Convective Outlook

Day 4-8 Outlook

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0223 AM CDT Sat Oct 31 2020

Valid 031200Z - 081200Z

...DISCUSSION...
The extended range forecast will feature a changing pattern from
zonal flow during the midweek period followed by an amplifying
large-scale trough over the West Coast towards the end of next week.
Relatively dry/stable conditions will prevail across much of the
contiguous United States and result in very low severe weather
potential for the entire extended period.

Updated 31 October 2020 | 2:26 am

SPC 0730Z Day 3 Outlook

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0158 AM CDT Sat Oct 31 2020

Valid 021200Z - 031200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorms are not currently forecast across the contiguous
United States on Monday.

...Synopsis...
A long-wave mid-level trough will exit the East Coast into the
western Atlantic as a ridge builds over the High Plains.  Surface
high pressure centered over the lower MS Valley will lead to
tranquil conditions for a large part of the area east of the
Rockies.  Models show a weak mid-level trough over southern CA.  A
few high-based showers and possibly a thunderstorm could develop
over southern NV and perhaps the far southern Sierra Nevada. 
However, the thunderstorm risk appears too negligible to warrant an
areal thunderstorm highlight at this time.

..Smith.. 10/31/2020

Updated 31 October 2020 | 2:00 am

SPC 0600Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1259 AM CDT Sat Oct 31 2020

Valid 011200Z - 021200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
NORTH CAROLINA INTO FAR SOUTHEAST VIRGINIA...

...SUMMARY...
Isolated severe thunderstorms are possible over eastern North
Carolina and far southeast Virginia on Sunday.

...NC northward to southeast coastal NJ...
An intense and amplifying mid-level trough will evolve into a closed
500 mb low as it moves from the Great Lakes on Sunday morning to the
Northeast by early Monday morning.  In the low levels, a surface low
initially over northeast Ontario will consolidate with a surface low
developing off the NJ coast and a strong surface cyclone is forecast
over the Gulf of Maine/coastal Maine late Sunday night.  

During the morning to midday hours, the strengthening surface trough
over the Mid-Atlantic states will aid in intensifying low-level flow
and the northward transport of mid-upper 50s F dewpoints into the
Delmarva and lower 60s in eastern NC.  Strong differential advection
via cooling aloft in the mid levels and moistening in the low
levels, will result in a destabilizing boundary layer by early
afternoon.  Operational suite of models are generally showing the
development of 500 J/kg SBCAPE over eastern NC with 100-200 J/kg
MUCAPE as far north as the southern half of NJ.  Forecast soundings
show very strong low-level shear and enlarged hodographs over the
narrow warm sector near the immediate coast.  Strong mid-level
height falls (90-150 m per 12 hr) are expected to overspread the
VA/NC warm sector during the day.  Given the above mentioned
factors, it seems plausible a forced convective line will evolve
over the Mid-Atlantic states.  The risk for isolated strong to
severe gusts may accompany this convective line before moving off
the coast by early evening.  Farther south over eastern NC, a
supercell threat could evolve near the immediate coast with an
attendant isolated wind/tornado hazard.  

Elsewhere, dry/stable conditions will generally prevail across much
of the remainder of the contiguous United States.

..Smith.. 10/31/2020

Updated 31 October 2020 | 1:05 am

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 PM CDT Fri Oct 30 2020

Valid 311200Z - 011200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Aside from parts of the southern Florida Peninsula, the risk for
thunderstorms appears negligible across much of the U.S. today
through tonight.

...Discussion...
Amplification within the westerlies is underway across the
mid-latitude Pacific into western North America, and this appears
likely to translate eastward, across the Rockies toward the Atlantic
Seaboard, later today through tonight.  This includes a building
large-scale ridge near the Pacific coast, which may build further
while also expanding eastward across the Rockies by late tonight.

To the east of the ridging, an intensifying short wave trough is
forecast to sharply dig southeastward out of Alberta and
Saskatchewan, through the northern U.S. Great Plains and much of the
Mississippi Valley by 12Z Sunday.  This will be accompanied by
another cold front.  However, in the wake of recent cold intrusions
to the lee of the Rockies, including cold surface ridging still
present across much of the eastern U.S. through much of the
northwestern Gulf of Mexico, models indicate that pre-frontal
moistening will be quite modest to weak.  With colder mid-level air
also lagging to the northwest of the surface front, this will result
in negligible destabilization and risk for thunderstorms.

A narrow plume of deep-layered moisture/seasonably high precipitable
water is forecast to linger along a weakening remnant frontal zone
across the southern Florida Peninsula.  This regime likely will
include upper 60s to lower 70s surface dew points, which probably
will contribute to boundary-layer CAPE in excess of 1000 J/kg with
daytime heating.  Perhaps aided by weak large-scale forcing for
ascent, to the south of a remnant mid-level cyclonic shear axis,
this is expected to support a few thunderstorms today.  Generally
weak lapse rates and weak deep-layer mean flow/shear, among other
factors, suggest the potential for severe weather is negligible.

..Kerr/Dean.. 10/31/2020

Updated 30 October 2020 | 11:36 pm