00z NAM Thoughts

Well, this latest run of the NAM is showing a potential tornado outbreak on Wednesday for areas south of D/FW and a flooding potential for basically the entire area especially for areas down by San Angelo and Abilene where current models are advertising a 4+ inch event for them. For Decatur, the NAM is advertising a 2 to 3 inch event with isolated 4 inch amounts. The NAM is showing a very large hole up and down the I-35 corridor where DFW may only see 1 to 2 inches with a light 1 inch amount down by Hillsboro/Meridian area. Here's the 84 hour accumulated rainfall map from the 00z NAM.

Now, the tornado threat is also there due to the upper low's proximity and how the atmosphere will be basically lifting and producing thunderstorms. The low will provide ample shear over Central Texas that could give thunderstorms the proper ingredients to produce a tornado or two. Up here in North Texas, we may be too cold to have tornadic or severe thunderstorms here as temperatures will be in the 40's and 50's. But if we can get the warm front, another ingredient needed in the making of severe thunderstorms, to move north enough, we may have to readjust our forecast. With an 80 to 90 knot jet streak over Central and East Texas, that along with modest moisture, warmer than usual temperatures, and shear from the cutoff low, all that combined with just enough instability could provide a tornado event for areas south of D/FW.

Now, to the potential start and ending to all of this mess on Tuesday, Wednesday and even into Thursday. The 00z NAM begins the light shower activity around 9am Tuesday and a lull begins Tuesday Night as we look off to the Big Bend for the heavy activity to fire. Here are the images for 9am and 9pm Tuesday.

So, as you can see around 9pm Tuesday, the full extent of the difluence in the atmosphere is beginning to become realized as the air splits between the jet stream and the low pressure across Midland/Odessa and San Angelo. Our showers from 9am have become thunderstorms from I-35 and points east towards the Arklatex region. 

Three hours later around midnight, that small mass of heavy rain becomes an extensive rain shield for Abilene and San Angelo. Rain intensity should begin to pick up at this point with more and more heavy scattered showers becoming the norm around midnight.

By 6am Wednesday, that is when we could see things pick up for an hour or two with still the main convective band still out west near Abilene and San Angelo. Vernon and Quanah could see some very heavy rainfall if this verifies. 

Then, the band of heavy showers and thunderstorms begins to move east, but somewhat weaker than previous runs and hours of the 00z, but nonetheless, heavy rain will still be the case even at 6pm Wednesday.  Some snow will be possible for sections of the Davis Mountains and New Mexico as there will be a cold pocket or two with this system.

Once the dry slot moves in around midnight Thursday, the rain ends for areas west of I-35 but, the event is still ongoing for DFW and east and southward with the NAM forming a squall line too. This squall line is racing northeastward on the next hour of the 00z with very heavy rain and potentially damaging winds with it. 

The current 00z only goes out to Thursday Morning, but we may have to watch areas near Wichita Falls and Vernon for another area of potential precip that could skirt them from the north in Oklahoma about 84 hours out.

