- Day Three
acus02 kwns 051655
Storm Prediction Center ac 051654
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1054 am CST Thu Dec 05 2019
Valid 061200z - 071200z
..no severe thunderstorm areas forecast...
the risk for severe thunderstorms appears negligible across the
U.S., Friday through Friday night.
Within one branch of split westerlies across the mid-latitude
eastern Pacific, models indicate that amplified troughing will begin
to advance inland across the Pacific coast region during this
period. An initially broad and deep lower/mid tropospheric cyclone
is embedded within this feature, but it is forecast to weaken
considerably as it approaches the coast, and may still be centered
several hundred miles west of the northern California/southern
Oregon coast at 12z Saturday.
Downstream of the troughing, there may be some flattening/broadening
of short wave ridging shifting across The Rockies through the
Mississippi Valley. As this occurs, the remnants of a mid-level low
(initially digging into the lower Mississippi Valley at 12z friday)
are expected to turn eastward and accelerate across the eastern Gulf
states, into the western Atlantic by late Friday night.
..Pacific coast region...
The initially broad -22 to -24 c 500 mb cold core of the approaching
trough and cyclone may begin to warm during this period, with
coldest temperatures likely to remain offshore. However, models do
indicate that -20 to -22 c 500 mb temperatures may gradually begin
to overspread Washington, Oregon and northern California late Friday
through Friday night. Destabilization inland of coastal areas seems
likely to remain weak to negligible, but could become maximized
across the Shasta/Siskiyou region and northern Sierra Nevada late
Friday night. This is where a preceding influx of moisture from the
lower latitude Pacific, coupled with strengthening
south/southwesterly low-level flow and associated orographic lift
and warm advection, may contribute to thermodynamic profiles
sufficient for convection capable of producing occasional lightning.
..lower Mississippi Valley/central Gulf states...
Mid-level cooling and forcing for ascent associated with the digging
southern stream perturbation may be contributing to scattered
thunderstorm development across southeast Arkansas and adjacent
portions of the lower Mississippi Valley region at the beginning of
the period. This will be aided by moistening southerly return flow,
likely rooted above a stable boundary layer, and may continue into
the day Friday. How long, and how far east/southeastward across the
central Gulf states, remains unclear, with weak thunderstorm
activity expected to diminish as the mid/upper impulse accelerates
eastward toward the South Atlantic coast and low-level moisture
return becomes cut off.
..maximum risk by hazard...
Tornado: <2% - none
wind: <5% - none
hail: <5% - none