Area Forecast Discussion
Issued by NWS Bismarck, ND

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975
FXUS63 KBIS 230530
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1230 AM CDT Wed May 23 2018

.UPDATE...
Issued at 1221 AM CDT Wed May 23 2018

Focus for thunderstorms remains across the southwest where back
building storms produced heavy rain across Adams County Tuesday
evening. Current trends show these storms now beginning to move
northward so the immediate threat for additional flash flooding is
less. The next round of storms currently across southwest South
Dakota will move north toward western and south central North
Dakota around or just before sunrise. These should have a forward
moving component. Will evaluate the flash flood warning at 130 am
CDT but may be able to let this expire at shortly after 2 am CDT.


UPDATE Issued at 1020 PM CDT Tue May 22 2018

Scattered thunderstorms have congealed around Bismarck in central
ND late this evening. Additional thunderstorms were located near
Hettinger. This area is within a PW max and low level convergence.
The severe threat has all but ended. However, heavy rainfall
remains an issue, especially around Hettinger where storms there
continue to regenerate just east of Hettinger. A flash flood
waring remains in effect through late tonight and may need to be
extended into Wednesday.

Main changes for the update were adjusting Pops based on latest
radar.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 249 PM CDT Tue May 22 2018

Convective potential highlights the short term forecast.

Two areas of potential convective initiation are possible late
this afternoon across the southwest and south central. First
across the Beach and Medora areas along a weak convergence line,
and a second along a density gradient along the northern periphery
of the cumulus field from near Bowman to Mandan/Bismarck, and
Napoleon. This is evident in the GOES-East Day Cloud Phase
Distinction RGB and Visible imagery through 2042 UTC showing
towering cumulus with ice at cloud top. However, upper level
forcing is rather weak, and sustained initiation would seem to be
another hour or two off. SPC has maintained the marginal risk
across the southwest and south central where MLCAPE around
900-1500 j/kg and deep layer shear of 25-30 kts supports an
isolated severe threat through sunset. Additional, less intense
convection is expected to develop across the northwest late this
afternoon into the early evening where upper level forcing is
greater, but, instability weaker.

Thunderstorms may be sustained across the southwest through the
overnight with a low level jet propagating into the northwest by
early Wednesday morning.

On Wednesday, widespread surface dewpoints in the upper 50s to
mid 60s are forecast to be in place across much of western and
central North Dakota ahead of a surface warm front that will
propagate into southwest North Dakota late Wednesday afternoon.
With the arrival of multiple impulses late Wednesday afternoon
and through evening ahead of the upper low across Montana,
convective initiation within the moisture axis ahead of the warm
front appears to increase after 21 UTC. ML CAPE around 1500-2500
j/kg and deep veering wind profiles with 0-6km shear around 30kts
oriented perpendicular to the moisture axis supports the potential
for a discrete supercellular mode late Wednesday afternoon and
into the early evening. All hazards are possible with the discrete
convection including large hail to golfball size, damaging winds
to 70 mph, and a tornado or two cannot be ruled out. Convection is
likely to congeal as it propagates north through the late evening
into the overnight.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 249 PM CDT Tue May 22 2018

Convective potential Thursday, and warm temperatures Thursday and
Friday highlight the extended forecast.

An upper level low is forecast to propagate into central North
Dakota by Thursday afternoon. The greatest instability axis may
remain across the James River Valley Thursday afternoon to support
possible strong to severe convection with dewpoints well into the
60s.

The 12 UTC NAEFS depicts 850 mb mean temperature anomalies in the
90th percentiles and above Thursday and Friday across western and
central North Dakota. With westerly winds, favored the warmer
edge of the 12 UTC global suite. This would put highs in the mid
to upper 80s Thursday, and the upper 80s to the lower 90s on
Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1221 AM CDT Wed May 23 2018

Main hazards to aviation include scattered thunderstorms across
western and central North Dakota today as low pressure and an
associated warm front move slowly northeast across South Dakota.
VFR conditions are expected through the 06Z TAF period.

&&

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

$$

UPDATE...WAA
SHORT TERM...PA
LONG TERM...PA
AVIATION...WAA



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