527
FXUS65 KGGW 181513
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
913 AM MDT Wed Sep 18 2024

.DISCUSSION...
Going foreast still intact through tonight.

With the area of heaviest rain mainly west of Phillips and
Petroleum, the threat for flooding may be diminished, but not
confident enough to cancel the Hydrologic Outlook. Flatwillow
Creek in southern Petroleum County has begun to rise and will
likely do so into tomorrow (Thursday). TFJ

KEY MESSAGES:

1) Phillips and Petroleum Counties may see some heavy rain at
heavy rain at times today. Lower rainfall amounts are expected to
the east. A Hydrologic Outlook is in effect for this plus the
threat for higher stream runoff from central Montana (i.e.
Flatwillow Creek). Rainfall is expected to end tonight.

2) A High Wind Warning has been issued from 9 am this morning
until 9 pm this evening for strong NW winds. The strong NW winds
today will be confined to the SW zones of the forecast area. The
NW winds will spread east across the forecast area tonight at
lower wind speeds but will be strong enough for a Lake Wind
Advisory for tonight and Thursday.

WEATHER PATTERN OVERVIEW:
The surface low was located near the U L Bend area of Fort Peck
Lake at 08z (2am MDT) this morning with the upper low over south
central Montana. The surface and upper low will be stacked over
eastern Montana today and will slowly drift NE across the region
today and move to the NE tonight.

Heavy rain is expected on the west side of the low today with dry
slotting on the east side of the low. This means that Phillips
and Petroleum Counties will be the eastern edge of the heavy rain
today. The remainder of the forecast area will have periods of dry
weather today mixed in with isolated to scattered showers and
thunderstorms in an unstable atmosphere. The showers and
thunderstorms will continue at times tonight as the stacked low
moves NE out of Montana and diminish Thursday morning.

The probability of 2 inches or more of total rainfall for SW
Phillips and Petroleum Counties remains between 50 and 70 percent
for today and tonight. Will maintain a Hydrologic Outlook for this
area. Another concern are the streams that feed from central
Montana where even heavier rain is possible, particularly the
Flatwillow Creek.

Areas SW of the low today will have strong NW winds with a tight
surface gradient. The probability of a 60 mph wind gusts for
Petroleum County is high enough (70 percent) that a High Wind
Warning has been issued from 9 am this morning to 9 pm this
evening. Winds will be much lighter to the NE of this area today
being closer to the low. The strong NW winds will spread east
tonight with lower speeds but they will be strong enough that a
Lake Wind Advisory is likely for Fort Peck Lake tonight and
Thursday.

The upper level low will depart to the northeast on Thursday
taking the rain with it. The next upper trough moves through on
Friday with a cold front that will bring below normal temperatures
on Saturday.

FORECAST CONFIDENCE & DEVIATIONS:

High confidence of rainfall greater than 1" occurring west of
Malta and Winnett today and tonight with low confidence in the
location and timing of any showers and thunderstorms to the east.

High confidence in the strong NW winds over Petroleum County but
medium confidence on whether or not a gusts to 60 mph will occur.

Used the NBM 90 percent with Petroleum County winds today and did
increase the base probability of precipitation at times today and
tonight to provide a better hour to hour consistency.


&&

.AVIATION...
Last Updated: 0845Z

CATEGORY: VFR most of the time with occasional MVFR today and
tonight.

DISCUSSION: The TAF sites will be in the dry slot of a strong
stacked low today which will result in VFR conditions most of the
time. An unstable atmosphere will allow for showers and
thunderstorms at times especially this afternoon and tonight that
could bring a period of MVFR conditions. Also, some low clouds are
expected late tonight as the low exits the region which could
bring some MVFR ceilings.

WINDS: SE to south today 5 to 15 knots this morning increasing to
10 to 20 knots this afternoon. The surface low moving NE across
the TAF sites will bring a period of variable winds in the late
afternoon and early evening (22Z to 03Z). Then winds will be NW at
10 to 20 knots late tonight.

&&

.GGW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 9 PM MDT this evening for Petroleum.

&&

$$

weather.gov/glasgow