Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 210512
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1212 AM CDT Thu Sep 21 2017

.UPDATE...
Issued at 1201 AM CDT Thu Sep 21 2017

Latest satellite imagery shows high clouds streaming from southwest
North Dakota, northeast into central ND. Previous forecast discussion
was honing in on an increasing low level jet across south central
and the James River Valley overnight through Thursday morning.
This thinking remains on track, as a sharp 850mb baroclinic zone
slides from eastern Montana 12z Thursday into the James Valley
Thursday evening before stalling out. In response, the 00z
NAM/GFS and latest RAP/HRRR show 850mb winds increasing up to
around 55kt south central/James River Valley 09z-18z. Bufkit
soundings show the thermal profiles becoming adiabatic between 9AM
and 10AM, mixing the higher level winds down to the surface. At
this point, will monitor the BIS VAD wind profile overnight to
see how winds are materializing aloft. A wind advisory Thursday
morning may not be out of the question from Bismarck through the
James Valley.

UPDATE Issued at 954 PM CDT Wed Sep 20 2017

Scaled back on POPs as not seeing any reports to our west. Very
dry low levels. Otherwise previous thinking is on track for
tonight.

UPDATE
Issued at 703 PM CDT Wed Sep 20 2017

Main updates were to maintain/expand slight chance for showers
west and north central, and focus on strong low level jet winds
late tonight through mid morning Thursday.

An embedded wave and associated trough of surface low pressure
will bring an increase in clouds and a chance for light rain
across western and portions of central ND tonight. Dry low level
atmosphere in place and will persist through the overnight so not
expecting much more than a trace of moisture if any rain can
reach the surface.

Ahead of the surface low, an increasing pressure gradient will
contribute to a strong low level jet of 50-60Kts developing from
09-15Z across south central and eastern ND. Strong low level wind
shear will result for KBIS and KJMS. BUFFER soundings indicate
some of these stronger winds will reach the surface as the mixing
layer rises after 13Z Thursday morning. I thus increased winds
over my south central counties and the James River Valley. The
James River Valley will likely see stronger winds continue into
the afternoon. Will need to watch future model runs later this
evening as the 18Z Nam wants to bring 50-55Kts to the surface for
a brief window Thurs AM after 12Z. Other models keep these
stronger winds above the mixed layer.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 239 PM CDT Wed Sep 20 2017

An upper level trough over the western U.S. and southwest Canada
will elongate, with a northeast to southwest frontal boundary
developing over the state. This will produce a sharp temperature
gradient between cool temperatures northwest and mild temperatures
southeast on Thursday.

A lee side surface trough is already beginning over central
Montana with a moderate southwest flow across the forecast area
today. As the upper trough begins to split tonight we will see an
increasing low level jet and warm advection in response to the
digging portion of the upper trough along the West Coast. Tonight
our main forecast issue will likely be increasing low level wind
shear from west to east as this process occurs. Late tonight into
Thursday morning, shortwave energy tracking through the southwest
upper flow, coincides with the strong warm advection, producing an
area of increasing clouds and a few showers from west central
into north central ND. Utilized a blend of short term guidance for
pops and amounts will be light with likely only a narrow band of
any light accumulating precipitation. Highs Thursday will range
from the mid 60s northwest to the upper 70s over the southern
James River Valley.

.LONG TERM...(Thursday night through Wednesday)
Issued at 239 PM CDT Wed Sep 20 2017

An active southwest flow pattern will persist over the northern
plains through early next week, followed by a slow transition to a
drier and warmer pattern from mid to late week.

Daytime highs will be mainly in the 50s over the weekend with
overnight lows in the mid 30s to mid 40s. We will likely be dealing
with at least a mention of frost for portions of the forecast area
each day through the weekend and into early next week. We then warm
up into the 60s Tuesday and Wednesday. Although not a complete
washout, we will likely see at least a slight chance of
precipitation through the weekend. Best chances will be Friday into
Saturday. The next wave will spread widespread rain from the
southern Rockies into the Great lakes region Saturday night through
Sunday night, but latest model trends keep the bulk of the
precipitation associated with this system just to our south and
east, but we will probably see at least a glancing shot of
precipitation across our southern and eastern zones.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1201 AM CDT Thu Sep 21 2017

VFR conditions are forecast for the 06Z TAFs. The hazards to
aviation will be some wind shear forecast for KMOT-KBIS-KMOT as
increasing southerly wind shear develops from the surface to 2
thousand agl between 09-15Z. After 15Z the winds mix down to the
suraface. Look for increasing surface winds to 30 KTs after 15Z.

&&

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

$$

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



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