Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0245 PM CDT Fri Jul 03 2020
Valid 032000Z - 041200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON INTO TONIGHT ACROSS PARTS OF EASTERN MONTANA...ADJACENT
NORTHWESTERN SOUTH DAKOTA...AND WESTERN/CENTRAL NORTH DAKOTA...
Severe thunderstorms capable of producing mainly large hail and
strong wind gusts are possible late this afternoon into tonight
across eastern Montana and parts of the Dakotas.
...20Z Outlook Update...
Categorical and probabilistic lines have been adjusted in an attempt
to account for the gradual progression of synoptic and sub-synoptic
features, and latest trends concerning destabilization, evident in
latest observational data/imagery.
For details concerning the severe weather potential through the
remainder of this period, please refer the 1630Z discussion appended
below, and the latest SPC Mesoscale Discussions (including recently
issued MD 1092).
.PREV DISCUSSION... /ISSUED 1138 AM CDT Fri Jul 03 2020/
...Northern High Plains...
Widely scattered to scattered thunderstorms are expected to develop
this afternoon into tonight, with large hail and damaging winds
expected. The most likely scenario will be for storm
development/intensification to initially occur late this afternoon
and early evening across southwest/south-central Montana within a
corridor of post-frontal upslope flow and heating over the higher
terrain/mountains. While some supercells can be expected
particularly across southeast/east-central Montana, storms should
aggregate and linearly organize this evening/tonight as they
progress through the instability axis from far eastern Montana into
North Dakota/northwest South Dakota.
...Central High Plains to southern Plains/Ozarks...
Strong diurnal heating, acting upon both the higher terrain of
central/northern Colorado and southeastern Wyoming, and composite of
outflow boundaries across Kansas/Oklahoma, will combine with a moist
boundary layer to weaken MLCINH through the afternoon. Widely
scattered to scattered thunderstorms should develop across the
region, aided by an MCV across eastern Kansas. These storms will
predominantly be multicellular, but with transient/localized
supercell characteristics possible. The main concerns should be
isolated severe gusts and large hail.
A relatively moist/moderately unstable air mass resides along/south
of a southward-sagging cold front. Widely scattered thunderstorms
are expected to develop and intensify this afternoon, initially
across eastern/southern New York and western
Massachusetts/Connecticut, with the strongest storms capable of
isolated damaging wind gusts. Modest mid-level lapse rates will keep
peak MLCAPE in the 500-1200 J/kg range over much of the area. Weak
low/middle-level winds and a related lack of substantial deep-layer
shear will limit organization and should keep the overall severe
potential relatively marginal/isolated.
Moderate to strong destabilization will continue to occur this
afternoon on the western/southern fringes of ongoing early day
thunderstorm clusters across the region. Thunderstorms should
diurnally intensify within the moist/unstable air mass and modestly
enhanced mid-level northerly winds could contribute to some
organization/sustenance. A few instances of locally damaging winds
could occur through the afternoon/early evening hours.
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0139 PM CDT Fri Jul 03 2020
Valid 041200Z - 051200Z
An isolated dry thunderstorm area was introduced for portions of the
Central Rockies for Day 2/Saturday/4th of July Holiday. While storms
are expected to be slow moving and pulse like in nature,
precipitable water values in the 0.50-0.75 inch range and a
sufficiently deep sub-cloud layer (based on the latest guidance)
suggest that at least a few dry strikes are possible. The isolated
dry thunderstorm area was delineated for areas that will most likely
see dry strikes, and where fuels are critically receptive to fire
Otherwise, the forecast remains on track regarding elevated wind/RH
conditions occurring across northern Nevada during the afternoon
hours. Portions of the central Great Basin/lower Four Corners may
also see localized elevated wind/RH by afternoon peak heating,
though the coverage and duration of such conditions appears too
limited for elevated area delineations at this time.
.PREV DISCUSSION... /ISSUED 0158 AM CDT Fri Jul 03 2020/
Upper-level troughing is expected to largely remain in place over
the west/northwest CONUS for Saturday, though mid-level winds should
be weaker than on Friday. While this will limit the potential for
widespread and robust fire weather concerns, hot and dry conditions
coupled with weak surface pressure falls across the interior West
will continue to promote some fire weather potential.
A weak upper-level shortwave trough is expected to move across the
greater NV region on Saturday, and favor weak surface pressure falls
across the interior West. This should maintain 10-15 mph
pressure-gradient winds across northern NV through the afternoon
hours. Peak daytime heating should allow for RH reduction down to
near 10% with deep boundary-layer mixing up to 850-700 mb. Despite
the deep mixing, there remains some uncertainty regarding the
magnitude of boundary-layer winds and the maximum gust potential.
While more aggressive guidance suggests wind gusts up to 25 mph are
possible, the most likely scenario appears to be frequent gusts
around 20 mph. While elevated conditions appear possible for this
northern/northwest NV region, locally elevated conditions can not be
ruled out across eastern and southeast NV, where critical RH values
are likely but winds will be weaker.
...Please see www.spc.noaa.gov/fire for graphic product...