I’m still waiting to see official observations from the CoCoRaHS network and other coop stations reporting to the National Weather Service…

SPC Day 1 Categorical Outlook, for Thursday 2/2/12. A slight risk of severe thunderstorms exists across parts of the southern plains.

On Thursday 2/2/12, while atmospheric conditions across the D/FW Metroplex are ripe for supporting thunderstorms, the lack of any lifting agent like a cold front or upper level trough will fail to spark any thunderstorm initiation during the daytime. Late Thursday into Friday however will be different…

SPC Day 2 Categorical Outlook, for Friday 2/3/12. A slight risk of severe thunderstorms exists between Oklahoma City, to Dallas/Fort Worth, then east to Little Rock.

Thunderstorm development should be in full swing across the Texas Panhandle on late Thursday near the center of the low pressure. A cold front attached to this low will be pushed eastward across our region and provide focus for significant thunderstorm development.

Scattered strong to severe thunderstorms are quite possible anytime between Thursday evening to Friday evening as the low pressure system strengthens. Dallas/Fort Worth will remain in the warm sector for most of this event, which places us in a zone of favorable thunderstorm development. While thunderstorms are quite possible Thursday evening through Friday evening, the main event in D/FW will occur Friday afternoon and evening.

Concerns outlined with the upcoming severe weather event are the standard hail and high winds, while a potential for tornadoes exists too. One other concern not typically observed with thunderstorms of this nature is flash flooding. Conditions may actually be favorable for multiple strong or severe thunderstorms to train over the same locations for hours at a time, leading to a localized flash flooding problem.

For a more advanced look into the upcoming weather, my own personal analysis of computer models shows a few separate instances of thunderstorm explosion. A few weak disturbances in the mid-atmosphere rotate around the jet stream and across the area before the main low pressure system arrives and cold front passes through. The atmosphere will be ripe for convection, so these weak disturbances rotating through should be all that is needed to kick off a few bursts of storms before the main event Friday evening. The first wave of t-storms may be very late evening Thursday, close to midnight.

BUFKIT displaying the NAM model’s forecast Skew-T Profile for Friday 2/3/12 1:00 AM. 

The above Skew-T profile shows ample lift in the mid-atmosphere (the white line around 20,000 ft indicates about -10 omega, or rising/lifting air) around 1:00AM Friday morning. CAPE values of around 1000 J/kg with no inhibition and ample moisture throughout the entire profile, and I’d say strong to possibly severe storms are expected. Lapse rates close to 7° C/km should support moderate hail development, and as the storms will be surface based a high wind risk exists too. Hodographs don’t appear ideal, but do show a potential for some tornado development.  0-2 KM shear of about 25kts and helicity of around 200 does indicate tornado development may be possible with some stronger storms, though these values aren’t ideal. Finally lifted index values of around -3° C do indicate a slightly to moderately unstable atmosphere throughout the entire event.

One final advanced analysis of the upcoming weather, flash flooding may actually be a concern with these storms. Storm motion appears to be NNE around 15 mph, but the overall propagation of thunderstorms may be southeastward near 10 mph. This sets up a scenario where multiple thunderstorms may train across the same areas for a few hours at a time, and create flash flooding concerns. Flash flooding may actually be the single most severe weather event out of these upcoming storms, funny enough.

Stay safe everyone, and keep watching the skies the next two days!

Radar estimates about 0.25 inches of rain across most of the metroplex, except north DFW where an estimated 1.5 inches fell.

You can see that CoCoRaHS reports actually verify the radar’s estimated rainfall fairly well. The radar may have even underestimated total rainfall in some areas.

CoCoRaHS.org volunteer network rain reports for the 24-hr period ending 1/26/12 7:00am CST. 

The entire region had at least some measurable precipitation the last 24 hours, which is great news for the drought stricken lone star state!

4.26 inches of rain fell at Dallas/Fort Worth Airport, while 4.49 inches fell at Dallas Love Field. See the complete list of 24-hour preliminary rainfall totals below.

EDIT: Several area lakes rose by several feet due to the widespread heavy rain as well. See below for lake level increases.

Radar estimated storm total rainfall as of 11:00am CST 1/25/12.

...Preliminary 24 hour rainfall totals ending at 11 am...

