptic Overview (GFS)

LL

Temp. Advection & Vertical Temp. Advection & Vertical Velocity (NARR)Velocity (NARR)

2100 UTC 27 Nov. 2002

Temp. Advection Profile (NARR)Temp. Advection Profile (NARR)

Vertical Motion Profile (NARR)Vertical Motion Profile (NARR)

Surface AnalysisSurface Analysis

2100 UTC 27 Nov. 2002

Sea Level PressureSea Level PressureSea Level Pressure

27-28 Nov. 2002

1016

1017

1018

1019

1020

1021

1022

1023

1024

12:00

13:00

14:00

15:00

16:00

17:00

18:00

19:00

20:00

21:00

22:00

23:00 0:

001:

002:

003:

00

Time (UTC)

SL

P (

hP

a)

KUCA KGFL KALB KPOU

Surface MeteogramSurface Meteogram

KUCA

KGFL

KALB

KPOU

KALB (72518) SoundingsKALB (72518) Soundings

Moist Boundary Layer

Moist Boundary Layer

1200 UTC 27 Nov. 2002 0000 UTC 28 Nov. 2002

Wind Direction During Wind Direction During Convergence EventsConvergence Events

6 Cases Total:6 Cases Total:Wind Direction For MHC Cases At KUCA/KSYR

(Occurrences Per 10° Wind Bin)

0

5

10

15000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°

Wind Direction For MHC Cases At KGFL(Occurrences Per 10° Wind Bin)

0

5

10000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°

Wind Direction During MHC Cases At KALB(Occurrences Per 10° Wind Bin)

0

5

10000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°

N=46


6 Cases Total:6 Cases Total: Wind Direction For MHC Cases At KUCA/KSYR(Occurrences Per 10° Wind Bin)

0

5

10

15000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°


0

5

10000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°


0

5

10000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°

N=48


6 Cases Total:6 Cases Total: Wind Direction For MHC Cases At KUCA/KSYR(Occurrences Per 10° Wind Bin)

0

5

10

15000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°


0

5

10000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°


0

5

10000°

010°020°

030°

040°

050°

060°

070°

080°

090°

100°

110°

120°

130°

140°

150°

160°170°

180°190°

200°

210°

220°

230°

240°

250°

260°

270°

280°

290°

300°

310°

320°

330°

340°350°

N=47

ConclusionsConclusions

Mohawk-Hudson convergence is a terrain-Mohawk-Hudson convergence is a terrain-induced mesoscale phenomenoninduced mesoscale phenomenon

In most of the cases studied, precipitation In most of the cases studied, precipitation associated with Mohawk-Hudson associated with Mohawk-Hudson convergence occurs under similar synoptic convergence occurs under similar synoptic conditions, including…conditions, including…


The prior passage of a 500-hPa troughThe prior passage of a 500-hPa trough The absence of strong forcingThe absence of strong forcing

Weak or neutral 500-hPa vorticity advectionWeak or neutral 500-hPa vorticity advection Weak or neutral 700-hPa vorticity advection by the Weak or neutral 700-hPa vorticity advection by the

thermal windthermal wind Weak low-level cold air advectionWeak low-level cold air advection

A statically-stable atmosphere with a well-A statically-stable atmosphere with a well-mixed, moist boundary layermixed, moist boundary layer

ConclusionsConclusions Higher sea level pressure at KGFL than at KPOUHigher sea level pressure at KGFL than at KPOU Higher sea level pressure at KUCA (KSYR) than at Higher sea level pressure at KUCA (KSYR) than at

KPSFKPSF Usual surface configuration: “Reverse-S” isobar Usual surface configuration: “Reverse-S” isobar

pattern with zonally-oriented pressure ridge nosing in pattern with zonally-oriented pressure ridge nosing in over zonally-oriented pressure troughover zonally-oriented pressure trough

Allows simultaneous North/NE winds in upper Hudson Valley Allows simultaneous North/NE winds in upper Hudson Valley and WNW winds in the Mohawk Valleyand WNW winds in the Mohawk Valley

Light to moderate winds at 850-hPa and below Light to moderate winds at 850-hPa and below (generally 10 m(generally 10 m··ss-1-1 or less) or less)


A greater understanding of the interactions of A greater understanding of the interactions of local terrain and overlying synoptic flows that local terrain and overlying synoptic flows that leads to Mohawk-Hudson convergence, such as leads to Mohawk-Hudson convergence, such as through this research, is necessary before one through this research, is necessary before one can reasonably expect to make an accurate can reasonably expect to make an accurate forecastforecast

Medium- and short-range forecasting of Medium- and short-range forecasting of precipitation caused by Mohawk-Hudson precipitation caused by Mohawk-Hudson convergence is possible, and limited only by convergence is possible, and limited only by human and/or model skill at forecasting the human and/or model skill at forecasting the overlying synoptic regimeoverlying synoptic regime

Impacts On Aviation WeatherImpacts On Aviation Weather

Prolonged period of IFRProlonged period of IFR Impact on aviation industryImpact on aviation industry Government Performance and Results Government Performance and Results

Act (GPRA) factored into our Terminal Act (GPRA) factored into our Terminal Forecasts (TAF)Forecasts (TAF)

Probability of Detection (POD) of Probability of Detection (POD) of correctly forecasting IFR is 0.63 correctly forecasting IFR is 0.63

False alarm (FAR) is 0.44False alarm (FAR) is 0.44 Critical for especially GA pilotsCritical for especially GA pilots

Impacts On The EconomyImpacts On The Economy

Part of National Weather Service mission Part of National Weather Service mission is the enhancement of the national is the enhancement of the national economy economy

Additional deployment of snow removalAdditional deployment of snow removal Whether or not to close schools and Whether or not to close schools and

businesses businesses

Dilemma Of The End Of Dilemma Of The End Of Millennium SnowstormMillennium Snowstorm

Heaviest elements of the snowstorm Heaviest elements of the snowstorm (meso-scale banding) came in earlier than (meso-scale banding) came in earlier than forecastforecast

Dry slot all but shut down snow by nightfall Dry slot all but shut down snow by nightfall (when we though it would be the heaviest) (when we though it would be the heaviest)

Then…Then…

Mohawk-Hudson enhanced precipitation Mohawk-Hudson enhanced precipitation appeared right after we decided to drop appeared right after we decided to drop the Winter Storm Warningthe Winter Storm Warning

An inch of fluffy snow nevertheless caused An inch of fluffy snow nevertheless caused slick roads after sunupslick roads after sunup

Saving grace – it was a Sunday!Saving grace – it was a Sunday!

Future WorkFuture Work

Develop an algorithm which uses overlying Develop an algorithm which uses overlying synoptic conditions to help forecast Mohawk-synoptic conditions to help forecast Mohawk-Hudson convergenceHudson convergence Integrate various meteorological parameters into Integrate various meteorological parameters into

AWIPS procedure so we can help identify if and when AWIPS procedure so we can help identify if and when Mohawk- Hudson convergence will take place Mohawk- Hudson convergence will take place

Investigate warm season cases (thus far Investigate warm season cases (thus far focused on cold ones, namely snowstorms)focused on cold ones, namely snowstorms)

Investigate “Null” casesInvestigate “Null” cases

Thank You!Thank You!

Questions?Questions?

Flow Channeling In The Mohawk & Hudson Valleys A Multiscale Case Study of Surface Flow Convergence...

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