Transcript PRTpres_10_08

Forecasting in the Field:
How to read the weather without a TV
or computer
What Conditions Do We Consider
Hazardous?
http://www.photos12-vintage.com/images/Explorateur_Latreille.jpg
http://www.alpine-guides.com/images/ski%20avalanche%20safety.jpg
http://www.co.cumberland.nc.us/
http://www.utahweather.org/
Outline

Some weather basics

Know Before You Go

Ok, so I see this cloud...

Practice Scenarios
Weather Basics- Solar Radiation
The sun shines...
Rock heats faster than grass/trees/bushes.
clouds!
What
happens
when you
heat the
ground?
Warm air rises!
Weather Basics- Fronts
What does this
mean for us?
Weather changes
depending on
where you are in
relation to the
fronts.
Weather Basics- Fronts
L
Weather Basics- Fronts
Cold Front Clues
Increased winds from
the south
 Increase in
temperature, “muggy”
feeling
Air pressure begins to
drop
Clouds thick, merge,
lower, and get darker

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter11/g
raphics/cf_xsect.jpg
Weather Basics- Fronts
Warm Front Clues
Approaching high
clouds
Stratus clouds
Surface winds from
east to southeast
Increase in air
temperature
Thickening, lowering
clouds

http://www.physicalgeography.net/fundamentals/images/warmfro
nt.GIF
Know Before You Go!
“We thought we had a window
in the weather, but we were
wrong.”
Know Before You Go!
The local National
Weather Service
webpage is a good
place to start.
Discussion is written by a NWS
forecaster- it explains why they
created the forecast the way they
did.
http://www.weather.gov/
Click on
the map
to change
your
location.
Mesowest: Surface Observations
Click on a station to get data for that location.
http://www.rap.ucar.edu/weather/
Forecast- see models
How to Build a General Idea of What Is Going to Happen
Check the NWS forecast to get a basic idea (read the forecast
discussion- pay attention for forecast uncertainty)
If no storm systems (fronts) are forecast, check Mesowest to see
if there are any weather stations in the area you plan to visit.
If you want, look at the RAP site to see satellite imagery- see if
there are clouds, afternoon thunderstorms, etc. (Do this the day
before to see what time thunderstorms develop)
Check sites for the area you’re visiting (park websites, etc.). See if
they have a webcam- these can give you a good idea of what is
going on.
Uncertainty in Forecasting
There is ALWAYS some
uncertainty in forecasting.
Summer hazards (afternoon
thunderstorms) tend to be
localized, short-lived, and
very difficult to predict.
Winter hazards tend to
occur on a larger scale, but
these events (cold fronts)
are more predictable.
Summer Hazards
Desert: Flash floods
Mountains: Lightning (and rain)
Bottom line:
How do we tell if
there’s going to be
a thunderstorm?
North American Monsoon
What is a monsoon?
A seasonal wind shift.
Moist air moves into the
Western US in July,
August, and September.
http://www.cpc.noaa.gov/products/outreach/Report-to-theNation-Monsoon_aug04.pdf
The NAM acts as a
moisture source for
afternoon thunderstorms.
Mountain Thunderstorms
What time of day do they form?
Why do they form some days and not
others?
Where do they form?
Afternoon
Moisture
Generally, over the
peaks. May move in
direction of mean flow.
Mountain Thunderstorms
First, pathetic little
clouds of the day!
Few hours later
Mountain Thunderstorms
Still later.... what differences do you
see?
Mountain Thunderstorms
Cumulus clouds as they continue to grow vertically.
Mountain Thunderstorms
anvil
Sometimes thunderstorms go so high that they hit
the tropopause- which is the layer between the
troposphere and stratosphere. Clouds can’t
continue to grow into the cold air of the
stratosphere, so the top of the cloud spreads out.
Mountain Thunderstorms
Mountain Thunderstorms
Will I be endangering my life if I go into an area and
thunderstorms occur?
Were there thunderstorms yesterday? When did they
occur? What time?
Are there clouds in the sky now? What do they look like.
Continue to monitor the development of cumulus cloudsif they continue to grow, there could be thunderstorms.
Have a plan in case thunderstorms occur.
Winter Hazards
Desert: Flash floods (to some
extent)
Mountains: Snow, ice, wind,
lightning leading to avalanches,
hypothermia, etc.
Bottom line:
Look at the
weather before you
go!!!
Winter Hazards
Many of these hazards
come from storm
systems moving into
the western US.
Whether or not a storm
will happen is not
difficult to predict- after
all, they are fairly large
and obvious.
The timing of these storms is another story.
Winter Hazards
Above: Visible satellite
Top Right: Radar
Left: View from campus
as the front approaches
Salt Lake.
Photo by Greg West
Signs of an Approaching Front
Cirrus clouds
Indication of
upper-level
moisture
These clouds
frequently precede
a storm by 24-48
hours.
http://www.theweather.com.au/uploads/sundog_tn.jpg
Signs of an Approaching Front
Lenticular Clouds
Another indicator of
moisture
Can be followed by
precipitation in 24-48 hours
www.livingwilderness.com
“When Mt. Rainier
wears a hat, rain is
likely to soon
follow.”
http://thudhead.blogspot.com/2007_02_01_archive.ht
ml
Signs of an Approaching Front
Other signs that a front could be approaching
Clouds that get lower with time (like cirrus turning to
altocumulus turning to stratus)
Gusty winds, especially from the south
Listen to your instinct- if it’s a big storm, you will feel
the energy of the atmosphere.
Other Helpful Resources
Mountain Weather- Jeff Renner
Book about backcountry forecasting and weather
safety
Mountain Meteorology- Dave Whiteman
The textbook on mountain meteorology
Jim Bishop’s Mountain Thunderstorm Document
(http://www.fs.fed.us/psw/cirmount/wkgrps/gloria/publi
cations/pdf/Bishop_mtn_thunderstorms_031607.pdf)
U of U Meteorology Department!
http://www.met.utah.edu