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.

Eta Model Physics

EXPLICIT CLOUD PREDICTION SCHEME (large scale)

The BMJ Convective Scheme

More about the BMJ scheme

The BMJ scheme

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

FOR ANY MODEL, ALWAYS BEWARE OF THE 1ST GUESS

WHAT HAPPENED?

A POOR INITIAL ANALYSIS CAN PRODUCE HUGE FORECAST ERRORS

IN THE PAST, ETA MODEL HAS HAD PROBLEMS PREDICTING THE STABILITY. PROBLEM IS OFTEN TIED TO THE 1ST GUESS

WHEN HIGH SOIL MOISTURE IS PRESENT, OR WHEN THE MODEL FIRST GUESS THINKS THE SOIL MOISTURE IS HIGH,

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

Forecast -Vs- Observed Best Cape
Spring 96

MORE ON ETA PERFORMANCE

ETA AND STORM TRACKS

COMMON ETA ERROR ALONG EAST COAST

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 LOW VERIFIES A LITTLE NORTH AND EAST OF THE NGM. REMEMBER, THE NGM IS TYPICALLY TOO SLOW WITH LOWS ALONG THE COAST.

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:

The Eta predicted a major east coast snowstorm. The NGM and AVN predicted light snow at best

HOW THE MODEL VERIFIED. NO MAJOR SNOWSTORM DEVELOPED.

LOWS TO THE LEE OF THE ROCKIES

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.

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.

The eta underplays the second shortwave diving into the mean trough and overplays the first one.

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.

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

Why models have problems with arctic airmasses

THE NGM AND AVN/MRF HAVE SERIOUS PROBLEMS WITH ARCTIC AIRMASSES.

WHEN USING MODELS, PATTERN RECOGNITION REMAINS IMPORTANT!

DO THE FORECASTS LOOK CONSISTENT WITH WHAT YOU SEE IN THE PACIFIC? CHECK SSMI DATA

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

THE MODEL’S TERRAIN IS AVERAGED OVER THE GRID BOX SO THE SLOPE OF THE TERRAIN IS USUALLY NOT STEEP ENOUGH

THINGS TO REMEMBER ABOUT MODEL QPFS IN COMPLEX TERRAIN DURING WINTER

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

IF THE MODEL IS SO DRY DURING THE SUMMER IN THE PLAINS, HOW DO I USE IT?

BOUNDARY LAYER WIND AND TEMPERATURE FORECAST V.T. 00Z 18 JULY

A STRONG LOW LEVEL JET IS PRESENT WITH LOTS OF MOISTURE. THIS IS A TYPICAL MADDOX TYPE SET UP.

OOZ 18 JULY FORECASTS OF

IS THIS A GOOD QPF? DO YOU THINK THE RAINFALL IS ORIENTED CORRECTLY

HOW DID YOU DO?

VERIFYING PRECIPITATION

MODEL BIAS AND THREAT SCORE

Slide 52

Regional ETA verification using model grid (80 km)

ETA .50” OR MORE PERFORMANCE DURING WARM SEASON

ETA PERFORMANCE FOR .50 OR GREATER AMOUNTS APR 96-NOV 97

PRIOR TO THE CHANGES LAST SUMMER, THE ETA MODEL WAS BEST

IN CONCLUSION