Map of rainfall across the Rio Grande Valley and Deep South Texas, December 2009 - February 2010 (click to enlarge) Map of rainfall departures from the 1971-2000 thirty year average across the Rio Grande Valley and Deep South Texas, December 2009 - February 2010 (click to enlarge)
What A Difference A Year Makes
Wet, Cool December–February 2009/10 Contrasts Warm, Dry December–February 2008/09

Overview
That raw, damp, wet feeling that pervaded Deep South Texas during the now completed meteorological winter (December through February), requiring jackets, sweaters, and rain gear at the ready, has now been confirmed in a preliminary analysis of this season's data: The December, 2009/2010 winter was among the top ten wettest for most locations, and among the top 25 coolest. If not for a mid January thaw, where temperatures ranged some 8 to 12 degrees above average, the entire winter may well have ranked in the top ten coolest, as well.

Rainfall Capsule
Some quick, preliminary statistics as of March 1st: For Brownsville, the seasonal rainfall of 10.33 inches (6.68 inches above the 1971–2000 average) ranked second wettest, all time, behind 1957’s huge 15.50 inches. Contrast that to this time in 2009, when the December to February rainfall was only 1.05 inches, or the 5th driest. A similar wet/dry contrast was noted at McAllen’s Miller Airport, where the Winter of 2009/10 had a whopping 8.30 inches of rain (4th wettest, 4.54 inches above the 1971–2000 average) compared with a paltry 0.75 inches (7th driest) in 2008/09. Other locations around the Rio Grande Valley and Deep South Texas showed the same tendencies.

Temperature Capsule
Including the January 18-28 ‘thaw’, the 2009/10 winter was a marked change from the much warmer winter of 2008/09. Unofficially, Brownsville’s 59.1°F average temperature ranked 25th coldest, a full 2°F below the 1971–2000 value (61.6°F) and the coldest since 1983/84. Contrast this with 2008/09, when the 65.3°F average, some 6°F above this past winter, rated a 9th place tie for warmest winter (records since 1878). For the Harlingen Cooperative site, the 57.39°F average fell 2.72°F shy of the 60.11°F 1971–2000 marker; in 2008/09, the same site’s 63.9°F value, more than 6.5°F higher than this past winter, ranked in the top 20 warmest (records since 1911). For McAllen/Miller, the 2009/10 average of 59.6°F fell 2.2° shy of the 1971–2000 marker, (61.8°F); ranking it 10th coolest since records began in 1960/61. Contrast this season with 2008/09, when the 65.8°F average, also a little more than 6°F higher, was a full 4°F above the marker and ranked 6th warmest, all time (since 1961).

Rainfall Table
The following are selected rainfall totals for December 2009–February 2010 across Deep South Texas.

Preliminary rainfall, winter 2009/2010
Location County Rainfall
Laguna Atascosa NWR
Cameron
13.31
South Padre Island Isla Blanca
Cameron
13.13
Port Isabel
Cameron
12.03
Rancho Viejo
Cameron
11.93
Sarita 7 E
Kenedy
11.53
San Benito 5.0 SSE
Cameron
10.85
Rio Hondo 9.4 NE
Cameron
10.82
Bayview/Cameron Co. Arpt
Cameron
10.68
Brownsville 4.1 E
Cameron
10.58
Brownsville 2.2 W
Cameron
10.51
Brownsville/SPI Intl Arpt
Cameron
10.33
Los Fresnos
Cameron
10.22
Port Mansfield
Willacy
10.14
Armstrong
Kenedy
10.00 (estimate)
Falfurrias
Brooks
9.88
McAllen 1.7 SSE
Hidalgo
9.85
Harlingen Cooperative
Cameron
9.84
Weslaco Cooperative
Hidalgo
9.72
Harlingen 2.6 ESE
Cameron
9.66
Hebbronville
Jim Hogg
9.42
McAllen 2.6 NE
Hidalgo
9.28
Pharr 5.1 N
Hidalgo
9.11
Alamo 1.5 NNE
Hidalgo
8.88
Linn/San Manuel NWR
Hidalgo
8.75
McAllen/Miller Arpt
Hidalgo
8.30
Mercedes
Hidalgo
7.70
Rio Grande City
Starr
7.55
Palm Valley 2.2 W
Cameronq
7.28
Falcon Lake
Starr
6.95
Harlingen/Valley Int'l Arpt
Cameron
6.26*
Falcon Dam
Zapata
5.13
*Rainfall may have been undermeasured.

