Here are a few forecasting tips that will hopefully help you when trying to
get an idea of that target area. Scroll down to the bottom of the page for links to popular forecasting sites.
FORECAST PARAMETERS
Look for 850mb winds of 25 knots or more.
Look for 850mb Td of 10 degrees C or more.
Look for 500mb winds of 40 knots or more.
A 500mb temp of -6C or higher will suppress vigorous convection.
When the 700mb temp is 14C or higher T-storm activity is unlikely without a
major triggering mechanism.
You need dry air at 700mb for supercell development. A T-Td spread more
than 5C with a Td less than 0C.
Look for 300mb winds of 70 knots or more.
Look for a 45 degree veering of winds between the surface and 700mb.
In May, June look for 500mb temps of -13C or colder for severe WX.
In March, April, and October look for 500mb temps of -15C or colder for
severe WX.
Look for a surface pressure of 1005mb or less.
Look for a freezing level of 615mb or lower for large hail.
The CCL should be below 780mb.
The LFC should be below 660mb.
On 850 mb maps Look for convergence, divergence, confluence, and diffluence.
Air rises due to low level convergence and confluence.
Low level warm air advection contributes to synoptic scale rising air; Low
level cold air advection contributes to synoptic scale sinking air.
850 mb Chart is good for assessing low level warm air and cold air
advection.
A vertical velocity of 6 -ub/s is significant while a vertical velocity of
10 or greater is very significant (also need moisture!).
The main objective when looking at 850 mb charts is to look for WAA and CAA.
The main objective when looking at 500 mb charts is vorticity.
A rough guide to the intensity of a vort max is: less than 14: small
vorticity; 14 to 20: moderate; 22+ large. The value of the vorticity maximum
does not tell the whole story. For strong upward motion to result with a
vort max, there must also be a strong wind flow (long wind vectors) flowing
through the vort max.
A FRZ level with a pressure level of 650 mb or closer to the surface in a
severe weather situation generally will support large hailstones.
A negatively tilted trough is a trough that is oriented from the NW to the
SE.
A positively tilted trough is a trough that is oriented from the NE to the
SW.
Shortwaves are best examined on the 700 and 500 millibar charts.
The 500 millibar chart is one of the best charts for studying the
following: vorticity advection, the trough/ridge pattern, and shortwaves.
Jet streaks within the jet stream cause air, which is closer to the surface
of the earth, to rise due to a vacuum effect the jet streaks create. As a
jet streak enters into a trough, it can energize the trough causing the low
pressure to deepen and heights to fall. A strong jet streak will have winds
of 120 knots or greater.
The atmosphere can become thermodynamically unstable by solar heating of
the earth's surface.
Adding moisture to the low levels of the atmosphere makes the atmosphere
more unstable.
Low level instability can be rapidly brought about by warm air along with
moisture advection (bringing of a warm and humid airmass into a region).
Cooling the middle and upper levels of the atmosphere causes the atmosphere
to become more unstable.
Strong speed and directional wind shear can cause the atmosphere to become
more unstable. Examples include: Jet streaks, vorticity, low level jet, low
level horizontal vorticity.
Cold air advection into the midlevels of the atmosphere and warm air
advection into the low levels can also lead to a steep (much greater than
normal) lapse rate. A steep lapse rate is indicative of an unstable
atmosphere.
For severe weather to be associated with cold fronts, look for the
following: high dewpoints ahead of the front (60 F or greater), strong upper
level winds (300 mb wind greater than 120 knots), front movement between 10
and 20 mph, and convergence along the front. Storms tend to be strongest on
the southwest edge of the frontal boundary due to a combination of the
following: higher dewpoints, more convective instability, cap breaks there
last, uninhibited inflow into storms, storms are generally more isolated and
thus realize more convective energy.
