Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 06/11/18

Area Forecast Discussion

National Weather Service Bismarck ND

 1102 PM CDT Sun Jun 10 2018

.UPDATE...
Issued at 1036 PM CDT Sun Jun 10 2018

Line of convection from Bottineau to Linton continues to move east
across central ND. Current watch expires at 11 PM. After
coordination with SPC and surrounding offices, will not extend the
watch east. CAMS suggest that the convection will continue to hold
together as it tracks into eastern ND. However current low level
lapse rates are minimal and upper flow is parallel to the line
with no strong forcing for line segements to bow out. We could
still see some isolate severe reports, especially along the South
Dakota border, but the probability of widepsread severe activity
requiring a watch is low and will not be extending the watch area
to the east. Will be sending out a cancellation for the watch at
the top of the hour.


UPDATE Issued at 642 PM CDT Sun Jun 10 2018

Quick update to cancel the Severe Thunderstorm Watch for Divide,
Williams, McKenzie, Billings, and Slope counties where dry post
cold front air has overtaken. Will maintain the watch across
Bowman county for convection propagating north out of Harding
county in South Dakota.

&&

.SHORT TERM...(This evening through Monday)
Issued at 317 PM CDT Sun Jun 10 2018

Severe thunderstorm potential through tonight is the main focus of
this forecast.

As of 20 UTC, visible satellite imagery shows a well-defined cold
front from just east of Williston to near Medora and Bowman. There
are signs of an agitated and deepening cumulus field in proximity
to that frontal zone as height falls are beginning to impinge on
that region of low-level mesoscale ascent, which is aiding with
the erosion of the stout capping layer seen on regional 12 UTC and
the 19 UTC Rapid City RAOBs at the base of a formidable elevated
mixed layer which has 700-500 mb lapse rates as large as 9 C/km.
Given surface dewpoints in the mid 60s F just ahead of the frontal
zone and its associated wind shift, significant MLCAPE on the
order of 2500 to 4000 J/kg has developed. As capping continues to
erode, we expect convective initiation to occur along the length
of the cold front from the Canadian border south to the SD state
line before 22 UTC, which is an expectation long-heralded by
nearly every CAM simulation available. The strongest wind fields
aloft associated with the shortwave trough approaching the region
from the northern Rockies are still expected to lag the primary
frontal interface, and that will likely serve as a limiting factor
to the overall strength and longevity of individual convective
elements during the afternoon and early evening. Models call for
effective bulk wind differences mainly on the order of 30 to 40
kt. Moreover, the orientation of the deep-layer shear and anvil-
level storm-relative flow vectors relative to the cold frontal
boundary all support upscale growth into a linear complex with
time following initial multicellular or transient supercell modes.
This falls in line with CAMs through the 18 UTC HRRR. Initially,
large bouyancy including through the hail growth zone will favor
risks for large hail within a few hours of initiation until a
full-scale linear mode is established, though the lack of stronger
deep-layer shear in favor of somewhat tempered mesocyclones will
likely subdue high-end hail sizes. Both the large hail and
significant hail parameters favor peak hailstone sizes generally
less than 2 inches in diameter. Damaging winds will also be a
concern, especially as upscale growth occurs by evening, and very
heavy rainfall will be a concern too given slow storm motions and
precipitable water values as high as 1.50 inches. However, we have
held off from issuing a Flash Flood Watch at this time given some
uncertainty in the magnitude of the threat.

Mesobeta-element (Corfidi) vectors suggest that the orientation of
mean cloud-layer winds and related mean outflows and the southerly
low-level jet will not favor gust-front-induced convergence and
that will temper the longevity and downshear propagation of the
cold-pool-related MCS. Therefore, the eastward progression of the
convection will be slow, and that may limit the magnitude of wind
gusts, as well. However, the density of wind reports could still
be significant, and is the primary motivation for the Enhanced
Risk from SPC. Moreover, some CAM guidance has suggested storms
will form over the higher terrain of northeast WY into western SD
and propagate into far southwest and south central ND after about
01 UTC. This convection could be slightly post-frontal in nature
and would have access to stronger deep-layer wind fields with
effective bulk wind differences potentially in excess of 40 kt.
That is reflected in HREF updraft helicity output which has peak
values from any member in the 2-5 km layer up to 200 m/2s across
north central SD, and which some iterations of the operational
HRRR have brought as far north as Bismarck. Either way, after
about 00 UTC the severe threat will be greatest in south central
ND even with the initial line, within the axis of largest CAPE.

Otherwise, Monday will be cooler and breezy in the post-frontal
regime, but the 12 UTC global model suite suggests that maximum
winds in the well-mixed boundary layer will be insufficient for
Wind-Advisory-type conditions. That`s further supported by the
consensus of 12 UTC MOS guidance.

.LONG TERM...(Monday night through Sunday)
Issued at 317 PM CDT Sun Jun 10 2018

Global models suggest a cooler and mainly dry period will be in
place through midweek as weak and transitory ridging crosses the
region. However, the 00 and 12 UTC models also suggest a stronger
upper-level shortwave trough will cross the region by Thursday
night. Taken at face value both the GFS and ECMWF support strong
instability driven by boundary layer dewpoints potentially in the
middle to upper 60s F along with strengthening wind fields aloft,
which would support potential severe storms once again from
Thursday into Thursday night.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1036 PM CDT Sun Jun 10 2018

A line severe thunderstorms associated with a slow moving cold
front from near Bott. Strong southeast winds with gusts to 35kts
will continue ahead of the cold front this evening.

Widespread rain showers and embedded thunderstorms will fill in
behind the cold front across most of western and central North
Dakota overnight with MVFR conditions expected. Rain showers will
end across central North Dakota Monday morning.


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...TWH
SHORT TERM...CJS
LONG TERM...CJS
AVIATION...TWH




Area Forecast Discussion

National Weather Service Denver/Boulder CO

 833 PM MDT Sun Jun 10 2018

.UPDATE...
Issued at 824 PM MDT Sun Jun 10 2018

Cool front was moving across nwrn CO and should affect nern CO
by midnight. A brief period of gusty northwest winds will occur
behind the front. Otherwise with a dry airmass in place no precip
is expected with the front. Meanwhile smoke from the fires over
swrn CO should stay to the south and southeast of Denver based on
hrrr smoke model. It has best concentration of smoke affecting
portions of Elbert and Lincoln counties overnight.

&&

.SHORT TERM...(This evening through Monday)
Issued at 244 PM MDT Sun Jun 10 2018

A positively-tilted upper trough is swinging into the northern
Rockies this afternoon, the hot, dry and breezy conditions
continue with southwesterly flow aloft. Temperature readings are
in the 90s across the plains, with a few in the upper 90s. With
some daylight left, wouldn`t be surprised to see a few 100 degree
readings over the lower elevations of the plains. Gusty southwest
winds across the area will continue into the late afternoon. Fire
activity over southwestern Colorado has increased significantly,
s