330
FXUS65 KGGW 062129
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
329 PM MDT Mon May 6 2024

.DISCUSSION...

KEY MESSAGES:

- High Wind Warning remains in effect for most locations south and
  west of Fort Peck Lake. Strongest winds which could lead to
  damaging impact are expected overnight tonight through Tuesday.
  Crosswind concerns and dangerous chop on Fort Peck Lake are
  heightened.

- Widespread periods of moderate to heavy rain will persist
  through Wednesday night. A Hydrologic Outlook as been issued for
  the area receiving the heaviest rainfall.

- Flood concerns increasing for small streams Tuesday and
  Wednesday, leading to rises along the Milk River late in the
  week.

WEATHER PATTERN OVERVIEW:

The slow-moving strong spring storm system will sit and spin over
this region for the next several days. Most of the associated
heavy rain will last through Wednesday morning. By the weekend, a
flat ridge will push in from the Pacific Northwest across the
northern Rockies.

CONFIDENCE AND POTENTIAL DEVIATIONS FROM BASE FORECAST:

Probabilities for high wind have decreased slightly with both
speed and area. Still looking at high probability (70-90%) for
wind gusts over 55 mph for Phillips county (excluding the north),
Petroleum and Garfield counties. For Prairie county, the high
winds will be mostly in the west over the Big Sheeps, and Valley
county will see the strongest winds across the ridge tops near
Fort Peck Lake. So have upgraded these zones to a High Wind
Warning. Other zones in northeast Montana will have much lower
probability for reaching high wind criteria.

Rainfall amounts for the region from today through Wednesday night
remain very high. Probability for at least 1 inch is over 70% for
the entire region. Confidence for 2 inches or more drops off to
30-50% east of Opheim, Poplar and Glendive while staying at 60-90%
for most of the area to the west. Probability for more then 3
inches is not insignificant, setting at 30-40% for Malta, Glasgow
and Jordan, and peaking at 60% around the Little Rockies.

With the widespread high precipitation amounts, flooding will
become a concern from midweek into the weekend. Updated RFC river
point forecasts are showing sharp rises for the Milk River at
Tampico and Glasgow by the end of the week. Small stream flooding
and impassable gravel roads are also expected mainly for
Phillips, Valley and Garfield counties.

BMickelson



&&

.AVIATION...

PATTERN: The unusually strong and slow-moving spring storm
system, will continue to push wave after wave of moderate to heavy
rain across the area for at least the next few days.. A region of
dry air will act to slightly diminish rainfall amounts especially
near the Montana/North Dakota border.

FLIGHT CONDITIONS: MVFR to borderline IFR will persist through
most of this TAF cycle. IFR is possible in the bands of heaviest
rainfall.

WINDS: The slow-moving storm system is accompanied by a nearly
stationary cold front. East of the front, winds remain light from
the east. Behind the front northwest winds will are increase to
the 25G35KT range. The location of this wind shift will waffle
back and forth across NE MT over the next few days. KGGW and KGDV
may occasionally see these stronger winds, but will also revert
back into light and variable.

BMickelson

&&

.HYDROLOGY...

Widespread heavy rainfall has impacted many locations already
since this morning. Smaller creeks and streams are expected to
begin rising this evening especially near and west of MT Highway
16. The responsible storm system is large and slow-moving and is
very efficient is producing multiple bands of precipitation.

As the storm system stalls over our area through the next few
days, rainfall accumulations are expected to exceed 1 inch for
most locations, and 2 inches for many other locations. A few
isolated areas could receive in excess of 3 inches.

Low-lying areas and poor-drainage areas will easily begin ponding
water this afternoon and evening. Small creeks and streams will
soon rise and begin to run. All of this water will eventually flow
into the larger, main stem rivers in the next few days with some
sudden rises being possible. It is not yet known whether the Milk
River will reach minor flood stage this weekend. We will continue
to monitor conditions and provide updates as needed.

BMickelson


&&

.GGW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until midnight MDT Tuesday night for Central
and Southeast Phillips-Central and Southern Valley-Garfield-
Petroleum-Prairie-Southwest Phillips.

&&

$$

weather.gov/glasgow