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The SPC
Enhanced Resolution Thunderstorm Outlooks 
The Storm Prediction Center (SPC) in Norman,
Oklahoma issues convective outlooks depicting thunderstorm and severe
thunderstorm threats across the continental United States.
The Day 1 (today) and Day 2 (tomorrow) outlooks are issued as a
forecast valid over a 24 hour period, although the initial Day 1
outlook
(upper right) issued at 0600 UTC is updated or reissued four times
throughout the
day. In addition to the severe risk categories (SLGT, MDT and
HIGH), the Day 1 and Day 2 convective outlooks contain a forecast
depicting a
10-percent or higher probability of thunderstorms during the valid
period. This 10-percent line (shown in brown) essentially
encompasses the
areas (to the right of that line) where the SPC believes are the
greatest risk for organized deep,
moist convection.
Since the
Day 1 and Day 2 thunderstorm outlooks cover a 24 hour period with only
the
10-percent probability contour, they provide little in the way of
temporal or spatial resolution. These outlooks are fantastic
planning tools, but from a general aviation pilot's perspective, a
valid period of 24 hours isn't as useful given that most flights are
six hours or less in duration. The SPC now produces a product
with a higher temporal and spatial resolution. This new
product is called the Enhanced Resolution Thunderstorm
Outlook (shown upper left). It is currently in an
experimental status, but will likely become an operational product.
During the daytime and early evening
hours when thunderstorms are the
most active, the SPC issues three enhanced thunderstorm outlooks valid
for a four hour period. These include outlooks valid 1600 UTC
- 2000 UTC, 2000
UTC - 0000 UTC and 0000
UTC - 0400 UTC. These outlooks
are initially issued at 0600 UTC and updated again by the SPC at 1300
UTC. At 1630 UTC, the SPC updates the latter two outlooks
above and
issues the "overnight" outlook valid 0400 UTC - 1200 UTC.
Each of these enhanced outlooks
(example shown on the right) could contain
10-percent, 40-percent and
70-percent contours for the probability of thunderstorms during the
valid forecast period. This allows the pilot to identify the
thunderstorm threat much better in time and space than the operational
Day 1 convective outlook.
When using this product, keep in mind
that the later outlooks will
typically contain less certainty. For example, most pilots
will typically look at this product in the morning even if they are
making a flight later in the afternoon or evening. The 0000
UTC - 0400 UTC outlook may contain a
40-percent contour when it was initially issued at 0600 UTC.
As the weather unfolds and the forecaster is more certain of the
outcome, a 70-percent contour may be added at 1630 UTC when the product
is updated.
Currently
there isn't an enhanced outlook issued for the period from
1200 UTC through 1600 UTC. The SPC is considering adding this
outlook in the future.
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