Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 240340
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1040 PM CDT Fri Sep 23 2016

.UPDATE...

Issued at 1040 PM CDT Fri Sep 23 2016

Convection continues to increase/lift north/northeastward into
and across southwest and central North Dakota, along a low level
convergence zone as forcing aloft increases as divergent flow
overspreads the Northern Plains. Modified POPs based on latest
model data and radar trends. HRRR is catching up and I was able
to actually use its reflectivity output somewhat for this update.

Will need to keep a close eye on precipitation totals as the area
of convection over the southwest continues north into northwest
and north central areas. These areas received the higher rainfall
totals the past 12-24 hours and additional moisture may create
some problems depending if the robust convection can sustain
itself.


UPDATE
Issued at 833 PM CDT Fri Sep 23 2016

As forcing begins to increase from south to north, showers and
storms are now flaring up across portions of the southwest and
south central. Quick update sent to speed up the increase in POPs
and to try to fine tune the aerial coverage.

While we remain in the Marginal Risk area (southwest), SPC has
removed the Slight Risk area from North Dakota. Agree with this
change.

UPDATE
Issued at 615 PM CDT Fri Sep 23 2016

We are mainly dry across western and south central ND at the
moment so significantly reduced POPs for these areas. Main band of
showers and scattered thunderstorms currently lifting north-
northeast across north central and eastern ND. Kept high POPs for
these areas. Models are trying to catch up to radar, so populating
POP grids was a bit tricky for this update. High res models
continue to be in agreement with convection developing over or
into southwestern ND this evening and lifting north and northeast
across the area. Additional development possible elsewhere as the
surface low lifts north and embedded mid level energy approaches
the state this evening. Will likely have to send 2-3 updates over
the next 3-5 hours to account for radar trends. Last couple of
HRRR iterations have backed off on robust convection across the
southwest, so will see if this trend continues. Will continue to
mention possible severe storms in the State Forecast and HWO
products for the southwest.

Other update was to trend sky cover down over my south central and
southeast a bit more. Latest visible satellite imagery shows
clearing moving towards my far southeast counties now with both
the HRRR/RAP/NAM showing this trend continuing north and slightly
northwestward as we progress through the evening and into later
tonight.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 248 PM CDT Fri Sep 23 2016

Severe thunderstorm potential southwest this evening and tonight
highlights the short term forecast.

The 15-18 UTC operational and experimental HRRR iterations
continue to show strong run to run consistency in developing
convection across eastern Wyoming this afternoon, and propagating
this convection into southwest North Dakota by 02-04 UTC,
sustained by a strengthening low level jet and a resurgence of
upper level forcing ejecting out of the intermountain west upper
level low. This is supported by the greater 12 UTC CAM suite.
These HRRR iterations continue to depict in their 2-5 km updraft
helicity fields tracks of 75-100+ m2/s2 across southwest North
Dakota, supporting the potential for organized convection
possibly in the form of elevated low topped supercells to survive
from Wyoming into southwest North Dakota. Large hail and damaging
winds are the primary threats given the likely elevated nature of
these storms.

For Saturday, followed a blend of the 12 UTC global suite given
good agreement amongst the larger scale guidance for the
aforementioned upper level low to propagate into southwest North
Dakota by early Saturday evening. A dry slot is favored across
much of the south central for Saturday, with wrap around
stratiform precipitation across the far west, and potentially more
convective precipitation across the north central and James River
Valley.

.LONG TERM...(Saturday night through Friday)
Issued at 248 PM CDT Fri Sep 23 2016

Strong winds across the west Saturday night with a dry forecast
for the remainder of the period thereafter highlight the extended
forecast.

Given good agreement, followed a blend of the 12 UTC global
guidance suites for most fields. The nearly stacked low from the
short term is forecast to propagate across North Dakota Saturday
night. All ingredients will be available for strong winds on the
backside of the low, with a tight pressure gradient and strong
cold air advection aided by isallobaric forcing. 0.5 km winds
around 50 kts are forecast across the west, which will have to be
monitored for the next few models runs should a high wind watch
become necessary across the west for Saturday night into Sunday.

Thereafter, broad upper level ridging builds across the central
CONUS Tuesday through the remainder of next week, signaling a
drier pattern with near to slightly above average temperatures.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)

Issued at 1040 PM CDT Fri Sep 23 2016

Widespread IFR/LIFR conditions in stratus, fog, rain showers and
thunderstorms will continue across western and central North
Dakota tonight. A brief improvement to MVFR-Low VFR remains in the
forecast for KBIS/KJMS late tonight into Saturday morning as dry
air works north-northwestward from South Dakota into the storm
system impacting our area.


&&

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

&&

$$

UPDATE...NH
SHORT TERM...AYD
LONG TERM...AYD
AVIATION...NH



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