Forecasting in the Field: How to read the weather without a TV or computer

Forecasting in the Field:Forecasting in the Field:How to read the weather without a TV How to read the weather without a TV

or computeror computer

What Conditions Do We Consider Hazardous?

http://www.photos12-vintage.com/images/Explorateur_Latreille.jpghttp://www.alpine-guides.com/images/ski%20avalanche%20safety.jpghttp://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.

L



Cold Front Clues

Increased winds from the south Increase in temperature, “muggy” feelingAir pressure begins to dropClouds thick, merge, lower, and get darker

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter11/graphics/cf_xsect.jpg


Warm Front Clues

Approaching high cloudsStratus cloudsSurface winds from east to southeastIncrease in air temperatureThickening, lowering clouds

http://www.physicalgeography.net/fundamentals/images/warmfront.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 HappenHow 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-the-Nation-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.


First, pathetic little clouds of the day!

Few hours later

Still later.... what differences do you see?



Cumulus clouds as they continue to grow vertically.


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.

anvil



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 clouds- if 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

Photo by Greg West

Above: Visible satelliteTop Right: Radar Left: View from campus as the front approaches Salt Lake.

Signs of an Approaching Front

http://www.theweather.com.au/uploads/sundog_tn.jpg

Cirrus clouds

Indication of upper-level moisture

These clouds frequently precede a storm by 24-48 hours.

www.livingwilderness.com

http://thudhead.blogspot.com/2007_02_01_archive.html


Lenticular Clouds

Another indicator of moisture

Can be followed by precipitation in 24-48 hours

“When Mt. Rainier wears a hat, rain is likely to soon follow.”


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 RennerBook 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/publications/pdf/Bishop_mtn_thunderstorms_031607.pdf)

U of U Meteorology Department! http://www.met.utah.edu

Documents

Forecasting in the Field: How to read the weather without a TV or computer