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Bob's Burgers

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    January 10-11 Severe Weather Threat

    in Central/Western States

    Posted

    20 minutes ago, nrgjeff said:

    I expect supercells in Texas Friday evening. If things go early enough, maybe late afternoon. Trying to find positives for storm chasers that way, haha.

    LLJ indeed will increase with time, and do so quickly and substantially. SPC rightly talks about the line possibly breaking up into supercells. We normally discuss the more common opposite, sups congeal to line. However with a rapidly strengthening and backing LLJ lines can and do occasionally break up into supercells. It's most common right after the line develops (as opposed to sup line sup). In this case a line may develop; then within 1-2 hours, actually break up into supercells for a couple hours.

    In all cases sups eventually go linear (or go back to linear) this weather pattern. You won't see me travelling to chase this. However I know people closer who are watching it.

    I remember that phenomena happening on May 1st, 2018. Rather unimpressive squall line evolved into a few discrete cells which eventually dropped a massive EF-3 near Salina, KS. 

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    January 10-11 Severe Weather Threat

    in Central/Western States

    Posted 

    Area Forecast Discussion
National Weather Service Birmingham AL
607 AM CST Wed Jan 8 2020
    
Friday will mark the beginning of an extended period of unsettled
weather as a trough strengthens and becomes increasingly dynamic
over Texas and New Mexico. Strengthening southerly flow will lead
to isentropic lift as a warm sector begins to advance northward.
Widespread showers with isolated embedded elevated thunderstorms
are expected across much of the forecast area on Friday.

As the upper-level trough transitions from a neutral to negative
tilt Friday night, rapid pressure falls are expected near the
Mississippi River at 6 AM Saturday. An extremely strong low-level
jet is anticipated in advance of a well-organized QLCS, with mid
to upper 60s dewpoints overspreading the forecast area by noon
Saturday. As it stands, a significant severe weather event appears
likely beginning as early as 9 AM in our western counties. SBCAPE
is currently modeled at 500-1000 J/kg by most model guidance, but
my hunch is that these values may be a little on the low side due
to the effects of erroneous-looking QPF as noted in the ECMWF
data. Even taking CAPE a face value, strong forcing combined with
extreme low-level winds and wind shear would result in a QLCS
capable of producing widespread damaging winds and embedded
tornadoes. The ECMWF shows a wide swath of 70-80 kt 700mb winds
with pockets up to 100 kts, meaning that a derecho cannot be ruled
out particularly across our northwestern counties. The potential
for supercells ahead of the QLCS will depend on the state of the
warm sector. If the warm sector is relatively uncontaminated and
the current timing holds true, temperatures would rise into the
70-74F range during the late morning and early afternoon hours,
aiding in the formation of cellular convection ahead of the QLCS.
In order for any cellular activity to become tornadic in the
presence of extreme wind shear, robust updrafts will be required.
Otherwise, these updrafts will be torn apart.

This system should exit the area late Saturday afternoon or
Saturday evening, and dry conditions expected on Sunday with the
exception of a slight chance of showers across our southeastern
counties. Here the front is expected to stall and return northward
as a warm front Sunday afternoon into Monday. Showers and embedded
thunderstorms should expand in coverage and move northward to
near I-59 on Monday. These high rain chances will continue into
Tuesday across most of the forecast area.

87/Grantham
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