Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 220558
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1258 AM CDT FRI JUL 22 2016

.UPDATE...
Issued at 1258 AM CDT Fri Jul 22 2016

Elevated thunderstorms have blossomed out of an altocumulus field
in south central ND rather quickly since 0445 UTC. These storms
are likely being driven by mid-level Theta-E advection, which is
acting on the very unstable air mass sampled by the 00 UTC RAOB
taken at Aberdeen. Based on that sounding and RAP-based mesoscale
analysis data from SPC, the elevated storms in south central ND
have access to around 3000 J/kg of MUCAPE and effective shear in
excess of 50 kt. Large hail is possible overnight. In fact, the 00
UTC 4 km NAM guidance we relied heavily on to modify the PoP
forecast through 15 UTC Friday (because it best matches the radar
trends so far) suggests the risk of an elevated, large-hail-
producing supercell is very real across south central ND in the
next 6-9 hours.

UPDATE Issued at 936 PM CDT Thu Jul 21 2016

Only change was to add more clouds in the low level warm
advection south central early Friday morning. Nam shows the
southeast flow between h925-h850 bringing up some low level moist
air that should result in a period of cloudiness around sunrise
between linton and oakes.

UPDATE Issued at 632 PM CDT Thu Jul 21 2016

Bowman radar shows an isolated cell in Harding county South Dakota
that should track south of the state. Believe this convection
will subside with the normal diurnal trend. Several runs of the
HRRR suggest weak convection this evening west central sections
but so far see only some weak mid level convection (ACCAS) and
dont see thunderstorms developing yet. NWS radars still have a
few boundaries left over from last nights convection. will not add
any pops this evening. Skies will become mostly clear after
sunset. temperatures and winds trending ok.

&&

.SHORT TERM...(This evening through Friday)
Issued at 326 PM CDT Thu Jul 21 2016

The main forecast concerns begin on Friday, when the chances of
thunderstorms increase, with the potential for severe thunderstorms
and some locally heavy rainfall.

Currently...dry surface high pressure centered over western Montana
continues to push into North Dakota. At upper levels a dry zonal
flow today should continue most of tonight.

Tonight will mainly be quiet, with lows in the 60s. Late tonight
there is a slight chance of thunderstorms in the far southwest, with
the approach of the next system to affect our area.

Models are in agreement regarding a vigorous shortwave trough off
the Pacific Northwest coast today begins moving into the Rockies at
the US/Canadian border Friday. This will induce southwesterly flow
aloft upstream across the Rockies into the western plains...and the
leading edge of a series of upper level impulses approaches western
North Dakota Friday morning. A southerly low level jet develops
quickly, allowing 60s/lower 70s dewpoints to return to the state. As
the previous forecast crew did earlier, we increased dewpoints from
the consensus guidance given the low dewpoint biases from the past
several days. The Nam and ECMWF did pick up on these higher
dewpoints and felt confident continuing this trend of raising
dewpoints.

MU CAPE values of 2000-3000+ J/kg with 0-6km bulk shear values of 40-
55 knots will develop by Friday afternoon. This occurs as an upper
level shortwave impulse moves eastward across the state. Plenty of
lift with the aid of the nose of the low level jet punching into
western North Dakota. The Storm Prediction Center outlook for Friday
depicts a slight risk for severe storms for all of western and
central North Dakota. This is consistent with earlier outlooks.

.LONG TERM...(Friday night through Thursday)
Issued at 326 PM CDT Thu Jul 21 2016

The potential for severe thunderstorms Friday night through Saturday
is the highlight of the long term forecast.

Friday night another very potent shortwave impulse emanating from
Wyoming/Montana, along with the strengthening low level jet, will
continue the threat of severe thunderstorms. As per the previous
forecast package, it appears that the individual severe storms could
merge and form into an MCS by later Friday evening/night, with the
thunderstorms continuing across our region late Friday night. By
Saturday morning the earlier mentioned upper level Pacific Northwest
shortwave low will have crossed the Rockies and will be over central
Montana by daybreak Saturday. This will induce a surface low near
the Montana/Saskatchewan/North Dakota border by Saturday morning.
The surface low/cold front moves east across North Dakota during the
daytime Saturday, while the upper low hangs back a bit over the
Saskatchewan/Manitoba/ND border. The upper low then moves east
across southern Manitoba Saturday night.

Thus additional rounds of thunderstorms and potential severe weather
are possible Friday night through much of Saturday. Locally heavy
rainfall is a good possibility simply because of the anticipation of
several rounds of thunderstorms beginning Friday and continuing into
Saturday afternoon/early evening.

Thereafter, the upper-level flow across the Northern Plains is
forecast to be mainly a zonal west-to-east flow, with a few embedded
shortwaves that would bring chances of thunderstorms. Saturday night
through Monday appear to be mainly dry...with the consensus models
indicating the next chance of showers and thunderstorms beginning
Monday night, with daily chances of rain through much of next week.

High temperatures should be seasonable, with temperatures around 80
to 90 through the long term.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1258 AM CDT Fri Jul 22 2016

Sct to bkn mvfr cigs forecast at KBIS and KJMS between 12z and 17z
Friday. Vcfg was also briefly added to KJMS between 11z and 15z
Friday. Otherwise expect vfr cigs outside of any thunderstorms,
which should develop and increase in coverage throughout the TAF
period. Tried to time the showers/thunderstorms where confidence
seemed highest Friday, which included the KISN/KDIK/KBIS terminals.
A vcts/vcsh was utilized elsewhere.

&&

.BIS Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...CJS
SHORT TERM...JV
LONG TERM...JV
AVIATION...KS


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