RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Fri Jul 3 18:43:01 UTC 2020.
No Mesoscale Discussions are in effect as of Fri Jul 3 18:43:01 UTC 2020.
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1138 AM CDT Fri Jul 03 2020
Valid 031630Z - 041200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
EASTERN MONTANA AND THE DAKOTAS...
...SUMMARY...
Severe thunderstorms capable of mainly large hail and severe wind
gusts are possible late this afternoon and into tonight over eastern
Montana and parts of the Dakotas.
...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.
...Northeast States...
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.
...ArkLaTex/Louisiana...
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.
..Guyer/Jewell.. 07/03/2020
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
1242 PM CDT Fri Jul 03 2020
Valid 041200Z - 051200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THERE IS A SLIGHT
RISK OF SEVERE THUNDERSTORMS SATURDAY INTO SATURDAY NIGHT ACROSS
PARTS OF CENTRAL AND EASTERN NORTH DAKOTA INTO NORTHWESTERN
MINNESOTA...AND ACROSS PARTS OF EASTERN MONTANA INTO ADJACENT
PORTIONS OF NORTHWESTERN SOUTH DAKOTA AND WESTERN NORTH DAKOTA......
CORRECTED FOR TYPO AND WORDING
...SUMMARY...
A couple of organized clusters of severe storms may develop across
parts of the northern plains Saturday into Saturday night, posing a
risk for strong wind gusts and large hail.
...Synopsis...
Models suggest that there may be substantive weakening of prominent
mid-level ridging (initially centered near the Southwestern
international border through the southern high plains, and extending
northeastward across much of the southern Rockies, plains and Upper
Midwest) during this period. It appears that this may be largely
due to the progression of significant troughing within the
westerlies, northeast of the Canadian and northern U.S. Rockies into
the Canadian Prairies by late Saturday night.
This may be preceded by a convectively induced or enhanced
perturbation migrating eastward along the North Dakota and Minnesota
international border area. A weaker trough in the westerlies may
lag to the southwest, gradually turning inland of the Pacific
Northwest coast, into the northern intermountain region. And
stronger (30-50 kt around 500 mb) westerly mid-level flow may
develop east-northeast of the northern Rockies, through North Dakota
and northern Minnesota.
Downstream, another belt of stronger cyclonic mid-level flow
(initially curving southeast of Hudson Bay through the Canadian
Maritimes) may amplify southwestward through Quebec, toward the
lower Great Lakes and New England. This probably will be
accompanied by a reinforcing cold front, in the wake a preceding
front which may advance southward/southwestward into parts of the
Mid Atlantic.
Otherwise, deep-layer mean flow will remain generally weak across
much of the nation, beneath the remnant ridging and weak, lingering
downstream troughing across southeastern portions of plains and
lower Mississippi Valley into the Southeast.
Seasonable moisture may contribute to destabilization supportive of
scattered thunderstorm activity across parts of the southern Rockies
and plains into the lower Mississippi Valley, Southeast and Mid
Atlantic. Some of this activity could pose at least a risk for
strong/potentially damaging wind gusts. However, coverage is
expected to remain sparse, resulting in severe probabilities near or
below 5 percent. Potential for organized severe storm development
appears most probable across parts of the northern plains.
...North Dakota into Minnesota...
Seasonably moist boundary-layer conditions will be maintained within
weak surface troughing, and perhaps along an effective warm frontal
zone, beneath the northern periphery of a plume of warm elevated
mixed-layer air. In the presence of steep lower/mid tropospheric
lapse rates, models suggest that large CAPE on the order of
3000-4000+ J/kg will develop, as the convectively induced or
enhanced perturbation progresses along the international border
vicinity.
The extent of ongoing convection at the outset of the period
associated with this feature remains unclear, but re-intensification
of ongoing or new convective development seems probable. In the
presence of at least moderately strong deep-layer shear, the
environment seems likely to become conducive to organized
convection. This may include isolated supercells initially, before
convection grows upscale into an organizing cluster. Due to spread
within the various model output, some uncertainty lingers concerning
more precise time and location.