WARM FRONTS: Severe weather generally occurs on the warm side of the warm
front but is most favorable in the vicinity of the warm front boundary. This
is due to the fact that the greatest directional wind shear is located along
the warm front boundary. When storm chasing warm front convection, a good
location would be to stay near the warm front boundary while at the same
time being relatively close to the mid-latitude cyclone which connects to
the warm front. As a general rule, severe weather is not as common along
warm front boundary as compared to out ahead of cold front boundaries for
these reasons: A smaller frontal slope results in less frontal convergence,
east of the Rockies convective instability (dry air in mid-levels) is not as
well defined with warm fronts, convection tends to be more horizontally
slanted, the temperature gradient from one side of the frontal boundary to
the other is generally less in association with warm fronts.
DRYLINES: The higher the dewpoint gradient from one side of the dryline to
the other is a good indication of dryline intensity. Critical point: No
convergence along the dryline results in NO storms. Drylines are most common
in the high plains in the Spring and early Summer. Certain factors must be
in place for a dryline to produce severe convection. As mentioned, the most
critical is convergence. This convergence can be intensified by a
combination of the following: Strong upper level winds overriding the
dryline (can produce dryline bulge), warm moisture rich air being advected
directly toward the dryline boundary (e.g. 850 mb Southeast wind at 30 knots
ahead of the dryline, West wind at 35 knots behind dryline), and a upper
level trough. Severe storms in association with drylines tend to be classic
or LP supercells. The shallowness of moist air ahead of the dryline boundary
limits the amount of PW and moisture the storms can convect. The cap is
critical to determining if a dryline will produce storms. If convergence is
not strong enough, the cap (inversion above PBL) will prevent convection
from occurring. Strong convergence will break the cap. Generally, drylines
are most intense and significant when a mid-latitude cyclone over the High
or Great Plains forces warm moist air from the Gulf and dry air from the
high plains to advect over the top of the warm moist air.
Why is a moisture tongue important?
1. They are associated with low level instability. Warm and moist PBL air
enhances a large thermodynamic instability.
2. The high speed air associated with a moisture tongue fuels developing
thunderstorms by producing a large storm relative inflow and helicity (speed
and directional shear in the PBL).
3. Warm air advection and moisture advection are a dynamic lifting
mechanism (warm moist air is less dense which causes a stretching and
subsequent dynamic lifting of the low levels of the atmosphere).
4. Since a moisture tongue is a region of instability, thunderstorms often
develop and become strongest within the moisture tongue region.
5. Precipitable Water values (PWs) will be higher in the moisture tongue.
6. Isentropic lifting of a moisture tongue can cause widespread
precipitation north of a warm front.
DYNAMIC TRIGGER MECHANISMS: Without a trigger mechanism, such as when a
strong cap is present, storms may not form. Here are examples of dynamic
trigger mechanisms:
1. dryline
2. cold or warm front
3. outflow boundary
4. jet streak
5. strong upper level vorticity
6. orographic lifting
7. low level warm air advection (strong gradient of warmer temperature
moving toward a fixed point)
8. Low level jet
9. Gravity waves
10. Meso-lows
PBL WIND SHEAR: Speed shear (wind speed increasing with height in the PBL);
directional shear (wind veering, turning clockwise more than 45 degrees in
the PBL); Average PBL wind greater than 20 knots (It has been found that for
tornadoes to develop the PBL inflow needs to be greater than 20 knots, the
higher the better)
The best chart to use when
examining the trough / ridge pattern is the 500-millibar chart.
The atmosphere is most unstable when a large trough in association with a
strong mid-latitude cyclone becomes NEGATIVELY TILTED. Why? Because on the
right side of the trough, the negative tilt causes cold air advection in the
upper levels of the atmosphere while the PBL is warm and humid (especially
if this situation occurs east of the Rocky Mountains in the fall or spring).
