FXUS65 KGGW 052006

Area Forecast Discussion
National Weather Service Glasgow MT
206 PM MDT Fri Jun 5 2020


...Multiple Rounds of Severe Weather Possible...


Storms will fire over the higher terrain in southwest Montana this
afternoon. These storms will make their way into the
Phillips/Petroleum County area after 9PM or so. The storms will be
isolated in nature, but they will have the potential to become
severe with primarily a large hail threat, though some strong
winds will be possible prior to 11 PM. Storms will become more
widespread across the far northeast corner of the state late
tonight into Saturday morning.


As we head into Saturday storms will become much more widespread
starting during the mid-late afternoon. A surface low moving into
the area will bring a warm front north to near the Missouri River
with surface dewpoints rising into the lower and middle 60s,
particularly across the Yellowstone River Valley. The low-level
jet will ramp up to around 50 knots Saturday evening with around
40 to 50 knots of 0-6km shear. MLCAPE will be on the order of 1000
to 2000 J/Kg with the low-level inversion likely being eroded by 3
to 4 PM or so.

While there may be some scattered showers during the day Saturday,
the primary development of thunderstorms is not expected to occur
until the mid-late afternoon. These storms may quickly become
severe as they move north. Large, curved hodographs by Saturday
evening combined with anomalously high levels of moisture and
moderate instability suggest a threat for transient supercells and
bowing segments. All modes of severe weather will be possible
with damaging winds in excess of 70 mph and hail larger than golf
balls the primary threats. A tornado will also be possible,
particularly across the Yellowstone River Valley.

In addition to the severe threat, flash flooding will be of
concern as we could see some training thunderstorms, most notably
along the track of the surface low.


A lot of the low-level moisture will be scoured out by Sunday as
the surface low moves out of the area, however, there will still
be sufficient shear and lift for more thunderstorms to develop
during the afternoon and evening hours. MLCAPE will only be around
500 J/Kg or so, but this could be enough to get a couple of severe
storms with hail to around an inch and wind gusts to 60 mph.

Many locations will see half an inch to an inch of precipitation
by the end of the weekend, though it is likely some locations will
see more than this wherever multiple rounds of storms occur.

Next week...

Lingering showers and thunderstorms will be possible through mid-
week before a ridge builds in. This ridge will dry things out and
bring about warmer temperatures by the end of the week.



Flight Cat: VFR

Winds: Winds rapidly increase out of the southeast this evening at
15 to 25 knots with higher gusts. This will continue through the
overnight hours.

Synopsis: Isolated thunderstorms will affect the area this evening
through tonight mainly after 03Z to 06Z. GGW and OLF have the best
chances to see a severe storm with large hail. More widespread
thunderstorms are expected Saturday afternoon and evening.


Lake Wind Advisory from 6 PM this evening to noon MDT Saturday
For Fort Peck Lake for Central and Southeast Phillips...Central
and Southern Valley...Garfield...McCone...Petroleum.



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