Area Forecast Discussion
Issued by NWS Bismarck, ND

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397
FXUS63 KBIS 240326
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1026 PM CDT Sun Apr 23 2017

.UPDATE...
Issued at 1004 PM CDT Sun Apr 23 2017

Potent system will affect western and central ND tonight through
Monday morning. Decided to issue a winter weather advisory for
most of the forecast area from the I94 corridor to the
International Border.

Last several iterations of the RAP/HRRR indicate a band of
freezing precipitation spreading from southwest through central ND
late tonight through mid morning Monday. The new NAM extend
possible freezing rain even farther north into the northern tier
counties. However, think the northward extent of warm air might be
a little overdone. Mesoscale models are showing 2-4 inches of snow
mainly over the Highway 2 corridor, north of the band of mixed
precipitation. This also may be a bit overdone, but 1-3 inches
seems reasonable, with some possible higher amounts, and even a
little freezing rain possible before the snow starts. Road surface
temperatures are the coldest up north, so if there is any
appreciable freezing rain, it would likely stick to sidewalks and
roadways.

Farther south, things are not as clear cut. We do think the
potential for precipitation is almost given along an north of the
interstate. The question is the type and if freezing rain, will
surface temperatures be cold enough for any ice accumulation. We
were a little generous with the southern extent of the advisory
as most of the models are iffy for freezing rain along the
interstate. However, we started out colder this evening than the
models were picking up on. We are currently at or below freezing
over a good portion of central ND. Metro model surface
temperatures along the interstate are currently forecast to be
right at or above 32F Monday morning. Considering the possible
impacts along the interstate and the major metropolitan areas
along the interstate, though it best to include these counties and
let the midnight shift refine the advisory farther north if
things don`t pan out. SREF ensembles from 21 UTC Sunday show
around a 30 percent chance of a 0.05 freezing rain accumulation
mainly between highway 200 and highway 2, so the greater potential
does look to be a little farther north. With our current
temperature trend, wondering if the next run shifts a little
south. Either way, think we have things covered at least for now
with a winter wx advisory covering both the light snow
accumulations north and a mix central, with a lot of this falling
during the morning commute Monday. All text products should be
out.


UPDATE Issued at 712 PM CDT Sun Apr 23 2017

Main updates early this evening were to current pops and
temperatures. Band of light snow/flurries over Bottineau and
Rolette counties moving east and not expected to produce any
additional accumulations this evening. Next system to affect the
area will be moving into the west late this evening or overnight
and spreading east across the forecast area through the early
morning hours.

Updated temperatures to current conditions and we are still colder
than the forecast, so adjusted temperatures lower this evening.
With the strong east to northeast flow over all but the far west,
this seems reasonable. This also shifted the area of potential
freezing rain a little farther south. Latest RAP/HRRR BUFKIT
soundings indicate Williston may remain all snow while just to the
south at Watford city, the potential for freezing rain appears.
Even with the shift south, the area of freezing rain is still
within the current SPS. Will look this over for some possible
adjustments to wording. Did keep a mention of thunder in the
far southwest 03-06Z. With the cooler temperatures, not real
impressed but it is a strong shortwave and will see how things
play out with convection currently moving through Montana. Updated
products will be sent shortly.

&&

.SHORT TERM...(This evening through Monday)
Issued at 329 PM CDT Sun Apr 23 2017

Active short term period ahead. Highlights include a window of
opportunity for some thunderstorms/non-severe, across the far
southwest this evening. Elsewhere, a wintry mix is forecast to
develop west and spread into portions of central North Dakota
tonight before tapering off later Monday morning.

For the near term, through early evening, frontogenetical forcing
per SPC Mesoanalysis continues across Pierce, Sheridan, and Wells
counties. Will continue with snow for the rest of the afternoon
before ending it 00z Monday.

The NAM Bowman BUFKIT Sounding and SREF 3hr Calibrated Thunderstorm
potential indicates potential for an elevated thunderstorm mainly
between 03z-06z Monday. This is associated with shortwaves from
central Idaho this afternoon ejecting into eastern Montana.
Regional radar is picking up on lightning strikes across central
Idaho and will monitor potential for timing adjustments as it
edges closer this evening. Certainly potential for an elevated
thunderstorm or two with maximum omega/vertical motion advertised
at around 700mb.

Otherwise, large scale ascent increased tonight through Monday
morning as a mid/upper level shortwave trough shifts from the
Northern Rockies into the Northern High Plains. Precipitation
will increase west tonight and expand east. NAM/RAP/HRRR BUFKIT
sounding profiles across the west and central indicate a warm
pocket of air advecting in via a southerly flow aloft. Temperature
profiles are warm/deep enough to melt ice crystals/snow from the
saturated Dendritic Growth Zone (-12c to -20C), then falling to
the ground in sub-freezing surface temperatures. This appears to
occur for at least a few hours before winds aloft turn more southwesterly
and westerly advecting in colder temperatures associated with the
upper trough. We have issued a Special Weather Statement concerning
the wintry mix and impacts for the Monday morning commute. This
may need some adjusting as the precipitation edges closer tonight
and better sounding profiles become available.

Otherwise, after a messy morning, precipitation chances wane from
west to east. Cool temperatures continue with highs in the mid 30s
north to mostly 40s south. The far southwest and southern James
River Valley may get into the lower 50s Monday afternoon.

.LONG TERM...(Monday night through Sunday)
Issued at 329 PM CDT Sun Apr 23 2017

Generally dry and cool weather is expected Tuesday through
Thursday with highs rising from the 30s and lower 40s Tuesday,
through the 40s to around 50 by Thursday. Expect partly cloudy
conditions through this time period. Much uncertainty remains
Friday through Sunday concerning a storm system originating in the
southern stream and ejecting northeast from the four corners. The
GFS and ECMWF continue to waffle on whether or not the track and
impacts shift into western and central North Dakota. The latest
gridded Superblend precipitation forecast clips southern ND over
the weekend. Highs Friday through Sunday are forecast to rise back
into the 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1004 PM CDT Sun Apr 23 2017

Widespread MVFR-IFR conditions remain across all TAF sites tonight
and through the day Monday. A mix of rain/snow and possibly
freezing rain will spread west to east across the area late
tonight and Monday morning. Strong easterly wind will subside late
tonight and shift northeast and eventually north on Monday.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 PM CDT /noon MDT/ Monday for
NDZ001>005-009>013-017>023-025-031>037.

&&

$$

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



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