SPC Issues Slight Risk For Most Of Area

 SPC AC 200730        DAY 3 CONVECTIVE OUTLOOK      NWS STORM PREDICTION CENTER NORMAN OK    0230 AM CDT SUN MAR 20 2011        VALID 221200Z - 231200Z        ...THERE IS A SLGT RISK OF SVR TSTMS TUE/TUE NIGHT FROM PARTS OF THE    CNTRL PLAINS THROUGH THE MID MS VALLEY...SOUTHWARD INTO THE SRN    PLAINS...        ...SYNOPSIS...    MODELS INDICATE THAT THE LARGE-SCALE TROUGH...LIFTING THROUGH THE    INTERMOUNTAIN WEST AND ROCKIES BY 12Z TUESDAY...WILL GRADUALLY BE    FORCED EASTWARD INTO A CONFLUENT REGIME TO THE SOUTHEAST OF AN    EVOLVING BLOCKING RIDGE OVER THE CENTRAL CANADIAN PROVINCES...AS    ANOTHER AMPLIFYING SHORT WAVE TROUGH APPROACHES THE CALIFORNIA    COAST.  THE PROCESS IN WHICH THIS OCCURS STILL APPEARS LIKELY TO    SUPPORT INCREASING CONVECTIVE POTENTIAL ACROSS PARTS OF THE CENTRAL    U.S...AS A SIGNIFICANT EMBEDDED IMPULSE EMERGES FROM THE SOUTHERN    ROCKIES AND PIVOTS NORTHEASTWARD INTO AND NORTHEAST OF THE MID/LOWER    MISSOURI VALLEY BY TUESDAY EVENING.  AS LARGER SCALE UPPER TROUGHING    TAKES ON AN INCREASINGLY NEGATIVE TILT...STRONGER MID-LEVEL HEIGHT    FALLS ARE PROGGED TO OVERSPREAD THE WARM SECTOR OF A SUB 1000 MB    SURFACE LOW MIGRATING ACROSS THE MID MISSOURI VALLEY AND UPPER    PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY.  THIS FORCING WILL BE    FOCUSED ALONG AND NORTH OF A STRONG MID/UPPER JET STREAK /AROUND 90    KT AT 500 MB/...WHICH APPEARS LIKELY TO GRADUALLY VEER FROM A    SOUTHWESTERLY TO WESTERLY COMPONENT AS IT DEVELOPS EASTWARD ACROSS    THE SOUTH CENTRAL PLAINS/OZARK PLATEAU AND MIDDLE MISSISSIPPI VALLEY    REGION.        AT LOWER LEVELS...STRONG SOUTHERLY LOW-LEVEL JETS MAY BE    CONCENTRATED IN TWO BROAD CORRIDORS...ONE FROM THE SOUTH CENTRAL    PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY...JUST AHEAD OF THE    SURFACE CYCLONE...ANOTHER ON THE PERIPHERY OF A RETREATING SURFACE    RIDGE ACROSS THE OZARK PLATEAU INTO THE LOWER OHIO VALLEY.  THIS    SURFACE RIDGING...CENTERED OVER THE GULF OF MEXICO AND FLORIDA    PENINSULA...STILL APPEARS LIKELY TO IMPEDE SUBSTANTIVE INLAND    BOUNDARY LAYER MOISTURE RETURN.  AND IT STILL APPEARS THAT THE    OVERALL CONVECTIVE POTENTIAL MAY NOT REACH THE LEVELS THAT IT    OTHERWISE COULD...GIVEN THE STRONG FORCING.     HOWEVER...DESTABILIZATION IN THE WARM SECTOR OF THE LOW...SOUTHWARD    ALONG THE DRY LINE INTO THE SOUTHERN PLAINS... SHOULD BE SUFFICIENT    FOR SEVERE STORMS.        ...PLAINS/MISSISSIPPI VALLEY...    CONVECTIVE DEVELOPMENT MAY BE ONGOING EARLY IN THE PERIOD ALONG AND    NORTH OF A WARM FRONT...EXTENDING EAST SOUTHEAST OF THE    LOW...NORTHEAST OF THE MID MISSOURI VALLEY INTO PORTIONS OF THE    UPPER MISSISSIPPI VALLEY.  HOWEVER...THE PRIMARY STORMS OF CONCERN    DO NOT APPEAR LIKELY TO EVOLVE UNTIL LATE TUESDAY AFTERNOON AND    EVENING...NEAR THE LOW AND WARM FRONT ACROSS EASTERN    NEBRASKA/WESTERN IOWA/NORTHWEST MISSOURI.  INITIALLY ACTIVITY MAY BE    IN THE FORM OF SUPERCELLS...BUT FORCING IS EXPECTED TO SUPPORT    UPSCALE GROWTH INTO A MESOSCALE CONVECTIVE SYSTEM THAT SHOULD TRACK    ALONG AND JUST SOUTH OF THE WARM FRONT THROUGH UPPER PORTIONS OF THE    MIDDLE MISSISSIPPI VALLEY TUESDAY EVENING.  DAMAGING WINDS AND LARGE    HAIL LIKELY WILL BE THE MOST PROMINENT CONCERNS...AND IT DOES NOT    APPEAR OUT OF THE QUESTION THAT THIS COULD CONTINUE INTO THE LOWER    OHIO VALLEY OVERNIGHT.        ADDITIONAL SCATTERED STORM DEVELOPMENT IS EXPECTED SOUTH OF THE    SURFACE LOW...ALONG THE DRY LINE...INTO THE SOUTHERN PLAINS.  IN THE    PRESENCE OF STEEP LAPSE RATES...WEAK TO MODERATE CAPE...AND STRONG    SHEAR...A FEW SUPERCELLS ARE POSSIBLE...PRIMARILY WITH LARGE HAIL    AND LOCALLY DAMAGING WIND GUSTS.