...Anderson...
psnt2    Palestine crn                        1.97

...Bell...
nelt2    Temple                               2.83
tpl      Temple AWOS                          1.98

...Bosque...
aqlt2    Aquilla                              3.71
vmat2    Valley Mills                         3.15
ctnt2    Clifton                              3.14

...Collin...
ddnt2    Dallas alert 735(preston @ Olive rd) 5.32
prpt2    Prosper                              4.90
dwht2    desert water coop#2                  4.65
mckt2    McKinney                             4.41
tki      McKinney ASOS                        4.31
bvwt2    Blue Ridge                           4.16

...Comanche...
dllt2    deleon                               3.46
dsbt2    deleon                               3.20
coat2    Comanche RAWS                        2.96
mkn      Comanche AWOS                        2.56

...Cooke...
vvwt2    Valley View 4s                       4.23
gllt2    Gainesville                          2.99
gle      Gainsville muncipal                  2.52

...Coryell...

...Dallas...
dcct2    west joe's creek @ Walnut Creek      5.04
Dal      Dallas Love ASOS                     4.49
rbd      Dallas Red Bird ASOS                 4.36
gprt2    Grand Prairie                        4.24
adst2    Addison Airport                      4.07
gpet2    Mountain Creek Lake                  4.03
lnc      Lancaster Airport                    3.72
chit2    Cedar Hill 4ne                       3.72
dalt2    Dallas                               3.66
cdht2    Cedar Hill S.P. RAWS                 3.64
cart2    Carrollton                           3.37

...Delta...
sclt2    jim Chapman Lake                     2.52
copt2    Cooper                               2.41

...Denton...
dcjt2    Justin                               4.21
sget2    Sanger                               3.98
dto      Denton ASOS                          3.49
eflt2    Lewisville                           3.19
rrlt2    lake ray Roberts                     3.01

...Eastland...
llet2    Lake Leon                            2.87

...Ellis...
lwwt2    Lake Waxahachie                      4.45
avat2    Avalon #2 larc                       3.49
jwy      mid-way regional ap                  3.36

...Erath...
Sep     Stephenville                          4.18

...Falls...
hibt2    Highbank                             2.27

...Fannin...
ladt2    Ladonia                              3.49
cddt2    Caddo wildlife mngt                  2.91

...Freestone...
stet2    Streetman                            2.88

...Grayson...
covt2    Collinsville                         4.80
gyi      Sherman/Denison ap                   3.91
cvet2    Collinsville                         3.28

...Hamilton...
hict2    Hico                                 4.02
hmlt2    Hamilton                             2.33

...Henderson...
tddt2    Trinidad                             2.29
rhat2    Athens RAWS                          2.19

...Hill...
bbdt2    Brandon                              4.78
bumt2    Blum                                 4.33
inj      Hillsboro Airport                    3.60
aqat2    Aquilla creek blw dam                2.88
alat2    Aquilla lake                         2.53
mlet2    Malone                               2.21

...Hood...
gryt2    Granbury RAWS                        5.13
gdj      Granbury Municipal ap                4.61

...Hopkins...
subt2    Sulphur Bluff                        2.36

...Hunt...
lvtt2    Celeste                              4.49
msct2    Commerce                             2.99
scst2    Commerce                             2.82
gelt2    Greenville RAWS                      2.62
gvt      Greenville Airport                   2.56
gnvt2    Greenville                           2.34

...Jack...
tbmt2    bear mtn reptr (post office)         2.79
jakt2    Jacksboro                            2.60
tant2    Antelope                             2.38
tvtt2    Truce                                2.14

...Johnson...
vnst2    Venus                                4.01
cpt      Cleburne municpal ap                 2.98

...Kaufman...
cnlt2    Crandall                             3.74
kaft2    Kaufman                              2.62
trl      Terrell ASOS                         2.26

...Lamar...
myst2    pat mayse dam                        2.81
prx      Paris AWOS                           2.76
roxt2    Roxton                               2.70
cppt2    Cooper                               2.61

...Lampasas...
ltct2    Lometa                               2.22
nnxt2    Lampasas                             2.03
lmot2    Lometa                               2.00

...Limestone...
grst2    Groesbeck                            2.95
llmt2    lake Limestone Marin                 2.13

...Leon...
llst2    lake Limestone                       2.11

...McLennan...
mcgt2    McGregor                             3.01
act      Waco ASOS                            2.87
crft2    Crawford                             2.81
megt2    McGregor RAWS                        2.64

...Milam...
tdct2    Thorndale                            3.30
cmnt2    Cameron                              2.42

...Mills...
gect2    Goldthwaite                          2.57

...Montague...
mgut2    Montague                             3.03
bcat2    lake amon Carter                     2.38
0f2      Bowie                                2.37

...Navarro...
crs      Corsicana ASOS                       3.04
trht2    Richland                             2.33
rcet2    Rice                                 2.28

