So they do flip coins.

Here's how the National Weather Service has created this week's forecast for Pittsburgh:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
335 PM EDT SUN JUN 2 2002

IN THE FACE OF RECENT MODEL DISPARITIES...OPTED TO GO MORE THE ETA 
RUN FOR DAYS 1-2 THEN AVN FOR DAYS 3-4 AND MRFX AND RELATED 
ENSEMBLES FOR DAYS 5-7.

ETA HAS MIDWEST SYSTEM MOVING EASTWARD ALONG WARM FRONT AND 
AFFECTING THE HEAD OF THE OHIO REGION MONDAY...PERHAPS NOT TIL 
AFTERNOON FOR WESTERN PENNSYLVANIA AND NORTHERN WEST VIRGINIA. 
TEMPERATURES WILL STRUGGLE TO MAKE THE UPPER 60S. CONCUR WITH HPC 
THINKING THAT THERE MAY BE HEAVY THUNDERSTORM RAINFALL MONDAY 
NIGHT...CONSIDERING THE INCREASE IN MOISTURE AND LIFT WITH THE 
NORTHWARD MOVING WARM FRONT. THE AVERAGE RAINFALL IN MANY BASINS 
SHOULD EXCEED 1 INCH. 

ON TUESDAY...ETA HAS THE HEAD OF THE OHIO REGION IN THE WARM 
SECTOR...WITH HUMID CONDITIONS. THE ETA AND AVN SHOW AT LEAST TWO 
SMALLER SCALE SOURCES OF LIFT MOVING THROUGH THE REGION THEN. 
DIURNALLY THE BEST OPPORTUNITY FOR THUNDERSTORMS WILL BE AFTERNOON 
AND EARLY EVENING. 

THE AVN THEN SHOWS THE SPLIT UPPER FLOW OUT WEST DEVELOPING AN UPPER 
LEVEL TROUGH IN THE MIDWEST. THE OPERATIONAL MRF SHOWS THE DEEPEST 
DEVELOPMENT OF THIS SYSTEM WITH A CUTOFF BY THURSDAY. HOWEVER THIS 
IS AN ENSEMBLE OUTLIER...AND USING HPC THINKING FROM RECENT 
DISCUSSIONS...WENT WITH THE MRFX AND THE GENERAL LOCUS OF ENSEMBLE 
SOLUTIONS...THAT SHOWED THE MIDWEEK MIDWEST TROUGH PROGRESSING 
EASTWARD TO THE EAST COAST THIS WEEKEND. THIS WAS LIKEWISE SUPPORTED 
BY THIS MORNINGS AVN RUN. SO KEPT SHOWERS AND THUNDERSTORMS FOR 
WEDNESDAY AND THURSDAY...BUT THEN WENT TO DRY CONDITIONS FOR FRIDAY 
AND THE WEEKEND. 

FOR TEMPERATURES...WENT CLOSER TO ETA MOS FOR MONDAYS HIGHS...A 
BLEND OF ETA AVN AND NGM MOS FOR TUESDAY...AND MRF ENSEMBLE MEANS 
MOS FOR DAYS 4-7. ...GIORDANO