Watching the Skies

Severe thunderstorms still on track for Friday afternoon and evening. Strong forcing, plentiful moisture, and favorable low level wind shear will be supportive of severe thunderstorms. Tornado chances will be enhanced on Friday with the low level wind shearing forecast. However instability may be limited by a persistent cloud deck limiting afternoon heating. If a gap in clouds can develop and heating can initiate instability, then strong storms with tornadoes are a distinct possibility.

As I like to say here, keep watching the skies folks.

One of the snowiest winters in D/FW history has finally ended, with official totals reaching 17.1 inches. Some areas even received 25 inches of snowfall this year!

A table of the top 10 snowiest winters, provided by the National Weather Service. This season ranked number 2, just half an inch behind breaking the record.

   1   17.6   1977-78
   2   17.1   2009-10*
   3   15.3   1963-64
   4   13.5   1923-24
   5   10.4   1976-77
   6    9.5   1909-10
   7    9.2   1916-17
   8    8.8   1947-48
   9    8.1   1937-38
  10    7.3   1965-66
        7.3   1941-42

The cause is undoubtedly related to El Nino, which has an indirect effect on allowing more Gulf moisture to make its way into the southern plains. This also causes the southern branch of the jet stream to bring pacific storm systems over the southern plains with greater frequency.

The National Weather Service wrote up a great summary of the numerous snowfall events this season, and can be found here

• http://www.srh.noaa.gov/fwd/?n=wintersnow09-10

DFW Airport is just 7 days short of breaking yet another record during our cold season, this time for most consecutive days below 80 degrees F.

Looks like we may end this record just a few days shy, as forecasts for Wednesday and Thursday bring our high temps above the 80 degree mark.

10 years ago today a pair of tornadoes struck heavily populated areas in Fort Worth and Arlington, killing two and injuring 80 others. The first tornado developed quickly and moved through downtown Fort Worth, causing severe damage to numerous high rises along with other structures and vehicles. A significant hailstorm also affected areas north of Fort Worth like Lake Worth and Saginaw, causing significant damage to roofs and vehicles.

(KFWS 00:25 Zulu Base reflectivity/Velocity)

The above screenshot demonstrates the storm as it was passing over downtown Fort Worth. The storm briefly produced F3 damage to the Cash America building, and F2 damage along a substantial part of its track.

(KFWS 01:05 Zulu Base Reflectivity/Velocity)

This image shows the second tornado with the strongest radar velocities near Arlington along I-20. This tornado tracked just south of I-20 for a few minutes before turning left and dissipating.

Below is a summary developed by the NWS about the tornadoes and the impact they had on the region.

NWS March 28 Fort Worth Tornado Summary

Strong winds and a fire hazard exist for Saturday across north Texas. Additionally, a slight chance of thunderstorms exists across the eastern parts of north Texas on Saturday afternoon.

A strong low pressure system currently located over the Texas panhandle will send a dryline through the region Saturday mid-day, increasing winds and posing a fire weather hazard. This dryline will act as a focus for some isolated thunderstorms that may develop in the afternoon east of I-35. These storms are likely to form just east of the immediate DFW Metroplex, so most of us will likely experience just dry and windy conditions in the afternoon. However storms that do develop will rest in an environment that could be supportive of strong to severe storms, and would be worth keeping an eye on.

Weather Saturday morning may be mostly cloudy or overcast, but quickly switch to clear skies after the dryline passes around noon. The rest of the day should remain clear, dry, and windy. The next 5 days including Sunday appear to remain dry and finally bring about a warming trend, with temps finally reaching 80 degrees by Thursday.

However Friday brings around our next significant storm system, with computer models already picking up on a good shot of severe weather for Friday afternoon or evening. Exact timing or locations of severe weather is hard to determine this far out, but computer models are all in good agreement that with plentiful moisture available, this storm system has alot of severe potential already. I will keep an eye on this developing situation and send updates as needed.

A Severe Thunderstorm Watch has been issued for parts of north central Texas, including the DFW metroplex, expiring at 10pm.
Thunderstorms are developing inside a destabilizing air mass along a cold front moving eastward. The storms arrival now brings it through the region within the next 2 or so hours, or before 5:30 to 6:00pm. Hail remains the primary risk, but severe winds are also a possibility. Tornado threats still remain low.

URGENT – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 34
NWS STORM PREDICTION CENTER NORMAN OK
320 PM CDT WED MAR 24 2010

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

PART OF WEST CENTRAL  AND NORTH CENTRAL TEXAS

EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 320 PM UNTIL
1000 PM CDT.

HAIL TO 2 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 70
MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 30 MILES SOUTH
SOUTHWEST OF SAN ANGELO TEXAS TO 65 MILES EAST NORTHEAST OF
DALLAS TEXAS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).