...Parker...
weat2    Weatherford                          4.15
bnct2    Cresson                              4.05
twrt2    Springtown (walnut c                 3.98
dnnt2    Dennis                               3.85
wtht2    Weatherford                          3.62
tagt2    Agnes                                2.11

...Robertson...
lhb      Hearne Airport                       2.46
rprt2    Round Prairie RAWS                   2.15

...Stephens...
bkd      Breckenridge AWOS                    1.76

...Somervell...
glrt2    Glen Rose                            3.65
grot2    Glen Rose                            3.30

...Tarrant...
eamt2    Eagle Mountain Lake                  4.53
mnft2    Mansfield                            4.49
gky      Arlington ASOS                       4.28
dfw      Dallas/Fort Worth ap                 4.26
bcht2    Fort Worth                           4.17
fwdt2    NWS Fort Worth                       4.10
nfw      ftw joint Reserve base               3.91
afw      ftw Alliance ASOS                    3.90
ftw      ftw Meacham ASOS                     3.84
fwot2    Fort Worth                           3.75
wftt2    Fort Worth                           3.73
ermt2    Everman                              3.73
gpnt2    Grapevine dam wx sta                 3.65
bnbt2    lake Benbrook                        3.61
fwht2    Fort Worth                           3.59
wrpt2    Fort Worth federal bldg              3.53
twft2    trwd sump 13                         3.43
tcet2    Cement Lake                          3.19
bmct2    marys creek                          3.19
tctt2    trwd sump 17                         3.15
twvt2    trwd sump 3                          3.08
tmct2    marine Creek Lake                    2.99
flwt2    Lake Worth                           2.79
cfbt2    Benbrook                             2.64

...Wise...
boyt2    Boyd                                 3.86
lud      Decatur Municipal ap                 3.07
avot2    Alvord 4ne                           3.07
lbjt2    LBJ Grasslands RAWS                  2.88
tsat2    Paradise (salt creek)                2.82
tcft2    Crafton                              2.70
tbnt2    Boonsville                           2.59

...Young...
lmgt2    Lake Graham                          2.93
sout2    South Bend                           2.63

          ....North Texas lakes are on the rise...

The widespread heavy event of the past 24 hours has brought some
significant recharge to the lakes in North Texas. Rainfall totals
averaged 3 to 5 inches across the area from midday Tuesday through
noon Wednesday. 

Lake                Lake elevation gain through 3pm Wednesday

Grapevine           3.1 feet
Lewisville          1.8 feet
Joe pool            2.7 feet
Lavon               2.5 feet
ray Hubbard         1.4 feet
ray Roberts         1.5 feet
Arlington           5.4 feet
Eagle Mountain      2.2 feet
Bridgeport          1.3 feet
possum kingdom      1.2 feet
Granbury            3.6 feet
Bardwell            2.2 feet
Richland Chambers   0.5 feet
Cedar Creek         0.5 feet
Whitney             1.5 feet

The rain will start Tuesday 1/24 in the early afternoon as a weak front slides by and stalls just south of the region. Elevated CAPE values around 500 J/kg with no CIN to inhibit storm growth, plus mid-level lapse rates near 7 degrees C/km should allow the production of hail with some stronger t-storms. Thunderstorms will likely be scattered and embedded within the overall wide-spread rain, but an isolated severe t-storm is possible.

Forecast NAM model Skew-T chart for Tuesday Jan 24 8:00pm CST. Red line is temp, green line is dew point. White line is ‘Omega’, indicating rising or sinking air. Thin yellow line indicates CAPE. This chart shows an almost fully saturated atmosphere below 17,000ft with plenty of rising air, and 534 J/kg of CAPE with almost zero inhibition from about 3,000 ft.

The heavy rain will continue overnight into Wednesday morning. Some additional thunderstorm development is possible early Wednesday morning around or just before sunrise, but these storms wouldn’t be strong or severe.

Expect the Wednesday morning drive to be difficult as very heavy rain combines with urban street flooding. A flash flood watch or warning wouldn’t be surprising to see on Wednesday. The heaviest rain will ease late afternoon Wednesday.

The rain will likely continue as light sprinkles or scattered rain showers until Thursday afternoon when it will likely end.

Forecast NAM model precipitation per hour, and precipitation total. Heaviest rainfall appears likely during the daytime Wednesday 1/25. Time progresses from right to left.

Forecast NAM model 96-hr total rainfall, from 1/23 12:00pm CST to 1/27 12:oopm CST. North Texas looks set to receive very heavy rain, in the 2-4 inch range.

