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000
FXUS63 KBIS 131006
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
506 AM CDT Sat Apr 13 2024

.KEY MESSAGES...

- Warm today with highs from the lower 70s north to the lower
  80s far south. Slight chance of showers north.

- Breezy to windy this afternoon behind a weak cold front. Near
  critical fire weather conditions northwest.

- Increasing rain chances next week, especially Monday night and
  Tuesday, with greatest chances (60 to 80 percent) coming to
  central and into eastern North Dakota.

- Colder temperatures mid to late in the work week with
  lingering chances (30 to 50 percent) for rain and snow.

&&

.DISCUSSION...
Issued at 221 AM CDT Sat Apr 13 2024

Currently, a warm front was pushing from western into central
North Dakota. Some light reflectivities were located along the
International border but as of yet we haven`t see any shower
activity since late last night over eastern Montana. We are
still carrying a slight chance of showers today mainly along and
north of the Highway 200 corridor associated with a surface low
and it`s associated warm/cold front as it move east across
southern Canada and a weak mid level impulse trailing the cold
front. Any precip amounts would be negligible.

The main forecast issue today deals with fire weather concerns.
Forecast highs are in the lower 70s north to lower 80s far
south under partly sunny skies. This afternoon much dried air
moves into the state behind the trailing cold front. Since there
really isn`t much cold air behind the cold front, all we really
get is some subsidence and steep lapse rates developing, which
will result in a unidirectional northwest wind to above 5000
feet. All model guidance has increased winds since yesterday,
and we blended in some RAP/HRRR guidance this afternoon to
better depict the wind potential this afternoon across the
forecast area, but especially the north. We also blended the
HRRR/RAP dewpoint guidance, bringing the NBM humidities down
quite a bit. We will mention near critical fire weather
conditions in the Northwest this afternoon. There are some
uncertainties, such as the extent of the dry air, cloud cover,
and duration of low humidities with strong winds. Will let the
day shift continue to monitor. Perhaps the near critical mention
will need to be extended farther east and/or south.

Sunday should be less windy and although not quite as warm as
today, it should be dry through the daytime, with rain chances
picking up in the evening. We get one last impulse moving
through the quasi-zonal flow, congruent with an area of warm
advection ahead of cyclogenesis in the lee of the Rockies.
Although thunder potential looks minimal, there is some elevated
instability with a strengthening low level jet, thus some
thunder can`t be ruled out.

The main forecast issue next week will be the Monday through
Tuesday timeframe which brings the potential for showers and
thunderstorms, some possibly with heavy rain. The forecast trend
compared to yesterday is slower and farther south.

We`re going to look at the same timeframe as yesterday: 7 PM
Monday through 7 PM Tuesday. This is when we see the highest
probabilities of showers and thunderstorms. In our discussion
yesterday, the ECMWF/GEFS raw model ensemble surface low
positions tracked from northeast Colorado into southern
Minnesota. Today the track is similar but there is definitely a
shift to the south with the mean low position tracking a little
more due east initially and then lifting through a portion of
north western Iowa before reaching Minnesota. The same can be
said (a southward shift) with the mid and upper level features.

Timing wise: Yesterday it looked like the best potential for
thunderstorms would be moving into southern ND around peak
heating. Now it`s delayed maybe 3-6 hours, limiting the
potential for late afternoon/early evening thunderstorms with
high rainfall rates. We are still seeing some signals for
higher qpf from the ECMWF SA page, but shifted farther
southeast, and for very high PWAT values from the GEFS Ensemble
SA page, roughly in the same area (I-94 corridor form Bismarck
to Jamestown). Thus the potential remains for some hefty
rainfall amounts, if we can fire off some convection. A look at
the showalter index from the deterministic GFS/ECMWF shows the
elevated instability has shifted south compared to yesterday,
barely reaching into ND, thus the potential for convection seems
to be trending lower over our forecast area.

In addition, as mentioned yesterday, there does still look to
be some interaction between the northern/southern stream lows
and this can be seen/inferred from the deterministic and
ensemble data. In the deterministic guidance both the GFS/ECMWF
show an area of mid level forcing and resulting area higher qpf
lifting southwest to northeast across (in general) central ND.
It now is later, moreso Tuesday than Monday night. If we don`t
get any convection Monday night, there may still be a band of
higher qpf lifting through the general area on Tuesday, while
the majority of the forcing, and thus precipitation, remains to
our southeast. The chance of thunder by this time looks minimal
and as mentioned yesterday the mid level forcing is there, but
there is also upper level ridging (between the two lows) moving
into this same areas, so there are uncertainties to the extent
of this precipitation as well.

Beyond Tuesday, we may see a fairly substantial dry period as
the trend of the northern stream system is to stay to our north.
Thus Tuesday nigh and Wednesday we would be in the dry sector of
this upper low, before it (possibly) drops down over the area
bringing colder temperatures and better chances of rain and snow
showers. Ensemble spread increases quite a bit by this time, so
uncertainty is high. The potential for snow on the back end of
the northern stream low has diminished quite a bit from
yesterday. Late in the week and into the weekend we do begin to
warm up a bit.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1220 AM CDT Sat Apr 13 2024

LLWS at KBIS, KMOT and KJMS to begin the 06Z TAF period.

Strong winds of up 65 kts noted on the KBIS and KMBX VWP product
from the south to south southeast. Kept the level at 1000ft but
increased the wind 5 knots and backed direction about 20
degrees. Forecast soundings indicate we could mix out with winds
a little stronger than currently forecast Saturday afternoon.
Will take a closer look with the 12Z issuance, but for now
introduced some wind gusts to around 25 knots. Otherwise VFR
conditions are expected through the 06Z TAF period.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...TWH
AVIATION...TWH