Tuesday, June 20, 2017

June 19 chase forecast

This evening I had a bit of a peek at the model output before writing this, and it's still amazing to me, after all these years, how much things change from run to run.  The imminent tropical depression/tropical storm is such a big pattern changer that even small deviations in its track will make for big chase changes.

Day 1 (June 23):
GFS: eastern NM to central OK
GEFS: southeast CO/eastern NM
GDPS: AL to middle TN
ECMWF: northeast CO
CFSv2: northeast NM to central OK

Day 2 (June 24):
GFS: southeast NM
GEFS: southeast NM/southern TX panhandle
GDPS: the Carolinas?
ECMWF: central KS
CFSv2: eastern NM

Day 3 (June 25):
GFS: eastern NM
GEFS: southeast CO/northeast NM
GDPS: maaaaaybe western KS
ECMWF: Kentucky and middle Tennessee?
CFSv2: central AB

Day 4 (June 26):
GFS: eastern CO
GEFS: eastern NM to western KS
GDPS: southwest MB
ECMWF: AB elbow
CFSv2: south-central AB, SK/MB border to central SD

Day 5 (June 27):
GFS: eastern SD/eastern NE
GEFS: northeast NE
GDPS: central MN
ECMWF: central AB
CFSv2: southeast SD

Day 6 (June 28):
GFS: northeast CO to western WY
GEFS: southeast SD
GDPS: southern NE
ECMWF: central AB-central MT
CFSv2: eastern WY/western NE

Day 7 (June 29):
GFS: eastern WY/southeast NE
GEFS: southern MN
GDPS: southwest SD
CFSv2: southwest SD

Day 8 (June 30):
GFS: eastern KS/western MO
GEFS: southeast SD
CFSv2: northern TX panhandle

Day 9 (July 1):
GFS: eastern NE/southwest IA
GEFS: eastern NE/most of IA
CFSv2: southeast NM/southern TX panhandle

Day 10 (July 2):
GFS: central SD, NE/IA border, central IL
GEFS: IA/southern MN
CFSv2: southwest SD

So I'm a little skeptical about the moisture returning to Alberta the way some model runs depict it. There are 2 potential sources of moisture--advection and evapotranspiration.  Evapotranspiration is only maaaaaaybe just starting up at this point, so I don't think we can count on a big boost from it.  As for advection, models depict moisture being shunted southward to, alternatively, New Mexico, Texas or even the Gulf of Mexico.  Then it magically appears in Alberta?  I don't know that that's a reasonable thing to happen in such a short time.  So at this point it looks to me like farther south plays will be likely, in the higher(ish) terrain of Montana, Wyoming, and Colorado; perhaps New Mexico is in the cards, too.  Later in the period the Gulf is forecast to open up and give a good stream of moisture to the southern and central plains.  This would mean better tornado chances, if better flow can get juxtaposed overtop.

Although a lot is inconsistent, I am encouraged by the consistency of the forecast of a) a mid-level trough acting on that airmass sometime in the June 26 to 30 range, and b) deep moisture return.

Details have yet to be ironed out but, as Pat said in a message earlier today, I'd maybe plan for (but not be 100% set on) a later departure.  The direction will be either west or south, and my money is on south.

Also of note, we have been doing these trips on and off since 2005.  I don't want to toot our own horns, but I will reluctantly do so: in all the years we've chased with this group, I can't remember more than 1 or 2 times when we've missed a forecast, and those times it was a forecast of marginal storms; the big stuff, we've nailed.  Our history shows that we almost always get to the best storm that is feasibly reachable for us.  I hope and plan to keep this streak going.


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