Severe Storms Next Week?

Right now, WFAA has mentioned a possibility of showers & thunderstorms late next week into early next weekend. The question on everyone's mind is, will we see storms out of this disturbance? Well, usually these disturbances have been known to "peel" away the cap in order to induce forcing (how the thunderstorms punch through.) I am going to post a series of Upper Air Soundings showing the difference in the soundings to tell whether there is a cap or no cap. (Measure of the Earth's Atmosphere)

Sounding Examples

GFS Sounding from Lubbock, Texas (3/19/2011 at 04z (11:00 pm))

This sounding shows 4 lines. Focus on the main red one which is the actual temperature. As you can see, the line is going up at a steep angle and is not curved. This means there is not a capping inversion in the atmosphere. There was a severe weather situation occuring in Lubbock due to this no capped atmosphere. Plus there was a dryline and stationary front to fuel it all.

GFS Sounding of Decatur, Texas (3/19/2011 at 04z (11:00pm))

This sounding shows 2 caps in the atmosphere. One at about 920 mb and one at between 850 and 700 mb's. This shows the strength of the inversions. Inversions also produce long distance radio reception, so if you are one of those people that likes to go out and listen to long distance radio stations, tonight may be a win or a fail for you.

Looking to the Future

We are going to look at a few soundings to determine if the cap "peels" back and lets some liquid gold in. Remember, focus on the red line.

GFS Sounding in Decatur, Texas Friday Morning 8:00am

This is a perfect example of a "morning inversion". If you avid long distance radio listeners have noticed a spike in the amount of stations received in the morning, this is why. A morning inversion is normal across the US, but what really gets everyone is that this morning cap burns off, but if you live close to the source (Mexican Plateaus), you may see a longer lasting capping inversion (Texas). Now, at 8am, there is a strong inversion here. Surface temp is at 13 degrees Celsius or 55 degrees. And where the peak bump is at 925 mb or so: 69 degrees. So a relatively cool day for Spring here in North Texas. But, we also look at the dew point (green) which is not very healthy. Only 46 degrees at the surface.

GFS Sounding from Decatur, Texas at 18Z (1PM CDT)

Now the difference has become a lot clearer. The surface temps are decreasing with height but, there is a minor cap at 850 mb. There has to be some type of cap there to decrease the forcing, too much equals a LOT of rain and that equals TONS of flooding. Now, the dew points are little more healthier suggest the atmosphere is moistening up a lot more. This may not be healthy though. Dew points are only in the lower to mid 50's. The surface temps are at 77 to 79 degrees suggest healthy surface temps. That 850 mb cap may have some on edge. That cap is at 68 degrees so the cap is weakened but can limit forcing enough to keep us from flooding. And the separation of these lines suggest no cloud cover in the morning or afternoon suggesting potent heating all day.

GFS Sounding in Decatur, Texas at 00Z (8pm)

All right, the moisture is totally in place, there is enough heating, but that 700 and minor 925 mb cap is bugging the crap out of us, and all the lines convergence on the 850 mb level so lets break it down. 1. The dew point temp is showing dew points up to 66 degrees! That is an over load of moisture at the surface and definately shows that the dryline hasn't passed through yet. 2. The surface temp has cooled down a tad from that 78 degrees at 1PM to 74 degrees. Plenty of heating and moisture, its the fact that the inversion is coming back. 3. The cap is a now a tad warmer than the surface, 76 degrees. Minor yes, but will it be enough to flatten the storms? At the 700 mb level is where we REALLY look for a big inversion, but any inversion can flatten a storm if too strong and if the storm has a small updraft. The 700 mb inversion is at around 70 degrees. Making it thin line here to say if the storms will flatten or not. But here's the kicker, 4. The cloud layer at 850 mb. This suggest that the skies may be cloudy suggesting that the storms may be on top of us by then. So the cap, we may not have to worry about. But what really concerns us is if this holds out or not. Cause if this does, a line of storms may come through here Friday Night. If it doesn't, then no storms for us.

DISCLAIMER: This is not the only thing that can predict severe weather. Other dynamics need to be there in order for this to pan out. So the idea here is do not rely solely on soundings. I am just showing the atmospheric dew points and capping inversions to show if the cap will "peel back" or not. Plus, this is GFS looking 140 to 160 hours out. I wouldn't rely on these pics.

