Forecast Day Announcements Grading example Forecast Exercise Topics

Announcements • Horiz_Motion is due Mar 13 at 11: 59 AM (noon). • Test

Grading - an example Mar 8, 2002 This number is junk AFTER 25 Forecasts

Grading - an example 36 * 10 Forecasts Forecasting (25%): 245/360 = 17 Problem

Wind speed and direction Help Inside Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences

Wind directions at the surface L Mar 8, 2002 H Cinzia Cervato, Dept. Geol&Atm

Wind Speed Wide Spacing Less than 2 isobars across Iowa < 5 knots 2

This Year’s Pressure Field Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002

Last Year’s Pressure Field Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002

Advection Need to know. . . . 1) Wind speed and direction and 2)

Think warm thoughts Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 11

50 s 40 s 60 s No Advection Cold Advection Warm Advection Mar 8,

COLD Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 WARM 13

Quiz #9 Question 1 Which position will have the strongest warm advection? a. A

Quiz #9 Question 2 Which position will have the strongest cold advection? a. A

Quiz #9 Question 3 Which positions will have the least advection? a. A and

Quiz #9 Question 4 Which statement is true according to the figure? a. Greater

Predicting Advection for tomorrow You need both: 1. wind speed TWC and NCAR 1.

Determine the wind for tomorrow morning (12 z) Live internet Now remember the wind

Determine the temperature gradient Visualize the wind in relation to the isotherms over IA.

Do we pick cold advection then? Minimum conditions: 10 knot wind blowing directly across

Even if you pick “No”, you must evaluate three precip influences! Mar 8, 2002

If Precipitation is NO , why is Moisture Supply YES. . . ? ?

The likely and unlikely combinations of Precipitation and Precip Influences Precip Moisture Frontal Chance

Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 25

Unstable? We need to know the temps at each level. The 25 degree difference

It reads. . “A temperature difference between 850 mb and 500 mb which is

We now need to introduce you to forecast maps, that is, computer generated predictions.

Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 29

If you check all 4 boxes, use the last 3 sets of maps if

Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 31

To calculate stability for this time over Iowa (Careful of timing!! Example 00 UTC

Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 33

Slides: 33

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Forecast Day • Announcements • Grading example • Forecast Exercise Topics • Wind Speed and Direction • Advection Quiz • Precipitation and Precipitation Influences • Moisture Supply • Stability • Q & A -- Extra Credit Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 1

Grading - an example 36 * 10 Forecasts Forecasting (25%): 245/360 = 17 Problem sets (30%): 253/287= 27 Quizzes (17%): 21/22 = 16 Exam 1 (7%): 65/100 = 4. 6 Exam 2 (7%): 75/100 = 5. 3 Total (4 tests @ about 5% per test) = 80 or AEnough extra credit (max 5%) would put this grade to an ACinzia Cervato, Dept. Geol&Atm Mar 8, 2002 4 Sciences © 2002

Wind Speed Wide Spacing Less than 2 isobars across Iowa < 5 knots 2 -3 isobars across Iowa 5 -15 knots 3 -4 isobars across Iowa 10 -20 knots 4 -5 isobars across Iowa 15 -30 knots Narrow Spacing Cinzia Cervato, Dept. Geol&Atm Mar 8, 2002 7 Sciences © 2002

Quiz #9 Question 4 Which statement is true according to the figure? a. Greater advection occurs ahead of the warm front than behind the cold front b. Greater advection occurs ahead of the cold front than behind the warm front c. Greater advection occurs ahead of the fronts than behind them d. Greater advection occurs behind the fronts than in front of them Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 17

Do we pick cold advection then? Minimum conditions: 10 knot wind blowing directly across a temperature gradient of 10 F over the space of IA Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 21

If Precipitation is NO , why is Moisture Supply YES. . . ? ? Getting a rain storm is like getting a fire…… Fuel you need Mar 8, 2002 Match and a INSTABILITY IS THE GASOLINE to start a fire. Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 23

The likely and unlikely combinations of Precipitation and Precip Influences Precip Moisture Frontal Chance Supply Position Comments no no no Likely Logical situation yes yes Likely Logical situation no no yes Likely No fuel no yes no Likely No match no fire yes no Likely Nonfrontal lifting yes no yes Unlikely Moisture not at 850 mb no yes Match and fuel not together at the same time Cinzia Cervato, Dept. Geol&Atm Mar 8, 2002 yes no fire no Unlikely Sciences © 2002 24 Unlikely Spontaneous combustion

Unstable? We need to know the temps at each level. The 25 degree difference (criteria value) determines a lapse rate. This is like determining which people are taller at different levels 500 mb Mar 8, 2002 850 mb Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 26

It reads. . “A temperature difference between 850 mb and 500 mb which is at least 25 degrees Celsius is representative of this conditional instability and favors upward motion of cloudy air parcels and, thus, precipitation. ” Recall that the more the temperature cools with height in the atmosphere the more unstable it is. We have selected this test as an estimate of something between 10 C/km and 6 C/km Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 27

If you check all 4 boxes, use the last 3 sets of maps if before 9 pm use the first 3 sets of maps if after 9 pm. Make sure of the times. x x Mar 8, 2002 x x Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 30

To calculate stability for this time over Iowa (Careful of timing!! Example 00 UTC 2/23 is 6 pm the 22 nd) T(850) - T(500) is -13 - (- 25) = -13 + 25 = 12 This is less than 25 so the condition is stable. How about unstable in terms of cloud development? ? … See the next slide. . . Mar 8, 2002 Cinzia Cervato, Dept. Geol&Atm Sciences © 2002 32