Area Forecast Discussion
Issued by NWS Bismarck, ND

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KBIS 160910

Area Forecast Discussion
National Weather Service Bismarck ND
410 AM CDT Sun Oct 16 2016

.SHORT TERM...(Today and tonight)
Issued at 410 AM CDT Sun Oct 16 2016

A windy and mild day is expected the with passage of an energetic
shortwave trough and weak cold front. Highs today are forecast to
range from the mid 60s in the north to the low to mid 70s F south.

Overnight GOES-13 moisture channel imagery has been showing rather
significant drying in the wake of a shortwave trough that`s moving
through ID as of 0830 UTC. Although that drying has been becoming
less pronounced in the last few hours, it`s nonetheless indicative
of the strength of the wave and an attendant 120-140 kt 300-mb jet
streak following it onshore. Moreover, several lightning strikes
have occurred overnight ahead of the primary mid-level vorticity
maximum associated with wave, further reflective of its intensity.
The 00 UTC global model guidance is supportive of observational
trends in taking the axis of the 500-mb shortwave trough into
north central ND by 00 UTC. A weak cold frontal boundary will
follow the mid-level wave accordingly.

Winds are the primary forecast challenge with this seasonably-
dynamic wave passage. The KBIS WSR-88D VAD wind profile has been
showing a steady increase in southerly flow aloft since 07 UTC,
with winds near 3000 ft AGL at 30 kt already. All of the 00 UTC
global model guidance expects a core of southerly 850-mb winds of
50-60 kt transiting central ND today in a warm advection regime.
Model-forecast soundings suggest the boundary layer could extend
to a deep enough layer for mean wind speeds to exceed 30 kt with
peak winds at its top near 50 kt, especially along and south of
Interstate 94 from Bismarck to Jamestown between 15 and 20 UTC.
However, low-level vertical motion will co-exist with those peak
wind speeds in the warm advective pattern, which is expected to
inhibit full momentum transfer. It`s also hard to ignore all of
the mid- and high-level cloud cover streaming into the area out
of the west, which may act to slow surface warming and in turn
could result in a more shallow boundary layer than modeled, as
happened on Friday. Given those issues, and the quick eastward
propagation to the strongest low-level pressure/height gradient
and resultant wind speeds, we chose to hold off on the issuance
of a wind advisory at this time. That being said, relying on a
blend of the 00 UTC MAV and MET MOS guidance yielded winds very
near advisory criteria with sustained speeds of 20 to 25 mph, and
gusts around 40 mph today in south central ND. Winds in the wake
of the cold front will also increase with gusts to 30 mph in
southwest ND this afternoon.

Despite the windy conditions, the absence of lower fuel moisture
values and forecast minimum humidity values over 20 percent
precluded the need for a red flag warning.

We are carrying some 20-40 percent chances of showers in the north
today, mainly this morning. There will be a burst of moderate to
strong QG-forcing moving across the area ahead of the shortwave,
and simulated radar images from the HRRR and the 00 UTC WRF-ARW
and WRF-NMM support showers, especially north. However, forecast
soundings show a dry lower atmosphere with most saturation in the
layer above 700 mb, and the same models that have rather wet-
looking radar simulations don`t generate that much actual QPF.
This likely implies that a significant amount of virga will occur,
with only light and perhaps spotty precipitation reaching the
ground. It`s for that reason that we held PoPs a bit lower than
would otherwise be implied.

Finally, steep mid-level lapse rates of 7 C/km will likely be
spreading across the area today, but the 21 UTC SREF calibrated
thunderstorm guidance kept the chance of storms under 10 percent
for all but the James River valley, so we refrained from making
an explicit mention of those in the forecast at this time.

Expect clearing and a quiet night tonight behind the wave.

.LONG TERM...(Monday through Saturday)
Issued at 410 AM CDT Sun Oct 16 2016

A mainly dry and uneventful weather pattern is expected this week.

A powerful 300-mb jet streak on the order of 130 kt is forecast to
reach the central Plains Monday. Vertical motion in the left exit
region of that jet may interact with a mid-level frontal zone over
SD, and given modest baroclinicity and access to relatively steep
mid-level lapse rates to the south of the front, there`s a chance
for a frontogenetically-induced band of rain along the ND and SD
border Monday. The 00 UTC multi-model consensus keyed on that and
thus carries a chance of rain over much of southern ND Monday. As
that jet streak shifts east, a mean 500-mb trough is forecast to
become established over the north central United States by the
middle of the week, with cold advection taking 850-mb temperatures
down to about -5 C over north central ND by Wednesday night. That
will yield a cooldown with highs dropping from near 60 F Monday
to only the mid 40s to lower 50s by Wednesday. Only a few low-
grade opportunities for precipitation will occur in this scenario.

By late in the week, mid-level ridging is forecast by the 00 UTC
GFS and ECMWF to flex eastward again. The multi-model consensus
calls for highs rising back to around 60 F by Friday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 410 AM CDT Sun Oct 16 2016

VFR conditions are expected throughout the period. Southerly winds
will increase across the state with winds becoming westerly during
the afternoon as a cold front crosses the state. Low level wind
shear is also expected over most locations, especially during the




AVIATION...JNS is the U.S. government's official web portal to all federal, state and local government web resources and services.