511
FXUS63 KBIS 150616
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
116 AM CDT Thu May 15 2025

.KEY MESSAGES...

- Very heavy rain and isolated thunderstorms through tonight.
  Periods of heavy rain through Friday morning may produce rain
  amounts up to 4 inches.

- Breezy to windy, especially southwest and central Thursday
  and Friday.

- Much colder late in the work week and through the weekend.
  Frost is likely and even some freezing temperatures on
  Saturday and Sunday mornings.

&&

.UPDATE...
Issued at 111 AM CDT Thu May 15 2025

Most of the area has stable enough air within the rain showers
to not produce lighting anymore. The rain showers will continue
overnight, sliding westward some. Portions of the south central
have already received 1.5 to 2 inches of rain in the last 24
hours.

UPDATE
Issued at 1000 PM CDT Wed May 14 2025

Broad area of showers with embedded thunderstorms continue to
lift northward through western into parts of central North
Dakota, while over the remainder of central North Dakota into
the James River Valley thunderstorms remain more
isolated/scattered. With the loss of daytime heating, appears
that the severe threat has diminished over the area, with the
only concern remaining is the possibility of heavy rain over
some areas, which will continued to be monitored.

UPDATE
Issued at 718 PM CDT Wed May 14 2025

So far storms have remained quite tame over the area as the
area of higher instability appears to be further east where deep
layer shear is lacking, thus have just had little storms pop up
and then die more or less east of Highway 83. Can not rule out
one possibly strengthening, but the odds for that will continue
to diminish as the evening progresses. Otherwise, broad area of
rain has developed to the west of Highway 83, with some embedded
thunder.

&&

.DISCUSSION...
Issued at 211 PM CDT Wed May 14 2025

A brief synopsis followed by a more in depth discussion on the
key points.

A strong storm system will impact western and central North
Dakota this afternoon through Friday. Initially, the threat will
be mainly severe thunderstorms with very heavy rain. Some
training storms are possible through this evening. Localized
flash flooding is possible. After the sever threat this evening,
showers and some thunderstorms with heavy rain will continue
into Thursday morning. Thursday afternoon through early Friday
the threat for thunder will diminish greatly, but moderate to
heavy rain is expected to continue. Strong to very strong winds
are expected Thursday through Friday. Colder air is expected
behind the system, with the potential for frost and possibly
some freezing temperatures possible Saturday and Sunday
mornings.

Another system will lift into the Plains states early next week,
and possibly as early as late Sunday. There is a lot of
uncertainty with this system. For now will stick with the NBM,
which already is showing some high chance to likely pops already
by Sunday night into Monday. This system is part of a double
barreled upper low that swings into the Plains. Would not be
surprised to see a lot of uncertainty in the next few runs as
energy between the northern and southern upper lows gets
resolved.

     Severe Weather...

The main severe weather threat today looks to be early on in the
event, along and either side of the Missouri River and mainly south
of the I-94 corridor. We did pull the mention of severe storms
slightly west, mainly just west of the River. The main hazards
today into this evening will be winds to 70 mph and hail to the
size of half dollars. A brief tornado can not be ruled out, most
likely this afternoon. Very heavy rainfall is also possible with
any storms that develop. With a meridional flow today and this
evening, the potential for training storms will exist. More
about the heavy rain later.

With the axis of instability pushing into ND this afternoon,
right along the Missouri River, the main severe hail threat
looks to be right along and just east of the Missouri River.
Along and west of the Missouri, the shear vectors are parallel
to the surface boundary. Ongoing convection over southwest ND
will remain sub-severe. Convection developing over Grant County
and pushing northward would favor upscale growth but probably
messy convection considering that it`s so near to the sub-severe
convection just to the west.

The tornado threat does look to be low, however with a north to
south boundary indicated through Emmons county and into eastern
Burleigh county. Will need to monitor convection along this
boundary. WoFS was indicating some increased 0-2km UH values
here this afternoon. After this afternoon, think the threat for
tornadic storms is quite low.

Overall, the WoFs indicates the overall 4hr probability for
severe weather is relatively low, and situated along and just
east of the Missouri River. Will need to monitor convection
along the cold front this afternoon. WoFS also indicates a good
probability of >40dbz into Bismarck around 22Z. As can be seen
with the slow progression of convection over the southwest, once
convection develops and begins tracking north, it may continue
for a while.

