Severe Weather Discussion for October 28 – November 3, 2013

Severe Weather Discussion for October 28 – November 3, 2013.
Issued:  10/27/2013.
Highlights:
–  Severe thunderstorms are possible on Monday in northwest Oklahoma and the panhandle.  Primary threat is large hail.
–  Severe thunderstorms are again possible on Tuesday in western Oklahoma.
–  Another round of severe thunderstorms may develop on Wednesday into early Thursday across a large part of Oklahoma.  Heavy rain looks likely at least late Wednesday into Thursday.
–  Temperatures will be in the mid 70s Monday-Wednesday, upper 60s Thursday, near 70F Friday-Saturday, and mid 60s Sunday.
–  Time change Sunday November 3rd at 2am.
Probabilities:
–  Severe Thunderstorms in Oklahoma:  50%
–  Storm Chase:  25%
Discussion:
Model variability has been quite high the past few days with respect to the Monday-Wednesday time frame.  Luckily much of the inter and intra model variance decreased with the recent 06z/12z runs.  As such, the forecast confidence is a little higher.  Unfortunately forecasting severe weather this time of year has greater risks than May.  However, a severe weather setup appears to be in-place for Monday-Wednesday for much of Oklahoma.
All models forecast a large upper system to take shape over the western U.S. by Monday afternoon with a dryline setting up in the Texas/Oklahoma panhandles.  Upper forcing is seemingly absent, but would expect some minor wave to initiate convection Monday afternoon.  SPC has highlighted western Oklahoma into the panhandle with a slight risk.  A 10% hatched area is also present for far northwest Oklahoma, seemingly for large hail.  By Tuesday the upper system moves a little east and much strong winds impinge across the area.  The dryline is progged to be a little farther east (closer to the TX/OK border) by Tuesday afternoon.  Deep layer moisture will be present with CAPE values near 1500 J/Kg.  Models indicate weak or neutral forcing along the dryline.  However, impressive 500mb jet streak moves into the region during the late afternoon and any small waves would seemingly initiate convection.  NAM has 850mb winds veered a little west of 180 and the GFS also does.  This may or may not mean anything for the setup.  NAM and EC are generally quiet while the GFS does develop convection.
Longwave trof ejects east-northeast on Wednesday, driving the dryline well into Oklahoma.  Wednesday has the potential to be a medium-end event or a huge cluster of thunderstorms (low-end).  Very difficult to tell and time of year would certainly favor the latter.  I’m not in the camp of unidirectional shear although the 850mb winds are more veered than Tuesday.  However, these are just model progs and the ultimate solution could be different.  It is important to know that the models are frequently too fast in ejecting this type of system, so changes seem likely.  The upper system will be much better sampled by the upper air  network tonight, with the 00z and 06z model runs improving on the current set.
SPC has highlighted much of central/eastern Oklahoma in the Day 4 (Wednesday), pointing to 30% probabilities and potentially a moderate risk.  Way too many questions right now and I’ve considered special discussions.  For now I’ll hold off but may initiate such tomorrow.
Beyond Thursday, mild and dry conditions will follow in wake of the upper trof.  Temperatures will be average for this time of year.
First guess as numbers were close and only modified Sunday to be inline with the NWS.  I really didn’t care much about D7 as the main impacts this week will be felt Monday-Wednesday.
Chase wise, I just can’t help myself.  Tuesday seems decent if convective initiate becomes more likely.  I’ll certainly keep an eye on Wednesday assuming the threat is farther west than current.
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