RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Sat Nov 27 08:54:02 UTC 2021.
No Mesoscale Discussions are in effect as of Sat Nov 27 08:54:02 UTC 2021.
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1129 PM CST Fri Nov 26 2021
Valid 271200Z - 281200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Thunderstorms are not forecast across the contiguous United States
on Saturday.
...Discussion...
Gradual amplification of the upper flow pattern over the U.S. is
expected today, as short-wave troughing progressing southeastward
across the Canadian Priairie provinces and northern/central Plains
states eventually begins phasing with a southern-stream trough
crossing the south-central states. The eventual result will be a
broad trough over the East, and upstream ridging over the West.
At the surface, a weak low/front will shift out of the Plains and
across the mid and lower MS/OH/TN valleys with time, while high
pressure prevails elsewhere.
With a continental airmass largely in place over the U.S., little
potential for thunderstorms is evident. The lone exception could be
across the Texas vicinity, where a few sporadic lightning flashes
could occur with weak/elevated convection, within an area of
QG-forced precipitation associated with the aforementioned upper
short-wave trough. However, coverage appears likely to remain
sparse, precluding inclusion of the 10% area.
..Goss/Elliott.. 11/27/2021
Read more
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1100 PM CST Fri Nov 26 2021
Valid 281200Z - 291200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
The risk of thunderstorms appears negligible across most of the U.S.
Sunday through Sunday night. However, some lightning may accompany
stronger lake-effect snow showers and bands expected to develop near
and southeast of Lake Erie during the late afternoon and evening.
...Discussion...
Models indicate that amplification within the main belt of
westerlies emanating from the mid-latitude Pacific will translate
from ridging, inland of the Pacific coast into the Great Plains,
into downstream troughing, east of the Mississippi Valley into
western Atlantic. Within this regime, the most prominent short wave
trough is forecast to dig sharply southeast of the upper Great
lakes, through the northern/mid Atlantic Seaboard vicinity by late
Sunday night. As it does, associated forcing for ascent appears
likely to contribute to renewed surface cyclogenesis offshore,
accompanied by a reinforcing cold intrusion across much of the East.
At the same time, the remnants of a cut-off low appear likely to
continue to weaken while becoming absorbed within a confluent regime
across the Gulf Coast states, through the base of the large-scale
mid-level troughing, across and offshore of the south Atlantic coast
by Sunday evening. While this may be accompanied by mid/upper-level
moisture return and weak high-based convection across the Gulf coast
vicinity and Florida Peninsula, generally dry and stable
near-surface conditions appear likely to persist across this region,
as an initial low/mid-level moisture return to Texas on Saturday
becomes suppressed southward across the northwestern into central
Gulf of Mexico.
...Lake Erie vicinity...
A corridor of strong mid-level cooling (including temps of -20 to
-30 C in the 700-500 mb layer) due to lift and cold advection is
forecast to nose southeastward, across and southeast of the Lake
Erie vicinity late Sunday afternoon and evening. This will
contribute to steepening low-level lapse rates and weak CAPE,
particularly near the relatively warm lake waters. The latest NAM
forecast soundings, supported by the Rapid Refresh, suggest that
thermodynamic profiles might become conducive to convection capable
of producing lightning, primarily after 28/21Z into the 29/03-04Z
time frame.
..Kerr.. 11/27/2021
Read more
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
1155 PM CST Fri Nov 26 2021
Valid 291200Z - 301200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY...
The risk of thunderstorms appears negligible across the U.S. Monday
through Monday night.
...Discussion...
It appears that mid-level troughing will take on more of a negative
tilt orientation off the Atlantic Seaboard during this period, as
the most vigorous embedded short wave perturbation pivots northeast
of the northern Mid Atlantic and New England coast. Models indicate
that associated large-scale forcing for ascent will contribute to
considerable further deepening of a surface cyclone, east/southeast
of the Cape Cod vicinity into the Canadian Maritimes by late Monday
night.
In the wake of this feature, and ahead of building mid-level ridging
across the northeastern Pacific into the Pacific Northwest and
Canadian Rockies, much of interior North America will remain under
the influence of northwesterly flow. Cold surface ridging will also
likely be maintained beneath a confluent mid-level regime across
much of the Gulf Coast/Southeast and northeastern Gulf of Mexico,
contributing to the continuation of generally dry and/or stable
conditions across most of the U.S.
