Monday 9/30/2019 Day 1 Marginal Risk

A place to discuss upcoming severe weather setups. Unless otherwise noted, all posts of weather graphics are for informational purposes only, by non-meteorologists. All posted weather models should be taken with a grain of salt. Please refer to your local news or radio and other official sources for up-to-date weather information.
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Monday 9/30/2019 Day 1 Marginal Risk

Post by minime » Sat Sep 28, 2019 6:12 pm

day3otlk_0730.gif (28.6 KiB) Viewed 141 times
SPC AC 280730

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Sat Sep 28 2019

Valid 301200Z - 011200Z


Isolated strong to severe storms will be possible on Monday across
parts of the Upper Midwest and northern/central Plains.

...Upper Midwest into the Northern/Central Plains...
At least scattered storms should be ongoing Monday morning in a
low-level warm air advection regime across the eastern Dakotas into
MN and northern WI. A surface low is forecast to develop
northeastward across this region as a strong mid/upper-level jet
continues to overspread the northern/central Plains into the Upper
Midwest. Substantial destabilization appears likely in the wake of
the morning convection across MN/WI to the south of a surface warm
front where upper 60s to lower 70s dewpoints should be present.
However, 00Z model guidance exhibits a fair amount of variability in
the track of the surface low, and in the northward extent of the
warm sector across the Upper Midwest by late Monday afternoon. This
introduces considerable uncertainty in where a corridor of greater
severe potential may exist. In addition, persistent southwesterly
flow aloft through mid levels may tend to limit convective
development across the warm sector through Monday afternoon owing to
a low-level temperature inversion.

Storms do appear likely to develop Monday evening/night along a
southeastward moving cold front that should extend from MN into the
northern/central Plains as a south-southwesterly low-level jet
strengthens. Even though storms that develop along this boundary
will probably have a tendency to be undercut fairly quickly, they
may pose an isolated severe risk initially given the strong shear
that is forecast to be present. Regardless, given all of the
aforementioned uncertainties, a broad Marginal Risk has been
included for now, with potential for higher severe probabilities
once mesoscale details become clearer.

..Gleason.. 09/28/2019

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Re: Monday 9/30/2019 Day 1 Marginal Risk

Post by thunderchaser83 » Mon Sep 30, 2019 12:26 pm

day1otlk_1200.gif (30 KiB) Viewed 137 times
SPC AC 300555

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1255 AM CDT Mon Sep 30 2019

Valid 301200Z - 011200Z


Isolated strong to severe storms will be possible from the upper
Great Lakes to the central Plains as well as over the southern High

...Upper Great Lakes to Central Plains...

Strong mid-level speed max is forecast to translate across
WY/Dakotas during the day, then into northwest MN during the evening
hours. In response, a surface cyclone will track across northeastern
SD to near the MN/ON border by 01/00z with a trailing front arcing
through northwestern IA into northeast CO. Large-scale height falls
are forecast to spread across the northern Plains into MB/western ON
with the southern influence of the short-wave trough expected to
glance the international border region. Early in the period,
low-level warm advection will likely be responsible for one or more
clusters of convection across the upper Great Lakes region. While
some of this activity could be strong, possibly generating hail at
times, the primary concern early in the period will be immediately
ahead of the mid-level speed max over eastern ND into northwest MN.
This activity will be an extension of ongoing thunderstorms (at
0530z) that are growing upscale just north of a warm front along the
SD/ND border. Strong/severe elevated thunderstorms should continue
through daybreak north of the surface low where relatively steep
mid-level lapse rates and MUCAPE in excess of 2500 J/kg are
expected. Strong shear suggests storm rotation is possible and a few
supercells can be expected. Large hail is the primary risk before
this activity advances into ON.

Across the warm sector, considerable uncertainty exists regarding
the prospect for surface-based convection. Forecast soundings
suggest parcels will struggle to reach their convective temperatures
except for southwest NE/northeast CO. Even across the central High
Plains it appears any storms that develop along the front will lift
north of the boundary and become elevated. Convection should
increase north of the front after sunset across NE, especially as
LLJ increases into this region. Will maintain 5% severe for this
scenario but a considerable number of storms may ultimately warrant
higher probs for possible hail.

...Southern High Plains...

Strong upper high will hold firm across the Mid-South region
ensuring a very moist southerly trajectory around the western
periphery of the anticyclone into the southern Rockies/High Plains.
While lapse rates will necessarily be poor within this moist plume,
thunderstorms should readily develop by afternoon from northern
Mexico, across far west TX into the TX Panhandle. Modest mid-level
flow should allow for some organization along with a low risk for
damaging winds, and perhaps some hail.

..Darrow/Cook.. 09/30/2019

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