363
FXUS63 KBIS 300611
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
111 AM CDT Tue Apr 30 2024

.KEY MESSAGES...

- Widespread rain showers are expected to move across the state
  from west to east late tonight through Tuesday.

- Windy in southwest North Dakota on Tuesday, with critical fire
  weather conditions possible in the afternoon and early
  evening.

- Daily chances (low to medium) for rain through the rest of the
  week, with temperatures slightly below normal.

&&

.UPDATE...
Issued at 100 AM CDT Tue Apr 30 2024

No major changes were needed for the late night update. Just
blended in the latest observations to the going forecast. Rain
continues to slowly move towards the North Dakota border from
eastern Montana.

UPDATE
Issued at 941 PM CDT Mon Apr 29 2024

Main change with this update was just freshening up the cloud
coverage, as some mid level clouds have been entering the area
from the south. A small area of radar returns continue to show
up across the far north, however we haven`t seen any observed
precipitation with these echoes. Apart from cloud coverage,
we`ve just blended the current observations into the forecast.

UPDATE
Issued at 638 PM CDT Mon Apr 29 2024

Not much was needed to be changed with this update. We boosted
PoPs in the northwest and southwest corners of the state due to
some radar returns associated with some more prominent cumulus
growth, but have those PoPs decreasing within the next hour or
so. Otherwise, the forecast largely remains on track.

&&

.DISCUSSION...
Issued at 302 PM CDT Mon Apr 29 2024

A closed upper low is spinning northeastward over northern Minnesota
this afternoon. At the surface, a meridional ridging axis cuts
through the central Dakotas. The ridge axis roughly marks the
delineation of the widespread stratus associated with the downstream
cyclone. The lower cloud deck should slowly erode from west to east
this afternoon, clearing past the Highway 83 corridor but not
reaching the Highway 281 corridor. Meanwhile, a sunny sky will
prevail across western North Dakota this afternoon, aside from some
passing altocumulus clouds over the far west. Highs in the west
should easily reach the lower to mid 60s this afternoon, but could
be limited to the lower and mid 40s underneath the clouds from the
Turtle Mountains through the James River Valley.

A potent shortwave will eject from the base of a Pacific Northwest
trough this evening and quickly pivot into the Northern High Plains
by Tuesday morning. Global and high-resolution ensembles are in good
agreement that a band of widespread rain showers will move across
the state from west to east late tonight through Tuesday afternoon.
There is some minor timing uncertainty, with the HRRR and RAP
consistently showing a quicker progression. Mean ensemble QPF is
advertising around two to four tenths of an inch of rain across
northern and eastern North Dakota, decreasing to only trace amounts
in the southwest.

Highs on Tuesday will mainly be in the 50s, but could be slightly
cooler to the north and east should rain and clouds persist longer
through the day. Winds with the push of colder air on Tuesday are
now looking less impressive than previous forecasts, evident in
deterministic BL analysis, the NBM, and the ECMWF EFI. Temporally
speaking, the strongest winds aloft and greatest momentum transfer
are now favored earlier in the day over southwest North Dakota. This
forecast trend lowers confidence in both meeting advisory criteria
wind speeds and gusts and critical fire weather conditions (see Fire
Discussion below).

An overall active pattern is expected to persist through the rest of
the week, including the upcoming weekend. The first half of
Wednesday should remain dry preceding a transition to southwest flow
aloft, except perhaps along the Canadian border. Shortwave energy in
the southwest flow will then increase rain chances by Wednesday
evening, followed by a deeper trough digging into the Northern
Plains on Thursday. Wednesday is now looking like the warmest day of
the week for the eastern half of the state with highs in the lower
to mid 60s. The digging trough is then forecast to bring
temperatures below normal for Thursday and Friday, with highs only
in the mid 40s to mid 50s. Lows over this time period will mainly be
in the 30s. It is possible that snow could mix with rain wherever
precipitation occurs during the late night and early morning hours
late this week, but no impacts are expected. A warm up finally
appears to be in the cards early next week as ensembles show
positive temperature anomalies, with a jump in the NBM high
temperature distribution on Sunday. The NBM maintains low PoPs over
this time period, and with the warmer air, chances for thunderstorms
could eventually be introduced to the forecast. In fact, machine
learning guidance does imply a low potential for stronger convection
next week Monday when ensemble mean height fields hint at a stronger
wave, though it should be noted there is considerable ensemble
spread at this time range.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 100 AM CDT Tue Apr 30 2024

An upper level disturbance and surface cold front will cross the
state from west to east Tuesday morning and afternoon, bringing
widespread rain showers and MVFR to IFR ceilings. MVFR
visibilities will also be possible under any heavier showers.
Winds will shift to out of the northwest behind the front,
becoming gusty across most of the west. Sustained winds will
approach 30 mph with gusts to 40 mph over portions of the
southwest Tuesday afternoon. Winds will decrease fairly quickly
Tuesday evening. Most areas will see improvement into VFR
categories (from west to east) late Tuesday afternoon and into
the evening.

&&

.FIRE WEATHER...
Issued at 302 PM CDT Mon Apr 29 2024

A cold front is forecast to enter southwest North Dakota Tuesday
morning, with winds quickly switching to the west-northwest and
increasing to 25 mph with gusts to around 40 mph. Winds will remain
strong through the afternoon, with perhaps just a slight uptick in
both sustained speeds and gusts. A very dry air mass being advected
in behind the front will lower dewpoints into the teens in southwest
North Dakota by late Tuesday afternoon. The minimum relative
humidity forecast for Tuesday has mostly remain unchanged, with
values as low as 18 percent in the southwest corner of the state and
less than 30 percent for all of southwest North Dakota. However,
there has been a decreasing trend in the magnitude of the wind
forecast over time, as well as the spatial extent of stronger west-
northwest winds. There is also potential for a wetting rain Tuesday
morning, though probabilities are lowest over southwest North Dakota
compared to other parts of the state. Taking all this into
consideration, we have decided to maintain the Fire Weather Watch
for this forecast package.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from this afternoon through this evening
for NDZ031>033-040>045.

&&

$$

UPDATE...ZH
DISCUSSION...Hollan
AVIATION...ZH
FIRE WEATHER...Hollan