Garrison, North Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

807
FXUS63 KBIS 141753
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1253 PM CDT Wed May 14 2025

.KEY MESSAGES...

- Isolated to scattered severe storms are possible this
  afternoon and evening, mainly across the south central and the
  James River Valley. Main threat is 70 mph winds and a brief
  tornado.

- Showers and thunderstorms and much cooler temperatures are
  expected through the rest of this week. An active weather
  pattern will continue into early next week.

- Torrential rainfall (up to 4 inches) possible through Friday
  morning.

- Breezy to windy all week, then patchy frost Saturday and
  Sunday morning.

&&

.UPDATE...
Issued at 1240 PM CDT Wed May 14 2025

For this update we did pull the western edge of the severe
weather threat a little farther west to include Morton, Grant
and Sioux counties. We also upped the hail size to half dollar
size. This would most likely be with any convection that may
develop along the Missouri River This afternoon. Convection is
moving north through western South Dakota towards the ND border.
Convection approaching southwest ND attim is expected to remain
below severe levels, but will monitor. Updated pops mid morning
and this should hold based on latest radar trends.

UPDATE
Issued at 1015 AM CDT Wed May 14 2025

The morning update was mainly for pops. Showers and
thunderstorms lifting north along the International Border. Some
light shower activity extends south into SD, just west of the
Missouri River. Mostly dry over much of the west and the James
River Valley. A lot of the short term guidance was overdone this
morning so mainly hand drawn pops early, then trending to a
HRRR/RAP blend with more NBM and Previous Fcst into the
afternoon to match up with late afternoon pops.

We did add a mention of heavy rain with the thunderstorm
activity this afternoon through mid evening. The severe threat
for this afternoon/evening remains over the south central into
the JRV. Early on, think the better chance may lie along and
either side of the Missouri River and up to around the I-94
corridor, with the better shear west and best instability east
of the river.

UPDATE
Issued at 643 AM CDT Wed May 14 2025

Scattered to numerous thunderstorms continue along Highway 85
and east. There is new development now in the Turtle Mountains.
These are still forecast to continue this morning and redevelop
along and east of Highway 83.

&&

.DISCUSSION...
Issued at 445 AM CDT Wed May 14 2025


A line of thunderstorms is extending from the South Dakota
border, up to the big lake as of 4am CT near HWY 85. Lots of
lightning is present with these. They are being energized from
the low level jet, and surface trough. These storms are moving
due north and will continue through the morning, although new
development is occurring on the eastern side. Aloft, diffluent
flow is entering western North Dakota, and will become more
amplified by the afternoon across all of North Dakota. A cold
front is sitting in southern Canada, moving south into the state
today. A low pressure is sitting over the Missouri River on the
Dakota border, and is forecast to slowly lift northeast. Today
will be the last day for a week of temperatures nearing 90, but
the northwest will only warm to the upper 50s with that cold
front.

The severe weather today will be on the warm side of the low
where the cold front interacts with it. This area is roughly
east of HWY 83, and south of HWY 2. It looks like convective
initiation based off the CAMs is around 3pm CT over the
Missouri River. MUCAPE seems to be lacking a little from
yesterday, it is more like 1700 J/kg now instead of 2500. There
is a small area of over 2000 so the potential is still there for
70 mph winds. Most of the shear seems to be behind the front,
leading to mostly a wind threat. The storm mode also points to a
wind threat as it will be a line of storms. There could a brief
tornado in the south central along the line as low level
helicity is in the 200s and low level shear is above 30 kts.

Showers and thunderstorms will then last all night and through
all of Thursday for most areas. Torrential rainfall amounts are
expected with rainfall exceeding 1 to 2 inches. The probability
of greater than 2 inch around 85 percent in the central and
south central. There is probably a good chance that areas with
training strong thunderstorms will receive close to 4 inches by
the time this is all done. As the low moves off to the east
Friday, the rain will slowly end west to east, leaving a dry
Saturday. Aloft during this time, a brief ridge will move over.
On the backside of the low, cold temperatures will be pulled
down from Canada. Lows for Saturday morning will be in the 30s,
same for Sunday morning. We may be issuing Frost Advisories
those nights, especially in the north where lows will be below
30. Sunday night southwest flow aloft sets up again and we start
all over with an active week.

This current week will be breezy to windy, especially Thursday
in the southwest. A strong pressure gradient from the low and
some cold air advection in the southwest will create strong
winds. We mixed the NBM with the NBM 90th percentile to raise
winds for this reason. Friday will also be windy, more so in the
James River Valley from the same pressure gradient.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1240 PM CDT Wed May 14 2025

A low pressure system developing over the central and northern
Plains will bring widespread showers and thunderstorms to
western and central North Dakota this afternoon through the 18Z
TAF period. Thunderstorms will be the main concern this
afternoon and this evening, with the most probable area for
severe storms being over the south central, including Bismarck.
Showers and thunderstorms will spread south to north across much
of central ND by this evening. Over western ND, MVFR to IFR
ceilings will continue through much of the period. LIFR ceilings
are possible later tonight through Thursday morning. LIFR
ceilings will also spread east to envelop much of central North
Dakota by Thursday morning. Strong north to northwest winds will
also develop over western and central ND Thursday morning, with
the strongest winds expected beyond the 18Z TAF period.


&&

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

&&

$$

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