..Kerr.. 11/27/2021
Read more
Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0250 AM CST Sat Nov 27 2021
Valid 301200Z - 051200Z
...DISCUSSION...
It appears that mid/upper flow across North America may de-amplify
by the middle of next week, in the wake of a deep cyclone migrating
north-northeast of the Canadian Maritimes. However, guidance
suggests that the mean pattern may remain at least broadly cyclonic
east of the Mississippi Valley into the Atlantic, downstream of
broad ridging across the eastern mid-latitude Pacific into the
Rockies and Great Plains. As a weaker belt of westerlies also
lingers from the subtropical eastern Pacific through the Gulf of
Mexico and Florida Peninsula, a generally confluent mid-level regime
may maintain potentially cold surface high pressure across much of
the Gulf Coast and Southeast, inhibiting boundary-layer moistening
over the Gulf of Mexico and substantive inland moisture return.
Even if significant renewed amplification within the westerlies were
to take place east of the Mississippi Valley into the Atlantic
Seaboard late this week into next weekend, as at least some model
output has indicated, it is not clear that low-level moistening off
the Gulf of Mexico and/or western Atlantic will be sufficient to
support an appreciable risk of severe weather by that time.
Read more
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1256 AM CST Sat Nov 27 2021
Valid 271200Z - 281200Z
...Synopsis...
A cutoff mid-level low is forecast to become absorbed by a
large-scale trough as it moves from near the Texas/New Mexico and
Mexico border this morning into the southern/southeastern United
States through tonight. As this occurs, broad mid-level ridging is
forecast to build across much of the western United States.
Meanwhile, a relatively weak area of surface high pressure is
forecast to remain over the Great Basin.
...Southern California...
Poor (to very poor) overnight RH recoveries coupled with lingering
breeziness will likely promote at least pockets of elevated to
locally critical fire weather conditions through this morning and
into this afternoon over the interior mountains/valleys of Southern
California. The most likely area for locally critical fire weather
conditions is from portions of the Ventura Valley into the San
Gabriel Mountains. Fire weather conditions are forecast to generally
improve by mid/late afternoon as the pressure gradient weakens
further and winds speeds relax (though single digit RH values will
remain).
Elevated to locally critical fire weather conditions may redevelop
later tonight into Day 2/Sunday as modest strengthening of the
surface pressure gradient promotes breezy surface winds amidst poor
overnight RH recoveries.
...Southern Plains...
Breezy and dry post-frontal northeast surface winds are forecast
from late this morning through late this afternoon as a cold front
sags southward across the Southern Plains. At least a few hours of
elevated fire weather conditions are likely as sustained surface
winds of 15-20 mph overlap minimum RH values near 20% and at least
modestly receptive fuels (ERCs generally exceeding the 80th
percentile). The Elevated area was expanded farther eastward into
the Texas Panhandle and portions of far western Oklahoma to match
the most aggressive guidance (e.g., HRRR, FV3, GFS) as they tend to
perform best in post-frontal regimes. Any fire weather concerns will
diminish rapidly by this evening as wind speeds decrease and RH
values improve.
...Southeast...
A dry and relatively cool continental air mass is forecast to remain
across much of the Southeast United States through today. While
near-critical RH values are likely from midday into the evening,
surface wind speeds should generally remain light enough to preclude
large-scale fire weather concerns. One exception could be across the
higher terrain of the Appalachians where topographic enhancement may
promote pockets of locally elevated fire weather conditions for a
few hours.
..Elliott.. 11/27/2021
...Please see www.spc.noaa.gov/fire for graphic product...
Read more
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1259 AM CST Sat Nov 27 2021
Valid 281200Z - 291200Z
...Synopsis...
A broad mid-level ridge over the western United States is forecast
to gradually recede southward through Day 2/Sunday as a mid-level
shortwave trough approaches the eastern Pacific coast. Meanwhile, a
relatively weak area of surface high pressure if forecast to remain
over the Great Basin.
...Southern California...
Elevated to locally critical fire weather conditions are forecast
much of Day 2/Sunday as a persistent dry airmass (single digit
minimum RH values and poor overnight recoveries) overlaps lingering
breeziness (sustained winds of 15-20 mph) and critically-receptive
fuels (ERC values exceeding the 90th percentile). In general, the
lack of appreciable upper-level support will preclude a more robust
fire weather threat.
..Elliott.. 11/27/2021
...Please see www.spc.noaa.gov/fire for graphic product...
Read more
|
RSS Feed