Development and Propagation of a Narrow Cold Frontal Rain Band in Northern California KC King M.S....

Development and Development and Propagation of a Narrow Propagation of a Narrow Cold Frontal Rain Band in Cold Frontal Rain Band in

Northern CaliforniaNorthern California

KC KingKC KingM.S. StudentM.S. Student

Desert Research InstituteDesert Research InstituteFebruary 11, 2009February 11, 2009

IntroductionIntroduction

►On January 4, 2008, the Truckee/Reno area On January 4, 2008, the Truckee/Reno area experienced a precipitation event of heavy experienced a precipitation event of heavy rain that turned to snow late in the day rain that turned to snow late in the day

►Forecast from the National Weather Service Forecast from the National Weather Service missed the timing of the change from rain missed the timing of the change from rain to snow and over forecasted the snowfallto snow and over forecasted the snowfall

►This presentation will describe the This presentation will describe the dynamics and thermodynamics of the dynamics and thermodynamics of the event on both synoptic and mesoscales event on both synoptic and mesoscales using both observations and model using both observations and model generated data.generated data.

Presentation OutlinePresentation Outline

►Forecast for January 4, 2008 Forecast for January 4, 2008 ►Quick Dynamics ReviewQuick Dynamics Review►Observations of the eventObservations of the event

Synoptic ScaleSynoptic Scale MesoscaleMesoscale

►Modeled ResultsModeled Results►Hypotheses on Model ErrorHypotheses on Model Error►ConclusionsConclusions

Forecast for January 4, 2008Forecast for January 4, 2008

►On Jan 3, 2008 at On Jan 3, 2008 at 1:30 pm, the NWS 1:30 pm, the NWS issued a blizzard issued a blizzard warning over the warning over the northern Sierras northern Sierras and Carson Rangeand Carson Range

NWS ProductsNWS Products► Blizzard Conditions:Blizzard Conditions:

►High Wind WarningsHigh Wind Warnings

The “Blizzard” of 2008The “Blizzard” of 2008Northstar Resort Weather BlogNorthstar Resort Weather Blog

December 31, 2007 - 5:51 PMDecember 31, 2007 - 5:51 PM► “ “ Took a long hard look at the four forecast Took a long hard look at the four forecast

models. They are all telling the same story models. They are all telling the same story and it's not bobbling around: POTENTIALLY and it's not bobbling around: POTENTIALLY EPIC SNOW COMING TO TAHOE THIS EPIC SNOW COMING TO TAHOE THIS WEEKEND.”WEEKEND.”

► ““Ok, let me see if I can explain it in a way Ok, let me see if I can explain it in a way that everyone can understand:that everyone can understand: Short Term (New Years Day, Wednesday, Short Term (New Years Day, Wednesday,

Thursday) - BEAUTIFUL SKI/RIDE DAYSThursday) - BEAUTIFUL SKI/RIDE DAYS Extended (This Weekend) - POWDER BEYOND Extended (This Weekend) - POWDER BEYOND

YOUR WILDEST DREAMS”YOUR WILDEST DREAMS”

But it rained… and rained.But it rained… and rained.

So what happened?

Jan. 4 Observations at RenoJan. 4 Observations at Reno

Narrow Cold Frontal Rain BandsNarrow Cold Frontal Rain Bands((NCFR)NCFR)

►Narrow focused Narrow focused precipitation precipitation associated with a associated with a cold frontcold front

► Characterized by Characterized by large updrafts and large updrafts and intense precipitationintense precipitation

► Strong cross-frontal Strong cross-frontal gradients over a gradients over a small areasmall area

More on NCFRsMore on NCFRs

► Caused by forced convection of the density Caused by forced convection of the density current associated with the low-level leading current associated with the low-level leading edge of a cold frontedge of a cold front

Jet DynamicsJet Dynamics

► Strong upper level Strong upper level jet off the west coastjet off the west coast

