Flow Channeling In The Mohawk & Hudson Valleys A Multiscale Case Study of Surface Flow Convergence Ninth Annual Northeast Regional Operational Workshop/NWS/CESTM 7-8 November 2007 Michael E. Augustyniak Lance F. Bosart Department of Earth and Atmospheric Sciences, University at Albany State University of New York, Albany, New York Hugh W. Johnson IV NOAA/NWS, Weather Forecast Office, Albany, New York

Flow Channeling In The Mohawk & Hudson Valleys Known locally as Mohawk-Hudson convergence, it occurs when surface air parcels traveling down the upper Hudson Valley (from north to south) meet air parcels traveling down the Mohawk Valley (from west to east) Known locally as Mohawk-Hudson convergence, it occurs when surface air parcels traveling down the upper Hudson Valley (from north to south) meet air parcels traveling down the Mohawk Valley (from west to east)

Flow Channeling In The Mohawk & Hudson Valleys Low-level convergence generates a resurgence of precipitation behind departing low pressure, which is unrelated to lake effect Low-level convergence generates a resurgence of precipitation behind departing low pressure, which is unrelated to lake effect Why study it? Why study it? “Mohawk-Hudson convergence” tends not to be forecast very well by today’s models, which poses a problem for forecasters “Mohawk-Hudson convergence” tends not to be forecast very well by today’s models, which poses a problem for forecasters It tends to occur over the region’s population centers It tends to occur over the region’s population centers The effects of a poor forecast are amplified when snowfall is involved, or during peak travel times The effects of a poor forecast are amplified when snowfall is involved, or during peak travel times

Case Studies Discussed today: Discussed today: 27 Nov (The day before Thanksgiving) 27 Nov (The day before Thanksgiving) Studied as part of M.S. Thesis research: Studied as part of M.S. Thesis research: Dec Dec Jan Jan Jan Jan Mar Mar Jan Jan. 2007

Geography of New York & New England

27 November 2002 Case Study (The day before Thanksgiving)

Surface Features 1200 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 0958 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 1202 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 1400 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 1558 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 1803 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 2001 UTC 27 Nov. 2002

Albany, NY (ENX) Radar Imagery 2229 UTC 27 Nov. 2002

Synoptic Overview (GFS)

L

L

Temp. Advection & Vertical Velocity (NARR) 2100 UTC 27 Nov. 2002

Temp. Advection Profile (NARR)

Vertical Motion Profile (NARR)

Surface Analysis 2100 UTC 27 Nov. 2002

Sea Level Pressure

Surface Meteogram KUCA KGFL KALB KPOU

KALB (72518) Soundings Moist Boundary Layer 1200 UTC 27 Nov UTC 28 Nov. 2002

Wind Direction During Convergence Events 6 Cases Total: 6 Cases Total: N=46

Wind Direction During Convergence Events 6 Cases Total: 6 Cases Total: N=48

Wind Direction During Convergence Events 6 Cases Total: 6 Cases Total: N=47

Conclusions Mohawk-Hudson convergence is a terrain- induced mesoscale phenomenon Mohawk-Hudson convergence is a terrain- induced mesoscale phenomenon In most of the cases studied, precipitation associated with Mohawk-Hudson convergence occurs under similar synoptic conditions, including… In most of the cases studied, precipitation associated with Mohawk-Hudson convergence occurs under similar synoptic conditions, including…

Conclusions The prior passage of a 500-hPa trough The prior passage of a 500-hPa trough The absence of strong forcing The absence of strong forcing Weak or neutral 500-hPa vorticity advection Weak or neutral 500-hPa vorticity advection Weak or neutral 700-hPa vorticity advection by the thermal wind Weak or neutral 700-hPa vorticity advection by the thermal wind Weak low-level cold air advection Weak low-level cold air advection A statically-stable atmosphere with a well- mixed, moist boundary layer A statically-stable atmosphere with a well- mixed, moist boundary layer