Temperature Table
The following are selected Deep South Texas temperature averages, and departures, contrasting the winter of 2008/2009 (warmer than average) with the winter of 2009/10 (cooler than average), based on the 1971–2000 thirty–year averages.

Preliminary Temperature Assessment and Comparison
Location County Winter 09/10 Average Winter 08/09 Average 30 Year Average 2009/10 Departure 2008/09 Departure
Weslaco 2 E
Hidalgo
57.28
64.1
61.7
-4.42
+2.4
Hebbronville
Jim Hogg
53.3
60.4
57.7
-4.4
unkn
Falfurrias
Brooks
53.61
60.0
57.67
-4.06
+2.33
Rio Grande City
Starr
55.55
62.1
58.79
-3.24
+3.31
Raymondville
Willacy
56.47
63.2
59.7
-3.23
+3.5
Harlingen/Valley Intl
Cameron
57.2
64.7
60.47
-3.2
+4.3
Port Isabel
Cameron
58.2
63.6
61.36
-3.16
+2.24
Falcon Dam
Zapata
56.0
62.4
58.75
-2.75
+3.65
Harlingen/Coop
Cameron
57.39
63.9
60.11
-2.72
+3.79
Port Mansfield
Willacy
56.04
62.4
58.65
-2.61
+3.85
Santa Rosa 3 WNW
Cameron
58.1*
64.2
60.4
-2.3
+4.2
McAllen/Miller
 
Hidalgo
59.6
65.8
61.8
-2.2
+4
Brownsville/SPI Intl
Cameron
59.1
65.3
61.1
-2
+4.2
McAllen/Coop
Hidalgo
58.66
64.3
60.36
-1.7
+3.97
Sarita 7 E
Kenedy
52.77
60.5
n/a
n/a
n/a
Bayview/Cam. Co arpt
Cameron
57.88
65.35
n/a
n/a
n/a
Mercedes
Hidalgo
57.38
63.1
n/a
n/a
n/a
* More than 10% of data are missing as of writing.

Rainfall Charts
The following are charts showing contrasts in rainfall for the winters of 2008/09 and 2009/10, for most cooperative and airport locations across Deep South Texas. Departures are based from the 30 year average, 1971–2000.

Rainfal Chart #1 Rainfall Chart #2
Rainfall Chart #3 Valley Area Airports Rainfall Chart

How It Happened, In Brief
El Niño was generally expected to result in a great opportunity for above average winter rainfall when we wrote about it late last summer; indeed, the experts’ forecast for a moderate bordering on high El Niño/Southern Oscillation Index played out almost perfectly. As autumn slid into winter, the increased subtropical jet stream developed almost on cue, and the rains began as November turned to December. The chill felt in Deep South Texas was likely from a combination of the increased cloud cover along with a persistent negative Arctic Oscillation teleconnection, which aided the import of colder air behind developing storm systems moving from the northern Gulf through the Mid Atlantic region. El Niño looks to be holding on as we move into early spring. For more on the possible evolution of Deep South Texas weather conditions as we move through March and April, click here.

Map of United States Weather and selected impacts, December 2009 through February 2010 (click to enlarge)
United States Weather Impacts, in general, for the winter of 2009/2010. Cyan dashed arrow across the northern U.S. and Canada shows typical mid latitude jet stream; red dashed arrow (hidden by many impacts) across the southern U.S. shows typical subtropical jet stream. Surface storm track is shown by large "L".

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