► Based on the 4-Based on the 4-quadrant jet streak quadrant jet streak model:model: Divergence/Rising Divergence/Rising

motion (shown in motion (shown in blue) in the right exit blue) in the right exit regionregion

Ageostrophic return Ageostrophic return branch circulation branch circulation (shown in red) at (shown in red) at lower levels lower levels

250mb height/wind speed (m/s) 1/4/2008 at 00 Z

Observations of Jan. 4 EventObservations of Jan. 4 Event

500 mb heights, 500 mb heights, absolute vorticity absolute vorticity (x10(x10-5-5/sec)/sec)

850 mb heights, 850 mb heights, winds (knots)winds (knots)

Upper Air ObservationsJan. 4, 2008 00Z

Upper Air DynamicsUpper Air DynamicsJan. 4, 2008 12Z – 250 mbJan. 4, 2008 12Z – 250 mb

Upper Air ObservationsJan. 4, 2008 12Z

500 mb heights, 500 mb heights, absolute vorticity absolute vorticity (x10(x10-5-5/sec)/sec)

850 mb heights, 850 mb heights, winds (knots)winds (knots)

Upper Air DynamicsUpper Air DynamicsJan. 4, 00ZJan. 4, 00Z

IR Satellite View of Large ScaleIR Satellite View of Large ScaleJan. 5 00ZJan. 5 00Z

Surface ObservationsSurface ObservationsJan. 4, 2008Jan. 4, 2008

12Z 00Z

Stratospheric Ozone MapStratospheric Ozone Map

High potential vorticity air masses from the stratosphere were brought down to the troposphere

Observed Mesoscale FeaturesObserved Mesoscale Features

►MSLP Map: 21ZMSLP Map: 21Z Mesolow forming by Mesolow forming by

21Z over the Sierras21Z over the Sierras

► Surface Surface Temperature: 21ZTemperature: 21Z Pool of cold air over Pool of cold air over

the CA/NV/OR the CA/NV/OR borderborder

Tongue of cold air is Tongue of cold air is pushing south pushing south almost to Reno almost to Reno

Progression of Mesoscale Progression of Mesoscale FeaturesFeatures

23Z

00Z

Radar Returns from EventRadar Returns from Event

► 1410Z – Jan 4, 20081410Z – Jan 4, 2008► Radar returns show Radar returns show

precipitation precipitation occurring over most occurring over most of Northern CA and of Northern CA and into Reno by 14:10Z into Reno by 14:10Z (6:10 am PST)(6:10 am PST)

► Red box highlights Red box highlights large amounts of large amounts of precipitation over precipitation over area near area near Bishop/Mono LakeBishop/Mono Lake

KDAX Radar at 20ZKDAX Radar at 20Z

► By 20Z we see By 20Z we see the intensification the intensification of precipitation of precipitation over the Sierras over the Sierras south of Tahoe south of Tahoe

► Strong returns Strong returns over the foothillsover the foothills

► At this point, it At this point, it was still rainingwas still raining

Truckee Wind Profiler DataTruckee Wind Profiler Data► Strong low level winds Strong low level winds

(~10 mph) out of the (~10 mph) out of the south from 12Z-23Z south from 12Z-23Z to a height of at least to a height of at least 2.5 km 2.5 km

► Veering of wind with Veering of wind with height height warm warm advection through the advection through the column column

► 00Z on January 5 00Z on January 5 surface winds shift to surface winds shift to southwesterly southwesterly

► Melt level also falls to Melt level also falls to near surface level at near surface level at 0Z after rising for the 0Z after rising for the 3 hours prior3 hours prior

Surface MeteogramsSurface Meteograms

Summary of ObservationsSummary of Observations► Upper level low pressure system associated with a Upper level low pressure system associated with a

straight jet streak approaching the west coast of the straight jet streak approaching the west coast of the United States United States

► Tropopause fold bringing an intrusion of high Tropopause fold bringing an intrusion of high potential vorticity stratospheric airpotential vorticity stratospheric air

