RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Tue Sep 22 19:41:02 UTC 2020.
No Mesoscale Discussions are in effect as of Tue Sep 22 19:41:02 UTC 2020.
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1109 AM CDT Tue Sep 22 2020
Valid 221630Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE UPPER TEXAS AND SOUTHWEST LOUISIANA GULF COAST....
...SUMMARY...
A brief/weak tornado cannot be ruled out today along the upper Texas
and Louisiana coasts in association with Tropical Cyclone Beta.
...TX/LA...
Scattered outer bands of TD Beta continue to affect parts of the
upper TX Gulf Coast and coastal LA. Shear profiles in this area are
minimally strong to support rotating updrafts or brief tornadoes in
the more robust cells, but so far activity has been weak. Continued
pockets of daytime heating may be sufficient for some
intensification of storms this afternoon in areas where the
mid/upper 70s dewpoints are present. However, the overall threat of
brief spin-ups appears marginal.
..Hart/Leitman.. 09/22/2020
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SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0233 PM CDT Tue Sep 22 2020
Valid 222000Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
TEXAS COAST REGION EAST ACROSS PORTIONS OF COASTAL LOUISIANA...
...SUMMARY...
A brief/weak tornado cannot be ruled out today along the upper Texas
and Louisiana coasts in association with Tropical Cyclone Beta.
...Discussion...
Current forecast reasoning remains representative of convective
evolution across the upper Texas Coast region, and points east. As
such, no changes to the existing MRGL risk area appear necessary at
this time.
..Goss.. 09/22/2020
.PREV DISCUSSION... /ISSUED 1109 AM CDT Tue Sep 22 2020/
...TX/LA...
Scattered outer bands of TD Beta continue to affect parts of the
upper TX Gulf Coast and coastal LA. Shear profiles in this area are
minimally strong to support rotating updrafts or brief tornadoes in
the more robust cells, but so far activity has been weak. Continued
pockets of daytime heating may be sufficient for some
intensification of storms this afternoon in areas where the
mid/upper 70s dewpoints are present. However, the overall threat of
brief spin-ups appears marginal.
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1226 PM CDT Tue Sep 22 2020
Valid 231200Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF EAST CENTRAL/NORTHEASTERN MINNESOTA AND ADJACENT NORTHWESTERN
WISCONSIN...
...SUMMARY...
A few strong to severe storms may occur Wednesday evening across
parts of northeastern Minnesota and into northwestern Wisconsin.
Large hail should be the main threat, along with potential for a
strong gust or two.
...Synopsis...
Weak flow aloft will prevail over roughly the southern 2/3 of the
CONUS this period, with T.D. Beta -- moving slowly northeastward
across east Texas and Louisiana through the period -- the primary
feature of interest. Please refer to the latest forecast
information from the National Hurricane Center, regarding T.D. Beta.
Farther north, a short-wave trough will advance steadily eastward
across the north-central portion of the country, ahead of a
larger/stronger trough over the Gulf of Alaska. A short-wave piece
of the larger trough is forecast to shift inland into the Pacific
Northwest overnight.
At the surface, a cold front is forecast to advance across the
northwestern states ahead of the aforementioned trough, while a
weaker low lingers in the vicinity of the mid Missouri Valley. A
warm front extending east-northeastward from this low to the Lake
Superior vicinity may focus a small area of strong to severe storms
during the second half of the period.
...Upper Mississippi Valley region...
Isolated evening thunderstorms are expected to develop across
portions of east central and northeastern Minnesota, and then spread
into northwestern Wisconsin overnight, near a warm-frontal boundary
forecast to extend east-northeastward across this area, east of a
weak mid Missouri Valley surface low.
Though westerly mid-level flow near 40 kt across the area suggests
shear sufficient for organized storms, modest CAPE is expected,
which should hinder overall storm intensity/severe potential. Thus,
will maintain only 5%/MRGL risk for hail, and possibly and stronger
wind gust or two.
...Louisiana vicinity...
