Weather Delays When Should They Be Granted?

Transcription

1 Weather Delays When Should They Be Granted? If Weather Data is Normally Distributed, When Is the Weather Abnormal? Marty Cuerdon Senior Consultant 1

2 Weather Delays Normally Excusable but not Compensable (Contractor gets time but no money.) Exceptions (when weather delays = $): Liquidated Damages Owner delay pushed work into inclement weather. 2

3 Weather Delays Contractor has the burden of proving three conditions 1. The weather condition was adverse, i.e., it impacted construction operations. 2. The weather was unusual, i.e., it could not have been foreseen by the contractor. 3. The completion date was impacted by the delay, i.e., critical path activities were delayed. 3

4 Weather Delays Two Types of Weather Delays Generally Recognized 1. Direct impact Scheduled activity not performed because of an adverse weather event, i.e., workers sent home. 2. Indirect impact Scheduled activity duration extended due to the effects of an adverse weather event, i.e., lowered worker productivity during the weather event and/or lingering effect of the event. 4

5 Weather Delays Applicable Weather Events Temperatures (High, Low, Threshold Frequencies) Precipitation (Amounts, Effects, Frequencies) Snowfall (Amount, Duration, Impact on Operations) High Wind (Dust, Impact on Crane Operations, Painting) 5

6 Weather Delays Contractually Shared Risk Contractor assumes the risk of delays due to normal weather conditions. Owner and Contractor each assume the cost of their individual extended overhead costs due to delays from abnormal weather conditions. 6

7 Weather Delay Contract Language: AIA 201 (1997 ed.) If adverse weather conditions are the basis for a Claim for additional time, such Claim shall be documented by data substantiating that weather conditions were abnormal for the period of time, could not have been reasonably anticipated and had an adverse impact on the construction schedule. 7

8 Weather Delay Contract Language: Federal Acquisition Regulation (48 CFR (b)) (b) The Contractor s right to proceed shall not be terminated nor the Contractor charged with damages under this clause, if (1) The delay in completing the work arises from unforeseeable causes beyond the control and without the fault or negligence of the Contractor. Examples of such causes include (i) acts of God or of the public enemy, (v) floods, [or] (x) unusually severe weather. 8

9 Weather Delay Contract Language: USACoE Regulation Definitions.... b. Unusually severe weather weather that is more severe than the adverse weather anticipated for the season or location involved. 9

10 Weather Delays Undefined Threshold In the absence of specific contractual guidelines, however, it may be difficult to determine in advance the point at which adverse weather satisfies the threshold requirement for becoming an excusable delay. Under typical contract language, there is no bright-line rule, and an excusable delay is generally one triggered by events that are not self-defining, such as unusually severe, adverse, or abnormal weather conditions. (Bret Gunnell, Adverse Weather and the Construction Process, Construction Briefings No. 98-6) 10

11 New Weather Delay Methodology? Analytical Challenges 1. Contractually define a bright line boundary between normal weather and abnormal weather. 2. Calibrate the results of the methodology to adjust to the amount of risk the parties have negotiated. 11

12 New Weather Delay Methodology Probability statistics can be used to calculate adverse weather recurrence intervals in the same way the 100 Year Flood is calculated. Contractual Weather Delay language could be modified to define the specific recurrence interval. (10 Years, 20 Years, etc.) 12

13 50% 45% Standard Normal Probability Distributions 100% 90% Instant Probability 40% 35% 30% 25% 20% 15% 10% 80% 70% 60% 50% 40% 30% 20% Cumulative Probability 5% 10% 0% % No. of Standard Deviations From the Mean 13

14 40% Standard Normal Probability Distribution 35% 30% 50% Area = +/ Std Dev Probability 25% 20% 75% Area = +/ Std Dev 15% 10% 5% 90% Area = +/ Std Dev 95% Area = +/ Std Dev 99% Area = +/ Std Dev 0% Number of Standard Deviations From Mean Value 14

15 September October November December No. of Occurances 150 Month August July June May April March Histogram of Daily Mean Temperature Mean Temp February Denver, Colorado Source: Stapleton NWS January 15

16 August Daily Mean Temperatures, Denver Colorado Source: NWS Stapleton Airport Descriptive Statistics Number of Occurences No. of Observations = 1673 Average Mean Temp = Modal Mean Temp = 73 Medial Mean Temp = 72 Standard Deviation = 4.67 Skew of Distribution = Correlation to Normal = 98.71% Confidence Intervals Standard Normal Curve 50 50% % % % % Daily Mean Temperatures (Degrees F) 16

