Severe Weather Discussion for March 28 – April 3, 2011.

Severe Weather Discussion for March 28 – April 3, 2011.
Issued:  03/27/2011.

Highlights:

–  Showers are likely late Monday through Tuesday across mainly central and eastern Oklahoma.

–  A thunderstorm or two may be possible late Saturday, although the potential is rather low.

–  Thunderstorms, some possibly severe, are possible on Sunday.

–  Temperatures will be in the upper 50s Monday, low 50s Tuesday, mid 50s Wednesday, mid 60s Thursday, mid 70s Friday, 80F Saturday, low 80s Sunday.

Probabilities:

–  Severe Thunderstorms in Oklahoma:  30%
–  Storm Chase:  25%

Discussion:

Not sure I should even mention how bad last weeks forecast was for yesterday/today.  At least I only blew the temperature by 20F today, I guess not too bad seven days out.

Northern stream Omega block will continue across central Canada a few more days and eventually dissolve by next weekend.  Models are in good agreement on this occurrence and appears that the 12z GFS and 00z ECMWF are the best runs for today’s forecast.  12z ECMWF seems way out to lunch on a developing low latitude system over Baja and then ejecting it northeast at D10 as a stronger Pacific medium wavelength trof approaches.  This is in contrast to the GFS, which for the past several days, has insisted on a closed low moving through the northern Gulf.  Luckily that has abated and subsequent destruction of Gulf moisture seems less likely.  To this end the 12z/18z GFS and 00z/12z ECMWF are in agreement.

Three shortwave trofs will impact the region early in the week with additional systems traversing the central U.S. late week.  The first system is the same as prior systems, in that it is a a weak shortwave trof and will be east of the region early Monday.  The only impact from this system has been widespread cloud cover and associate temperature bust.  The next system will follow quickly late Monday.  Moisture will increase as this system approaches late Monday into Tuesday.  The resulting WAA pattern should be good for widespread showers and thunderstorms.  Severe thunderstorms are not anticipated.  Given the ongoing extreme drought, tough to get all that excited about rain chances right now.  However, this does appear to be the best opportunity for widespread rain in quite some time.  BTW – as of today, no tornadoes in the month of March for Oklahoma.  The third system in this string, takes shape early Wednesday and moves across the region through Thursday as it amplifies.  Moisture looks to be lacking with this system, so will forgo POPs at this point.  Although, clouds may be an issue with it.

System clears the area Thursday as we undergo shortwave ridging.  This will help temperatures steadily increase through the weekend.  More interesting weather may be at the D7 time period, as has been the case a lot recently.  As noted above 00z ECMWF showed a very interesting setup for 04/03.  However, the 12z was completely different.  The 12z/18z GFS runs lend a little creditability to the 00z ECMWF although not near as amplified.  In any other year, I’d question the lower amplified solution especially given the GFS’s tendency to minor out waves.  However, in this pattern said solution certainly cannot be ignored.  I went ahead with storm chances on Sunday and the severe probabilities are again set for climo.  I’d like to go lower since I’m a little tired of these D7 severe weather busts.  Something of interest to watch in the whole thing is the limited impact on the Gulf from Wednesday’s system.  As such, the GFS shows low 60s dewpoints in Oklahoma by late Saturday.  Given the lack of a strong surface ridge in the Gulf, modified Gulf air is not as big of a problem this go-around.  GFS even develops some CAPE on what can loosely be called a dryline Saturday afternoon and ahead of this feature in far eastern Oklahoma late Sunday.  Shortwave ridging should keep convection down on Saturday, but I went ahead and put isolated storm chances in for the potential.

If the system expected for Sunday amplifies, the severe weather threat would seemingly increase.  There could end up being a slow down of the system as it is not on the coast and a pattern change is in-progress.  Models have been horribly unreliable beyond D5 and so the forecast for D6/D7 is low confidence.  If we can manage to get a severe weather threat, this will be handled with special discussions.

I went with the party line of temperatures much of the week, not making any major changes to MOS.  Going 10-15 degrees below normal the first three days of the forecast period is drastic enough.  The warmup for Thursday-Saturday looks real good.  I’m not sure I went warm enough on Sunday, but low 80s is fine.  Heck, after going 60F and only hitting 40F today not sure I should be too worried.

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