As Beta drifts slowly northeastward across the Sabine River Valley
area, bands of convection will continue spreading across the lower
Mississippi River Valley area. Widespread clouds should largely
hinder potential for any appreciable heating/destabilization, and
thus expect convection to remain weak. Though low-level shear is
expected to be sufficient for some low-level rotation in any
stronger/sustained convective cell, risk for a brief/weak tornado
appears too low at this time to warrant introduction of a 2% tornado
probability/MRGL categorical risk area.
..Goss.. 09/22/2020
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1113 AM CDT Tue Sep 22 2020
Valid 221700Z - 231200Z
An elevated risk area was introduced for portions of New England for
this afternoon. Late morning surface observations show RH values
already falling into the 35-40% range (which is verifying lower than
recent ensemble forecasts for some locations) with sustained winds
near 15 mph. Regional VAD observations and 12 UTC soundings show a
nearly unidirectional low-level wind profile with 20-30 mph flow
just off the surface. These winds should be able to mix down more
efficiently by the afternoon hours as low-level lapse rates steepen.
Given the dry fuels across this region and increased confidence in
wind speeds at or above 15 mph, an elevated risk appeared warranted.
A mix of wet and dry thunderstorms has been ongoing this morning
across the broader Four Corners region. This trend is expected to
continue through today due to an increase in mid-level moisture over
the past 24 hours. While a dry thunderstorm is possible, coverage of
dry thunder is expected to remain limited. Elsewhere, the forecast
remains on track (see discussion below).
..Moore.. 09/22/2020
.PREV DISCUSSION... /ISSUED 0125 AM CDT Tue Sep 22 2020/
...Synopsis...
Broad upper-level ridging will continue over a majority of the U.S.
today. An upper-level trough off the Northeast coast will continue
to phase with Hurricane Teddy. The pressure gradient around Teddy
should broaden and help increase surface winds in parts of the
Northeast. Across the Northwest, mid-level winds will relax in the
wake of a weak trough. Towards the end of the period, a more
substantial trough will arrive.
...Southeast OR/Northeast CA/Northwest NV...
Locally elevated conditions are possible during the afternoon as a
few locations may see 15 mph winds with RH falling below 20%. There
continues to be uncertainty as to how long these conditions will
coincide. Cloud cover from the approaching Pacific trough, a weak
surface gradient, and a relative lull in flow aloft during the
afternoon all contribute to reduced confidence in sustained elevated
conditions.
...Portions of New England...
Continued dry northerly flow is expected, though winds should be
stronger than previous days due to the influence of Teddy. Winds are
still expected to reach 10-15 mph in most places. RH could drop as
low as 25-35% during the afternoon. With moderate flow just off the
surface, strong gusts are possible even without sustained wind
meeting elevated criteria. With fine fuels have dried out over the
past week, locally elevated conditions are possible where winds can
exceed 15 mph.
...Please see www.spc.noaa.gov/fire for graphic product...
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SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0143 PM CDT Tue Sep 22 2020
Valid 231200Z - 241200Z
The previous forecast remains on track with only minor adjustments
needed for the ongoing elevated risk area. Guidance continues to
show reasonably high probabilities for increasing mid-level winds
that could support stronger surface gusts, and morning guidance
compares well with the observed deepening of the upper-level low
over the northeast Pacific. However, confidence in meeting and
sustaining critical RH thresholds (below 15%) remains low.
...Dry Thunderstorms...
A similar scenario to today is expected again on Wednesday. Storms
today have mostly produced rain rates well above 0.1 inch/hour (per
MRMS estimates) across the Four Corners region. Given forecast PWAT
values between 0.5 to 0.7 inches across southern CO into NM again
for tomorrow, similar results are expected, though a dry storm or
two will remain possible.
..Moore.. 09/22/2020
.PREV DISCUSSION... /ISSUED 0157 AM CDT Tue Sep 22 2020/
...Synopsis...
A strong upper-level trough will move into the Pacific Northwest on
Wednesday. A cold front will approach from the west and move ashore
late in the afternoon. While high and mid-level clouds will remain
across the region, both mid-level winds and the surface pressure
gradient will be more favorable than Tuesday. Increasing mid-level
moisture may keep some areas from seeing RH below 20%. However,
15-20 mph downslope flow will likely coincide with 15-20% RH on a
broad enough basis that elevated highlights are warranted.
...Please see www.spc.noaa.gov/fire for graphic product...
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