4/19/04 FCST: Southern high plains

[Kevin Scharfenberg]

60-62 dewpoints should be maintained in the OK/TX panhandles through tomorrow on sustained southerly flow. Model progs suggest mid-level temperatures will cool tomorrow somewhat, and with increasing flow aloft and more mixing from increased insolation, the dryline should become better-defined, roughly from Clayton NM to Lubbock TX.

The combination of a stronger dryline circulation, more heating, cooler temps aloft, and 60ish dewpoints, should be sufficient for storms to develop along the dryline as far south as the Lubbock area tomorrow. It will take awhile for all the features to sharpen up, so it could be after 5pm before storms are going.

Shear profiles will be sufficient for supercells. There could be some weakness in the mid-level winds before dark, and 20 degree dewpoint depressions should lead to fairly high cloud bases. These factors make me think the tornado threat is not "too" high (5% by SPC's method). However, after dark, shear profiles are progged to improve somewhat.

Initial (virtual) target: Canyon, Texas

Post your forecast discussions here:

 

[Lance Maxwell]

Ya, I was thinking very much along those same lines Kevin. I think that if dewpts could somehow get up to around 63-65 in western OK, we could see some very nice supercells tomorrow. With CAPE's near 2000 J/kg in the TX panhandle tomorrow at 0z and 3km Helicity values between 250-300, as well as very little CINH, I see initiation occurring somewhere near Amarillo at about 21z.

 

[Robert Dewey]

After looking at the 18Z MM5 soundings and 18Z ETA data...I am not very impressed. The dry line appears to be retreating to the west, which would minimize convergence. Instability is decent...With CAPE values of 1500-2000J/KG (T/Td parcel of 78/59 at CDS). Wind shear is OK, but not real good...With CDS forecast sounding for 03Z TUE reporting around 150M2/S2, and 0-6KM shear of only 25KNTs. Best speed and directional shear is located too far east of the dry line, and away from instability. Given the above, combined with a slight CAP and retreating dryline, expect the threat for storms to be really low.

With that being said...If I had to pick a target, it would be CDS in TX between 21Z MON and 03Z TUE, with the main threat being hail and wind.

Robert

 

[Kevin Martin]

My Forecast(W.I.R.T.) Weather Intensity Research Team.

well based the formula, Id say

NE TX/SE OK Panhandle BORDER

Probability of Severe Thunderstorms is 55%
So with that 55% it corresponds with my charts on.........

Severe Thunderstorm Risk.
NO SEVERE RISK(NONE)
GREEN ALERT(LOW)
YELLOW ALERT(SLIGHT)
ORANGE ALERT(MODERATE)
RED ALERT(HIGH)
PINK ALERT(EXTREME)

Type of Event.
NO SHOWERS
SHOWERS
NO THUNDERSTORMS
WEAK THUNDERSTORMS
STRONG THUNDERSTORMS
SEVERE THUNDERSTORMS
HIGH RISK SEVERE THUNDERSTORMS

Thunderstorm probability is 65%.
no Thunderstorms expected
Slight Chance
Chance
Possible
Likely
Run For the Hills

Forecast Discussion.

Dewpoints in the Mid 50's and termperatures in the Lower 70's will yield to a fairly unstable atmosphere across the region today. CAPE is forecasted to be in the Lower 1000's value, so expect some explosive development. Models indicate a rapid moisture decrease the further west you go, indicating a dryline is in place. This dryline will push to the east, setting off forecasted convection. 850MB LLJ at 15-20 knots suggest a very weak to nil inflow, and Thunderstorms in this area will be Short Lived. 500MB winds at 40 knots for the potential for bow Echo Thunderstorms, with damaging winds possible. Hail values at 375 as calculated for VERY large hail possible. Helicity values show 175, for weak tornadoes possible, F0 to F1 damage only, so A Tornado Watch has been issued by W.I.R.T.

Severe Risk: Moderate

Main Concernsamaging Winds, Large Hail, and Isolated Tornadoes.

MARTIN

Check out other forecasts and maps around the Area.
www.powow.com/orbiteradds/severe.html

Kevin Martin

 

[Shane Adams]

You've been pretty vague with revealing your actual process for determining parameters. If there are no tornadoes in your watch tomorrow, might you explain those parameters and why they failed? Be a good learning process for everyone.

 

[Lance Maxwell]

This will make for a good discussion on the other board -- I look forward to seeing it.

 

[Robert Dewey]

After looking at the 00Z MON ETA data, I am even less impressed. CAPE now forecasted be AOB 1250J/KG...And with pretty weak convergence, I still do not see anything significant. Using the high-res ETA, the dryline also does not move much during the day or evening (perhaps a bit of westward movement), so the dry air won't really be "slamming" into the moist (if you can call it that) air. Shear in the lowest 0-3KM is OK, at best...With very little shear between 0-6KM, leading to a decreased supercell threat. Any storms that do occur, will likely be isolated and weak "general" type storms...

Robert

 

[Amos Magliocco]

We have created a new topic for discussion of Kevin's new Math Technique in the Weather and Forecasting area.