17 Number of Occurrences August Monthly Precipitation Denver, Colorado Source: NWS Stapleton Airport Monthly Precipitation (Inches) Descriptive Statistics No. of Observations = 54 Avg Monthly Precipitation = 1.60 Median Monthly Precipitation = 1.23 Standard Deviation = Skew of Distribution = 2.16 Correlation to Normal = 82.70% 17

18 Weather Delay Recurrence Interval Mathematical Formula Recurrence Interval = 1 / (1-Cumulative Probability) Example 100 Year Recurrence Interval = 1 / (1 0.99) Formula with Excel Spreadsheet Probability Function Recurrence Interval = 1/(1 - NORMINV(probability,mean,standard_dev,TRUE)) (10 Year Probability = 0.90, 20 Year = 0.95, 50 Year = 0.98, 100 Year = 0.99) 18

19 Daily Maximum Temperatures Daily Mean Temperatures Daily Minimum Temperatures Monthly Sum of Cooling Degree Days (Base=65F) Monthly Sum of Heating Degree Days (Base=65F) Monthly Sum of Precipitation Monthly Sum of Snowfall Stapleton Airport, Denver, Colorado, Weather Data ( ) Monthly Data Summaries Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Highest Daily Max Highest Monthly Mean Max Lowest Monthly Mean Max Avg Daily Max Std Dev Max Daily Mean Min Daily Mean Avg Daily Mean Std Dev Lowest Daily Min Highest Monthly Mean Min Lowest Monthly Mean Min Avg Daily Min Std Dev Max Min Avg Std Dev Max 1,502 1,190 1, ,051 1,466 Min Avg 1, ,013 Std Dev Max Min Avg Std Dev Max Min Avg Std Dev

20 No. of Days with Temperatures >100 Degrees No. of Days with Temperatures > 90 Degrees No. of Days with Maximum Temperatures < 32 Degrees No. of Days with Minimum Temperatures < 32 Degrees No. of Days with Minimum Temperatures < 0 Degrees No. of Days with Precipitation > 0.01 Inches No. of Days with Precipitation > 0.10 Inches No. of Days with Precipitation > 0.50 Inches No. of Days with Precipitation > 1.00 Inches Stapleton Airport, Denver, Colorado, Weather Data ( ) Monthly Frequency Summaries Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev Max Min Avg Std Dev

21 Weather Delays Recurrence Interval Methodology Example: Denver s electric utility company wanted an excusable delay for installing an underground service connection because the high number of 90+ Degree days in the Summer of The weather caused high electric power demand, strained the electrical distribution system, created lots of outages and diverted their distribution crews from completing their underground service connection. 21

22 Historical Monthly 90 Degree Days vs 2001 Denver Colorado Year High 25 Monthly Days Exceeding 90 Degrees F Yr Low /- One Standard Deviation 53 Yr Avg 5 0 Jan Feb Mar Apr Historical Data: No. of Days with temperatures > 90 Degrees May Jun Jul Aug Sep June July August 3 Month Total Max Min Avg St. Dev Actual Data: No. of Days with temperatures > 90 Degrees Calculated Recurrence Interval (Years) No. of Excusable Days Based On Recurrence Interval (Year) Threshold of: Oct Nov Dec 22

23 Weather Delays 2 nd Recurrence Interval Methodology Example: Should contractors be granted excusable delays for Denver s historical March 2003 Blizzard? 23

24 Colorado's Worst Blizzard in 90 years! Up to 7 Feet of Snow!! March 17-19, 2003 (DENVER) - Governor Bill Owens announced today that President Bush has approved Owens' request for federal assistance to help financially-strapped cities and counties defray large portions of the costs of snow removal during the state's March blizzard. 24

