Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 211658
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1158 AM CDT Sun May 21 2017

.UPDATE...
Issued at 1125 AM CDT Sun May 21 2017

Latest observations and local/regional radars indicate sprinkles
at KJMS with only trace amounts last couple of hours. This is
associated with a slow moving closed upper low currently located
over eastern Minnesota. Latest suite of GOES 16 imagery channels
captures the thicker clouds associated with the closed upper low,
stretching from the Turtle Mountains south into the James River
Valley. Cirrus clouds were noted across central ND, and convective
clouds were seen bubbling in the west with a few lightning strikes
occurring southeast of Glendive, MT. This is associated with weak
shortwaves noted on the upper level water vapor band across
eastern MT sliding southeast with time. Also, associated with the
weak shortwaves is a weak surface trough residing in the west.
Cyclonic flow along with the aforementioned surface trough will
strengthen/enhance the lower level convergence field this
afternoon. Current SPC mesoanalysis indicates fairly
steep/conditionally unstable low/mid level lapse rates (7C/km mid
levels to 8.5C/km lower levels). Per RAP13 BUFKIT soundings,
parcels reaching the level of free convection across the west this
afternoon will tap into weak cape/shear of 200-400 J/kg and
roughly 20kt-25kt 0-6km bulk shear. Previous shifts thinking that
an upstream shortwave/large scale ascent sliding south from
central Saskatchewan remains mostly a non- player this afternoon
as it doesn`t arrive until the 06z-12z timeframe across the west.
Thus strongest forcing does not align with max heating and
greatest instability in the west this afternoon/early evening.
Bottom line is the going forecast advertising isolated to
scattered showers and some thunderstorms randomly sprouting across
the west this afternoon/evening remains on track.

UPDATE Issued at 801 AM CDT Sun May 21 2017

This update will expire the frost advisory. Made some minor
adjustments to the sky grids. Otherwise expect the chances for
rain to trend down east with a few showers west this afternoon.

UPDATE Issued at 642 AM CDT Sun May 21 2017

Will let the frost advisory run its course. Widespread mid 30s
across much of western ND with a few lower 30s and upper 20s over
portions of the southwest. To the east, light rain continues over
the James River Valley but band of persistent rain overnight is
beginning to break up. Updated sky and pop grids based on latest
satellite and radar trends. Otherwise no significant changes to
the going forecast.

&&

.SHORT TERM...(Today and tonight)
Issued at 214 AM CDT Sun May 21 2017

Morning rain east and afternoon/evening thunder west highlight the
short term forecast.

A nearly stacked low pressure system will continue to lift
northeast from southern Minnesota early this morning, into
southern Ontario by late tonight. Synoptic scale forcing with this
system will continue to lift away from eastern portions of the
forecast area this morning. However, a lingering deformation zone
over far eastern portion of the forecast area will keep at least a
chance of rain through the morning with a few showers possible
into the afternoon. Another upper low over northern
Saskatchewan/Alberta will drop south today and bring scattered
showers and thunderstorms to western ND late this afternoon and
this evening. Weak instability with 21 May 00 UTC NAM indicating
afternoon ML Cape at KISN around 400 J/KG, and 0-6km bulk shear
around 25 knots with decent unidirectional speed shear. Problem
will be timing with the shortwave energy spinning around the low,
dropping south into the area, not meshing with peak daytime
heating in western ND. Still think a few thunderstorms will be
possible in the far west early this evening with some locally
gusty winds and small hail. The main upper low drops south through
western ND late this evening through early Tuesday morning,
keeping a slight chance of showers through the night mainly along
and west of the Highway 83 corridor.

.LONG TERM...(Monday through Saturday)
Issued at 214 AM CDT Sun May 21 2017

Cyclonic upper level flow will wane over the forecast area on
Monday as the upper low over the Great lakes begins to shear apart
with a portion lifting into eastern Canada and another part
dropping south into the upper Midwest. Perhaps a few lingering
showers or isolated diurnally driven thunderstorms within the
weakening cyclonic flow, but instability is even weaker than
Sunday as upper level ridging pushes in from the northwest.

A brief warm-up and dry spell Tuesday and Wednesday as shortwave
ridging traverses the forecast area. There could be an afternoon
shower over the far southeast CWA Tuesday as the remaining
remnants of the upper low mentioned above finally exits the
region. Otherwise dry conditions are expected with temperatures in
the 60s to lower 70s Tuesday, and widespread 70s on Wednesday.

During this Tuesday-Wednesday timeframe another quick moving upper
low exits the eastern Pacific and races across the southern
Canadian Rockies, only to stall over the Canadian Prairie
Provinces and U.S. Northern Plains as downstream blocking impedes
it`s progress. Thus after our quick mid-week dry spell, we once
again enter a slightly cooler and unsettled period with near daily
chances of showers and isolated thunderstorms. Highs will mainly
be in the 60s and lows in the 40s late in the work week and into
next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1055 AM CDT Sun May 21 2017

Large slow moving surface low pressure across Minnesota will move
northeast. Trough of low pressure will rotate around the low and
pull lower clouds back through the James river valley Monday
morning. MVFR at KJMS will improve to VFR Sunday afternoon then
low VFR/MVFR possible again Monday morning. Clouds at or above 7
thousand agl KISN-KMOT-KDIK-KBIS becoming 3 to 5 thousand AGL aft
08z Monday. Isolated SHRA/TSRA Western North Dakota Sunday
afternoon and evening with too much uncertainty to include in TAF
at this time.

&&

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

$$

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



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