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000
FXUS63 KBIS 190548
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1248 AM CDT Tue Sep 19 2017

.UPDATE...
Issued at 1148 PM CDT Mon Sep 18 2017

Latest satellite imagery shows increasing mid/high level clouds
west with Bowman radar indicating increasing reflectivitys. The
fog/stratus loop shows an expanding line of low clouds from east
to west. Overnight low clouds/fog will be shifting into the Turtle
Mountains and James River Valley. This is supported by the latest
HRRR visibility and NBM cloud cover forecast. Will be monitoring
for the potential of a dense fog advisory. Current gridded data
has this handled well and no changes with this update.

UPDATE Issued at 937 PM CDT Mon Sep 18 2017

Rain showers continue to develop over central/eastern Montana
pushing our way with the initial wave. Have backed off a little on
the timing of the showers as they push towards our area. Remainder
of forecast looks good.

UPDATE Issued at 639 PM CDT Mon Sep 18 2017

For early evening update the main change was adding fog through
the James River Valley into north central North Dakota. Models
continue to indicate visibilities dropping late tonight as
moisture starts to surge up into the area. There is a possibility
that this may just hold as low cloud cover, but with the recent
trend of fog easily forming along with the surface moisture
surging in figured it was worth mentioning the possibility.
Updates have been sent.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 220 PM CDT Mon Sep 18 2017

Quiet this evening as upper level ridging propagates across the
forecast area. Upper low and associated shortwave energy
translating through it, will impact the weather across western and
central ND late tonight through Tuesday. increasing moisture
return ahead of developing lee trough is expected to produce low
stratus advecting from Minnesota westward into the eastern and
central Dakotas. In addition strong winds aloft will spread from
western into central causing concerns for Aviation weather tonight
in the form of IFR conditions and Low level wind shear.

On Tuesday, an upper low takes shape over southern Alberta with
strong shortwave energy lifting northward through eastern MT. In
addition, a strong upper jet will track across the northern
rockies and into South Dakota. This will produce strong upper
level divergence over the eastern forecast area. The associated
surface trough/front will move from western ND Tuesday morning,
into central ND by Tuesday afternoon. This will set the stage for
potential strong to severe storms over central and eastern ND
Tuesday afternoon and evening.

Current SPC Day 2 outlook is very similar to this mornings, and
our thinking here has changed little from previous forecast.
Conditions look favorable for thunderstorm development from north
central SD into east central ND during the afternoon as strong cap
begins to erode. Timing of erosion of low stratus may affect the
eventual timing/placement of thunderstorm initiation, but the
probability of occurrence still appears high considering the
strength of the synoptic system.

NAM forecast soundings over the southern James River Valley
indicate Strong 0-6km shear congruent with 1000-1500 J/kg MLCape
and and 2-300 m2/s2 of 0-3km Helicity. This area looks to be the
most favorable for severe storms, including possible tornadic
storms, especially if initial development can remain discrete.
However, with the strength of the synoptic system, severe weather
can not be ruled out most anywhere along and east of the highway
83 corridor.

Overall few changes from the previous forecast for Tuesday.

.LONG TERM...(Tuesday night through Monday)
Issued at 220 PM CDT Mon Sep 18 2017

Severe threat will linger into Tuesday evening over the James
River Valley. As we transition into evening, threat will likely
change to more of a wind threat with linear MCS convection.

Wednesday is expected to be dry and relatively quiet. There is
some elevated instability Wednesday afternoon, so a few showers
can not be ruled out. Also it appears to be a good mixing day in
the afternoon. We bumped up winds over our given guidance,
utilizing a consensus of MOS based products.

Another upper level trough moves into the area Thursday night into
Friday. This will bring cooler temperatures with a threat of
showers. Thunderstorms can`t be completely ruled out, but higher
threat remains south and east of the forecast area.

Cooler and showery weather continues into the upcoming weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1131 PM CDT Mon Sep 18 2017

Low pressure in eastern Montana will move into North Dakota
today. An increasing southeast windflow will favor stratus and
fog across eastern North Dakota, impacting KJMS, as well as wind
shear KBIS-KDIK-KISN-KMOT this morning. Wind shear ending and
VLIFR conditions improving to VFR after 16Z KJMS. Otherwise, the
main hazard to aviation after 18Z will be thunderstorms Tuesday
afternoon and Evening. At this time only added VCTS to TAFs for
KBIS-KMOT-KJMS due to timing uncertainty. But conditions favor a
line of thunderstorms with gusty winds, possibly impacting KJMS
after 00Z.

&&

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

$$

UPDATE...KS
SHORT TERM...TWH
LONG TERM...TWH
AVIATION...WAA