Transcript AVN/MRF OFTEN HAS PROBLEMS HANDLING UPSLOPE EVENTS

SEMI-INTELLIGENT USE OF
THE ETA MODEL
WES JUNKER
HYDROMETEOROLOGICAL PREDICTION CENTER
CAMP SPRINGS, MD
E-MAIL ADDRESS: [email protected]
COMAP SYMPOSIUM 99-1
18 May 1999
Why models have forecast problems



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
Initialization and quality control smooth data fields, but
some of the lost detail may be important.
May have poor first guess
Lack of data over the oceans and Mexico.
Atmospheric processes are non-linear; small changes in
initial conditions can lead to large forecast variations (this
is the basis for ensemble forecasting).
Model physics are approximations
 for
lower resolution models, convection is
parameterized
 for higher resolution models the micro-physical
processes are parameterized
INTELLIGENT USE OF THE
MODEL REQUIRES THAT THE
FORECASTER
COMPARE THE INITIAL 00HR
FORECAST WITH DATA
 BE FAMILIAR WITH CHARACTERTIC
MODEL ERRORS AND BIASES.
 HAVE A ROUGH UNDERSTANDING OF
HOW APPROXIMATIONS OF THE
PHYSICS MAY NEGATIVELY IMPACT A
FORECAST.

The performance characteristics of
the eta have changed dramatically
during the past year.


QPF forecasts during the past winter deteriorated
when compared to the AVN or NGM.
ETA surface and 500 mb forecasts have also been
worse compared to the other models.
 April
1999 ETA 500 h and 250 mb forecasts usually
verified worse than the AVN.
32-km terrain
Know the difference between model and real terrain!
DESPITE ITS RECENT PROBLEMS, THE ETA IS
STILL USUALLY BETTER THAN THE AVN OR
NGM FORECASTING PRECIPITATION OVER
COMPLEX TERRAIN DURING WINTER IN A
ZONAL PATTERN.
12-36 H ETA V.T. 12Z 3 JAN 97
12-36 H NGM V.T. 12Z 3 JAN 97
ANALYSIS V.T. 12Z 3 JAN 97
Note that the Eta max in California is a little too far west. It also often under
predicts precipitation over the Siskiyou Mountains of northern California.
Eta Model Physics

Eta model calculates grid-scale precipitation
using a simplified explicit cloud water
scheme
 includes
super-cooled water, simplified snow
processes and the advection of cloud water and
cloud ice
 but does not include horizontal advection of
snow and rain.
 In
fast flow snow can advect 50 to 100 km
downwind of its source region (Rauber, 1992)
EXPLICIT CLOUD PREDICTION
SCHEME (large scale)


Cloud condensation is allowed to occur when the RH
reaches a critical value
Cloud evaporation is allowed to take place only when the
RH falls below the critical value



70% over land, 80% over water
the difference in the critical value between land and water can
produce discontinuities along the coast
this may be one of the reasons the Eta over predicts cold season
precipitation along the Gulf and Atlantic Coasts.
The BMJ Convective Scheme

1st looks for deep convection
 step
1 is to look for most unstable layer within
the lowest 130 mb
 Next calculates LCL to get cloud base
 then lifts parcel to Equilibrium Level to get
cloud top
 then looks to see if the cloud layer is at least
290 mb in depth
 If
the cloud is not 290 mb then it searches for
shallow convection
More about the BMJ scheme
 then
develops sounding based on a reference profile.
The important thing to remember about the profile is it will not
allow the sounding to become completely saturated.
 The saturation pressure deficit is found for three levels (cloud
base, freezing level and cloud top) and the final reference
profile based on the type of cloud efficiency
 Saturation pressure deficits are then found for other points
along the profile

• when the saturation pressure deficits are exceeded, the moisture
produces rain.
• however, the amount of rainfall must be in balance with the
latent heating.
The BMJ scheme