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26 Denver's March 2003 Monthly SummaryDenver's March 2003 Monthly Summary (How to read this form) *****FOR UNOFFICIAL USE ONLY***** **THIS DATA AVAILABLE ON THE INTERNET: **The National Climatic Data Center (NCDC: is the official source of climate data** Preliminary Local Climatological Data (WS Form: F-6) Station: DENVER INTERNATIONAL AIRPORT Month: MARCH Year: N = Latitude W = Longitude Gnd Elev ft Std Time: MST Temperature in Fahrenheit :Precip : Snow :Wind :Fastest 2-Min: Sunshine : Sky :Peak Wind Columns a-6b Day Max Min Avg Dep. HDD CDD Water Snow Depth Avg. Speed Dir Mins. %PSBL SR-SS Weather Speed Dir T M M % 1, T M M % M M % M M % 1, T M M % 1, M M % M M % M M % M M % M M % M M % M M % M M % M M % M M % M M % M M % 8,3, M M % 1, M M % M M % M M % 1, M M % M M % M M % 1, M M % M M % T M M % T M M % M M % M M % M M % Sum Avg Fast Dir % Max Dir NOTE: SNOWFALL AND SUNSHINE DATA MEASURED BY COOP OBSERVERS AT THE FORMER STAPLETON INTERNATIONAL AIRPORT. [Temperature Data] [Precipitation data] Symbols used in column 16 Average Monthly: 40.0 Total for Month: 3.05 Departure from Normal: +0.4 Departure from Normal: = Fog Highest: 75 on 14 Greatest in 24 hrs: 1.53 on 17 2 = Fog reducing visibility Lowest: 7 on 5 to 1/4 mile or less SNOWFALL, ICE PELLETS, HAIL 3 = Thunder Records: 03/2003 5th wettest March Total for month: 35.2 inches 4 = Ice Pellets 03/2003 now snowiest March " Greatest snowfall in 24 hrs:22.9 on = Hail 13-Tied record high 74 last set 1989 Greatest snow depth: 22 on 19 6 = Glaze or Rime 18-Record 24 hr precip 1.53 old = Blowing dust or sand reducing 19-Record 24 hr precip 0.74 old 0.31 visibility to 1/2 mile or less [No. days with] [ WEATHER -No. days with] 8 = Smoke or haze 9 = Blowing snow Max 32 or below: inch or more precip: 7 X = Tornado Max 90 or above: inch or more precip: 3 Min 32 or below: inch or more precip: 3 Min 0 or below: inch or more precip: 1 [Heating Degree Days (Base 65) ] [Cooling Degree Days (Base 65) ] [ Pressure Data ] Total this month: 768 Total this Month: 0 Highest Sea-Level on 29 Departure from Normal: -20 Departure from Normal: 0 Lowest Sea-Level on 17 Seasonal Total: 5225 Seasonal Total: 0 Departure from Normal: -52 Departure from Normal: 0 26

27 14 March Monthly Precipitation Denver, Colorado Source: NWS Stapleton Airport Descriptive Statistics Number of Occurrences March 2003 Monthly Total Precipitation = 3.05" Includes "100 Year Blizzard" No. of Observations = 54 Avg Monthly Precipitation = 1.26 Median Monthly Precipitation = 1.16 Standard Deviation = Skew of Distribution = 3.24 Correlation to Normal = 83.66% Monthly Precipitation (Inches) 27

28 16 March Monthly Snowfall Denver, Colorado Source: NWS Stapleton Airport Descriptive Statistics Number of Occurrences No. of Observations = 54 Avg Monthly Snowfall = 12.7 Median Monthly Snowfall = Standard Deviation = 7.1 Skew of Distribution = 0.60 Correlation to Normal = 96.43% New Record March 2003 Monthly Total Snowfall 35.2 Inches Monthly Snowfall (Inches) 28

29 Weather Delays Denver March 2003: Memorable or Biblical Month? March Monthly Totals Monthly Monthly Precipitation Snow Total Totals Max Min Avg Std Dev March 2003 Actual Totals Recurrence Interval (Years) , Historical March Monthly Data From Stapleton Airport 29

30 Weather Delays Limitations to Recurrence Interval Methodology 1. The national weather service does not provide standard deviation data which is a critical element in calculating recurrence probabilities. Standard deviations must be calculated from detailed historical weather data. 2. A weather station with insufficient historical data and/or is located too remote from the construction jobsite may give misleading results. 30

31 Weather Delay Contract Language: Suggested Addition Existing AIA 201 (1997 ed.) Language If adverse weather conditions are the basis for a Claim for additional time, such Claim shall be documented by data substantiating that weather conditions were abnormal for the period of time, could not have been reasonably anticipated and had an adverse impact on the construction schedule. Suggestion Additional Language Reasonably anticipated weather conditions are defined as those conditions that have a probable statistical recurrence interval of less than or equal to years, as determined from a minimum of 20 years of daily weather data from the national weather bureau station located at. 31

32 Weather Delays Internet Weather Data Source Sites Denver-Boulder Weather Data: National Climatic Data Center: Worlds Largest Archive of Weather Data High Plains Regional Climate Center: (ND, SD, NE, KS, WY, CO) Midwest Regional Climate Center: (MN, IL, IA, WI, MO, KY, OH, IN, MI) Northeast Regional Climate Center: (ME, NH, VT, MA, RI, CT, NY, PA, MD, NJ, WV, DE) Southeast Regional Climate Center: (AL, FL, GA, NC, SC, VA, PR, and VI) Southern Regional Climate Center: (TN, MS, LA, TX, AR, OK) Western Regional Climate Center: (MT, WY, CO, NM, ID, UT, NV, AZ, WS, OR, CA, AL, HA) Am. Association of State Climatologists: Weather Delay Research Website: Commercial Weather Collection Service: Weather Channel: Good source of current weather forecasts but does not have historical weather data. Accuweather: 32