September 2009 in Review (UPDATED)

UPDATE: I’ve updated the post with NOAA’s statewide rankings maps for temperatures and precipitation.  Click “read more” and scroll to the bottom for the images.

At the beginning of the month, we took a look at the monthly weather outlook from CPC.  As promised, it’s time to take a look back and review the accuracy of the forecast as well as highlight the weather around the country for the past month.

To refresh the memory, here’s the CPC’s forecast for temperature departure from normal for the month of September:

CPC Outlook for September 2009.  Data are temperature departure from normal.

CPC Outlook for September 2009. Data are temperature departure from normal.

To summarize, here’s a table of cities in the southwest where temperatures were forecast above normal for the month.  I should note these data are preliminary, although the average temperatures shouldn’t change too much with the final weather summary.  If necessary, I’ll update the post later this week.

City Average September Temp Departure from Normal
Brownsville, TX 82F 0.9F
Del Rio, TX 79.2F -1.0F
Midland, TX 72.3F -1.7F
El Paso, TX 75.3F -0.2F
Albuquerque, NM 68.3F -0.9F
Phoenix, AZ 90.1F 2.6F
Flagstaff, AZ 59.2F 1.2F
Las Vegas, NV 86.7F 5.2F

b

In retrospect, it appears only the western portion of the above-normal area truly experienced the forecast conditions for the month. In fact, it should’ve been extended northward throughout much of the intermountain west. Salt Lake City, UT (6.1F), Elko, NV (6.2F), Boise, ID (7.0F), Reno, NV (7.7F), and Spokane, WA (5.2F) all experienced average temperatures well above normal for the month of September.

As for the northeast corner of the US, here’s their data for September:

City Average September Temp Departure from Normal
Bangor, ME 57.3F -1.7F
Millinocket, ME 56.9F 0.5F
Houlton, ME 53.6F -0.7F
Caribou, ME 54.5F 0.5F
Portland, ME 59.2F 0.3F
Concord, NH 58.1F -1.5F
St. Johnsbury, VT* 56.8F -1.8F

*St. Johnsbury, VT will not have a final monthly weather summary.

Judging by these data, it does not appear the forecast verified.  There are a few sites reporting monthly mean temperatures slightly above normal, but one could argue these values are within a normal range for expected monthly averages.  Furthermore, the sites with below normal values, of which there are more, show greater departures from the mean than the other sites.

Looking around much of the Northeast, it appears temperatures this month were near normal to slightly below normal.  In the Midwest, temperatures ran about 2-3F above normal while temperatures across the central and southern Plains were generally 1.5-2.5 F below normal.

Now, let’s take a look at the precipitation for the month.  Here’s the CPC forecast from the beginning of the month:

CPC Outlook for September 2009.  Data are precipitation departure from normal.

CPC Outlook for September 2009. Data are precipitation departure from normal.

Here is a look at precipitation totals out west in OR, CA, and NV:

City Total September Precip Departure from Normal
Burns, OR 0.08 in -0.40 in
Medford, OR 0.08 in -0.67 in
Redding, CA 0.12 in -0.33 in
Reno, NV Trace -0.44 in

b

Hard to say the CPC forecast was anything but accurate given these totals.  Job well done.

Here are the data for the forecast above normal locations in the nation’s heartland:

City Total September Precip Departure from Normal
Omaha, NE 1.72 in -1.36 in
St. Joseph, MO 2.72 in -1.06 in
Sioux City, IA 4.56 in 2.21 in
Sioux Falls, SD 1.21 in -1.30 in
Des Moines, IA 1.22 in -1.84 in
Mason City, IA 1.94 in -1.25 in
Hastings, NE 2.81 in 0.14 in

b

Generally, it appears the forecast was way off as most cities experienced below normal precipitation for the month. Somehow, Sioux City, IA managed nearly twice as much precipitation as normal.  According to the daily records, Sioux City received over three inches on September 3rd.  Other stations in the area received rain, but nowhere near three inches.  Either something was wrong with the rain gauge or Sioux City just happened to be under heavy rain for an extended period of time.

A little research finds this archived radar summary from Plymouth State College (NH):

It appears a significant storm passed through the area and the more intense areas of the storm remained nearly stationary over Sioux City for several of the very early morning hours.  I suppose this is the explanation.  It’s a great example how localized summer thunderstorms can affect monthly, seasonal, or even annual precipitation totals.

Finally, let’s take a look at FL:

City Total September Precip Departure from Normal
Jacksonville, FL 6.48 in -1.21 in
Orlando, FL 4.58 in -1.04 in
Tampa, FL 5.24 in -1.15 in
Fort Myers, FL 4.95 in -2.74 in
Ft Lauderdale, FL 3.91 in -4.09 in
Naples, FL 11.24 in 3.34 in
Key West, FL 5.01 in -0.27 in

b

With the exception of Naples, all other Florida cities recorded below normal precipitation for the month. In the case of Naples, they received several days with around an inch of rain, so we can’t point to just one day for the significant bump in precipitation.  We can say, in general, that this forecast was inaccurate.  This isn’t surprising given the total lack of tropical storms and hurricanes in what should be the busiest month of the season.

So where did it rain this September?  Exactly where it was needed – central TX.  Dallas, San Antonio, and Brownsville all recorded 2+ inches above normal for the month after experiencing drought conditions for several months.  Other areas in the southern Plains received normal to above normal precipitation.

We’ll see how this relates to the Fall forecast now that we’re 1/3 of the way through the season in a future post.  Also, we’ll take a look at the October outlook tomorrow.  Here’s a quick tease: there’s actually below normal temperatures forecasted somewhere in the US for the month.

UPDATE: Here are the statewide rankings for temperature and precipitation for the month of September:

Click for larger image

Click for larger image

Click for larger image

Click for larger image

The warmth experienced in the West was record-setting, especially in CA and NV where they experienced their warmest September on record.  The cooler temperatures in the South and Northeast are verified here.  In addition to the needed precipitation in TX, points east received near-record amounts of rain for the month of September.  You can read NOAA’s full press release here.

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