000
FXUS63 KBIS 180918
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
418 AM CDT Thu Apr 18 2024

.KEY MESSAGES...

- Windy conditions and below normal temperatures are expected
  through Friday, along with isolated to scattered snow showers
  (a 20 to 40 percent chance, highest in north central ND).

- Peak northwest wind gusts will be around 45 mph today, with a
  40 to 60 percent chance of gusts up to 45 mph again Friday.

- A warming trend is expected this weekend, along with dry
  weather and weaker winds. A 40 to 60 percent chance of rain
  returns Sunday night and Monday.

&&

.DISCUSSION...
Issued at 418 AM CDT Thu Apr 18 2024

An upper-level low is centered over southern Manitoba early this
morning, with an associated surface low north of Winnipeg. Low-
and midlevel cold air advection and cyclonic flow along with a
significant surface pressure gradient exists in the southwestern
quadrant of this midlatitude cyclone, across the Northern Plains.
The system is forecast to only slowly move eastward into Ontario
by Friday, maintaining below normal temperatures, windy weather,
and low to medium chances of snow showers across western and
central ND today through Friday.

Persistent low-level cold air advection overnight has prevented
the boundary layer from fully decoupling, which has allowed the
winds to remain elevated. The 00 UTC KBIS sounding had a well-
mixed layer to roughly 700 mb with peak winds in that layer in
the 40 kt range. The thermal profile will be cooler today due
to the continued cold air advection, but the observed sounding
closely matches model-forecast sounding profiles for today. We
thus expect winds to increase today as diurnal heating steepens
low-level lapse rates and deepens the boundary layer up to 700
mb once again. Forecast maximum winds in the well-mixed layer
are around 40 kt today, supporting peak gusts to around 45 mph.
NBM-based probabilities support this with high, 60-100 percent
chances of gusts over 40 mph today (highest in southern ND),
while the chance of gusts of 50+ mph is only around 30 percent.

Near-critical fire weather conditions are being messaged today
in southwestern ND, where a wedge of drier low-level air is
forecast, resulting in afternoon minimum relative humidity
values of 20 to 25 percent. This is focused on Slope, Bowman,
and Hettinger Counties per overnight HRRR cycles, which often
handle these scenarios well. We gave consideration to the need
for a Red Flag Warning given the expected winds and relative
humidity values, but potential rate of spread in grass fuels
will be mitigated to some extent by cool temperatures in the 40s
F, and with some uncertainty in cloud cover trends and the
duration of low humidity, we decided to continue communicating
this with "near-critical fire weather" wording rather than
issuing a warning.

The other consideration for today is the expectation of isolated
to scattered snow showers (a 20 to 40 percent chance, highest
in northwest and north central ND). Cyclonic flow, embedded
vorticity maxima aloft, and steep low- and midlevel lapse rates
that will yield low-topped bouyancy (SBCAPE up to 100 J/kg) all
suggest snow shower development will occur today. CAMs support
this expectation as well, albeit with differences in coverage,
especially with southern extent. Surface wet bulb temperatures
are forecast to be 32 F or less through the day, and considering
the convective nature of any precipitation, snow is the expected
precipitation type even with high temperatures in the mid 30s to
mid 40s F.

The overall pattern will only slowly change tonight and Friday,
though winds and snow shower coverage will diurnally diminish
after sunset tonight, then re-emerge during the day Friday. We
once again have 20-40 percent chances of snow showers forecast
on Friday, along with northwest winds gusting up to 40 mph. NBM
probabilities of Wind Advisory gusts (45 mph) on Friday are in
the 40 to 60 percent range. Highs Friday will only be in the mid
to upper 30s F in most areas.

This weekend will feature a warming trend, weaker winds, and a
dry forecast as shortwave ridging crosses the area. Given only
small spread in ensemble membership, we expect forecast highs
well into the 40s F Saturday, and 55 to 60 F on Sunday. Sunday
night and Monday global guidance remains consistent suggesting
a shortwave trough will cross the region, yielding a 40 to 60
percent chance of rain. Two scenarios exist with this shortwave
trough passage: 1) A slower, further-south passage that could
result in precipitation lingering into Tuesday, or 2) A slightly
further-north and faster trough passage, focusing precipitation
Sunday night into early Monday. Both scenarios have about a 50
percent chance of occurrence, and mainly represent a difference
in timing, since even the slower/further-south scenario appears
to lack sufficient cold air for more than a 10 percent chance of
snow being a dominant precipitation type.

By the middle part of next week, a longer-wavelength and more
amplified ridge is favored, with ensemble guidance suggesting a
70% or greater probability of highs returning to the 60s F on
Wednesday and Thursday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 418 AM CDT Thu Apr 18 2024

Low VFR to MVFR ceilings will impact northern and portions of
western ND through midday, impacting KMOT, KXWA, and KJMS. The
southern and western extent of the MVFR ceilings is uncertain,
with only a 30 percent chances of them impacting KBIS or KDIK.
West-northwest winds gusting up to 40 kt are expected across all
of western and central ND today. Isolated to scattered snow
showers are also expected, especially after 18 UTC, with a 20
to 30 percent probability of them impacting any given terminal.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 9 AM CDT /8 AM MDT/ this morning to 9 PM
CDT /8 PM MDT/ this evening for NDZ001>005-009>013-017>023-025-
031>037-040>048-050-051.

&&

$$

DISCUSSION...CJS
AVIATION...CJS