Was developed for tropical systems
 does
not handle elevated convection well
 the
convection may not extend through a deep
enough layer

does not develop realistic
downdrafts/outflow boundaries
 therefore,
during summer it sometimes predicts
the convective development too far north

the saturation pressure deficits in the
scheme are different over land and water
THE ETA OFTEN FORECASTS TOO MUCH RAINFALL
NEAR THE GULF AND SOUTHEAST COASTS
BECAUSE OF THE PROBLEMS WITH THE WAY THE
ETA HANDLES THE LAND-SEA INTERFACE
12-36 HR PRECIPITATION
FORECAST V. T. 12Z 1 APR
24 HR PRECIPITATION ANALYSIS
V. T. 12Z 1 APR
FOR ANY MODEL, ALWAYS
BEWARE OF THE 1ST GUESS
00 HR ETA SURFACE AND 1000500 MB THICKNESS
V.T.
00Z 3 SEP 1998
00 HR ETA 500 MB HEIGHT
AND VORTICITY
V.T.
00Z 3 SEP 1998
SURFACE ANALYSIS
V.T. 00Z 3 SEP 1998
TROPICAL STORM EARL WAS LOCATED JUST SOUTHWEST
OF THE FLORIDA PENINSULA. THE 1ST GUESS WILL
SOMETIMES OVERRIDE DATA WHEN INTENSE SMALL SCALE
FEATURES ARE PRESENT.
WHAT HAPPENED?
THE MRF 1ST GUESS FIELD TRIED TO DRAW TO THE DATA BUT THE FIRST
GUESS FIELD OVERWHELMED IT. IF NCEP HAS A COMPUTER FAILURE,
THE ETA DATA ASSIMILATION MAY BE CANCELLED AND THE ETA MAY
RUN ON AN EARLIER GLOBAL MODEL 1ST GUESS
A POOR INITIAL ANALYSIS CAN
PRODUCE HUGE FORECAST ERRORS
ETA 48 HR V.T. 00Z SEP 5
EARL
ETA 48 HR V.T. 00Z SEP 5
EARL
EARL
EARL
ETA 00 HR V.T. 00Z SEP 5
ETA 00 HR V.T. 00Z SEP 5
IN THE PAST, ETA MODEL HAS HAD PROBLEMS
PREDICTING THE STABILITY. PROBLEM IS OFTEN
TIED TO THE 1ST GUESS
HIGH SOIL MOISTURE CASE
WHEN SOIL MOISTURE IS
HIGH, THE ETA
DEWPOINTS ARE TOO
HIGH AND LOW-LEVEL
TEMPERATURES ARE TOO
LOW.
THE ETA FORECAST
CAPE=1177, LI=-4
OBSERVED
CAPE=5, LI=2
THIS SOMETIMES
CAUSES THE MODEL TO
BE TOO UNSTABLE
FORECAST
OBSERVED
WHEN HIGH SOIL MOISTURE IS PRESENT, OR WHEN THE MODEL
FIRST GUESS THINKS THE SOIL MOISTURE IS HIGH,
THEN, THE MODEL FORECASTS SURFACE DEWPOINTS TOO HIGH AND
SURFACE TEMPS TOO LOW.
32
28
24
SURFACE
TEMPERATURE
OBSERVED
20
24
20
16
ETA FORECAST
DEWPOINT
TEMPERATURE
12
1024
1020
1016
SURFACE
PRESSURE
1012
THE MODEL
UNDERPREDICTS THE
BOUNDARY LAYER
WINDS. HOWEVER,
MODEL FORECASTS
OF 850 MB WINDS
ARE OFTEN TOO
18/00
18/06
18/12
18/18
19/00
19/06
19/12
19/18
20/00
STRONG
WHEN LOW SOIL MOISURE IS PRESENT DURING SUMMER
OVER THE HIGH PLAINS, ESPECIALLY WEST TX, THE
FORECAST CAPE IS TOO LOW
WHEN SOIL MOISTURE IS LOW IN SUMMER IN THE
PLAINS, THE SURFACE DEWPOINT IS TOO LOW AND
THE TEMPERATURE IS TOO HIGH
THE DEWPOINTS IN THE PLAINS AND SOUTHWEST WERE TOO LOW THIS SUMMER
OKLAHOMA CITY
36
32
28
24
20
SURFACE
TEMPERATURE
OBSERVED
ETA FORECAST
20