New topic is here:

http://stormtrack.org/forum/viewtopic.php?t=1771

 

[Kevin Scharfenberg]

Are you sure you're looking at the right 00Z eta Robert? I'm seeing 500 mb winds are progged to be on the order of 40-50 kts at 00Z tomorrow across much of the Texas Panhandle, leading to good 0-6km bulk shear values (GFS agrees).

This looks less like a typical dryline day than before. The front moving through Kansas now should reach a ICT-GAG-DHT line by morning. The models have been consistent bringing a jet max and shortwave trough across southeast NM into the TX PH between 18-00Z, and are showing rapid surface pressure falls in the lee of the Rockies during the afternoon. The isallobaric forcing should cause winds to back and the moisture to be pulled northwestward. My forecast is the forcing from vorticity advection will encounter the deeper moisture (60ish dewpoints) and the remnant front in the northeast panhandles or northwest Oklahoma to pop a few good storms. Shear still looks good to me for supercells, though not great (0-6 bulk shear about 40 kts, and 0-3 helicity about 200 m2/s2). Throw in additional upward motion from warm air advection, and the progged moderate diffluence in the mid and upper layers, as well as slightly cooler temps aloft (4C at 700), and it won't take a lot to get a storm going along the old boundary.

The bad news: as mentioned, the instability doesn't look as good as before, and it appears that is due to more cloud cover in the models. Also, there will probably not be a clear target until later in the day, when the forcing kicks in. The best storms will probably not be going until about sunset.

My virtual target has moved to Canadian, TX with lower confidence.

 

[Robert Dewey]

Originally posted by Kevin Scharfenberg
Are you sure you're looking at the right 00Z eta Robert? I'm seeing 500 mb winds are progged to be on the order of 40-50 kts at 00Z tomorrow across much of the Texas Panhandle, leading to good 0-6km bulk shear values (GFS agrees).

I decided to take a second look (this is for 00Z TUE)...You are right in that 500mb winds are in the 40-50knt range, but forecast soundings from the area show 0-6km total shear of 32knts (which actually isn't too bad, would like to see 40knts though), and 0-3km total shear of 10knts (not good).

I also decided to take a look at the 00Z MM5 output valid 03Z TUE, and it actually looks very impressive...CDS showing CAPE of 2150J/KG (T/Td of 73F/59F)with 0-3km helicity of 250-300m2/s2. Shear values are greatest in the lowest 0-3km, with nearly 60knts of total shear...0-6km is weaker, at 30knts. There is a slight CAP of 2C at 800mb, with a CIHN of -46J/KG. Havn't looked at the horizontal plots of the MM5 to see how the dryline sets up or convergence...But in that environment, if storms were to develop, the probably would be severe...

As to which model is right? Thats still up in the air...

Robert

 

[Kevin Scharfenberg]

No big change to the forecast reasoning today...the big question with the cirrus shield around will be whether there is enough insolation to break through the cap and get a storm going. I think with the forcing and cooling mid level temps with time, the chances are slightly better than even.

The 12Z RUC does pop storms in the panhandle and has some pretty good numbers for supercells. Here's the RUC point forecast sounding for AMA valid at 00Z, near the time and location of initiation:

SFC temp/dewpoint 74/57
CAPE 1895 J/kg
CINH -29 J/kg

SFC wind 140/20
850 wind 160/28
700 wind 210/32
500 wind 230/44
250 wind 250/72
0-3 km Helicity 371 m2/s2
0-5.5 km bulk shear 53 kts
right-moving supercell motion 241/25

If I lived in the panhandle region I'd definitely have the batteries charged.

 

[Robert Dewey]

Looking at the latest RUC2...Things are starting to look better. The RUC is actually looking more like the MM5, which was pretty impressive. Best combination of instability/shear appears to be in the panhandle of TX, and consequently the RUC initiates convection there around 21Z.

The latest 12Z ETA shows less instability, with CAPE of 500-1000J/KG. Shear is stronger this go around with the ETA...With 0-3km helicities of 200-300m2/s2, which is stronger than the previous 00Z run.

So...I believe there is the decent chance for a few isolated severe cells to pop this afternoon...Mainly in the central and eastern TX panhandle.

Robert

 

[JR Hehnly]

http://209.40.151.75/ shows 50+ dewpoints are now in the eastern half of the TX panhandle. Vis satellite shows clearing and a nice Cu field near I-40 and the OK border. 74/63 in Shamrock right now. Also looks like a northbound outflow boundary across the lower half of the TX panhandle, near Childress. Maybe we can get some action this afternoon.

 

[KMcCallister]

It's interesting that the SPC tornado threat percentage outline is limited to only the northern part of the Panhandle. I assume this is due to the location of the cold front and therefore the best backed winds at the surface allowing more directional shear. This makes sense.

Right now, the lowest pressure (mslp) of 1014mb near ROW. If we have pressure falls there, then winds over the LBB area (and SW of LBB) west Texas should become more backed with time. With that area also being near the tightest gradient of moisture, wouldn't that area also have an improved tornado threat if the cap breaks due to the PVA indicated on the RUC?

(Thinking out loud LOL)

 

[Michael Shively]

somebody should post a forecast discussion thread for 4/20/04 for KS/MO