SPC - No watches are valid as of Sat Aug 19 11:00:01 UTC 2017

No watches are valid as of Sat Aug 19 11:00:01 UTC 2017.

SPC - No MDs are in effect as of Sat Aug 19 11:00:01 UTC 2017

No Mesoscale Discussions are in effect as of Sat Aug 19 11:00:01 UTC 2017.

SPC Aug 19, 2017 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook
      
Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0216 AM CDT Sat Aug 19 2017

Valid 211200Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS MONDAY INTO
MONDAY NIGHT ACROSS PARTS OF THE CENTRAL PLAINS AND LOWER/MIDDLE
MISSOURI VALLEY INTO THE UPPER MIDWEST...

...SUMMARY...
Strong thunderstorms may impact a corridor from the central Plains
into the Upper Midwest Monday into Monday night, accompanied by at
least some risk for severe weather.

...Synopsis...
The stronger mid-latitude westerlies likely will remain confined to
the northern tier of the U.S and southern Canada through this
period.  However, models indicate that amplification commencing
within this regime, across the northeastern Pacific into western
Canada on Sunday, will continue and translate downstream, with
significant upper troughing likely to evolve and dig across the
central Canadian/U.S. border area by late Monday night.  This is
expected to be accompanied by the southward advancement of a cold
front into and through much of Upper Midwest, lower Missouri Valley
and central Plains, and perhaps the initiation of cyclogenesis along
the front across the Great Lakes region by 12Z Tuesday.

...North central Plains into the Upper Midwest...
The possibility for considerable lower/mid tropospheric warm
advection driven convection to be ongoing at 12Z Monday near/east of
the middle Missouri Valley is one of a number of uncertainties
concerning convective potential for this period.  Also, relatively
cool mid-level air and stronger mid/upper flow appear likely to lag
behind the surface front.  However, models suggest that seasonably
moist low-level conditions may still contribute to moderate CAPE
with daytime heating.  And a belt of 30-40 kt westerly lower/mid
tropospheric flow may be sufficient to support organized convective
development.

Within an increasingly cyclonic regime aloft, to the south of the
main short wave trough, models indicate a possible consolidation of
forcing associated with one short wave perturbation emerging from
the southwestern monsoonal regime, and a mid-latitude impulse
digging southeast of the northern Rockies.  This seems to provide
the most obvious support for an appreciable evolving cluster of
thunderstorms.  However, this appears most likely to take place
across and east of the middle to lower Missouri Valley well after
dark, when boundary layer instability may be in the process of
waning.

While severe potential is evident for Monday into Monday night,
mostly in the form of evolving storms clusters accompanied by a risk
for potentially damaging wind gusts, this appears too conditional
for anything greater that 5 percent severe probabilities at this
time.

..Kerr.. 08/19/2017


Read more

SPC Aug 19, 2017 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
      
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0346 AM CDT Sat Aug 19 2017

Valid 221200Z - 271200Z

...DISCUSSION...
The mid-latitude westerlies may undergo further amplification
through the middle of the coming work week, including the evolution
of large-scale troughing across much of the Great Lakes, Ohio Valley
and Northeast.  Within this regime, models suggest that one
significant short wave impulse could support significant
cyclogenesis across Quebec, accompanied by a trailing cold front
which may advance through much of the eastern U.S. before weakening.
There remains a signal within model output that pre-frontal forcing
for ascent may be favorably timed with peak diurnal destabilization
across parts of the lower Great Lakes region and upper Ohio Valley
on Tuesday to support considerable vigorous thunderstorm activity. 
In the presence of 30-50 kt deep layer mean flow and shear,
organized severe storm development appears possible, with
potentially damaging wind gusts the primary hazard.  Continuation of
this threat across southern New England and the northern Mid
Atlantic on Wednesday remains more unclear, with possible early day
progression of the front off the coast.

Thereafter, late next week into early next weekend, upper
troughiness may linger across parts of the Upper Midwest/Great Lakes
and Atlantic Seaboard, as subtropical ridging becomes increasingly
prominent across the Intermountain West and Rockies.  Although short
wave developments within this regime remain more uncertain, there
appears little obvious at the present time to suggest anything more
than perhaps generally low severe weather potential.