     Heavy Rain...

Precipitable water values will increase substantially across western
and especially central ND. 850-300 MB mean winds are generally due
south this afternoon and evening over central ND. This increases the
chances of training thunderstorms over the same area and will need
to be monitored. Moisture transport will continue to increase into
the area through the day and into tonight. The threat for localized
flash flooding is not considered high, but the training
thunderstorms will pose at least some risk of flash flooding.
However, our significant soil moisture deficits will substantially
reduce expected runoff from a given rainfall total. Thus, these
rains are expected to be far more beneficial than hazardous. However
we will need to closely monitor for the potential of at least
nominal amounts of areal flooding in low-lying areas.

With our recent dry conditions and given the general configuration
of the forecast heavy rain, the main concerns for localized flash
flooding will most likely be early in the event (this afternoon
through tonight) and will result from training cells and very high
rainfall rates associated with thunderstorms. Given the location of
the heaviest qpf is located along the Missouri River basin, these
storms pose near zero risk of flooding on the Missouri River itself.
Regarding the streams west of the river, draining into the Missouri
(Cannonball, Heart and Knife) the highest qpf amounts are centered
over the eastern portions of these basins, even smaller streams like
Square Butte and Otter creeks are located entirely within the
highest qpf area, but are still not expected to rise out of their
banks. East of the Missouri, the Beaver, Apple, Painted Woods, and
Hay creek basins could be of more concern given their respective
watersheds all lie within the area of high qpf. McKenzie Slough will
help minimize any risk of flooding along Apple Creek by slowing
runoff. Farther to the north, (Souris Basin) total rainfall amounts
are also impressive, but the very high rainfall rates associated
with thunderstorms will be much less likely.

Overall, urban areas early in the event would be of greatest
concern. Training of storms, even outside of urban areas will also
be a concern this afternoon through late evening or the early
morning hours. Thereafter, we may still see localized overland
flooding concerns, especially within poor drainage areas,
through Thursday and even through Friday. In addition to
localized flooding of small creeks and streams. localized flash
flooding threats however, will diminish after tonight.

     Strong Winds...

We have issued a wind advisory for southwest and south central
North Dakota Thursday through Thursday evening. As the stacked
system deepens over the eastern Dakotas Thursday and lingers
into early Friday, Gradient winds will increase over western and
central ND. The strongest winds are expected to be in the
southwest Thursday morning. By Thursday afternoon, strong winds
will spread into the south central and towards the James River
Valley late in the Day. Overnight, strong winds may continue
over the JRV, with a lull in the southwest. On Friday winds may
increase again across all of forecast area, before from west
to east Friday afternoon and Friday night. It`s possible that we
may need to extend at least portions of the advisory through
Friday. It is also possible that portions of the advisory may
need to be upgraded to a High Wind Warning. The ECMWF SA page is
not overly impressed with winds at this time, and a good
portion of the strongest winds will occur overnight Thursday
night and early Friday morning. With this uncertainty, will
start with the advisory and let later shifts adjust as needed.

     Cold weather...

Highs on Thursday and Friday will be quite cold, mainly in the
40s within the deformation zone of the strong cyclone.
Fortunately the cloud cover should inhibit frost or freezing
temperatures Thursday night. Friday night and Saturday night
will bring the potential for frost, or even some freezing
temperatures over a good portion of western and central ND.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 111 AM CDT Thu May 15 2025

LIFR to IFR with rain showers and thunderstorms through the
entire period. VIS should stay above 5sm except in heavy
thunderstorms or showers. Winds will increase to 35kts from the
northwest by Thursday afternoon.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 10 AM CDT /9 AM MDT/ this morning to 10 PM
CDT /9 PM MDT/ this evening for NDZ017-018-031>033-040-041-043-
044.
Wind Advisory from 10 AM CDT /9 AM MDT/ this morning to 1 AM
CDT /midnight MDT/ Friday for NDZ019>022-034-035-042-045-046.

&&

$$

UPDATE...Smith
DISCUSSION...TWH
AVIATION...Smith