The revised product will be made publicly available on this website
in early May 2009.
Part 1 - Mission Connection
The Storm Prediction Center is the National Weather Service’s center
of expertise for forecasting convection, including economically-disruptive
weather events such as tornadoes, large hail, damaging winds and
heavy rainfall. Included within the convective outlooks is a forecast
for a 10% or greater probability of thunderstorms.
Since these thunderstorm forecasts cover a 24 hour period with only
the 10% probability contour, they provide little in the way of temporal
or spatial resolution.
Forecasts of thunderstorms are critical for the protection of life
and property since every thunderstorm contains lightning that is a
This Product Description Document replaces the existing PDD, whose
evaluation period expired on 15 February 2008, and revises the current
experimental SPC thunderstorm guidance product based on customer and
The revision to be tested this year provides greater temporal detail
to aid NWS aviation weather partners including NWS WFOs and to support
time-sensitive decisions related to thunderstorms.
This year’s test will also evaluate changes in the distribution of
SPC forecaster workload and the ability to maintain this product
for all scheduled convective outlook times.
The current enhanced resolution thunderstorm outlook was suspended
on 27 February, 2009 to facilitate transition to the new experimental
The SPC will again make the revised thunderstorm outlooks open to
all customers through its web site at
Web feedback from the broader community will be sought via an internet
link beginning on 7 April 2009 and ending on 5 February 2010, at
which time a decision to proceed with testing, revise the test or
to continue on the path to operational production will be made.
Internal NOAA evaluation will proceed the return to the public website
which is scheduled for Tuesday 5 May 2009.
Since the product will be in the public domain, this outlook can be
repackaged and re-transmitted in accordance with standard NWS product
Pending continued success, the SPC plans to distribute these probabilistic
thunderstorm outlooks via AWIPS and the NDFD for use by both NWS
WFOs and NOAA partners.
An NWS Public Information Statement (PNS) Service Change Notice (SCN)
will be issued prior to official operational product distribution.
Part II - Technical Description
Only a forecast for 0400 - 1200 UTC will be produced in conjunction
with 0100 UTC Day 1 Convective Outlook.
The issuance and valid times of the new product will be:
Issue Time Valid Periods (UTC)
0600Z 1600-2000, 2000-0000, 0000-0400
1300Z 1600-2000, 2000-0000, 0000-0400
1630Z 2000-0000, 0000-0400, 0400-1200
2000Z 0000-0400, 0400-1200
Each of these forecasts will contain 10%, 40% and 70% contours for
the probability of thunderstorms during the forecast period.
Similar outlooks have been produced both internally and publicly
by the SPC for three years and verification indicated these
forecasts are skillful and statistically reliable.
These thunderstorm hazard probabilities will provide SPC customers
and partners with information to help provide better public safety
for the United States public.