DEWPOINT
16
TEMPERATURE
12
1016
SURFACE
PRESSURE
19/00
19/06
MAY 1998
19/12
1008
19/18
20/00
20/06
20/12
20/180
21/00
ETA SURFACE
WINDS WERE
TOO WESTERLY,
WAS THERE
TOO MUCH
DOWN-SLOPE?
Forecast -Vs- Observed Best Cape
Spring 96
Line x=y
Line x=y
Forecast
precipitation
1 - less than .25”
2 - more than .25”
Note the large spread.
The model stability
forecasts are worst
when precipitation is
forecast
MORE ON ETA PERFORMANCE
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TOO WET IN FLORIDA
SOMETIMES OVERDEVELOPS LOW-LEVEL JET
HAS BEEN TOO FAST BRINGING SHORTWAVES
THROUGH THE ROCKIES INTO THE PLAINS.
HAS BEEN TOO FAR SOUTH WITH CLOSED LOWS
COMING EASTWARD INTO THE PLAINS
OVERFORECASTS THE STRENGTH OF
ANTICYCLONES
HAS PROBLEMS INITIALIZING TROPICAL
SYSTEMS
ETA AND STORM TRACKS
DURING 1999 TENDED TO BE TOO FAR SOUTH
WITH LOWS AS THEY REFORMED EAST OF
ROCKIES. THIS ERROR USUALLY CONTINUED
UNTIL THE LOW MOVED EAST OF THE
MISSISSIPPI RIVER.
BY CONTRAST, THE AVN IS SOMETIMES TOO
FAR NORTH
TENDS TO SOMETIMES TRACK LOWS TOO FAR
NORTH AND WEST WITH LOWSALONG THE
EAST COAST.
ESPECIALLY DURING MAJOR
CYCLOGENESIS WHEN A COASTAL
TROUGH IS PRESENT
COMMON ETA ERROR ALONG EAST COAST
WHEN A CLOSED UPPER LOW APPROACHES THE COAST THE ETA
SOMETIMES HAS PROBLEMS FORECASTING THE LOCATION OF THE
SURFACE LOW. NOTE WHERE THE UPPER LOW IS CENTERED AND
WHERE THE STRONGEST UPPER-LEVEL DIVERGENCE IS IMPLIED.
48 H ETA 500H V.T. 12Z 23 APR 98
48 H NGM 500H V.T. 12Z 23 APR 98
Based on the 500 h and vorticity pattern, where would you predict the surface low?
NOTE THAT THE ETA SURFACE LOW IS A LITTLE
WEST OF ITS 500 MB CENTER. THE NGM HAS A
MUCH BETTER FIT TO THE 500 MB PATTERN.
THE STRONG EASTERLY COMPONENT TO THE WINDS NORTH OF THE
ETA MODEL LOW ALLOWS IT TO WRAP MOISTURE AND PRECIPITATION
TOO FAR WEST
48 H ETA SURFACE V.T. 12Z 23 APR 98
48 H NGM SURFACE V.T. 12Z 23 APR 98
THE LOW VERIFIES A LITTLE NORTH AND
EAST OF THE NGM. REMEMBER, THE NGM IS
TYPICALLY TOO SLOW WITH LOWS ALONG
THE COAST.
VERIFYING SURFACE V.T. 12Z 23 APR 98
L
ETA SURFACE LOW
VERIFYING 500H V.T. 12Z 23 APR 98
When the NGM and AVN sheared 500 troughs approaching
the east coast in 1999, the eta often amplified the trough and
overdeepened the surface low. An example:
48 HR ETA 500
48 HR ETA SFC
48 HR NGM 500
48 HR NGM SFC
The Eta predicted a major east
coast snowstorm. The NGM and
AVN predicted light snow at best
36-48 hr ETA precipitation
36-48 hr NGM precipitation
HOW THE MODEL VERIFIED. NO
MAJOR SNOWSTORM DEVELOPED.
48 HR ETA 500
VERIFYING 500 MB
48 HR NGM 500
VERIFYING SFC
LOWS TO THE LEE OF THE
ROCKIES