► Left jet exit region falling over Northern California and Left jet exit region falling over Northern California and Nevada Nevada Creates a transverse low level southerly jet Creates a transverse low level southerly jet Low level jet advects warm air (due to latent Low level jet advects warm air (due to latent

heating) from the south keeping the North Tahoe heating) from the south keeping the North Tahoe and Reno areas warm and in rain rather than snowand Reno areas warm and in rain rather than snow

► Passage of the NCFR near 00Z leads to turning of the Passage of the NCFR near 00Z leads to turning of the winds from southerly to westerly allowing cold air to winds from southerly to westerly allowing cold air to be advected into the area and dropping the be advected into the area and dropping the temperaturetemperature

► Snow begins falling near 00ZSnow begins falling near 00Z

WRF SimulationsWRF Simulations

►Simulations using the Weather Simulations using the Weather Researching and Forecast Model (WRF) Researching and Forecast Model (WRF)

►Used North American Mesoscale Model Used North American Mesoscale Model (NAM) analysis data to initialize the model. (NAM) analysis data to initialize the model.

►27 km, 9 km, and 3 km grid size runs27 km, 9 km, and 3 km grid size runs►Model initialized at 12Z and 18Z on 1/4/08Model initialized at 12Z and 18Z on 1/4/08►Used to better understand the mesoscale Used to better understand the mesoscale

dynamics dynamics

Data from 9 km gridData from 9 km grid12Z initialization12Z initialization

►MSLP and wind MSLP and wind barbs at 20Zbarbs at 20Z

►Mesolow over the Mesolow over the Tahoe area is Tahoe area is shownshown

►Winds turn too Winds turn too soon from the soon from the south to the south to the southwest/westsouthwest/west

Evolution of MSLP and Wind Evolution of MSLP and Wind FieldsFields

9 km run, 12Z initialization9 km run, 12Z initialization

21Z 22Z

9 km Simulation, 18Z 9 km Simulation, 18Z InitializationInitialization

► To try to better To try to better simulate the simulate the southerly winds seen southerly winds seen in the observations in the observations the model was the model was initialized at 18Zinitialized at 18Z

► Hoped that the later Hoped that the later initialization would initialization would lead to a more lead to a more accurate simulation accurate simulation of the ageostrophic of the ageostrophic low level return jetlow level return jet 21Z: 250 mb heights, winds


► By 00Z on Jan. 5, By 00Z on Jan. 5, the shortwave the shortwave trough over the trough over the Sierras has Sierras has deepened and deepened and extended extended southwardsouthward

►Winds continue Winds continue out of the SWout of the SW

00Z: 250 mb heights, winds

9 km Simulation, 18Z 9 km Simulation, 18Z InitializationInitializationMSLP, WindsMSLP, Winds

20Z

22Z

21Z

23Z


► To get an even closer To get an even closer view, we used a 3 km view, we used a 3 km grid over the grid over the Reno/Tahoe regionReno/Tahoe region

► Wanted to capture the Wanted to capture the mesoscale dynamics mesoscale dynamics that kept the area that kept the area warm and the passage warm and the passage of the NCFRof the NCFR

► MSLP, winds shown to MSLP, winds shown to the rightthe right

► Mesolow just to east of Mesolow just to east of Truckee as seen in obsTruckee as seen in obs

21Z

22Z

3 km Simulation, 18Z 3 km Simulation, 18Z InitializationInitializationMSLP, WindsMSLP, Winds

► Winds begin to turn SW and Winds begin to turn SW and then W from 22Z – 0:40Zthen W from 22Z – 0:40Z

► Mesolow just to the east of Mesolow just to the east of Truckee, California deepensTruckee, California deepens

► Surface convergence likely Surface convergence likely leading to vertical motions, leading to vertical motions, condensation, precipitationcondensation, precipitation

► Flow is out of the south, Flow is out of the south, supporting the hypothesis supporting the hypothesis that warm advection of air that warm advection of air from the south keeps from the south keeps temperatures relatively temperatures relatively high leading to rain, not high leading to rain, not snowsnow

