RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Tue Nov 19 06:57:01 UTC 2019.
No Mesoscale Discussions are in effect as of Tue Nov 19 06:57:01 UTC 2019.
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 PM CST Mon Nov 18 2019
Valid 191200Z - 201200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS SOUTHERN ARIZONA...
...SUMMARY...
Strong thunderstorms may impact portions of southern Arizona late
this afternoon and evening, perhaps accompanied by at least some
risk for severe hail and wind.
...Synopsis...
Within the mid-latitude westerlies across the eastern Pacific,
models suggest that amplifying ridging will build northeastward
through British Columbia, the Yukon and portions of the Northwest
Territories, taking on more of a positive tilt during this period.
As it does, the southern portion of a splitting downstream short
wave trough, and a trailing perturbation, are forecast to dig near
and west of the Sierra Nevada, and eventually contribute to the
evolution of a deepening mid-level low near the southern California
coast by 12Z Wednesday.
In response to these developments, an initially cut-off mid-level
closed low, currently still west of Baja, likely will be forced
northeastward. A slow northeastward acceleration toward northern
Baja may be underway by 12Z this morning. As it progresses more
rapidly northeastward, it appears that the low will transition to an
open wave and perhaps undergo considerable further deformation while
overspreading southern Arizona and Sonora late this evening into the
overnight hours.
Farther downstream, beneath building larger-scale ridging across the
southern and central Plains into the lower and middle Mississippi
Valley, a southerly return flow may gradually commence across the
lower Rio Grande Valley into portions of the southern Plains, in the
wake of large-scale troughing beginning to shift east of the
Atlantic Seaboard.
While convective potential is expected to remain negligible across
most areas east of the Rockies, an influx of moisture from the lower
latitude eastern Pacific, and through the Gulf of California,
probably will contribute to destabilization supportive of scattered
thunderstorm activity across the Southwest. This may include
portions of the Colorado Plateau and southern Rockies into southwest
Texas, in addition to much of central and southern Arizona.
...Central and southern Arizona...
On the leading edge of the moisture return, increasing forcing for
ascent, perhaps aided by a mid-level perturbation pivoting around
the approaching closed low, may support considerable convection and
embedded thunderstorms across parts of northern Sonora into southern
Arizona by 18-21Z. This activity is expected to be generally weak
with negligible severe risk, and may tend to diminish while
spreading toward the Mogollon Rim.
In its wake, boundary layer moistening and breaks in overcast may
allow for the development of weak to moderate CAPE across Sonora
into at least the southern Arizona border vicinity. This may become
sufficient to support vigorous thunderstorm development,
particularly near the leading edge of the northeastward advancing
mid-level dry slot, where steepening mid-level lapse rates may
coincide with sufficient strengthening of deep-layer shear to
support isolated supercells. While strongest cells may initiate
across Sonora, activity may spread across the international border
into Arizona with at least some continuing risk for severe hail and
locally strong surface gusts, mainly during the 20/00-03Z time
frame.
..Kerr/Cook.. 11/19/2019
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SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1218 AM CST Tue Nov 19 2019
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
WEST TEXAS...
...SUMMARY...
A few storms may produce marginally severe hail over parts of west
Texas Wednesday.
...Synopsis...
An upper low will move east out of southern CA and into western AZ
on Wednesday with a cyclonically curved midlevel speed max sweeping
across AZ and NM. Lift with this system will result in widespread
showers and thunderstorms throughout the period, with minimal severe
threat.
To the east, a low-amplitude shortwave trough will move from
southwest TX into the central Plains during the day, and toward the
upper MS Valley by Thursday morning. A surface low will develop over
KS and move northeastward toward IA, with a dryline moving out of NM
and into west TX early in the day. Mid 50s F dewpoints will be
common over the southern Plains due to strong south winds. Despite
this, the boundary layer is expected to remain relatively cool and
stable, with only elevated thunderstorms likely.
...TX South Plains and Panhandle...
Storms will develop early in the day over NM and will move into west
TX by 18Z. Forecast soundings indicate around 1000 J/kg MUCAPE ahead
of the dryline, but boundary-layer temperatures will remain cool.
Therefore, despite strong low-level shear, this part of the
hodograph will be rendered ineffective. However, strong shear in the
cloud-bearing layer will support elevated cells capable of hail.
Storms will spread rapidly northeast into the central Plains later
in the day, but weaker instability is unlikely to support severe
hail.
...Central AZ...
Areas of showers and thunderstorms are expected throughout the day
which will likely minimize instability. Large-scale ascent as well
as southerly upslope flow along the Mogollon Rim will aid storm
development, beneath cooling temperatures aloft. If pockets of
greater instability can develop, then isolated marginal hail will be
possible. However, this is uncertain given the likelihood of clouds
and airmass contamination.
...MAXIMUM RISK BY HAZARD...
Tornado: <2% - None
Wind: <5% - None
Hail: 5% - Marginal
..Jewell.. 11/19/2019
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1248 AM CST Tue Nov 19 2019
Valid 191200Z - 201200Z
...NO CRITICAL AREAS...
...Synopsis...
A vigorous mid-level system will accelerate south-southeastward
along the California coast and carve out a longwave trough along the
West Coast. This will assist in forcing an initially cutoff low to
open and eject northeastward toward southern Arizona/New Mexico
through the end of the forecast period. Additionally, surface
cyclogenesis will occur across the western Great Basin through the
evening, while another lee surface low materializes across the
central High Plains through early Wednesday morning.
Generally, though breezy conditions across the Great Basin will lead
to locally elevated fire weather, these conditions should be
localized and brief enough to preclude fire weather highlights,
especially with clouds and showers related to an upstream system
limiting boundary-layer mixing. Localized elevated conditions may
also exist for a couple hours along the immediate Colorado Front
Range as well.
..Cook.. 11/19/2019
...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
1251 AM CST Tue Nov 19 2019
Valid 201200Z - 211200Z
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHERN AND CENTRAL
CALIFORNIA...
...Synopsis...
A vigorous mid-level disturbance across the Southwest will evolve
into a cutoff low, with very strong mid-level flow aloft across
California on the west side of the cyclone. A surface low will also
migrate slowly through the day beneath this mid-level low. A
surface high will slide southward across the northern Rockies as
well, setting up a favorable pressure gradient for strong northerly
flow across portions of northern and central California. Farther
east, cyclogenesis across the central Plains will result in a
downslope wind event across eastern Colorado/New Mexico, although RH
values should remain high enough in these areas to preclude any
heightened fire weather risk.
...Northern and central California...
The aforementioned synoptic surface pattern will result in increased
northerly surface flow beginning very early in the forecast period
and persisting throughout. 15-35 mph wind speeds, with higher gusts
in terrain-favored areas, will become common especially across the
central Valley and other terrain-favored areas of the region.
Meanwhile, RH values will fall to around 15% during peak heating
periods - locally lower. With dry fuels in place across the region,
elevated and critical highlights have been introduced for this
outlook. Elevated to locally critical conditions (15-25 mph
northerly winds, 20-30% RH) are expected to occur as far west as
coastal areas and as far south as San Joaquin County and vicinity
during the afternoon and early evening.
..Cook.. 11/19/2019
...Please see www.spc.noaa.gov/fire for graphic product...
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