Apr 012010

Tuesday, 6 April Update: Today’s setup from Oklahoma to Iowa

Veered (westerly) 850mb winds over KS/OK have really caused this setup to go downhill quickly.  The combination of a stronger cap and much drier air at 850 mb are both huge negative factors.  However, as we continue into the late afternoon and early evening, models suggest those 850 mb winds will back to the southwest/south-southwest, and allow for richer moisture to spread over eastern OK/KS.  This should support supercells and possibly tornadoes where the cap breaks .  Although, the tornado prospect looks more promising over southern Iowa/northern Missouri.


Monday, 5 April: Another Update

Tuesday (tomorrow) is looking better for tornadoes, and the risk is a bit further east.   Eastern OK, eastern KS/western MO into IA are looking better for the formation of elongated supercells with tornadoes, some potentially violent in the afternoon/early evening.  One big problem for anyone chasing is storms will be moving northeast around 50 mph, at least initially.  With very curved low level hodographs forecast by the GFS, the tornado potential will be pretty significant with any isolated supercells that form from Iowa to eastern Oklahoma.   I wouldn’t be surprised if there is one violent, long track tornado reported tomorrow.  My preference right now is eastern/southeast KS ahead of the pseudo dryline/cool front where the cap will be strong enough to keep storms somewhat isolated.


Monday, 5 April Update

4/5/10: Highly conditional setup from western OK/KS into eastern NE/IA

Along the dryline from western OK to Kansas, the cap will be very strong throughout much of the day.  In the absence of large scale upper forcing, it’s unlikely the combination of mixing along the dryline and daytime heating will be substantial enough to support surface based convection by the late afternoon/early evening.  Although, it’s not completely out of the question.  Should a storm or two fire, wind shear will support supercells.  In that scenario, the tornado potential is quite high.  But, the cap may be too strong to allow any storm that does manage to fire to survive long enough to produce a tornado.  Basically, it’s a very conditional setup, with a greater risk for a bust than a tornado.  Then again, crazier things have happened.

Extreme eastern Nebraska into central/southern Iowa looks a little more interesting.  A warm front lifting north throughout the day may become the focus for convection this afternoon into the evening.  But the cap will also be a huge factor.  Models show a weak upper impulse moving through around midday.  If that’s correct, there will actually be subsidence over the region by the late afternoon/early evening.  This will hurt the chances for surface based storms to form along the warm front.  Storm initiation looks highly conditional.  But should a surface based storm form, wind shear would support supercells and tornadoes.

I think the best chance for a tornado today will be just north of the warm front in south central Iowa early this evening.  Get an elevated supercell to become surface based where the cap is much weaker.  Otherwise, tornado potential today is extremely low and highly conditional.

4/6/10: South central KS/northern OK

This setup will depend quite a bit on how much the 850mb winds back late in the afternoon/early in the evening.  If they do, enough 850mb moisture will be in place to support tornadoes – some strong.  But right now models keep the 850mb winds out of the southwest all day.  This will build an enormous cap over OK/KS, and advect dry air into the region.  As the upper trough moves in from the west, it will provide forcing to cool the mid levels.  This, combined with forcing along the dryline and cool front intersection, will aid in storm initiation late in the afternoon.  Wind shear will be supportive of elongated supercells.   But the mid level moisture will be sacrificed, raising questions on tornado potential.

The biggest positive about 4/6 (Tuesday) is the upper air forcing, making storms likely to form.  Today (4/5), storm initiation is highly conditional, but the wind shear is very good for tornadoes, if a storm can actually form.


Saturday, 3 April Update

4/5/2010: Risky chase setup from the Texas panhandle into Kansas, Nebraska and Iowa

Now that we are only a couple days away from Monday’s setup, things are coming into better focus.  The slower eastward ejection of the trough as shown by the European/Canadian models on Thursday looks correct.  The GFS, and now the shorter term NAM, has slowed down the system.

What we have for Monday is intense lee troughing with a well pronounced dryline mixing east across the western plains during the day.  Unfortunately, all the large scale lift associated with the trough will be over the Rockies.  In addition, 850mb winds will be out of the southwest throughout much of the day from Texas to northern Kansas.  This will create an enourmous capping inversion, making storm initiation difficult, without some upper support.

By the early evening, models show the 850mb winds backing to the south across Texas, Oklahoma and most of Kansas.  This will allow for deep moisture to move into those regions and provide great low level wind shear for supercells and tornadoes.  But the only mechanisms available from this setup to get a storm to fire is from forcing along the dryline and daytime heating.  This will make storm initiation highly conditional.  No further interpretation can really help at this point, unless something in the models changes.   A storm or two may develop along the dryline.  If so, the storm would quickly become a supercell and have tornado potential.  On the other hand, there may just be a clear sky bust given the strong cap and lack of upper support.

Another area of interest is along the warm front from eastern Nebraska into Iowa.  There, the 700mb temperatures won’t be as warm as over TX/OK/KS, which suggests the cap will be weaker.  For Iowa, the 850mb winds will remain out of the south throughout the day, advecting warm, moist air into the region all day (as opposed to advecting very warm, dry air like over Texas, Oklahoma and Kansas). So for the eastern Nebraska and especially the Iowa region, the cap has a slightly better chance of breaking.  However, convergence along a warm front boundary is usually much weaker than along the dryline.   So even this area has a decent shot of seeing a clear sky bust in the evening.  For what it’s worth, the GFS does show convection firing just north of the warm front in central Iowa by 00z.

As you can see, the lack of upper support is really hurting this setup.  The storm system needs to speed up.  If it doesn’t, the strong cap could win.  If a supercell manages to form along the dryline (it’s possible), the wind shear would be very supportive of tornadoes.

4/6/2010: This could be a big day from Missouri into Illinois and Iowa.  The upper support will be ejecting into the Plains.  A strong 850mb jet underneath 70 knot 500mb winds could provide shear for strong tornadoes, should things come together correctly.  One big problem is storms will be racing northeast at an incredible rate.  As stated on Thursday, 4/6 could be the bigger tornado day vs. 4/5.  We will have a much better view on 4/6 tomorrow as models update.


Thursday, 1 April

Early to maybe even mid next week (April 5-7) looks primed for severe storms and tornadoes across the southern and central Plains.  If you look only at the GFS Operational model, Monday (April 5) looks like a big day, with numerous supercells and some tornadoes possible from Texas to Nebraska.  It would be nice if it were that simple.  Look at one model and see an amazing setup.  Unfortunately it’s much more complex than that .

The European models (as well as the Canadian) are slower to eject the shortwave into the Plains early next week.   That means the current GFS solution for Monday should be taken with a grain of salt.  This may actually be a good thing.  The European models suggest that Monday, Tuesday and even Wednesday could all be chase days across the southern/central Plains (the GFS only has Monday being a good setup).  According to the European models, Monday looks like a potentially good setup, but with cap issues.  Tuesday might be the best day for tornadoes as the leading upper impulse associated with the larger trough reaches the Plains, and provides enough upper support to break the cap.  In fact, it’s possible the good tornado setup the GFS currently shows for Monday will be delayed and occur Tuesday.  That’s what I would hope for based on the available data.   But, whatever the details may be, we do have to question the GFS solution for Monday.

Over the next couple days I’ll watch the model trends and see which day (or days) truly look the best next week for tornadoes.   But the bottom line is this:  There should be at least one big day with supercells and tornadoes across the southern to central Plains April 5-7.

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