00Z

00:40Z


Surface TemperatureSurface Temperature21Z 00Z

In general, surface temperatures are too low in comparison to the observations by 3-5 C


20 Min Precipitation20 Min Precipitation

► Well defined band Well defined band of precipitation of precipitation extending from extending from west of west of Sacramento to Sacramento to northwest of northwest of TruckeeTruckee

► This band is a This band is a manifestation of manifestation of the NCFR ahead the NCFR ahead of the cold frontof the cold front

22Z


20 Min Precipitation20 Min Precipitation23Z 00Z

Distinct, thin line of high rainfall rate (NCFR) moves SE and combines with another band of precipitation forming to the south over the next four hours.

Hypotheses on Model Hypotheses on Model PerformancePerformance

► WRF had large errors in both wind direction and WRF had large errors in both wind direction and surface temperaturesurface temperature

► These errors were lessened by initializing the model These errors were lessened by initializing the model closer to the time of interest (12Z versus 18Z)closer to the time of interest (12Z versus 18Z)

► The secondary circulation set up in the jet exit The secondary circulation set up in the jet exit region that sustains the southerly winds was very region that sustains the southerly winds was very sensitive to the initial conditionssensitive to the initial conditions This is likely due to the influence of terrain and the barrier This is likely due to the influence of terrain and the barrier

jet. Without proper forcing and initial state, the southerly jet. Without proper forcing and initial state, the southerly winds seem to be overwhelmed by westerlies / barrier jet.winds seem to be overwhelmed by westerlies / barrier jet.

This may be due to insufficient data from the area over the This may be due to insufficient data from the area over the ocean. ocean.

Important for forecasting because the simulations were so Important for forecasting because the simulations were so sensitive to the initial state/time.sensitive to the initial state/time.

Very difficult to forecast an event like this due to the Very difficult to forecast an event like this due to the complex interactions between the larger scale circulation, complex interactions between the larger scale circulation, mesoscale features, and the terrain.mesoscale features, and the terrain.

ConclusionsConclusions► The precipitation from the January 4 storm was likely due The precipitation from the January 4 storm was likely due

to a intense rising motion in the left exit region of an to a intense rising motion in the left exit region of an upper level jet streak and intensified by orographic lifting. upper level jet streak and intensified by orographic lifting. The snowfall seems to be associated with a narrow cold The snowfall seems to be associated with a narrow cold frontal rain band.frontal rain band.

► Both observations and model results support the Both observations and model results support the conclusion that ahead of the cold front a NCFR developed conclusion that ahead of the cold front a NCFR developed that brought intense precipitation (snow). that brought intense precipitation (snow).

► The jet dynamics likely led to intensification of the front The jet dynamics likely led to intensification of the front and sustained southerly flow over the Northern Sierras.and sustained southerly flow over the Northern Sierras.

► The southerly wind brought warm air from latent heating The southerly wind brought warm air from latent heating due to intense precipitation in the Sierras near Mammoth due to intense precipitation in the Sierras near Mammoth Lakes and Yosemite, keeping the melt level high and Lakes and Yosemite, keeping the melt level high and preventing formation of snow. preventing formation of snow.

► As the winds turned from out of the south to As the winds turned from out of the south to southwesterly effectively cutting off the source of warm southwesterly effectively cutting off the source of warm air, the cold front progressed and the precipitation air, the cold front progressed and the precipitation changed from rain to snow. changed from rain to snow.

► In order to effectively capture this event with the WRF, In order to effectively capture this event with the WRF, the initial state was crucial to developing the correct wind the initial state was crucial to developing the correct wind structure.structure.

ReferencesReferencesBrowning, K.A., Reynolds, R., 1994: Diagnostic Study of a Narrow Cold-Frontal Browning, K.A., Reynolds, R., 1994: Diagnostic Study of a Narrow Cold-Frontal

Rainband and Severe Winds Associated with a Stratospheric Intrusion. Rainband and Severe Winds Associated with a Stratospheric Intrusion. Quarterly Journal of the Royal Meteorological SocietyQuarterly Journal of the Royal Meteorological Society, , 120120, p. 235-257., p. 235-257.