...Eastern Montana into Dakotas...
Relatively moist easterly low-level flow may contribute to
moderately large mixed-layer CAPE by late Saturday afternoon, as the
trough in the westerlies aids forcing for ascent and convective
development across the mountains. Activity should develop off the
higher terrain into the stronger instability and intensify in the
presence of moderate to strong deep-layer shear. A few supercells
are possible, with upscale convective growth possible as activity
spreads across eastern Montana into adjacent portions of the Dakotas
through Saturday evening.
..Kerr.. 07/03/2020
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1053 AM CDT Fri Jul 03 2020
Valid 031700Z - 041200Z
The previous forecast appears to remain on track. Current visible
satellite depicts clear skies across much of the western CONUS,
allowing for the mixing of a deep diurnal boundary layer. Several
METARS across the Great Basin into the Central Rockies show surface
RH values that are near-critical, to critically low. Additional
drying is expected into the afternoon hours, with surface sustained
southwesterly winds increasing to near 15 mph across parts of the
Great Basin into the central Rockies, as supported by the latest
model guidance and warranting the maintenance of the elevated
delineations.
Latest guidance continues to show isolated dry thunderstorm
potential, mainly across central Utah, through the afternoon into
the early evening hours. Farther east-southeast into the Four
Corners southward into central Arizona/New Mexico, a couple dry
strikes may occur, but slow storm speeds and/or high precipitable
water values suggest that more wetting rains may accompany these
storms, precluding an isolated dry thunderstorm delineation.
..Squitieri.. 07/03/2020
.PREV DISCUSSION... /ISSUED 0118 AM CDT Fri Jul 03 2020/
...Synopsis...
Broad upper-level ridging across the central CONUS will continue to
favor little eastward movement of an upper-level trough located
across the far Northwest coast/southwest Canada. This regime will
continue to promote a belt of stronger mid-level flow across the
interior west, where conditions remain warm and dry, and into the
north-central US. While the central and eastern thirds of the
country will see relatively high RH values and scattered rain
chances, fire weather concerns will persist for portions of the
West.
...Nevada and adjacent areas of Utah, Idaho, and Oregon...
850-700 mb winds are expected to increase to 20-25 mph by this
afternoon within a belt of stronger mid-level flow across the
greater NV region. Limited cloud cover will promote daytime heating,
falling RH values, and deep boundary-layer mixing by the afternoon
hours. Although sustained surface winds are expected to largely
remain below 20 mph, these conditions should aid in mixing down the
stronger winds and allow occasional to frequent wind gusts up to 25
mph. With receptive fuels already in place, elevated to locally
critical conditions appear likely.
...Wyoming...
Recent ensemble guidance has come into better agreement with regards
to the likelihood of sustained elevated conditions and limited
precipitation across portions of southwest to central WY. Although
this region will likely be displaced from the better mid-level flow,
pressure gradient winds should remain between 10-20 mph with reduced
afternoon RH values. While ERC values across this region are not
overly concerning, fine-fuel moisture should be low enough to
support at least some fire weather concern.
...Dry Thunderstorms...
Ensemble guidance and recent observations continue to support the
potential for isolated dry thunderstorms this afternoon across
portions of central UT. Recent RAP mesoanalysis shows relatively
high precipitable water values in place across southern to central
AZ with decreasing values below 0.6 inches to the north into central
UT. Forecast soundings from this periphery of the better moisture
plume suggest sufficient MUCAPE may be in place during peak heating
this afternoon that will support the potential for dry
thunderstorms. While there is higher confidence in thunderstorm
potential to the south, higher precipitable water values should
limit the dry thunderstorm potential.
...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
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
spread.
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.
..Squitieri.. 07/03/2020
.PREV DISCUSSION... /ISSUED 0158 AM CDT Fri Jul 03 2020/
...Synopsis...
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.
...northern/northwest Nevada...
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...
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