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!

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 development will likely begin across central Oklahoma near Oklahoma City, and south along I-35. Wind profiles support forward propagation of these storms southward into north Texas as a line likely developing along an outflow boundary. Storm timing appears a bit difficult to determine with great precision, but the storms may enter north Texas around 10:00pm tonight.

Tonight’s main risk will be severe hail, but high winds are also possible. Because of the hail and ice production expected with these storms, frequent cloud to ground lightning would be expected as well.

Timing for the frontal passage will likely be early afternoon Monday for areas just north of DFW, around 6 to 9pm for the immediate Metroplex, and midnight for areas just to our south. The rest of the week will be dry, cool, and somewhat windy. Elevated fire weather conditions will exist as a result of the dry cold and gusty winds.

This disturbance will move from west to east and timing for rain or thunder to arrive in the DFW Metroplex looks to be around 2-3am Wednesday 10/12/11. Models are expecting this rain to stick around the region for a few hours, until probably 9am Wednesday.

Afterward, a cold front will trail about 24 hours behind this upper level disturbance. While modest moisture remains in the atmosphere, large scale subsidence in the wake of the upper disturbance will suppress nearly all rain development during the frontal passage. This means we can expect slightly cooler temps and a much drier atmosphere after the frontal passage overnight Wednesday into Thursday 10/13/11 early morning.

The upcoming weekend should be quite pleasant, moderate temperatures with light winds and moderate humidity. No storm systems expected for the weekend.

Long range, models are still showing signs of a strong cold front to move through the region around the middle of next week. Timing on the front next week now indicates Wednesday 10/19/11. Good rain chances appear to exist for the entire region, along with the possibility of stronger to maybe a severe storm or two. Temps afterward will be significantly cooler, with daytime temps in the low 70s and overnight temps in the low 50s.

GFS computer model – 24 hour estimated rainfall for 10/18/11

Timing on this event has been very well forecast for the last several days, and remains the same. Best chances of rainfall will occur for DFW after sunset, overnight and most of the day Sunday. Rainfall may still be occurring even through Monday morning at sunrise, as this upper level energy slowly pushes through the region.

I don’t anticipate any severe weather from this event myself, the National Weather Service has indicated that perhaps an isolated strong to severe storm may develop however. So if anyone in DFW has outdoor weekend plans, Saturday before sunset will be the best and only time to do them.