SPC Day 1 Fire Weather Outlook

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1033 AM CDT Mon Mar 18 2024

Valid 181700Z - 191200Z

An Elevated risk area is introduced for portions of southeast
Montana, northeast Wyoming, and the far western Dakotas. Although
morning guidance has initialized slightly too warm/dry compared to
observations, high-resolution runs have captured recent wind speed
trends fairly well. These solutions, supported by ensemble
probabilities, suggests a reasonably high likelihood of sustained
winds near 20 mph across the northern Plains this afternoon as a
surface low deepens across southern Canada. Although confidence in
reaching critical RH values is low, afternoon RH minimums near 25%
appear probable within the downslope flow regime, and given ERC
values between the 75-90th percentile, should support at least
regional fire weather concerns. Fire weather concerns may extend
further east into the central and eastern Dakotas, but confidence in
sustained, widespread elevated conditions is more limited due to
greater spread in deterministic/ensemble solutions.

Morning surface observations in the lee of the VA/NC Appalachians
are sampling rather dry conditions with RH values in the 20-30%
range. Localized fire weather concerns are probable in the immediate
lee of the higher terrain as a frontal surge increases winds to
10-15 mph (gusting upwards of 20 mph) this afternoon. However,
confidence in the spatial coverage of this threat is limited away
from terrain features.

..Moore.. 03/18/2024

.PREV DISCUSSION... /ISSUED 0130 AM CDT Mon Mar 18 2024/

...Synopsis...
The mid-level pattern over the US will be dominated by a deep
eastern trough with northwesterly mid-level flow across the central
US and a cutoff low over the southwest US. A secondary speed max
embedded in the large-scale flow should lead to a surface cyclone
near the US-Canada border, which may result in a few areas of
Elevated conditions across southeastern Montana and northeastern
Wyoming. However, these areas are expected to be localized, and
fuels have received some moisture in the last week. Elsewhere across
the central US, a large anticyclone is expected to keep winds weak.
For these reasons, no risk areas are introduced on this outlook.

...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
0118 PM CDT Mon Mar 18 2024

Valid 191200Z - 201200Z

...NO CRITICAL AREAS...

No forecast changes are needed. Elevated fire weather conditions may
emerge through much of the OH River Valley region tomorrow afternoon
as a surface trough/weak cold front push through the region. Strong
mid-level flow and modestly deep boundary-layer mixing should
support 15-25 mph winds with gusts upwards of 30-35 mph. Despite the
strong winds, RH values are expected to be relatively mild with
ensemble mean values near 30%; however, solutions that typically
exhibit deeper mixing suggest RH values may fall as low as 20-25%
through parts of the OH Valley (most likely along and south of the
OH river to the western slopes of the southern Appalachians). In
addition to the uncertainty in the RH forecast, fuel status is mixed
across the region with areas that are primarily characterized by
finer fuels (grasses and leaves) reporting sufficiently dry fuels to
support a fire concern. Dry conditions are expected to persist
across NC and VA, but weaker winds should limit overall concerns. No
highlights are introduced at this time, but relative humidity and
fuel trends will continue to be monitored.

..Moore.. 03/18/2024

.PREV DISCUSSION... /ISSUED 0131 AM CDT Mon Mar 18 2024/

...Synopsis...
The mid-level pattern through the day on Tuesday is expected to be
characterized a large trough across the central and eastern US with
a decaying cutoff low across the southwestern US. At the surface,
this would result in a ridge near the Gulf Coast. Although winds
across the northern and central Florida peninsula are currently
forecast to be light, relative humidity may be in the 30-40% range.
This may result in pockets of elevated fire conditions across this
region. However, given the moist fuels and the uncertainty on wind
speeds, will not introduce Elevated highlights for now. Elsewhere
across the continental US, higher relative humidity is expected to
generally keep fire concerns minimal.

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

Read more

SPC 1630Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1126 AM CDT Mon Mar 18 2024

Valid 181630Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
ACROSS CENTRAL FL AND MUCH OF THE FL ATLANTIC COAST...

...SUMMARY...
Isolated large hail and wind damage is possible this afternoon
across central Florida and along much of the Florida Atlantic coast.

...Central and eastern Florida Peninsula...
Morning water-vapor imagery indicates a shortwave trough over the
middle MS Valley digging southward into the base of a larger-scale
trough. This evolution will allow a related cold front to continue
southward across the central/southern FL Peninsula today. While the
FL Peninsula will generally be displaced from the associated
midlevel height falls/large-scale ascent, afternoon storm
development will be aided by ascent along the shallow frontal zone
and diurnal heating of a moist boundary layer amid leftover outflow
boundaries from morning convection. 

The development of 40-50-kt effective shear (characterized by a
long/mostly straight hodograph) will support a mix of organized
multicells and transient supercells along/ahead of the
southward-moving front and mesoscale boundaries over the warm
sector. These storms will be aided by relatively steep midlevel
lapse rates atop a moist/destabilizing boundary layer. A deep CAPE
profile (with moderate surface-based buoyancy) and the
aforementioned hodograph will support large hail up to 1.75 inches
and locally severe gusts near 60 mph with any sustained/organized
storms. Additionally, a brief tornado cannot be entirely ruled out
along the east coast, where locally backed flow may contribute to
slightly more low-level hodograph curvature. However, veered
low-level flow ahead of the front (along with a lack of large-scale
ascent) and deep westerly flow may both limit the coverage of
organized storms, and convective residence time in the most
favorable environment -- warranting the maintenance of the Marginal
risk.

...Arizona and southern California...
A mid/upper-level low centered over west-central AZ will move slowly
westward into southern CA today. On the eastern periphery of this
feature, 25-30-kt midlevel southeasterlies combined with cold
temperatures aloft/steep midlevel lapse rates could favor a couple
strong/loosely organized storms capable of mainly small hail and
locally strong gusts. Along the northern and western periphery of
the upper low, a stronger belt of midlevel flow (around 45 kt)
accompanying a westward-moving impulse will overspread west-central
AZ into southern CA this afternoon. Over parts of southern CA
(particularly west of the Desert), upper 40s/lower 50s dewpoints
beneath the steep lapse rates will contribute to more substantial
buoyancy amid 30-40 kt of effective shear. While convective
evolution/sustenance is uncertain given offshore/downslope flow
across this area, there is a conditional risk of near-severe hail
and gusty winds if any longer-lived storms develop. Overall,
confidence in this scenario is too low to add unconditional
5-percent hail/wind probabilities with this outlook.

..Weinman/Goss.. 03/18/2024

Read more

SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1155 AM CDT Mon Mar 18 2024

Valid 191200Z - 201200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms appears negligible across the
U.S., Tuesday through Tuesday night.

...Synopsis...
A cut off low will start to slowly drift east across Arizona on
Tuesday which will bring scattered thunderstorm activity. Elsewhere
in the CONUS, cool and dry/stable conditions are expected.

Diurnal thunderstorms are expected near the upper-low across Arizona
and vicinity on Tuesday as valley locations warm into the 60s and
the mountains warm into the 50s, generating around 500 J/kg MLCAPE.
Steep lapse rates amid the cool temperatures aloft will support
moderately strong updrafts. However, where these storms are most
likely, shear will be very weak. Therefore, no severe thunderstorms
are expected.

A few thunderstorms are possible along the mountains from southern
California into the central Sierra, but once again, shear should
remain too weak to support organized thunderstorms and an
appreciable threat for severe weather.

..Bentley.. 03/18/2024

Read more