899
FXUS63 KBIS 070618
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
118 AM CDT Tue May 7 2024

.KEY MESSAGES...

- Widespread showers are expected across western and northern
  North Dakota on Tuesday, with isolated to scattered showers
  south central into the James River Valley.

- Strong westerly winds are expected along and south of Highway
  12 in far southwest North Dakota on Tuesday.

- A transition to warmer and drier weather is expected for the
  end of the work week.

&&

.UPDATE...
Issued at 117 AM CDT Tue May 7 2024

At 1 AM CDT, surface and upper air analyses show a nearly stacked
low pressure over northwest South Dakota. Dry slotting across much
of southern North Dakota is now evident on both radar and satellite
imagery, with scattered showers across areas mainly north of Highway
200. Very little, if any lightning has been observed over the past
few hours, and current SPC mesoanalysis paints only a few hundred
J/kg of MUCAPE over west central North Dakota. Thunderstorm chances
have limited to 20 percent or less with this update. Other minor
forecast changes included blending the latest NBM and high-
resolution ensemble PoP projections through Tuesday afternoon.

UPDATE
Issued at 921 PM CDT Mon May 6 2024

Will allow the wind advisory to expire with this product
issuance. The majority of wind gusts the past couple of hours
have been below 40 mph, and should remain so for the rest of
tonight.

Also updated POPs based on latest radar and near term trends,
using a blend of the RAP/NBM and current location of
precipitation returns. Expect wrap around showers to then fill
back in eastward Tuesday morning and during the day as the low
shifts slowly east-northeast, with the better chances west and
north.

UPDATE
Issued at 753 PM CDT Mon May 6 2024

Will allow the severe thunderstorm watch to expire as scheduled.
Still around 500-1000 MLCAPE in southwest ND, though wind shear
is only 20-25 knots so the severe threat has ended for this
evening.

UPDATE
Issued at 640 PM CDT Mon May 6 2024

The risk for severe thunderstorms remains across far
southwestern North Dakota through early this evening. Surface
low is centered over northwestern South Dakota, with its
associated warm front now orientated west/northwest to
east/southeast across northwest into north central SD.
Convective updrafts continue to spawn north of the front over my
far southwest, but have lost their earlier organization as
instability has weakened and will continue to do so over the
next hour or two. Will keep the Watch as is with this product
issuance, but fully anticipate dropping the watch before its
expiration at 01Z (8pm central, 7pm mountain).

Farther east, scattered convection has developed between the
Missouri River and the James River Valley the past few hours,
and will continue as an embedded wave rotates around the upper
low and lifts north across the eastern Dakotas. Do not expect
any severe weather for this area with limited instability
present.

Will maintain the wind advisory for now, but will look to trim
off counties or expire altogether over the next couple of hours
if winds remain below criteria.

&&

.DISCUSSION...
Issued at 318 PM CDT Mon May 6 2024

Currently, a surface low sits across western South Dakota and
northeastern Wyoming, with an attendant warm front oriented
northwest to southeast across roughly the same area. Some windy
conditions are still present across much of central and eastern
portions of the state, with the highest measured sustained winds
around 25 to 35 mph. As such, the current Wind Advisories will
continue as planned, expiring at midnight CDT. Some showers are also
making their way north through the central parts of the state, with
an occasional rumble of thunder possible. These showers should
remain rather tame, as the instability in this area is not too
strong. Temperatures should max out in the mid 50s to lower 60s
today, with overnight lows in the 40s to 50s.