A widespread rain like this may actually bring parts of north central Texas out of any official drought category, and help relieve a large portion of central Texas’ extreme drought conditions. Widespread rain like this is encouraging, signs that the brutal back to back La Nina winter seasons may finally be reaching an end.

A severe thunderstorm risk exists for the entire D/FW Metroplex starting early to mid afternoon Wednesday 12/14. A low pressure system moving rapidly to the northeast will send a pacific cold front through the region.

Strong wind shear profiles, upper level dynamics, and rich surface moisture are all very favorable for severe weather development. Some limiting factors however are low to moderate instability due to heavy cloud cover blocking daytime heating, and poor wind shearing near the surface limiting tornado genesis.

These limitations aside, severe weather development still appears to be quite a possibility at this time. Storms would likely be linear in nature, eventually forming a nearly unbroken line of thunderstorms.

My own personal analysis of forecasted Skew-T charts for 3:00pm CST Wed 12/14 indicates a risk of microbursts, due to a very pronounced slot of dry air in the mid atmosphere around 15k to 18k feet above sea level. Lapse rates also appear favorable for hail development and a lightning risk.

Even without very ideal atmospheric instability, the other components of ample wind shearing being strong forcing along the cold front, and abnormally high moisture for this time of year will yield a risk of severe weather. At this point, determining the instability available will help determine just how severe the storms will be. If daytime surface temps rise into the 70s as expected after clouds break up and allow the sun to heat the ground, there will be a solid risk of severe weather for the region.

UPDATE 12/4/11 7:40 PM:
Today’s model runs have scaled back the winter weather impact for DFW, currently showing very minimal to non-existent winter weather here. Some models hint at non accumulating light snow flurries from midnight through afternoon Monday. Other models hint at very light snowfall from sunset Monday through Sunrise Tuesday. Neither of these scenarios result in a substantial impact to the Metroplex at this time. I think our first winter weather event of the season is now hardly worth mentioning.

UPDATE 12/3/11 3:00 PM:
The latest model runs push drier air in with the colder air, meaning when the cold air gets here the precipitation will have ended. Winter weather chances here now for Monday appear much less likely. This wobble in computer models is not surprising especially when you are dealing with just +1 and -1 temp inaccuracies making all the difference. I will keep an eye on this though, aren’t out of the woods yet.

The Dallas/Fort Worth Metroplex may get its first winter weather of the season early next week, as a strong cold front subducts warmer moist air over north Texas. The last few runs of the NAM and GFS models are now indicating that Monday any time after noon, winter weather may impact the Metroplex, with the northwestern areas much more favorable.

Each run of the computer models have the predictable wobble in timing and adjust temperatures by +1 or -1. With the forecast temperatures right at the freezing mark, obviously a +1 or -1 temperature difference makes all the difference between icy dangerous driving and standard rainfall.

Models the last 24 hours or so have consistently shown the potential for area wide rain to convert to a freezing rain or sleet mix, then possibly into a wet snow as Monday afternoon progresses. The freezing line would shift across the Metroplex from northwest to southeast during the day.

GFS computer model snow depth forecast for Tuesday 12/6/11 at 6:00am CST. 1-2 inches appear possible in D/FW.

Travel Impacts
Travel Monday afternoon and evening would of course be impacted, but the impacts may not be too substantial just yet as accumulation on the roads would be light and icing would be slow to occur. Monday overnight into Tuesday morning will present the beginning of the largest driving hazard. Overnight temps in the upper 20s combined with lightly traveled roads in DFW would greatly aid in road icing for Tuesday morning.

Tuesday during the day clouds will likely clear out and yield to sunshine, but temps are expected to stay in the low 30s due to strong cold air blowing in from the north all day. Sunshine Tuesday would likely help warm area roadways and melt accumulated ice during the daytime, but puddles may re-freeze overnight Tuesday into Wednesday morning as temps drop below freezing again. Travel late Tuesday into Wednesday morning may be hazardous as spotty patches of ice would likely remain on roadways. Wednesday temps will warm into the 40s and all remaining ice and snow should melt and evaporate.

Even minor winter weather events tend to have a pretty high impact on areas not hardened for winter weather like the Metroplex. I will continue to monitor any updates and provide them here!

The first warming temperatures, increasing humidity, and gusty south winds should begin as early as Friday 11/18. Mostly cloudy skies and humid conditions expected Saturday, with humidity and cloud cover increasing as the day goes on. Rain chances may begin as early as Saturday night as the heavily moistened atmosphere starts to generate some weak isolated showers. Low rain chances will continue into Sunday with more mostly cloudy skies expected.