From Sunny to Stormy on Saturday

We hope everyone is enjoying the sunny Spring-like conditions yesterday, and today, because later tonight, we'll see some thunderstorms develop, mainly along and south of Interstate 20. A few of the storms could be strong to severe with large hail, and damaging winds as wind shear and instability maximize in that particular area.

The strong storms continue on Sunday east of I-35 and again on Monday for most of our area ahead of an approaching Arctic front. That's when the cold, harsh reality sets back in. We'll see a chance of freezing rain on Tuesday afternoon. In addition, very cold and windy conditions are expected on Tuesday and Wednesday with wind chill levels dropping to the single digits and teens on Wednesday Morning. BRRRRRRRRR!!!!!

Unfortunately after the strong arctic front passes through on Tuesday, we won't get any higher than the 40s anytime soon. Then again, it is still after all, Winter. However, further analyses suggest that we may warm back up into the 50s by next weekend.

To end this entry, check out this video I've captured of the snow that fell in my hometown of Irving. Enjoy!!

*After this blog was made, the winter weather is gaining much more confidence in a major ice event for us and for parts of the DFW Metro area. Temps will not make it out of the 20's for Decatur.*



- Michael Raymond

From Wednesday Warmup to Friday Flurries?

Today, while many North Texans are still wanting to see more winter weather for the Christmas season (like last year), many others (like me) are taking this opportunity to put away their jackets and sweaters as highs today soar into the 70s and 80s. But we'll see a rapid cool-down on Thursday with temperatures steady in the 50s during that day and lows dropping to the 30s. The current disadvantage we're keeping an eye on is the high fire danger as a result of La Nina along and west of a Gainesville, Fort Worth, Cleburne, and Meridian line. West from there, cities along and within a Bowie, Decatur, Weatherford, Hamilton, Eastland, Graham, and Jacksboro bubble are under a Fire Weather Watch. The remaining Western 1/3rd of our coverage area is under a RED FLAG WARNING where the fire danger is critical. Within the Warning, humidities are falling to 8 to 14% and winds are forecasted to blow from the southwest at 10-20 MPH with gusts to 25-30. The combination thereof will produce wildfires.

We're also keeping an eye on a disturbance which is currently out in the rockies. At this point, it's producing winter weather in Northern Utah, Western Wyoming, and most of Colorado. It continues to slowly move southeast as the week progresses and will cover the Texas Panhandle tomorrow with some snow. As it inches closer to our region, it's gonna fall apart with (you know you wanna say it...) La Nina remaining in place. Many of us will be lucky if we even get a brief flurry or 2, but no significant accumulations and impacts are expected.

- Michael R.

Storm System on Tuesday

Since last week, we've been keeping an eye on a storm system in the Pacific Ocean. At this point it is making its way to the North Texas Region and by Tuesday, it's gonna bring a WHOLE LOTTA.....nothing. Yeah, I don't mean to get y'all worked up or anything, but as this low sweeps across the western US, it's gonna run out of fuel, so it won't produce any rain or snow as predicted last week. It will probably bring a sprinkle or 2 at best, but that's it.

As for the rest of the week, we'll see a slight warm-up by Saturday, and it will once again cool down on Sunday with lows falling back down to near freezing and highs in the lower 50s.

Chilly Weather This Thanksgiving

The next couple days are gonna be warm & humid across our region with highs in the upper 70s to lower 80s. There will be some showers for the eastern 1/2 of our map with the best chances east of the I-35 corridor on Tuesday. Wednesday is pretty much the same story, but by Midnight on Wednesday Night/early Thursday morning, a strong cold front is going to sweep through. By that time, our highs will be recorded into the upper 40s to lower 50s and they'll slowly fall from there, not to mention an even better chance of showers are forecasted that day (Couldn't be a better time to stay home and enjoy your Thanksgiving feast). When it's all said and done, we'll have our first significant freeze for some locations on Thursday Night/Friday Morning and again on Friday Night/Saturday Morning for the entire North Texas and Northwestern TX regions.

If y'all are planning on taking your trips to the northern states, have your coats, ice scrapers, rock salt, shovels, and/or snow plows ready.

Happy Thanksgiving and Stay Warm!!