Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 180242
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
942 PM CDT Mon Apr 17 2017

.UPDATE...
Issued at 928 PM CDT Mon Apr 17 2017

Little change with this update other than to blend to observed
trends and the 00 and 01 UTC hi-resolution rapidly updating
iterations. As of 0230 UTC, a dry slot was clearly evident ahead
of the potent shortwave that was located on the North Dakota and
Montana border. Strong moisture transport and low level warm air
advection ahead this potent shortwave into southwest and south
central North Dakota will continue through 08-09 UTC with
significant frontogenesis in the 925-700mb layer along the I-94
corridor. Thus, rainfall amounts in excess of 1 inch are possible,
especially across the James River Valley. Will also have to
monitor convection across the southwest and south central as the
HRRR through the evening has suggested the potential for isolated
organized storms within its updraft helicity forecasts in a high
shear/low CAPE/strongly forced environment.

UPDATE Issued at 537 PM CDT Mon Apr 17 2017

Given the presence of low level dry air, characterized by 20 to
30 degree temperature-dewpoint spreads, lowered PoPs through 03
UTC with the initial shortwave. Thereafter, greater forcing and
moisture arrives post 03 UTC as the surface low strengthens
across central North Dakota. Maintained the mention of
thunderstorms southwest and south central tonight highlighted by
SREF thunderstorm probabilities in the 20-45 percent range
associated with a strengthening low level jet and weak
instability.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 222 PM CDT Mon Apr 17 2017

This period will encompass a shortwave h500 trough and deepening
surface low forecast to track across the North and South Dakota
borders tonight. This low will bring widespread showers and
isolated thunderstorms to much of the region with some wet snow
mixing in late tonight north.

The fairly short wavelength of this h500 wave will bring some
sharp thermal profiles and a strong response in the h850 winds.
The North American Ensemble Forecast System (NAEFS) has a
V component of the wind near a climatological maximum tonight.
Supporting this model earlier runs of the NAM depicted 75kts of
h850 wind across NE South Dakota tonight. While the latest 12Z run
not quite as robust it still is quite strong. Although this wind
will not mix to the surface since it moves through around midnight
it will act to pull available moisture into the region. The NAEFS
precipitable water profile is also impressive near 90 percent of
the climatological max. So there should be plenty of moisture for
a decent precipitation event. With the ground now fairly dry the
soils should soak up the moisture.

Storm total rainfall is forecast between a quarter and three
quarters of an inch from southwest through northeast North Dakota
by Tuesday morning. A narrow band of CAPE supported by strong
0-6 km wind shear will support isolated to scattered thunderstorms
along a triple point in the frontal system as it moves across the
southern third of the region tonight.

.LONG TERM...(Tuesday night through Monday)
Issued at 222 PM CDT Mon Apr 17 2017

The extended period will see several h500 troughs move through but
in fairly weak mid level flow. The best chance for rain will be
Wednesday followed by generally below normal precipitation
chances. Highs will be in the 50s Wednesday and mostly in the 60s
Thursday through the weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 928 PM CDT Mon Apr 17 2017

Widespread rain showers with embedded thunderstorms will continue
to develop across southwest and south central North Dakota
tonight. IFR conditions are possible as ceilings lower through the
night. While rain showers will be less prevalent across northern
North Dakota, IFR ceilings will also develop through the night.
Some snow may mix with rain late tonight north.

&&

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

$$

UPDATE...AYD
SHORT TERM...WAA
LONG TERM...WAA
AVIATION...AYD



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