Hobbs, P.V., Persson, O.G., 1982: The Mesoscale and Microscale Structure and Hobbs, P.V., Persson, O.G., 1982: The Mesoscale and Microscale Structure and Organization of Clouds and Precipitation in Midlatitude Cyclones. Part V: The Organization of Clouds and Precipitation in Midlatitude Cyclones. Part V: The Substructure of Narrow Cold-Frontal Rainbands. Substructure of Narrow Cold-Frontal Rainbands. Journal of the Atmospheric Journal of the Atmospheric SciencesSciences, , 3939, p. 280-295., p. 280-295.

Kaplan, M., 2008, Class Notes from Synoptic Meteorology Class.Kaplan, M., 2008, Class Notes from Synoptic Meteorology Class.

Koch, S.E., Kocin, P.J., 1991: Frontal Contraction Processes Leading to the Koch, S.E., Kocin, P.J., 1991: Frontal Contraction Processes Leading to the Formation of an Intense Narrow Rainband. Formation of an Intense Narrow Rainband. Meteorology and Atmospheric Meteorology and Atmospheric PhysicsPhysics, , 4646, p. 123-154., p. 123-154.

Lin, Y.L., 2007. Lin, Y.L., 2007. Mesoscale DynamicsMesoscale Dynamics. Cambridge University Press.. Cambridge University Press.

Parsons, David B., 1992: An Explanation for Intense Frontal Updrafts and Narrow Parsons, David B., 1992: An Explanation for Intense Frontal Updrafts and Narrow Cold-Frontal Rainbands. Cold-Frontal Rainbands. Journal of the Atmospheric Sciences, Journal of the Atmospheric Sciences, 4949, p. 1810-, p. 1810-1825.1825.

Rutledge, S.A., Hobbs, P.V., 1984: The Mesoscale and Microscale Structure and Rutledge, S.A., Hobbs, P.V., 1984: The Mesoscale and Microscale Structure and Organization of Clouds and Precipitation in Midlatitude Cyclones. Part XII: A Organization of Clouds and Precipitation in Midlatitude Cyclones. Part XII: A Diagnostic Modeling Study of Precipitation Development in Narrow Cold-Diagnostic Modeling Study of Precipitation Development in Narrow Cold-Frontal Rainbands. Frontal Rainbands. Journal of the Atmospheric SciencesJournal of the Atmospheric Sciences, , 4141, p. 2949-2972., p. 2949-2972.

National Climatic Data Center, National Climatic Data Center, http://www.ncdc.noaa.gov/oa/ncdc.html.http://www.ncdc.noaa.gov/oa/ncdc.html.

Cable News Network, http://www.cnn.com.Cable News Network, http://www.cnn.com.

Reno Gazette Journal, http://www.rgj.com.Reno Gazette Journal, http://www.rgj.com.

Northstar Ski Resort, Unofficial Weather Blog, Northstar Ski Resort, Unofficial Weather Blog, http://northstarsnow.blogspot.com/.http://northstarsnow.blogspot.com/.

Utah State Meteorology, Mesowest, Utah State Meteorology, Mesowest, http://www.met.utah.edu/jhorel/html/mesonet/.http://www.met.utah.edu/jhorel/html/mesonet/.

Plymouth State Weather Center, Plymouth State Weather Center, http://vortex.plymouth.edu/make.html.http://vortex.plymouth.edu/make.html.

References Con’tReferences Con’t

Thank you!Thank you!

Special thanks to Michael Kaplan and Special thanks to Michael Kaplan and Chris Smallcomb for their time and Chris Smallcomb for their time and assistance.assistance.

Any questions?Any questions?

Development and Propagation of a Narrow Cold Frontal Rain Band in Northern California KC King M.S....

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