Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 251129

Area Forecast Discussion
National Weather Service Bismarck ND
629 AM CDT MON JUL 25 2016

Issued at 629 AM CDT Mon Jul 25 2016

No significant changes were needed with this update. Early-morning
surface observations show a pressure trough/weak wind shift taking
shape over far eastern MT and western ND. Most convection-allowing
model guidance expects that feature to be the focus for a couple
storms from south central ND into the James River valley by late
afternoon, when surface temperatures near 90 F may yield MLCAPE
around 1500 J/kg. Deep-layer shear will be weak, though, and that
will marginalize the threat of strong or severe thunderstorms.


.SHORT TERM...(Today and tonight)
Issued at 251 AM CDT Mon Jul 25 2016

Water vapor imagery loop shows a transition from northwest towards
more of a zonal flow into North Dakota early this morning. Overall
expect plenty of sunshine and warmer air to overspread western and
central ND. However, by mid to late afternoon, isolated showers
and thunderstorms begin to evolve, per latest Global and high
resolution models. A shortwave near Lewistown, Montana, will reach
western ND around 12z then hang over western and central ND this
afternoon. It is best reflected in the 700mb height fields and in
the 850mb isotherms, with a thermal trough/cooler pocket, along
with a surface and boundary layer wind shift noted in the RAP13
and GFS. It is along and ahead of this boundary that the first
signs of potential convection develop this afternoon per
Experimental HRRR/RAP 13 in and near the vicinity of the James
River Valley. Isolated showers/thunderstorms developing from 21z
to 00z Tuesday would favor far south central into the James River

NSharp soundings indicate low level warm advection/veering wind
profile today ahead of the surface wind shift noted above. 850mb
temperatures this afternoon range from +20C in the Turtle Mountains
to +27C in the southwest. This corresponds to surface highs of
around 82F at Rolla to around 96F at Bowman and Hettinger.

For tonight, a pair of shortwaves per water vapor imagery, one in
Pendleton Oregon, and the second near Burns in southeast Oregon
will both move east as well through the short term period. These
shortwaves will reach central Montana and central Wyoming by 12z
Tuesday. Boundary layer winds indicate that a surface low and warm
front develops from northeast Wyoming into southern ND tonight.
This low level convergence area along with increasing moisture
advection per 850mb southerly winds will spawn increasing chances
for shower/thunderstorm development across portions of southern ND
tonight. However, the SREF calibrated severe thunderstorm chances
remain low at 5 to 10 percent through 12z Tuesday.

.LONG TERM...(Tuesday through Sunday)
Issued at 251 AM CDT Mon Jul 25 2016

Tuesday and Tuesday night seem to favor the better chances for
showers and thunderstorms given the multiple shortwave activity
slated to move through and greater instability. Most of western
and southern ND remain in a Marginal Risk per SPC during this
time. The SREF probability of thunderstroms and severe thunderstorms
increase in southwest and south central Tuesday evening/night
through Wednesday morning, then decrease Wednesday afternoon
through Wednesday night. The upper flow transitions toward a
northwest flow Tuesday night, with another shortwave slated for
Wednesday night. However, as mentioned above, the SREF suggests
there will be low probabilities of severe weather during this time
period. SPC also has southwest ND in a Marginal Risk in the Day 3
which covers the Wednesday through Wednesday night period. There
seems to be enough uncertainty amongst the NAM and GFS at this
time in regards to strength of the wind shear.

Northwest flow with successive shortwaves follow for Thursday and
Friday keeping chances of showers and thunderstorms in the forecast.
A brief transitory ridge mitigates chances for precipitation Saturday
into most of Sunday.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 629 AM CDT Mon Jul 25 2016

VFR conditions will prevail today and tonight. We expect isolated
thunderstorms in the late afternoon and evening south. Confidence
in the exact location of storms is modest at best because only a
weak wind shift will likely serve as the trigger for them, so we
chose to withhold any mention of VCTS in the 12 UTC TAFs. However,
based on clustering in high-resolution model guidance, and the
general placement of the weak front, KBIS and KJMS will have the
highest probability of a storm, mainly between 22 and 03 UTC.


.BIS Watches/Warnings/Advisories...


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