Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 121623
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1123 AM CDT Sat Aug 12 2017

.UPDATE...
Issued at 1141 AM CDT Sat Aug 12 2017

Latest local radar shows an area of showers and thunderstorms from
earlier this morning, now into Kidder/Stutsman counties, as well
as the far southern James River Valley. These are being maintained
by the overlap of 925mb-850 frontogenesis and upper level
divergence per SPC Mesoscale Analysis. Very little change in POPs
needed here as previous forecast had it handled well.

Farther upstream, the latest GOES16 water vapor imagery shows the
main upper level low now circulating over northeastern Montana
extending into northwestern North Dakota. A 500mb cold pocket of
-17C was noted with the upper low, along with isolated
 showers/thunderstorms.

Attention for this afternoon and evening is directed toward a
700mb-500mb shortwave noted over Prairie/Custer counties in
eastern Montana, per water vapor imagery. The GFS initializes
this very well with the current location, and begins pushing this
shortwave into southwestern ND 21z-00z. Current Mixed layer CAPE
around 500 J/Kg, but this is expected to increase to between
1000-2000 J/kg later this afternoon as large scale ascent
increases and colder air aloft arrives. Air parcels will
encounter moderate instability (CAPE), Effective Bulk Shear values
of 40kt, and mid level lapse rates around 7.5C/km. With that
said, current gridded forecast has a mention of severe thunderstorms
in far southwest and into far south central ND. This is in line
with the Marginal Severe Thunderstorm Risk per SPC, and see no
reason to deviate from it at this time. Current forecast is on
track.

UPDATE Issued at 753 AM CDT Sat Aug 12 2017

Quick update for pops based on latest radar. Trimmed pops north
and west and adjusted pops south and east based on latest radar
analysis. Otherwise no significant changes at this time.

&&

.SHORT TERM...(Today and tonight)
Issued at 445 AM CDT Sat Aug 12 2017

Large areas of showers and storms were moving through southwest
and south central North Dakota as of this writing with radar
estimated rain amounts generally 0.50 to 1.50 inches, and spots
with more than that. This with a short wave.

A mid level low was centered over northeast Montana and set to
track east / southeast over the forecast area today. Moisture,
lift, and instability are all present for showers and storms
through the day. The next well organized batch should fire off
around Beach at mid day and push east with the next wave around
the mid level low. Widespread severe weather is not expected,
however, severe weather parameters are "elevated" along the South
Dakota border counties south of Dickinson to south of Bismarck for
the afternoon, where shear is most supportive for rotating
storms. RE: SREF Calibrated Probabilities for severe
thunderstorms. Higher chances for severe weather are into western
South Dakota. Individual storms will also produce heavy rain,
possibly in the respect of rain gauge totals but moreso with
respect to rain intensity definition of heavy rain.

.LONG TERM...(Sunday through Friday)
Issued at 445 AM CDT Sat Aug 12 2017

For Sunday the H5 low is over the Red River Valley and pushing
into the land of 10,000 lakes. Cyclonic flow continues over the
eastern half of the forecast area and with that cool pool aloft
showers should be expected there. Weak ridging moves overhead for
Sunday night into Monday for a dry period. This before the next
wave over Alberta approaches for Monday afternoon. By Monday
afternoon a surface boundary through eastern Montana provides low
level lifting and a low level moisture return, while diffluent H5
flow into western North Dakota supports upward motion through the
mid levels for storm chances. Numerous waves pass through what
becomes southwest flow over the forecast area for storm chances
right through Tuesday night.

For the end of the long term, a cool pool aloft remains over the
area. No organized triggers are foreseen so any showers and
storms would be isolated in the heating of the day.

Temperatures in the 70s for highs into mid week then 80s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1041 AM CDT Sat Aug 12 2017

Mid and upper level circulation will keep the threat of showers
and thunderstorms through the forecast period. Currently band of
showers and thunderstorms approaching KJMS and extending north
northwest to around KMOT. Will have a mention of showers and
thunderstorms for these areas as TAF period begins. Better risk of
stronger storms will be this afternoon into early this evening
for KDIK to KBIS and points south. MVFR cigs/vsbys will be
possible with any thunderstorms. East to southeast flow continues
through the period with indications of MVFR to IFR ceilings
Sunday morning, especially across the southern TAF sites. Will
bring MVFR ceilings and start off with a SCT layer of IFR and MVFR
Vsbys. Later shifts may need to trend lower with ceilings and
vsbys.

&&

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

$$

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



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