Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 180503
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1203 AM CDT Fri Aug 18 2017

.UPDATE...
Issued at 1157 PM CDT Thu Aug 17 2017

This update will focus on scattered thunderstorms over the north
central into the east centraL. Current POPs look pretty good and
just filled in some gaps. Current trends have a slight increase
in intensity but believe with the marginal instability and shear
the strongest period of storms my be over in about two to three
hours.

UPDATE Issued at 856 PM CDT Thu Aug 17 2017

Convection has notably increased in intensity over the past hour
across northwest North Dakota as of 02 UTC ahead of the shortwave
across far northeast Montana and into Saskatchewan. This increase
may be tied to locally enhanced deep layer shear ahead of the
wave which is suggested by the 01 UTC RAP analysis. The 00 UTC
HRRR, 22 UTC ESRL HRRR and 01 UTC RAP suggest convection may
become more numerous across the north central and through the
James River Valley through the night as the aforementioned wave
propagates southeast into a more moisture rich environment,
characterized by surface dewpoints in the 60s. Deep layer shear is
also at least marginally supportive of organized convection which
is confirmed by the updraft helicity signatures from the HRRRs.
Thus, cannot rule a few more elevated severe storms through the
night. The primary threats will be quarter to half-dollar size
hail, damaging winds to 60 mph and dangerous lightning.

UPDATE Issued at 645 PM CDT Thu Aug 17 2017

Isolated to scattered high based convection continues across
western into north central North Dakota with a few mid level
impulses ahead of the more boarder wave across northeast Montana
into Saskatchewan as of 2345 UTC. MLCAPE around 1000 j/kg and weak
deep layer shear suggests that the severe threat is rather low.
However, gusts of 30-40kts are possible with the stronger storms
given their high based nature. The CAMs through the 22 UTC HRRR
suggest at least isolated to scattered elevated convection will
propagate east and maintain itself through the night aided by the
aforementioned wave. However, a large spread in the CAMs remains,
with the HRRR the most aggressive in strengthening convection
overnight across central North Dakota. This is certainly not out
of the question, but still somewhat uncertain.

&&

.SHORT TERM...(This evening through Friday)
Issued at 156 PM CDT Thu Aug 17 2017

Fire weather concerns and Thunderstorm chances highlight the short
term forecast.

Currently, low pressure was situated near Watford City along a
trough situated from Saskatchewan through the western Dakotas.
Over far western ND and eastern MT, dewpoints have dropped behind
the surface trough with some gustier winds. However, a shortwave
tracking across Montana is bringing an area of increased
cloudiness into southwest ND at this time, and should may help
temper afternoon highs, which would inhibit fire weather potential
somewhat.

Tonight, mesoscale models are hinting at two areas of showers and
thunderstorms. the first is associated with the aforementioned
shortwave trough and tracks west to east along the ND/SD border,
extending south through SD. The strongest convection remains
mostly to the south of ND.

A second area of convection tracks across northwest and north
central ND, and then southeast into eastern ND during the
overnight hours. Severe thunderstorm appears on the minimal side,
but with around 1000 J/KG of CAPE and 25 to 35 knots of shear this
evening, an isolated severe storm can not be ruled out. Some of
the mesoscale models have indicated some weak to moderate updraft
helicity signatures dropping southeast from Canada this evening.

Warm and dry on Friday. We lowered the dewpoints from guidance in
the southwest Friday afternoon, but winds do not appear to be very
strong.

.LONG TERM...(Friday night through Thursday)
Issued at 156 PM CDT Thu Aug 17 2017

he extended forecast begins Friday night with a shortwave ridge
bringing warmer temperatures Friday and especially Saturday.
Highs should be in the 80s Friday with more widespread lower 90s
by Saturday. This will be followed by a Pacific cold frontal
passage cooling the region back into the 70s and lower 80s Sunday
through Tuesday. This will also bring a chance for scattered
showers and thunderstorms Sunday and Sunday night. Broad ridging
develops aloft by early to middle of next week suppressing
convection and returning warmer temperatures to the region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1157 PM CDT Thu Aug 17 2017

A weak trough of low pressure across central North Dakota will be
the focus for thunderstorms from KMOT-KJMS 06z-12z. Otherwise VFR
will prevail across the region.

&&

.FIRE WEATHER...
Issued at 156 PM CDT Thu Aug 17 2017

While there are some fire weather concerns today critical fire
weather conditions are not expected.

A warm thermal ridge will support high temperatures today around
90 southwest into west central North Dakota. While consensus
models show Minimum RH values around 20 percent opted to use the
dryer HRRR model which supports Minimum RH`s as low as 15 percent,
and also extended the lower humidities a little farther east. A
wind shift to the Northwest is forecast with the surface trough
passage late this afternoon. Again, raised winds a tad over
consensus to around 15 mph with gusts 20 to 25. Based in this
there should not be sufficient winds to create critical fire
weather conditions today.

Another warm day is forecast Saturday with a more significant
frontal passage late Saturday afternoon and night. We utilized a
blend of higher wind guidance over our given guidance. BUFKIT
forecast NAM/GFS soundings for Saturday afternoon support
sustained winds of 15 to 20 mph and gusts of 25 to 30 mph. This
period will certainly need to be monitored for possible critical
fire weather.

&&

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

$$

UPDATE...WAA
SHORT TERM...TWH
LONG TERM...TWH
AVIATION...WAA
FIRE WEATHER...TWH



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