483
FXUS65 KGGW 041252
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
652 AM MDT Sat May 4 2024

.DISCUSSION...
KEY MESSAGES:

- Unusually warm conditions are expected on Sunday. Southeast
  winds will be quite strong, with gusts into the 40s in some
  places.

- Another round of rain is expected starting Sunday night through
  at least Thursday. Ranges are looking on track to be around a
  inch and a half to 2 inches for many locations with above
  average confidence(60-80%).

- The first high wind signal is starting to show up Monday
  night/Tuesday across the Southwest. With diurnal timing being
  poor, will hold off on issuing a High Wind Watch yet. Low
  confidence(15-30%)

WEATHER PATTERN OVERVIEW:
Synoptic Setup: Forecast begins with a trough running down from
Manitoba into the Dakotas. A closed low is moving on shore of the
Pacific Northwest and northern California with a ridge formed up
between these two features running from the Four Corners through
the Western Montana and into Alberta.

Today through Sunday: There will be a cold start to this morning
with some places pulling out of the 20s for lows. Expect a
warming trend of 10 to 15 degrees each day as the ridge to the
west moves through the region. The ridge looks like it is going to
tap into Desert Southwest air which will make it unusually warm
for the region by Sunday with 70s and perhaps brief 80s for highs.
This is about 15 to 20 degrees above normal in some locations.
Meanwhile, the closed low from the PCNW will push itself into the
ridge, positioning itself over the Intermountain West while
stretching into a very amplified negative tilted trough in
response to the ridge.

Sunday night through Monday: A southern flow interface will setup
between the extremely warm temps of the exiting ridge and the
incoming trough over the Intermountain West. This will start
pulling gulf moisture into the Great Plains potentially all the
way up toward eastern Montana. The intense cool down will generate
a closed low over south central Montana with enough lift energy
to not only generate rain showers but also thunderstorms across
the region through these periods. Already small chances for any
severe TS have diminished further and thunderstorms look like
they have become mostly elevated. A signal for a northward moving
baroclinic leaf(50-70%) looks to be forming across the eastern CWA
which would increase rainfall totals Monday afternoon with any
convection.

Monday night through Thursday night: Closed low will migrate
northeastward and start to cut off/occlude from the warm air.
However, this just means that most of the convective elements will
become mainly stratiform. Main problem here onward is that
positioning of the surface low is still in question with a range
for its center position stretch anywhere from western South
Dakota all the way up to southern Saskatchewan.

Pressure gradient forces behind the low look to set up enough wind
to possibly(15-30% chance) lead up to a High Wind event Monday
night/Tuesday morning. Tonight`s forecast was the first signal
from the NBM for this and the position of the low along with poor
night time diurnal coupling could easily scrub this event.

The low also still looks to generate a trowal in most models
starting mid-day Tuesday through Wednesday which will bring a
heavy amount of rain to areas directly under or behind it. The
majority of the ensembles place this over central to eastern
Montana which could easily generate 1 to 2 inches to the area it
hits. This feature has remained consistent over the last 72 hours
raising confidence to above average(60-80%).

Friday onward: A new ridge looks to move into the area which will
raise temps and dry conditions out through the weekend. GAH


&&

.AVIATION...

LAST UPDATED: 1030Z

FLIGHT CAT RANGE: VFR

DISCUSSION: Clouds will diminish this morning with a deck hanging
on just northeast of KOLF-KSDY. This afternoon will feature
mainly clear skies with increasing high to mid clouds tonight.

LLWS: Some low level wind shear will be possible (20-50% chance)
across northeast Montana from 07-14Z tonight, but it looks to
only impact KSDY and/or KGDV for a couple hours at this time.

WIND: Light and variable through the morning. Becoming southerly
at 5 to 10 kts this afternoon. Then veering SE to E and increasing
to 5 to 15 kts this evening through tonight.

GAH



&&

.GGW WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory from midnight tonight to noon MDT Monday for
Central and Southeast Phillips-Central and Southern Valley-
Garfield-McCone-Petroleum.

&&

$$

weather.gov/glasgow