REMEMBER…A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION…STORMS ARE DEVELOPING ALONG AND AHEAD OF THE COLD FRONT
MOVING EWD ACROSS NWRN TX.  AIR MASS HAS SUFFICIENTLY DESTABILIZED
WITH HEATING TO SUPPORT STRONG UPDRAFTS. WITH THE 40-50KT OF DEEP
LAYER SHEAR AND STEEP MID LEVEL LAPSE RATES A FEW OF THE STORMS ARE
EXPECTED TO BECOME SEVERE AS THEY CONTINUE E/NE INTO THE EVENING
HOURS.  PRIMARY THREAT WILL BE LARGE HAIL…HOWEVER THERE IS THE
POSSIBILITY OF A COUPLE OF SUPERCELLS GIVEN THE IMPROVING LOW LEVEL
SHEAR LATER THIS AFTERNOON…ACCOMPANIED BY A DAMAGING WIND THREAT
AS WELL AS LARGE HAIL.

AVIATION…A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 24030.

Current forecasts from the Storm Prediction Center and our local weather forecast office have mentioned a severe storm risk for Wednesday late afternoon through evening.

Currently the computer models agree on the location for storm initiation across the western parts of north Texas near Wichita Falls through Breckenridge at 4 to 6pm. The storms will progress eastward throughout the evening, switching from a ’surface’ based storm to a more ‘elevated’ structure. What this means for us is that tornado risk decreases, while hail and wind risk remains the same. Computer models differ in regards to timing of these storms moving through the metroplex, but current thinking suggests approximately midnight. The environment will still remain supportive of severe thunderstorms at this time, so I would plan for some potentially severe weather in the form of hail and winds. The storms will continue eastward throughout all of north Texas and clear the region by sunrise Thursday.

Clearing skies with slightly cooler temps will spread over the area for Thursday and Friday. The next storm system will move through the region Saturday afternoon and evening, with a very similar setup as Wednesday. However there will be less moisture available Saturday, so storms will likely be less intense.

This is post number 500 for Watching the Skies, an exciting achievement!
The pictures here were taken in Frisco, TX during the afternoon of March 21, 2010 after our spring snow storm.

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This unseasonably late snowfall further increased the 2009-2010 snowfall totals for our area, bringing us within 1/2 an inch of the all-time snowiest winter on record! Additionally the last time this much snow fell this late in the season was March 29 1937! Preliminary snowfall totals listed graphically below.

As you can see, the heaviest snow was concentrated within Collin County including a report in Frisco of 6 inches, and 8 inches reported in Allen. DFW Airport officially documented 1.3 inches of snowfall total from this event. The statement from the NWS included below.

The snow will not remain very long, as temperatures will quickly recover to the 60s on Monday and 70s by Tuesday. The next storm system will begin to affect the region on Wednesday evening, with thunderstorms likely. A shot of cooler air will follow as this system passes, but nowhere near this level of winter weather we just received.

...Spring snow for dfw...

Dfw Airport recorded 1.2 inches of snow on March 20th. This breaks
the previous daily record for March 20th of 0.4 inches set in 1970.
An additional 0.1 of an inch officially fell on March 21st and the 

event total is 1.3 inches. 

The additional 1.3 inches brings the 2009-2010 winter total to 17.1
inches. This ranks second of all time and came 0.5 inches shy of
tying the all-time record of 17.6 inches set in 1977-1978. 

This snow event was unseasonably late in the year. The last time an
inch or more fell at dfw later than March 20th was when 2 inches
fell on March 29th in 1937.

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Dallas/Fort Worth - snowiest seasons

   1   17.6   1977-78
   2   17.1   2009-10*
   3   15.3   1963-64
   4   13.5   1923-24
   5   10.4   1976-77
   6    9.5   1909-10
   7    9.2   1916-17

   8    8.8   1947-48
   9    8.1   1937-38
  10    7.3   1965-66
        7.3   1941-42
--------------------------------------------------------------------

I thought Winter was over… but it apparently has one last bite before fading away. Snowfall is possible across the northern areas of the region on Saturday evening. Accumulations will be light, if any. Areas around the Red River could receive up to 1 inch of accumulation on exposed areas. Prior to the snow however a very strong cold front will move through the area, bringing a line of thunderstorms with it. The timing on these storms right now is probably in the overnight hours tonight, into early Saturday morning. Expect very windy and cold conditions immediately after the front moves through, with the snow following several hours afterward.

The last freeze of the season is expected for the region Saturday night, so take action on Saturday to protect any sensitive vegetation since the growing season has already begun.

Below is a diagram detailing the average date of last freezes across the region… It looks like we are right around average here.

I will send more details as needed later…