RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Mon Jan 20 18:46:01 UTC 2025.
No Mesoscale Discussions are in effect as of Mon Jan 20 18:46:01 UTC 2025.
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1028 AM CST Mon Jan 20 2025
Valid 201630Z - 211200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY...
No thunderstorms are expected across the U.S. through tonight.
...Synopsis...
Another surge of cold air is anticipated across the CONUS,
reinforcing the polar airmass already in place. This will result in
a maintenance of dry and stable conditions, with no thunderstorms
anticipated.
Some deeper convection is possible late tonight/early tomorrow along
the middle/upper TX Coast as warm-air advection strengthens
throughout the warm sector of surface low developing over the
western Gulf of Mexico. Model forecast soundings have thermodynamic
profiles with scant (and shallow) buoyancy between around 800 to 500
mb. These profiles also suggest sleet will be the predominant
precipitation type, with mixed-phase parcels combining with the
modest buoyancy to support a few lightning flashes. Even so, the
overall thunderstorm probabilities are still expected to be less
than 10 percent.
..Mosier.. 01/20/2025
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1102 AM CST Mon Jan 20 2025
Valid 211200Z - 221200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Thunderstorms are not forecast on Tuesday through Tuesday night.
...Synopsis...
Thunder potential will be nil across much of the CONUS during the D2
period. Deep convection will be relegated to the Gulf, initially
over the west-central portion before spreading towards the southeast
part late. The slimmest of elevated buoyancy (MUCAPE below 100 J/kg)
along the Upper TX to LA Gulf Coast may coincide with mixed-phase
parcels, supporting weak convection into late morning. A few
lightning flashes are possible along the immediate coast, but the
overall thunder probability appears to be less than 10 percent.
As deep convection progresses east across the Gulf, it is expected
to wane with approach to southwest FL and the Keys early Wednesday
morning. This decaying phase should occur in response poor mid-level
lapse rates downstream of a positive-tilt trough and subsiding
large-scale ascent.
..Grams.. 01/20/2025
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SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
1242 PM CST Mon Jan 20 2025
Valid 221200Z - 231200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Thunderstorms are not expected through Wednesday night.
...Synopsis...
Conditions will be too dry/stable for potential lightning-producing
convection across the CONUS through the period.
..Grams.. 01/20/2025
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1100 AM CST Mon Jan 20 2025
Valid 201700Z - 211200Z
...EXTREMELY CRITICAL FIRE WEATHER AREA FOR THE SAN GABRIEL
MOUNTAINS WEST TOWARDS THE SANTA MONICA MOUNTAINS AND SANTA SUSANA
MOUNTAINS...INCLUDING THE MALIBU COAST...
...CRITICAL FIRE WEATHER AREA FOR MUCH OF SOUTHERN CALIFORNIA...
The previous forecast (see below) remains on track, and no changes
were needed with this update. The LAX-DAG pressure gradient is
quickly tightening this morning, with the latest reading (as of 16Z)
around -3.8 mb. This trend will continue into the overnight/early
morning hours, yielding rapidly strengthening surface winds and
decreasing RH. The onset of critical to extremely critical
conditions is expected by early afternoon, with the most volatile
conditions still expected over the wind-prone Santa Ana corridor of
northern/western Los Angeles County into eastern Ventura County
during the overnight/early morning hours. Extremely critical
conditions will persist into Day 2/Tuesday morning here.
..Weinman.. 01/20/2025
.PREV DISCUSSION... /ISSUED 0208 AM CST Mon Jan 20 2025/
...Synopsis...
While most of the CONUS is dominated by cold air and high pressure,
a strong, positively-tilted mid-level trough will move southward
across California, with a highly amplified mid-level Pacific ridge
following behind it. As the trough axis reaches southern California
Monday afternoon, intensifying surface pressure gradients will
result in the development of strong Santa Ana winds.
The 00Z HREF guidance and global ensembles continue to forecast
strong LAX->DAG pressure gradients ranging from -8 mb to -11 mb,
with wind speeds trending upward to 40-45 MPH sustained (gusting 70
- 100 MPH on the mountains, 50 - 80 MPH in the valleys/coastal
regions). In addition to the upward trend in wind speed and gust
forecasts, relative humidity values have trended significantly
drier, with values as low as 2%-5%. These Extremely Critical
fire-weather conditions, supporting rapid wildfire onset and spread,
will begin Monday afternoon and reach peak intensity Monday evening
into Tuesday morning. The area of greatest risk lies from the San
Gabriel Mountains westward into the Santa Monica Mountains, the
Malibu Coast, and the Santa Susana Mountains.
Elsewhere, Critical fire-weather conditions extend southward to the
U.S./Mexico border, where strong (and critically dry) offshore winds
will persist overnight into Tuesday morning.
...Please see www.spc.noaa.gov/fire for graphic product...
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