The previously mentioned warm front is slowly moving roughly north,
along with the surface low, which is fueling the development of some
strong storms in western South Dakota. As the afternoon progresses,
this front will move north towards North Dakota, bringing along with
it the potential for continued severe storm development along it. As
a result, parts of southwestern and portions of far south central
North Dakota are currently under a Severe Thunderstorm Watch until 8
PM CDT (7 PM MDT), as well as a Marginal Risk (level 1 of 5) from
the SPC. The main hazards expected with this event will be winds up
to 60 mph, large hail up to quarter size, and the potential for a
tornado or two. While the ingredients are certainly supportive of
strong storm development, our main concern with this setup is
whether or not the instability will remain in our area for long
enough to get anything going. The most recent deterministic analysis
of SBCAPE suggests a narrow corridor focused along and moving with
the warm front, with values maxing out around 1500 to 2000 J/kg.
However, as soon as this corridor of instability moves into Bowman
and Adams counties, it begins to weaken rather quickly, nearly
dissipating entirely around 8 or 9 PM. 0 to 1 km shear values ahead
of the front are forecast to be around 20 to 30 kts, which combined
with forecasted 0 to 1 km SRH values of 150 to 300 m2/s2, help
support the possibility of a tornado or two, albeit being weak and
short lived tornados. Modest mid level lapse rates are expected to
be present as well, but once again, the timeframe is rather short
for all of these ingredients to line up, and as such, the overall
severe threat is expected to be short lived as well.

Overnight and into Tuesday, this large low pressure system is
expected to move further north into North Dakota, before weakening
and moving southeast into the Great Lakes region through the second
half of the week. Wrap around moisture will bring continued showers
to the area through tonight and Tuesday, with chances tapering off
into Wednesday. Current probabilistic guidance suggests portions of
far western North Dakota will see a 50 to 60% chance of exceeding
1.00" of rain through Wednesday morning, with those chances dropping
to around 10% in central North Dakota. Chances for exceeding 0.50"
of rain in the same timeframe are in the 60 to 80% range for almost
the entire area. Rainfall totals continue to slightly decrease with
each subsequent model run, but overall, the chances for receiving
precipitation remain in the 40 to 70% range for a majority of the
area. Temperatures Tuesday will be a bit lower than today, with
highs mainly in the 50s to lower 60s.

After this wet period, long range guidance suggests the start of a
drying and warming period, as signs point towards the development of
a large ridge across the western CONUS, building east into the Great
Plains through the end of the week and into the weekend. High
temperatures are forecast to warm into the upper 60s and lower 70s
by Thursday, continuing through the weekend. Current NBM spreads for
temperatures on Thursday and Friday are pretty tight, suggesting
increased confidence in a warm and dry end to the work week.
Following that, while temperatures are expected to remain warm, the
spread increases as a result of guidance beginning to disagree with
the synoptic flow pattern heading into the weekend. However, warmer
temperatures in general are expected to continue regardless of the
outcome.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 117 AM CDT Tue May 7 2024

A low pressure center will continue to spin over western and central
North Dakota through the forecast period.

Precipitation/visibility: Most terminals should see a break in
persistent rainfall overnight. During the day Tuesday, rain should
fill back in across western and northern North Dakota, with more
isolated to scattered shower activity across south central and
southeast North Dakota. A few flashes of lightning cannot be
completely ruled out, but the probability for TS is very low.
Visibility could be reduced to MVFR/IFR levels in heavier showers.

Ceilings: Parts of southern North Dakota will see some breaks in low
ceilings overnight, and this trend may continue at KJMS into Tuesday
morning. Otherwise, the overall expectation is for MVFR/IFR ceilings
to prevail.

Wind: Central North Dakota will continue to see strong east-
southeast winds overnight into Tuesday morning, with a gradual
decrease in intensity Tuesday afternoon and evening. Northwest North
Dakota will have easterly winds around 10 kts overnight, turning
slight to the northeast and increasing to around 15 kts with gusts
to 25 kts Tuesday afternoon. For most of southwest North Dakota,
expect easterly winds around 10 kts overnight, gradually turning to
the north and then west during the day Tuesday. The far southwest
corner of the state, primarily Bowman County, will see much stronger
westerly winds on Tuesday, with sustained speeds up to 50 kts and
gusts to 45 kts.

&&

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

&&

$$

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