Garrison, North Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

235
FXUS63 KBIS 221254
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
654 AM CST Sun Dec 22 2024

.KEY MESSAGES...

- Freezing rain is expected across northwest and central North
  Dakota later this morning through early this evening. Ice
  accumulations up to one tenth of an inch central and two
  tenths of an inch northwest are possible.

- The freezing rain could mix with or change over to snow this
  afternoon and evening, with snow accumulations up to one inch.

- Areas of dense fog will impact parts of northwest and north
  central North Dakota this morning, and will be possible again
  across all but southwest North Dakota tonight through Monday
  morning.

- Above normal temperatures are expected Christmas Eve through
  the end of the week.

&&

.UPDATE...
Issued at 654 AM CST Sun Dec 22 2024

The early morning forecast is trending well. The footprint of dense
fog has neither contracted nor expanded over the past couple hours.
No changes needed to the Dense Fog Advisory.

Recent runs of the HRRR and RAP are suggesting a slight delay in the
arrival of precipitation later this morning, but an increase in
icing amounts in the northwest. The higher QPF, which is being
output as freezing rain with local maxima greater than a quarter
inch of ice, seems to be driven by strong Q-vector convergence with
steep mid level lapse rates. But there are still run-to-run
inconsistencies in the exact placement of maximum QPF as well as
when, or if precipitation will transition to snow. Thankfully,
winds are expected to remain light in the northwest today, which
should help mitigate higher-end icing impacts.


&&

.DISCUSSION...
Issued at 444 AM CST Sun Dec 22 2024

A broad area of weak surface troughing underneath transient mid to
upper level ridging extends from southern Saskatchewan through the
western and central Dakotas early this morning. Dense fog has
developed across northwest and north central North Dakota. The fog
may continue to slowly expand southward through mid morning and lift
from west to east as precipitation enters the state later this
morning. Some parts of north central North Dakota could see the fog
persist through the afternoon.

A mid level shortwave will glide from southern Alberta this morning
to the central Dakotas this evening. Confidence remains high that
this wave will produce a band of light precipitation, with maximum
liquid equivalent amounts very unlikely to exceed one quarter inch,
from northwest to central North Dakota from mid morning into the
evening. RAP analysis shows maximum temperatures aloft this morning
are well above freezing, and are expected to remain so as
precipitation enters northwest North Dakota. We therefore expect
freezing rain as the dominant precipitation type in the northwest,
where a Winter Weather Advisory for up to two tenths of an inch of
ice is in effect. During the afternoon, the major axis of the band
of precipitation is forecast to be located from northwest to central
North Dakota, with a slow southeast motion. Wet-bulb cooling is
expected to transition the dominant precipitation type from freezing
rain to snow, but it remains uncertain exactly when this process
will occur, with possible outcomes ranging from as early as noon to
as late as 6 PM CST. It is also possible that temperatures aloft
cool sufficiently for snow only where precipitation rates are
highest, leaving surrounding edges as lighter freezing rain.
Confidence in at least a glaze of ice accumulation is now high
enough to add much of central North Dakota to the Winter Weather
Advisory, including Bismarck/Mandan, Beulah/Hazen, and Minot. But
the threat for higher ice accumulations is not as great here as it
is in the northwest. At this time, any snow accumulations are
expected to remain under an inch, but this could change if
precipitation transitions to snow earlier and/or is heavier, the
latter of which is projected by a few CAMs.

Accumulating precipitation is expected to end from northwest to
southeast through the evening as the mid level wave departs.
However, model guidance shows potential for another round of dense
fog tonight into Monday, possibly more widespread than this morning.
Another concern that bears watching over this time frame is the
potential for a deep enough of a near-surface saturated layer
combining with low level frontogenesis to produce light freezing
drizzle across central North Dakota. This aspect of the forecast may
need to be fine-tuned as the day progresses.

Above freezing high temperatures are expected today for areas along
and southwest of a line from Watford City to Fort Yates, possibly
reaching the mid 40s along the Highway 12 corridor. The forecast
high temperature gradient is sharp across our area, cooling to as
low as the mid teens from the Turtle Mountains to the Devils Lake
Basin. The low temperature forecast for tonight maintains a similar
geographic gradient, ranging from the single digits above zero north
and east to around 20 above southwest.

The favored synoptic pattern for Monday through at least Thursday
can be characterized by a series of transient ridges and troughs
embedded in split flow. This pattern is expected to allow milder
Pacific air to spill over the Rockies, bringing above normal
temperatures to the region for most of the holiday week. The eastern
half of the state will likely remain in the 20s on Monday on account
of poor to no boundary layer mixing and the potential for low
stratus to persist through the day. A drying warm air advection in
the lower levels Monday night should help scour out the residual
boundary layer moisture, paving the way for high temperatures mostly
around 30 to 35 north and east of the Missouri River, and 35 to 45
southwest of the river Christmas Eve through Saturday.

The NBM probability of precipitation does not exceed 15 percent at
any time or location throughout the extended period. However, there
is a system to be monitored after Christmas Day. There is
uncertainty in the phasing of two separate shortwaves ejecting into
the central CONUS later this week. One scenario (about 70 percent
ensemble membership) keeps these waves separate, and their energy
displaced to our south and east. Another scenario (about 30 percent
ensemble membership) creates a Fujiwara effect with the first wave
wrapping back into the second one. This outcome would introduce
chances for mixed precipitation from late Thursday through Friday,
as both near-surface air temperatures and maximum temperatures aloft
are forecast to be around freezing.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 654 AM CST Sun Dec 22 2024

Dense fog/LIFR ceilings will continue to impact parts of northwest
and north central North Dakota this morning. KMOT could remain right
on the edge of the fog/low stratus, while KXWA is less likely to be
impacted. Ceilings are eventually forecast to settle at IFR levels
across all of northern North Dakota later today and spread further
south into south central and southeast North Dakota tonight. Areas
of fog, possibly dense, could develop across a larger portion of the
state later tonight.

Mixed precipitation is expected across northwest and parts of
central North Dakota later this morning through the early evening.
KXWA has the highest chances where most, if not all of the
precipitation will fall as freezing rain. Areas from KMOT to KBIS
could see precipitation start as freezing rain later in the day and
then mix with or change over to snow. Chances for precipitation will
greatly diminish by the end of the evening, but some patchy freezing
drizzle cannot be ruled out across central North Dakota overnight,
along with the aforementioned fog and low ceilings.

Southwest North Dakota will see west to northwest winds around 10-15
kts this afternoon. Otherwise, winds will be light and variable.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for NDZ001>004-009>011.
Winter Weather Advisory until 6 PM CST /5 PM MST/ this evening
for NDZ001-002-009-010-017-018-031-032.
Winter Weather Advisory from noon CST /11 AM MST/ today to 9
PM CST /8 PM MST/ this evening for NDZ011-019>021-034-035.

&&

$$

UPDATE...Hollan
DISCUSSION...Hollan
AVIATION...Hollan