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Storm Prediction Center Forecast

RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Sun Sep 22 17:49:07 UTC 2019

No watches are valid as of Sun Sep 22 17:49:07 UTC 2019.

SPC - No MDs are in effect as of Sun Sep 22 17:49:07 UTC 2019

No Mesoscale Discussions are in effect as of Sun Sep 22 17:49:07 UTC 2019.

SPC Sep 22, 2019 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1117 AM CDT Sun Sep 22 2019

Valid 221630Z - 231200Z


Isolated damaging winds, and perhaps a tornado or two, will be
possible through this evening from parts of Oklahoma to Illinois.

...OK to IL...
No changes have been made to the ongoing forecast.  A band of
relatively fast winds aloft extends from the southern and central
Plains into the mid MS valley and Great Lakes region today.  A
strong shortwave trough embedded in this flow over western KS/OK
will track into MO/IL during this forecast period.  Considerable
cloud cover and areas of precipitation will continue to affect the
MRGL risk corridor this afternoon.  Despite the weak instability and
poor lapse rates, forecast soundings show sufficient vertical shear
to pose a limited risk of a storm or two becoming intense with
damaging wind potential and some tornado risk.

..Hart/Bentley.. 09/22/2019

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SPC Sep 22, 2019 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1228 PM CDT Sun Sep 22 2019

Valid 231200Z - 241200Z


Scattered storms, some of which may be severe with damaging winds
and large hail, appear possible over much of Arizona on Monday.

...Arizona into Southwestern New Mexico...
Embedded within large-scale upper troughing over much of the western
CONUS, an upper trough/low will develop southward across the western
Great Basin into the Southwest through the period. In advance of
this feature, low-level moisture is forecast to rapidly increase
along the CA/AZ border eastward into southern/central AZ by early
Monday morning. There are some indications that isolated
showers/storms may be ongoing at the start of the period Monday
morning across mainly southern AZ. The effect that this possible
early convection may have on destabilization and severe storm
potential later in the day remains unclear.

Regardless, strengthening west-southwesterly winds at mid levels in
combination with increasing instability suggest that at least
isolated severe storms will be possible across much of
southern/central AZ Monday afternoon and evening. MLCAPE should
reach to around 1000-1500 J/kg from the Mogollon Rim southward, with
locally higher values possible in far western AZ. 35-50 kt of
effective bulk shear will support supercells, with initial
convective development probably occurring along or just east of the
CA/AZ border. Isolated large hail will be possible with these mainly
discrete storms, as generally straight hodographs become elongated
at mid/upper levels.

As storms spread eastward through the afternoon, some clustering may
occur as low-level lapse rates steepen through diurnal heating and
mixing of the boundary layer. Damaging winds may become an
increasing concern with eastward extent across southern/central AZ
into Monday evening if this upscale growth occurs. An isolated
severe threat may persist Monday night into parts of southwestern NM
before instability eventually wanes. Across northern AZ, both
low-level moisture and related instability are forecast to be
weaker, with a more isolated/marginal hail/wind threat.

An upper trough/low will move quickly eastward from the Great Lakes
across the Northeast, OH Valley, and Mid-Atlantic on Monday. Strong
mid/upper-level winds will be present across these regions in
association with the upper trough/low. At the surface, a cold front
will likewise sweep eastward across these regions through the day.
Mid-level lapse rates over these areas are expected to remain quite
meager, and widespread cloudiness will likely be present. But,
surface dewpoints generally in the low to mid 60s ahead of the front
and modest diurnal heating will probably support weak instability by
Monday afternoon along/ahead of the front. MLCAPE should generally
remain at or below 500 J/kg. This meager instability will probably
temper the overall severe threat, even though strong shear will be
present owing to the strengthening wind field through mid/upper
levels. While some strong/gusty downdraft winds cannot be completely
ruled out with rain showers or any low-topped storms that develop,
the lack of stronger forecast instability precludes introduction of
5% severe probabilities for wind at this time.

Tornado:   2%     - Marginal
Wind:     15%     - Slight
Hail:     15%     - Slight

..Gleason.. 09/22/2019

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1200 PM CDT Sun Sep 22 2019

Valid 221700Z - 231200Z


Current water vapor satellite imagery shows a potent mid-level
trough beginning to dig into northern California. Dry air aloft is
quite evident with this feature and is forecast to impact portions
of the Northern Coastal Ranges during the overnight. Forecast
soundings capture this dry air aloft well, though relatively
efficient boundary-layer cooling in these soundings keeps this air
from mixing to the surface. However, some concern exists that strong
surface flow in localized areas will promote greater overnight
mixing than models suggest. High-resolution guidance continues to
the suggest that this will only occur on a spatially-limited basis
so no highlights will be introduced.

..Wendt.. 09/22/2019

.PREV DISCUSSION... /ISSUED 0126 AM CDT Sun Sep 22 2019/

An area of mid-level ridging is forecast to move from portions of
the Great Basin toward the central/northern Plains through tonight.
Meanwhile, a large upstream mid/upper-level trough -- and associated
area of enhanced mid-level flow -- is forecast to come onshore
across portions of northern California, Oregon, and Washington late
this afternoon and into the overnight. 

A few hours of locally elevated fire weather conditions are possible
this afternoon across portions of central/southwest Nevada, where
sustained surface winds of 10-15 mph occur in conjunction with
surface RH values near 15% and receptive fuels. However, the
brief/spotty nature of these conditions precludes the introduction
of a fire weather area. 

...Northern California...
Locally elevated fire weather conditions are possible late this
evening and into tonight across eastern portions of the Northern
Coast Ranges, as a tightening surface pressure gradient coupled with
overlapping enhanced mid-level flow promotes increasingly gusty
surface winds amidst pockets of poor overnight RH recoveries. A fire
area may be needed in a future update if trends in guidance suggest
greater coverage of elevated fire weather conditions.

...Please see www.spc.noaa.gov/fire for graphic product...

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