Cold air above warm air creates thermodynamic instability and convective
instability. A strong jet streak can cause a trough to become negatively
tilted and contributes to dynamic lifting. It is the jet stream and jet
streaks that are responsible for causing troughs to become more amplified or
less amplified. The jet streaks also contribute to the tilt of a trough.
Look at the 500-mb chart each day and see if the troughs over the US are
highly or weakly amplified and positive, neutral, or negatively tilted.
DEGREES
WIND BLOWING FROM THIS DIRECTION
360
N
75
NE
90
E
135
SE
180
S
225
SW
270
W
315
NW
CAPE
Value Degree
of Instability
0-1000
Marginally Unstable
1000-2500 Moderately Unstable
2500-3500 Very Unstable
>3500 Extremely Unstable
EHI
Value Supercell/Tornado
Potential
<2.0 Significant mesocyclone-induced
tornadoes unlikely to occur
2.0-2.4
Mesocyclone-induced tornadoes
possible, but unlikely to be strong or long-lived
2.5-2.9
Mesocyclone-induced tornadoes
likely
3.0-3.9
Strong tornadoes (F2-F3) possible
> 4.0
Violent tornadoes (F4) possible
NOTE: These guidelines assume
mid-level winds > 25 kts and 0-2 km storm-relative inflow >
20 kts
Lifted Index (oC) Degree of Instability
0 to -3 Marginally Unstable
-3 to -6 Moderately Unstable
-6 to -9 Very Unstable
Less than -9 Extremely Unstable
SPC Convective Outlooks
SPC Hourly Mesoscale Analysis Page
SPC Mesoscale Discussions
SPC Forecast Tools
SPC Current Convective Watches
National Weather Service
CAPS
UCAR
College of DuPage Weather Lab
Oklahoma Weather Roundup
Unisys Weather
NWS Forecast Maps/Models
HPC Short Range Forecast (Days 1 and 2)
Texas A&M Weather Interface
Real-Time ADAS ARPS Data Analysis System
STORM TRACK Weather Data Page
Texas Forecast Discussions
Oklahoma Forecast Discussions
Kansas Forecast Discussions
New Mexico Forecast Discussions
Colorado Forecast Discussions
Nebraska Forecast Discussions
College of DuPage Wind Profilers
SSEC Infrared Satellite
SSEC Visible Satellite
SSEC Water Vapor Satellite
GOES-10 Visible Satellite Image
Texas A&M Soundings Page
Various Sounding Plots
Skew-T Sounding and Hodograph Plots
College of DuPage Radar Sites
West Texas Mesonet Site
Oklahoma Mesonet Site
Kansas Mesonet Site
Southern Plains Surface Plot
Central Plains Surface Plot
Current Lightning Strikes
Last but not least. This site is probably the best weather site I have ever found on the internet for all around weather knowledge and forecasting. It covers all topics and aspects of forecasting weather and everything in between.
Weather Prediction.com
Hopefully these sites will help you to become a better chaser and forecaster!
POPULAR NOAA RADIO FREQUENCIES
TEXAS
Abilene 162.400
Amarillo 162.550
Borger 162.400
Dallas 162.400
Lubbock 162.400
Midland/Odessa 162.400
Plainview 162.450
San Angelo 162.550
Wichita Falls 162.475
COLORADO
La Junta 162.500
Lamar 162.525
Springfield 162.400
KANSAS
Dodge City 162.475
Goodland 162.400
Hays 162.400
Meade 162.425
Topeka 162.475
Tribune 162.550
Ulysses 162.450
Wichita 162.550
NEW MEXICO
Albuquerque 162.400
Clovis 162.475
Des Moines 162.550
Hobbs 162.400
Roswell 162.450
OKLAHOMA
Altus 162.425
Ardmore 162.525
Clinton 162.525
Enid 162.475
Lawton 162.550
Oklahoma City 162.400
Stillwater 162.500
Tulsa 162.550
Woodward 162.500
If you have any forecasting
tips you would like to send then please
e-mail
me and I will post them
|