72-hour rainfall estimate for Sunday 11/20 through Tuesday 11/22

On Monday we will see a cold front stall near the Red River to our north leaving north Texas to reside in the warm sector. Severe weather parameters appear quite encouraging. Wind shear profiles and hodographs appear very favorable for supercell development, capable of supporting tornadoes. Atmospheric instability appears to be moderate. Some moderate CIN appears to be in place, but this would only serve to support the development of some discreet supecells. The only component missing from models right now is a trough or some other upper atmospheric axis of instability to help initiate everything. Currently it appears the lower and upper level lows lag behind the instability by a few hundred miles, closer to the Texas/New Mexico border.

This is a Skew-T chart (left) and hodograph (right) for D/FW, as forecasted by the GFS model for 6:00pm Monday11/21. The red line (left) indicates temperature, green line represents dew point. Wind barbs on the right of the Skew-T indicate direction and speed. The bottom of the chart represents the surface, and 500hPa represents about 18,000 ft. This chart tells me a weak temperature inversion around 700hPa creating a weak cap or weak thunderstorm inhibition (quite favorable for supercell development). Also shows a dry slot in the atmosphere around 500hPa which shows a potential for microbursts to occur. Surface wind barbs from the southeast, with a sharp change to strong southwest winds above the surface tell me supercells with tornadic potential may occur. Overall, this tells me that tornadoes and strong straight line winds will be the main threats of the day, but large hail is also quite possible.

The hodograph on the right is used for determining storm mode and tornadic potential. This chart is plotted using both wind direction and speed. The angle in degrees from the center of the chart represents wind direction. The further distance from center represents wind speed. Each point represents a sample of wind speed from the surface through over 40,000ft. A curved hodograph like this tells me storms will be supercellular and tornado potential is favorable. In fact, this hodograph is almost a textbook example of a favorable supercell day.

In fact, the Storm Prediction Center has already highlighted this area as potentially severe on Monday 11/21.

The low pressure system does push through overnight Monday into Tuesday morning, which brings the cold front with it. This cold front is likely to bring heavy rainfall to the entire region, with the heaviest rainfall in areas from the DFW Metroplex and to the northeast. Timing on this 2nd round of rain is expected overnight Monday into Tuesday morning. The cold front passage may also contain a lower strong to severe weather threat with a linear storm mode.

Afterward expect clearing skies and cooler conditions as a high pressure system slides in behind the front briefly. Thanksgiving Thursday looks to bring great weather too, around dinner time expect temps in the mid 50s to around 60 under clear skies and light winds.

Anyone planning to camp out for black friday deals can expect morning temps in the mid-40s and light south winds.

Computer models are hard to determine what may happen exactly beyond this time period, but the GFS model depicts another weak cold front sliding through the region late Friday into Saturday the 26th. There may be some light rainfall with that system.

I will of course keep a close eye on the upcoming severe weather potential and post updates here.

The front is expected to move through the immediate metroplex around sunset on Wednesday, with the rain following soon after. High temperatures in the upper 50s along with intermittent rain most of the day is expected Thursday. If working late or if you plan to be out on Wednesday night, bring a sweater and an umbrella with you, as the daytime highs Wednesday may deceive you.

Rainfall totals for Wednesday and Thursday aren’t impressive however, with totals in DFW and northward expected in the 1/2 to 1 inch range.

Storm total rain as of 3:48am CDT

Storm total rain, zoomed in on D/FW.

I took several long exposure photos and uploaded them into my galleries. Lightning tonight wasn’t very photogenic, but when stitched together in time lapse, you can see the evolution and approach of the strong thunderstorm outflow boundary.

23-Oct-2011 01:51PENTAX PENTAX K-5 , 7.1, 16.0mm, 10 sec, ISO 160	23-Oct-2011 01:47PENTAX PENTAX K-5 , 7.1, 16.0mm, 10 sec, ISO 160	23-Oct-2011 01:40PENTAX PENTAX K-5 , 7.1, 16.0mm, 10 sec, ISO 160
23-Oct-2011 01:32PENTAX PENTAX K-5 , 7.1, 16.0mm, 10 sec, ISO 160	23-Oct-2011 01:34PENTAX PENTAX K-5 , 7.1, 16.0mm, 10 sec, ISO 160	23-Oct-2011 01:22PENTAX PENTAX K-5 , 7.1, 16.0mm, 10 sec, ISO 160

Click here to view the complete gallery.