November: Feast or Famine By Derek Arndt Assistant State Climatologist Oklahoma Climatological Survey 12/2/03 Another November has ended and will go on the record as dry. November 2003 precipitation totals are about an inch below the statewide normal of 2.83 inches. That puts it pretty close to the middle of the historical population. How can this be? Well, two factors are at play here. First, the 30-year normal precipitation totals for November are near their highest levels ever, due to very wet Novembers during the 1980s and 1990s. Second, November is a very bipolar month in the climate record, much like its autumn brethren September and October. In other words, November is either significantly wet, or significantly dry, but hardly ever in between. The likelihood of total precipitation landing within a quarter-inch of the long-term average for the month is quite low: it happens about once every nine or ten years in most of Oklahoma's climate divisions. In fact, falling within an inch (plus or minus) of the long-term average is a 50-50 proposition for most of Oklahoma. Out of the 109 Novembers on record since 1895, the table below shows the number of times the precipitation has been within a quarter-inch, half-inch or inch of the long-term average: Climate Long-term Within Within Within Division Average Qtr-inch Half-inch an inch Panhandle 0.88" 27 of 109 44 of 109 93 of 109 N. Central 1.64" 13 of 109 30 of 109 49 of 109 Northeast 1.43" 15 of 109 23 of 109 44 of 109 W. Central 1.43" 14 of 109 28 of 109 64 of 109 Central 2.15" 11 of 109 29 of 109 47 of 109 E. Central 3.18" 13 of 109 26 of 109 41 of 109 Southwest 1.48" 11 of 109 26 of 109 58 of 109 S. Central 2.46" 15 of 109 28 of 109 41 of 109 Southeast 3.98" 14 of 109 17 of 109 31 of 109 Obviously, the occurrences are relatively larger in the western divisions because the long- term average is so low (for example, a month with zero precipitation is within an inch of the panhandle's 0.88" average). So, let's look at the same issue, but break it down by percentages. Here's a table showing how often the November precipitation is within 10%, 25% or 50% of the long-term average. Climate Long-term Within Within Within Division Average 10 % 25 % 50 % Panhandle 0.88" 8 of 109 22 of 109 41 of 109 N. Central 1.64" 11 of 109 20 of 109 40 of 109 Northeast 1.43" 17 of 109 30 of 109 55 of 109 W. Central 1.43" 9 of 109 22 of 109 46 of 109 Central 2.15" 8 of 109 32 of 109 48 of 109 E. Central 3.18" 15 of 109 32 of 109 60 of 109 Southwest 1.48" 6 of 109 20 of 109 41 of 109 S. Central 2.46" 15 of 109 31 of 109 52 of 109 Southeast 3.98" 17 of 109 30 of 109 53 of 109 Just for clarity, the criterion for that last column is this: if a November is between the long-term average and plus or minus HALF of that long-term average, it counts. In parts of Oklahoma, almost two-thirds of Novembers are outside this range! So, a significantly dry (or wet) November is certainly not uncommon. What is significant about this November is that it follows several very dry months in a row. The cumulative effect of these low-precipitation months is causing significant-to-severe problems for much of the western half of the state. Media Contact: For Additional Information: Cerry Leffler Derek Arndt Public Relations Specialist Assistant State Climatologist Oklahoma Climatological Survey Oklahoma Climatological Survey 100 E. Boyd, Suite 1210 100 E. Boyd, Suite 1210 Norman, OK 73019-1012 Norman, OK 73019-1012 (405) 325-2541 Phone (405) 325-2541 Phone (405) 325-2550 Fax (405) 325-2550 Fax cerry@ou.edu darndt@ou.edu