THE AVN AND NGM USUALLY PREDICT
THEM TO FORM TOO FAR NORTH
THE ETA IS SOMETIMES A LITTLE TOO FAR
SOUTH
USE THE 300 MB UPPER LEVEL JET. THE
SURFACE LOW IS USUALLY FOUND IN THE
LEFT EXIT REGION OF THE JET, USUALLY
JUST TO THE NORTH
28 ETA model runs were evaluated during the
period from 00Z March 30-12 Z April 13.
During the entire period the mean 500h
pattern was similar to the one shown below.
A RIDGE AND POSITIVE ANOMALY
NEAR 160W, BELOW NORMAL
HEIGHTS OVER ALASKA AND A
TROUGH NEAR OF JUST INLAND
FROM THE WEST COAST WITH
BELOW NORMAL HEIGHTS
EXTENDING EASTWARD INTO THE
SOUTHWESTERN U.S.
THE ETA SHOWED A CONSISENT
CHARACTERISTIC ERROR DURING
THE PERIOD. THE NEXT FEW
SLIDES WILL DESCRIBE THE
ERROR
As the upper trough digs into the west the
ETA did not dig the shortwaves strongly
enough once the trough reached the ca coast.
Note how much lower the heights are across
NV and CA.
48 hr ETA valid 00Z 1 April
00 hr eta valid 00Z 1 April
The eta underplays the second shortwave
diving into the mean trough and
overplays the first one.
48 hr ETA 500 h and vorticity v.t. 12Z 4 April
00 hr ETA 500 h and vorticity v.t. 12Z 4 April
THE ETA PREDICTED THE UPPER LOW ASSOCIATED WITH THE FIRST SHORTWAVE
TOO FAR SOUTH AND EAST IN THE PLAINS. INSTEAD THE INITIAL SHORTWAVE
LIFTED MORE TO THE NORTH BEFORE BEING FORCED EASTWARD. THIS HAPPENED
SEVERAL TIMES DURING THE STUDY.
The eta was generally too fast and far southeast with
the 500h low over the Plains with 120 meter errors
over MO and IA. This can have a very serious
impact on frontal speed and on the position of the
low level convergence and resulting convection.
546
48 hr Eta v.t. 12Z 10 Apr
558
00 hr Eta v.t. 12Z 10 Apr
The Eta surface low and associated fronts can also be
affected. The slower eastward movement of the
ridge axis may allowed for the flow along the east to
be more northwesterly which allowed the surface
boundary to sink farther to the south
48 hr Eta v.t. 12Z 10 Apr
00 hr Eta v.t. 12Z 10 Apr
Why models have problems with
arctic airmasses