Read more

SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
          
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0144 AM CDT Sat Aug 19 2017

Valid 191200Z - 201200Z

...Synopsis...
An upper trough over AB/SK will progress eastward towards MB today.
30-40 kt of mid-level westerly winds attendant to this upper trough
will overspread eastern MT into ND by this afternoon. At the
surface, a low over southern SK will also develop eastward into MB
by this evening, with a trailing cold front advancing southeastward
across the northern Plains.

...Portions of the Northern Great Basin into the Northern/Central
Rockies and Northern Plains...
Strong/gusty low-level winds should develop both along and ahead of
the surface cold front this afternoon across eastern MT into western
ND and northwestern SD. Short-term guidance shows sustained
west-northwesterly winds of 15-20 mph occurring in conjunction with
RH values lowering into the 15-25% range with diurnal heating of a
relatively dry boundary layer, supporting an elevated fire weather
threat. RH values are forecast to increase behind the front,
although strong surface winds approaching 20 mph and veering to
northwesterly may allow for continued elevated fire weather concerns
into the evening hours. Locally critical conditions may be realized
briefly across a small part of the elevated delineation, but
confidence in widespread winds in excess of 20 mph remains too low
to include a critical area.

Elevated fire weather conditions should also develop this afternoon
across part of the northern Great Basin into portions of the
northern/central Rockies, as the southern fringe of enhanced
mid-level westerlies overlies this region. Localized enhancement to
the low-level winds appears likely across part of the Snake River
Valley and vicinity into western/southern WY, with sustained
west-southwesterly winds of 15-20 mph combining with RH values of
10-20% and dry fuels to support an elevated fire weather threat. The
lack of even stronger forecast low-level flow precludes a critical
designation across this region.

...Southwestern OR/Northern CA...
A strengthening surface pressure gradient to the west of the
Cascades will encourage increasing northeasterly to northwesterly
winds across southwestern OR/northern CA this afternoon and evening.
Sustained winds of 15-20 mph appear likely at lower elevations, with
stronger gusts possible at mid/high elevations. RH values will
easily lower into the 15-25% range by afternoon given the dry
airmass in place, and overnight RH recovery is expected to remain
poor, particularly at higher elevations. This expected combination
of strong/gusty winds with lowered RH values, very dry fuels, and
numerous ongoing large fires necessitates the introduction of an
elevated area across this region.

..Gleason.. 08/19/2017

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


Read more

SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0145 AM CDT Sat Aug 19 2017

Valid 201200Z - 211200Z

...Synopsis...
A large-scale trough will continue moving eastward across central
Canada Sunday, with a belt of enhanced mid-level westerly winds
remaining confined to the north-central CONUS. An upper ridge is
forecast to amplify over the eastern Pacific and western CONUS,
while a weak upper low remains just off the coast of southern CA. At
the surface, a cold front will advance eastward across the northern
Plains and Upper Midwest, with its trailing portion becoming
stationary and ill-defined across the northern High Plains into the
northern Rockies/Great Basin.

...Portions of the Northern Great Basin/Rockies...
Although the strongest mid-level flow will remain displaced to the
north of this region, around 20-25 kt of westerlies at 500 mb will
likely reach the surface as the boundary layer warms/mixes by Sunday
afternoon and early evening. Localized enhancement to the low-level
west-southwesterly flow appears likely across eastern portions of
the Snake River Valley into western WY, where sustained winds of
15-20 mph should occur. Some higher gusts will be possible. RH
values will once again become lowered into the 10-15% range across
this region as both the low-level airmass and available fuels remain
quite dry. These expected meteorological and fuel conditions support
the introduction of an elevated area across southern ID into far
southern MT and western WY. Locally critical conditions may occur
where winds exceed 20 mph, but this is currently expected on just a
brief and spotty basis.

..Gleason.. 08/19/2017

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


Read more