Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 240320

Area Forecast Discussion
National Weather Service Bismarck ND
1020 PM CDT Wed May 23 2018

Issued at 1007 PM CDT Wed May 23 2018

Pops are the main problem for the late evening update. Cut back
on pops quite a bit overnight but did keep some pops mainly in the
west and south central to the James River Valley. Current
convection over southwest ND into northeast MT is expected to
continue to lift northward. Lately this convection has been
producing some small hail and gusty winds to around 40 mph. Expect
this trend to continue, but an isolated severe wind gust is still
possible. Convection over Dickey and Mcintosh counties continues
to lift slowly north within an area of maximized cape. However,
expect CIN to continue increasing, which should help suppress
these storms. Localized heavy rain and small hail can still be
expected over the next hour or so. Farther south, stronger
convection over west central South Dakota is forecast to lift
north and east into north Dakota after midnight. Experimental HRRR
seemed to have a good handle on current convection and this is the
model we leaned toward for pops going forward overnight. This
brings a few stronger cells into south central ND after midnight
and lifts them almost due north as they slowly weaken.
Climatologically not a favorite time for severe weather but this
is when the forcing from the upper level system will be maximized
so a stronger thunderstorm late tonight over central can not be
ruled out.

UPDATE Issued at 648 PM CDT Wed May 23 2018

Latest Radar and satellite imagery shows convection trying to fire
over southeast ND with a strong to severe cell just south of
Dickey county in the southern James River Valley. Throughout the
afternoon, any convection here has had a hard time maintaining
its intensity. 00 UTC Bismarck sounding does show some capping
over the are, so will see if this convection can overcome this.
The most unstable area in the region remains from this convection
and back west northwest toward Bismarck. If we don`t see the
convection maintain itself over the James River Valley, or
additional convection doesn`t fire over the south central in the
next couple hours, it may not be until stronger forcing arrives
later tonight. Farther west, convection remains ongoing over
eastern Montana and into western South Dakota. This convection may
also push into western ND later tonight.


.SHORT TERM...(This evening through Thursday)
Issued at 250 PM CDT Wed May 23 2018

Convective potential highlights the short term forecast.

The CAMs through the 18 UTC HRRR suggest the the mostly likely
area for strong to severe convection is across northwest North
Dakota this evening. This would be in association with a
convergence line/inverted trough from across southeast Montana
into northwest North Dakota. GOES-East trends through 2020 UTC
depict a growing cumulus field under the dry slot across Montana,
with deeper convective initiation possible in the next 2-3 hours
that would propagate into northwest North Dakota this evening.
Deep layer shear and thermodynamic profiles support a possible
severe threat through sunset. Elsewhere across western and central
North Dakota, the potential convective coverage and severity
still remains uncertain, and is limited by weak forcing and cloud
cover. The one exception would be the James River Valley this
evening as convection that initiates across central South Dakota
may propagate northeast aided by a low level jet and the arrival
of greater mid/upper level forcing. An isolated severe threat is

For Thursday, the upper level low across Montana today will
propagate across North Dakota with an associated surface cold
front. Moderate CAPE with surface dewpoints in the 60s is expected
ahead of the front with deep layer shear of around 20-30kts. SPC
has the Turtle Mountains through the James River Valley in a
marginal risk for severe thunderstorms Thursday afternoon, with a
greater risk further east where instability will be greater.
Scattered organized, discrete convection is possible after 21 UTC
along the front. Its development seems to have a bit better
predictability given the greater forcing.

.LONG TERM...(Thursday night through Wednesday)
Issued at 250 PM CDT Wed May 23 2018

Above normal temperatures Friday through the weekend highlight the
extended forecast.

The 00 UTC NAEFS 850 mb mean percentiles from their 90-97.5th
percentiles Friday through the weekend signal a period of above
normal temperatures. With favorable westerly winds, widespread
highs in the upper 80s and lower 90s are forecast on Friday.
While mixing is weaker Saturday, the airmass is warmer and
widespread highs in the lower to mid 90s are possible. Above
normal temperatures in the 80s and lower 90s may continue on
Sunday with the upper level ridge across the Northern Plains. An
active thunderstorm period is possible late Sunday through mid
next week with southwest flow aloft. This period will have to be
monitored for severe convective potential.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1007 PM CDT Wed May 23 2018

VFR conditions to begin the TAF period. Expect mainly VFR
conditions through the period, but scattered convection remains
possible at all TAF sites. Some of these storms could be strong to
severe with large hail and damaging winds. But uncertainty remains
high. Southerly surface flow continues tonight. Flow turns
west over western ND Thursday afternoon.




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