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Terrain is averaged
Initialization process sometimes robs shallow
airmass of its coldness
Models have problems handling the strength of the
inversion
The sigma coordinate system, the Eta coordinate
system does better
The leading edge of the ETA LI gradient is often
the best indicator of the frontal position
THE NGM AND AVN/MRF HAVE SERIOUS PROBLEMS WITH
ARCTIC AIRMASSES.
L
36 HR NGM V.T. 00Z APR 09,
1995
36 HR AVN V.T. 00Z APR 09,
1995
AVN ANALYSIS
V.T. 00Z APR 09, 1995
TEMPERATURES ACROSS KANSAS WERE IN THE LOW TO MID
50s WITH STRONG NORTH WINDS. SOUTH OF THE FRONT
TEMPERATURES WERE IN THE UPPER 70s TO LOW 90s.
PRIOR TO THE 1998-99 WINTER SEASON ,ETA
USUALLY HANDLED ARCTIC AIR MASSES BETTER.
WHEN USING MODELS, PATTERN
RECOGNITION
REMAINS
IMPORTANT!
VALID AT BEGINNING OF PERIOD
MSL, THICKNESS AND 850 WINDS
PRECIPITABLE WATER (INCHES) AND 850
MB WINDS
SEVERAL THINGS TO NOTE: 1) A LONG FETCH OF DEEP
MOISTURE, 2) A BARRIER JET AND STRONG SOUTHERLY
FLOW UP THE SACREMENTO VALLEY. THIS JET HELPS
PRODUCE HEAVY RAINS NEAR SHASTA, 3) STRONG WARM
ADVECTION.
DO THE FORECASTS LOOK
CONSISTENT WITH WHAT YOU SEE IN
THE PACIFIC? CHECK SSMI DATA
VALID AT THE END OF THE PERIOD
MSL, THICKNESS AND 850 WINDS
PRECIPITABLE WATER (INCHES) AND 850
MB WINDS
OVERLAYING MODEL OUTPUT WITH SSMI IMAGERY
CAN GIVE YOU A GOOD IDEA OF THE MOISTURE
THAT WILL BE FEEDING INTO THE WEST COAST.
THE MODEL OUTPUT LOOKS REASONABLE
NOTE THE TROPICAL CONNECTION
AND PLUME OF PWS ABOVE 1.00”
THE MODEL’S TERRAIN IS AVERAGED OVER
THE GRID BOX SO THE SLOPE OF THE
TERRAIN IS USUALLY NOT STEEP ENOUGH
THIS CAUSES THE VERTICAL MOTION FIELD TO
BE SHIFTED AWAY FROM THE MOUNTAINS
THINGS TO REMEMBER ABOUT MODEL QPFS
IN COMPLEX TERRAIN DURING WINTER
BECAUSE OF THE SIMPLIFIED
MICROPYSICS AND
INADEQUATE RESOLUTION OF
MOUNTAINS.
MODELS USUALLY:
1) PREDICT PRECIPITATION
TOO FAR WEST AWAY FROM
MOUNTAIN PEAKS
2) DO NOT ALLOW ENOUGH
PRECIPITATION ON THE
IMMEDIATE DOWNWIND SIDE
OF MOUNTAIN RANGES
WHAT ADJUSTMENTS ARE
NEEDED TO THIS 24 HR QPF
WITH STRONG VERY MOIST SOUTHWESTERLY
FLOW AT 850 AND 700 MB NOTE HOW CLOSELY THE
PRECIPITATION CONFORMS TO THE TERRAIN
32 KM ETA TERRAIN
24 HOUR PRECIPITATION VALID
JAN. 9, 1995
WHEN SOUTHWESTERLY FLOW IS PRESENT A
BARRIER JET FORMS AND FUNNELS THE FLOW UP
THE SACREMENTO VALLEY.
IF THE MODEL IS SO DRY DURING THE
SUMMER IN THE PLAINS, HOW DO I USE IT?
USING PATTERN RECOGNITION AND
KNOWLEDGE OF TYPICAL MODEL ERRORS.
DOES THIS LOOK LIKE A MADDOX FRONTAL TYPE EVENT?
BOUNDARY LAYER WIND AND
TEMPERATURE FORECAST V.T. 00Z 18 JULY
THE BLUE LINE INDICATES A THERMAL BOUNDARY
THAT SHOWS UP IN THE FORECAST
A STRONG LOW LEVEL JET IS PRESENT WITH
LOTS OF MOISTURE. THIS IS A TYPICAL
MADDOX TYPE SET UP.
IS IT TIME TO CALL EMERGENCY MANAGERS? FOR WHICH
STATE? MINNESOTA? WISCONSIN? IOWA? ILLINOIS?
OOZ 18 JULY FORECASTS OF
250 JET AND DIVERGENCE
BEST LI AND BOUNDARY LAYER WINDS
A SHORTWAVE AND JET STREAK IS APPROACHING
THE RIDGE. UNSTABLE LIS ALONG SURFACE
BOUNDARY
IS THIS A GOOD QPF? DO
YOU THINK THE RAINFALL
IS ORIENTED CORRECTLY
WHICH WSFOS NEED TO CONTACT EMERGENCY MANAGERS?
HOW DID YOU DO?
DURING SUMMER THE ETA IS OFTEN UNDERPLAYS THE
PRECIPITATION ASSOCIATED WITH MCCS. IT ALSO OFTEN PREDICTS
ITS RAINFALL MAXIMUM TOO FAR NORTH BECAUSE IT CANNOT
HANDLE OUTFLOW BOUNDARIES, OR IN THIS CASE THE LAKE
BREEZE.
MODEL FORECAST
OBSERVED
6” OR MORE
3” OR MORE
1” OR MORE
VERIFYING PRECIPITATION
BIAS=FORECAST/OBSERVED
 EQUITABLE THREAT=(H-E)/(F+O-H-E)
 THREAT SCORE=H/(F+O-H)