Conclusions Higher sea level pressure at KGFL than at KPOU Higher sea level pressure at KGFL than at KPOU Higher sea level pressure at KUCA (KSYR) than at KPSF Higher sea level pressure at KUCA (KSYR) than at KPSF Usual surface configuration: “Reverse-S” isobar pattern with zonally-oriented pressure ridge nosing in over zonally-oriented pressure trough Usual surface configuration: “Reverse-S” isobar pattern with zonally-oriented pressure ridge nosing in over zonally-oriented pressure trough Allows simultaneous North/NE winds in upper Hudson Valley and WNW winds in the Mohawk Valley Allows simultaneous North/NE winds in upper Hudson Valley and WNW winds in the Mohawk Valley Light to moderate winds at 850-hPa and below (generally 10 m·s -1 or less) Light to moderate winds at 850-hPa and below (generally 10 m·s -1 or less)

Conclusions A greater understanding of the interactions of local terrain and overlying synoptic flows that leads to Mohawk-Hudson convergence, such as through this research, is necessary before one can reasonably expect to make an accurate forecast A greater understanding of the interactions of local terrain and overlying synoptic flows that leads to Mohawk-Hudson convergence, such as through this research, is necessary before one can reasonably expect to make an accurate forecast Medium- and short-range forecasting of precipitation caused by Mohawk-Hudson convergence is possible, and limited only by human and/or model skill at forecasting the overlying synoptic regime Medium- and short-range forecasting of precipitation caused by Mohawk-Hudson convergence is possible, and limited only by human and/or model skill at forecasting the overlying synoptic regime

Impacts On Aviation Weather Prolonged period of IFR Prolonged period of IFR Impact on aviation industry Impact on aviation industry Government Performance and Results Act (GPRA) factored into our Terminal Forecasts (TAF) Government Performance and Results Act (GPRA) factored into our Terminal Forecasts (TAF) Probability of Detection (POD) of correctly forecasting IFR is 0.63 Probability of Detection (POD) of correctly forecasting IFR is 0.63 False alarm (FAR) is 0.44 False alarm (FAR) is 0.44 Critical for especially GA pilots Critical for especially GA pilots

Impacts On The Economy Part of National Weather Service mission is the enhancement of the national economy Part of National Weather Service mission is the enhancement of the national economy Additional deployment of snow removal Additional deployment of snow removal Whether or not to close schools and businesses Whether or not to close schools and businesses

Dilemma Of The End Of Millennium Snowstorm Heaviest elements of the snowstorm (meso-scale banding) came in earlier than forecast Heaviest elements of the snowstorm (meso-scale banding) came in earlier than forecast Dry slot all but shut down snow by nightfall (when we though it would be the heaviest) Dry slot all but shut down snow by nightfall (when we though it would be the heaviest)

Then… Mohawk-Hudson enhanced precipitation appeared right after we decided to drop the Winter Storm Warning Mohawk-Hudson enhanced precipitation appeared right after we decided to drop the Winter Storm Warning An inch of fluffy snow nevertheless caused slick roads after sunup An inch of fluffy snow nevertheless caused slick roads after sunup Saving grace – it was a Sunday! Saving grace – it was a Sunday!

Future Work Develop an algorithm which uses overlying synoptic conditions to help forecast Mohawk- Hudson convergence Develop an algorithm which uses overlying synoptic conditions to help forecast Mohawk- Hudson convergence Integrate various meteorological parameters into AWIPS procedure so we can help identify if and when Mohawk- Hudson convergence will take place Integrate various meteorological parameters into AWIPS procedure so we can help identify if and when Mohawk- Hudson convergence will take place Investigate warm season cases (thus far focused on cold ones, namely snowstorms) Investigate warm season cases (thus far focused on cold ones, namely snowstorms) Investigate “Null” cases Investigate “Null” cases

Thank You! Questions?