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000
FXUS63 KBIS 181759
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1259 PM 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.

&&

.UPDATE...
Issued at 1247 PM CDT Thu Apr 18 2024

Increased amd expanded the aerial coverage of POPs for this
afternoon through this evening. Steep low level lapse rates
coupled with embedded mid level waves rotating through the
Northern Plains contributing to scattered light snow showers
across all of western and central ND, much more prevalent
compared to yesterday. Pretty much all of our main observing
sites have been reporting light snow off and on the past few
hours, with a few reporting visibility reductions less than 3
miles at times. A few of our ND DOT web cams also show some
light snow accumulation on grassy surfaces. Otherwise, the
forecast remains in good shape for today.


UPDATE
Issued at 1052 AM CDT Thu Apr 18 2024

The forecast for today remains on track. Opted to have isolated
to scattered light snow showers for most areas this morning and
afternoon, with decent returns already depicted on our local
radars, and multiple observing points reporting either
occasional reductions in visibility, light snow, and/or Trace to
light amounts of moisture. Other weather elements looking good,
and mainly blended current observations with near term trends.
Wing headlines also on track, with numerous reported wind gusts
in the 40-45 mph range already this morning.

UPDATE
Issued at 642 AM CDT Thu Apr 18 2024

We expanded the coverage of early-day snow shower chances (on
the order of 20 percent) to all of western and parts of south
central ND with this update in respect to radar and satellite
trends. Otherwise, winds are already reaching advisory criteria
on a sporadic basis due to the poor decoupling of the boundary
layer that occurred overnight, and we expect winds to increase
by mid morning as mixing increases with the onset of diurnal
heating. The Wind Advisory therefore appears on track.

&&

.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 mid-latitude 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 /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1247 PM CDT Thu Apr 18 2024

Will see mainly VFR ceilings across western and central North
Dakota terminals today through this evening, though could
occasionally see MVFR ceilings and possible reductions in
visibility associated with scattered snow showers about the
region this afternoon and evening. Northwest winds will gust to
40 knots today, diminishing a bit after 00Z, but will remain
gusty overnight, then increase again Friday morning. Ceilings
are expected to lower again as well into the MVFR category in
northern ND tonight (a 40 to 50 percent chance at KMOT and KXWA
after 06Z, with a lesser chance at our southern terminals KDIK,
KBIS, and KJMS).

&&

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

&&

$$

UPDATE...NH
DISCUSSION...CJS
AVIATION...NH