Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 212021
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
221 PM MDT Mon May 21 2018

.DISCUSSION...

Afternoon Update (2pm MDT): Generally the narrative from the
morning forecast remains intact, as well as the forecast in
general. The main updates were to the precipitation forecast in
the near and short terms, needing to account for current trends in
the convection that has formed in the vicinity of the Little
Rockies. Otherwise, no other major changes were made to the
forecast for the afternoon.

Bigelbach

PREVIOUS DISCUSSION: Expect a relatively warm and dry weather day
across northeast Montana for the most part. An upper level
shortwave will approach this afternoon from the west. Dynamic
forcing will enhance ascent, especially across upslope terrain
areas upstream of the CWA. That said, expect any convection to
spill into the western zones by this evening. Nam Bufkit forecast
soundings nicely show a little instability, and CAPE as high as
500 J/kg near Jordan this afternoon and evening. At this time,
little in the way of 0-6 km shear should prevent stronger storms,
but brief heavy downpours, as well as breezy conditions may
accompany some of the multicellular structures that evolve across
the area tonight.

While afternoon and evening convective activity will again be
possible on Tuesday, right now the focus is on Wednesday and
Thursday as being the most active. An upper shortwave trough and
associated vorticity maxima over northern Wyoming will lift into
southern and central Montana on Wednesday and eventually eastern
Montana by Thursday. Meanwhile, expect surface low pressure to
track well southeast of the CWA into the Plains during this time.
Low and mid level moisture will increase ahead of this shortwave,
and forecast Bufkit soundings show a more pronounced nice veering
wind profile with increasing levels of 0-6 km sheer across
locations within the CWA. Nice inverted V sounding in the low
levels in the southeast zones in particular in the presence of low
level shear suggest wind potential with any convection. While
models show in excess of 1000 J/kg surface-based CAPE over these
locations on Thursday, any elevated convection over complex
terrain and across portions of the CWA may be sustained well into
the evening hours. In short, will be closely monitoring Wednesday
and Thursday for at least an isolated stronger or possibly severe
storm over portions of NE Montana, and if anything, with
precipitable water values between 1.00" and 1.50" do think locally
heavy rainfall may result as well.

The forecast beyond the midweek was trended toward consensus model
blends given the usual spread in guidance at larger time scales
and lower predictability of mesoscale features. Early indications,
however, suggest a building ridge over the western U.S. with
warmer and dry weather conditions. Maliawco

&&

.AVIATION...
Flight Category: VFR.

Synopsis: Mainly sunny skies will continue to dominate across the
region through the rest of the afternoon. This evening, a weak
disturbance will spread scattered shower activity over the sites.
Tomorrow afternoon, some of these showers could gain strength and
some isolated thunderstorm activity may impact aviation
operations if such storms were to pass over the airfield(s).

Wind: Expect winds today to continue to come out of the southeast
and be under 10 kts. Light and variable winds overnight will
increase to around 7-12 kts out of the north-northeast. If any
thunderstorms pass over the sites tomorrow, expect gusty and
erratic winds.

Bigelbach

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

weather.gov/glasgow


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