N=NUMBER OF HITS, F=NUMBER OF GRID POINTS FORECAST,
O=GRID POINTS OBSERVED, E=(F*O)/N
MODEL BIAS AND THREAT
SCORE
IS DEPENDENT ON RESOLUTION OF
MODEL
 HOW THE MODEL IS DISPLAYED.
THE FAX VERSION OF ETA IS NOT
DISPLAYED WITH FULL MODEL
RESOLUTION!
 HOW THE MODEL IS VERIFIED

 WHETHER
VERIFIED AT A POINT, OR
AVERAGED OVER A GRID BOX
ETA THREAT SCORES HAVE BEEN
LOWER THAN THOSE FROM THE
SUBJECTIVE AND AVN GUIDANCE
Regional ETA verification using
model grid (80 km)
WARM SEASON 1.00” OR MORE VERIFICATION
VERIFIED TO AN 80 KM GRID
.64
.15
.59
.19
.35
.09
.98
.15
.65
.14
.47
.08
.93
.17
.83
.12
.97
.18
Regional ETA verification using
model grid (80 km)
COLD SEASON 1.00” OR MORE VERIFICATION
VERIFIED TO AN 80 KM GRID
.69
.17
.71
.27
.58
.10
.94
.18
.74
.09
.71
.15
BIAS
ETS
1.07 1.36
.23 .22
1.04
.19
AGAIN NOTE HIGH BIAS ALONG EAST COAST
AND LOW BIAS OVER WEST
Regional ETA verification using
model grid (80 km)
.01” OR GREATER AMOUNTS DURING COLD SEASON
VERIFIED TO AN 80 KM GRID
1.43
.25
.81
.37
.95
.26
1.05
.35
1.23
.23
.79
.32
1.07
.35
1.11
.34
1.07
.35
HIGHEST THREATS ALONG WEST COAST.
HIGH BIAS OVER UPSLOPE AREAS EAST
OF ROCKIES AND OVER PLAINS
Regional ETA verification using
model grid (80 km)
.01” OR GREATER AMOUNTS DURING WARM SEASON
VERIFIED TO AN 80 KM GRID
1.11
.28
1.00
.37
.82
.23
.92
.37
1.21
.19
1.01
.32
.81
.34
.96
.39
.99
.38
BIG DIFFERENCES WITH POINT VERIFICATION. USING A
POINT VERIFICATION, YOU SEE THE HUGE BIASES OVER
THE SOUTH
ETA .50” OR MORE PERFORMANCE
DURING WARM SEASON
VERIFIED TO AN 80 KM GRID
.77
.21
.82
.28
.88
.12
1.09
.25
.82
.17
1.07
.24
1.10
.23
.62
.14
BIAS
ETS
.86
.20
DURING SUMMER ETA UNDERPREDICTS
.50” OR GREATER AMOUNTS IN PLAINS.
MESO-ETA HAS SAME BIAS
ETA PERFORMANCE FOR .50 OR
GREATER AMOUNTS APR 96-NOV 97
VERIFIED TO AN 80 KM GRID
.89
.23
1.00
.83 .15
.35
1.10
.23
.97
.13
.90
BIAS
THREAT
1.13
.31
1.10
.26
.23
ETA OVERPREDICTS .50 OR
GREATER ACROSS SOUTH AND
ALONG EAST COAST. MESO-ETA
HAS SAME BIAS
1.32
.31
PRIOR TO THE CHANGES LAST
SUMMER, THE ETA MODEL WAS
BEST



AT HANDLING ARCTIC AIRMASSES
PLUNGING SOUTHWARD ALONG THE
FRONT RANGE OF THE ROCKIES
FORECASTING PRECIPITATION ALONG THE
WEST COAST INCLUDING THE CASCADE
AND SIERRA RANGES
USUALLY BEST IN FORECASTING COLDAIR DAMMING ALONG THE EAST COAST
(ITS LI FORECAST IS OFTEN THE BEST
INDICATOR)
IN CONCLUSION


THE ETA MODEL HAS HAD SERIOUS PROBLEMS SINCE
3DVAR WAS IMPLIMENTED.
PRIOR TO 3D-VAR ETA QUANTITATIVE PRECIPITATION
FORECASTS WERE BETTER THAN THOSE OF THE AVN.



AVN PRECIPITATION FORECASTS HAVE BEEN SUPERIOR
DURING THE PAST 7 MONTHS
BETTER VERIFICATION IS NEEDED OF OPERATIONAL
MODELS. THE VERIFICATION NEEDS TO BE SHARED WITH
FORECASTERS. EMC IS NOW MAINTAINING A VERIFICATION
SECTION ON ITS HOMEPAGE.
EACH TIME A MODEL IS CHANGED, IT MAY AND PROBABLY
WILL CHANGE THE PERFORMANCE CHARACTERISTICS.