Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 201930

Area Forecast Discussion
National Weather Service Bismarck ND
230 PM CDT WED JUL 20 2016

Issued at 227 PM CDT Wed Jul 20 2016

Upgraded much of the Heat Advisory to an Excessive Heat Warning
across much of south central North Dakota and into the James River
Valley. Surface dewpoints in the upper 70s to the lower 80s are
observed across these areas given strong evapotranspiration. With
temperatures quickly climbing into the 90s, heat index values to
110 degrees are likely to continue to the afternoon and early
evening. While dewpoints will mix out a bit the rest of the day,
all guidance is under-doing surface dewpoints this afternoon.

UPDATE Issued at 1240 PM CDT Wed Jul 20 2016

Again, little change in the overall thinking compared to the 939
am CDT update. The mostly likely scenario is the 11 UTC HRRRX,
which develops a few isolated, yet likely severe storms, by 23 UTC
between US Highways 83 and 85 along a weak surface boundary
currently across extreme western North Dakota into southeast
Montana. All threats are possible. See the 1630 UTC SPC Day 1
Convective Outlook for details.

UPDATE Issued at 939 AM CDT Wed Jul 20 2016

No significant changes with this forecast update other than to
blend to observed trends through 14 UTC. The consensus of the 12
UTC CAM suite is for potential isolated to scattered convective
initiation between 22-00 UTC along a weak cold front/density
gradient across eastern Montana this morning that will propagate
to between US Highways 83 and 85 early this evening. Given the
weak forcing and high instability, the spread of the CAM
solutions is wide. However, the convective signal as a whole is
greater compared to Tuesday. Any storms that develop are favored
to become severe.

UPDATE Issued at 647 AM CDT Wed Jul 20 2016

Minor changes with this update cycle included 1) adding patchy fog
to east central ND from Linton to Jamestown and Rolla through 14
UTC based on recent observations, and 2) refining low-end PoPs in
western ND this morning. Radar imagery through 1130 UTC reveals an
area of high-based, elevated showers and a few rumbles of thunder
moving through western ND, possibly aided by a weak impulse aloft
and/or a renewed surge of steeper lapse rates within the elevated
mixed layer. Indeed, RAP analysis data suggests 700-500 MB lapse
rates have increased to 9 C/km in west central ND the last couple
of hours. This is likely related to the intensely heated boundary
layer in MT and WY yesterday afternoon being advected eastward.
Regardless, this advection-related ascent is occurring above the
stable boundary layer and there are no signs in either radar data
or convection-allowing guidance that it will deepen sufficiently
for any storms of significance this morning.

Otherwise, uncertainty remains high with regard to the initiation
of deep moist convection late this afternoon and this evening in
the face of weak large-scale ascent and residual capping despite
the very hot and moisture-laden boundary layer. There has been
little in the way of consistency in HRRR and experimental/parallel
HRRR simulations in the last few hours with regard to potential
storm development due to those factors.


.SHORT TERM...(Today and tonight)
Issued at 320 AM CDT Wed Jul 20 2016

The main focus for the short term is hot temperatures and

Compressional warming with a nearby front and a large dome of very
hot air aloft will mix down and lead to another sultry day. Widespread
temperatures around 100 will be common across the southern half
of North Dakota. Heat indices around 105 are expected across
portions of central North Dakota and the James Valley.

A very moist and unstable airmass is in place. A weak front will
slide across North Dakota today and interact with this unstable
airmass. This could provide enough lift to overcome any capping in
place. If this does occur rapid thunderstorm development and
intensification is possible. Short-term models are all over the
place with respect to time and location of any storm development.
At this time it appears the most likely opportunity for storms
is late this afternoon across central and northern North Dakota.
With ample instability and a decent shear profile with southerly
winds at the surface and westerly aloft, rotating updrafts and
supercells are possible.

.LONG TERM...(Thursday through Tuesday)
Issued at 320 AM CDT Wed Jul 20 2016

A cooler day is expected Thursday behind the front. Temperatures
are still expected to climb into the 90s, but humidity should be
noticeably less.

Thunderstorms are possible once again Friday as another wave moves
out of the mountain west. If thunderstorms develop they could
become severe with very high instability, steep lapse rates and
modest shear in place.

Cold air advection will take hold this weekend. Temperatures will
fall back into the 70s and 80s.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 227 PM CDT Wed Jul 20 2016

Isolated to scattered thunderstorms are possible late this
afternoon and evening, especially across central North Dakota. A
few storms could be severe with large hail and damaging winds.
Storm coverage is expected to be low with impacts to the terminals
uncertain at this time.


.BIS Watches/Warnings/Advisories...
Excessive Heat Warning until 9 PM CDT /8 PM MDT/ this evening
for NDZ019>023-025-034>037-042-045>048-050-051.

Heat Advisory until 9 PM CDT /8 PM MDT/ this evening for



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