National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KTFX 160033
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
630 PM MDT Wed May 15 2013

.DISCUSSION...
Wednesday through Friday...A change in the weather pattern is
expected as the upper level ridge of high pressure slowly exits
the as a cooler and a generally unsettled weather pattern replaces
it. A large scale trough should begin its approach over the
Pacific Coast by late this evening and will stream moisture in
ahead of it. This upper level diffluence along with above average
moisture should allow for some showers and thunderstorms to
develop over the higher terrain and move off slowly towards the
north east. Severe thunderstorms are not expected at this
time...however strong gusty winds and hail could occur with any of
these storms. Temperatures will begin to return toward seasonal
averages and struggle to get out of the 60s as the short term
progress and more moisture flows into the area with the cooler
temperatures. Exact timing of the larger impulses of upper level
support is a point of inconsistency between the models however the
cooler wetter pattern with showers and afternoon thunderstorms
should carry into the long term forecast. Suk

Friday night through Wednesday...An unsettled weather pattern is
expected through much of the period as a broad trough moves into the
area Friday night. This trough will be the dominate weather feature
through the weekend before pushing east Monday evening.  By Tuesday
the next upper level low is positioned off the Pac NW coast. Even
with the trough in place temperatures will be near normal.
Precipitation on Friday evening will be mostly confined to the
southwest.  However by Saturday and Sunday the area of
afternoon thunderstorms expands into north-central Montana. Model
soundings show deep moisture and some instability...mostly Saturday
afternoon...however there is not good spatial agreement with
convective parameters such as cape...shear and LIs. So do not expect
a lot of svr t-storms over the weekend. By Monday and Tuesday models
start to differ regarding the strength of ridging which tries to
make its way into Montana. The EC model is the strongest and
warmest. The current forecast is a model blend with a little more
weight with the EC. This is short-lived as the affects of the next
upper-level low off the Pac NW coast starts to move into western and
central Montana by mid to late week. Mercer

&&

.AVIATION...
UPDATED 0030Z.
VFR conditions will prevail throughout the TAF period. Mid and upper
clouds will continue to move into the area from the west southwest
with some overnight and early morning isolated showers possible
across Southwest Montana. The confidence of any individual airport
seeing showers is low so have kept only VCSH in for now. Low level
moisture increases after 18Z Thursday as a trough moves in from the
west. Confidence is moderate in the 24 to 36 hour period including
lower ceilings and showers at most of the TAF sites.

&&

.HYDROLOGY...
Increased releases out of Gibson Reservoir are causing rises along
the Sun River and the higher flows are expected to continue at
least through this week. At this time, these rises are not
expected to exceed flood stage. Elsewhere, cooler temperatures will
moderate the melting of the snowpack. However, the increased chance
of precipitation will also increase the chance for further
rises in rivers and streams across much of north central and
southwest Montana through the upcoming weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  65  42  62 /  20  50  30  40
CTB  40  65  38  63 /  20  50  30  30
HLN  47  66  43  61 /  20  50  40  50
BZN  44  68  41  63 /  30  60  50  60
WEY  42  62  39  60 /  30  60  50  60
DLN  43  65  40  60 /  20  60  50  60
HVR  45  70  43  71 /  10  50  40  20
LWT  44  63  41  61 /  20  60  50  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

weather.gov/greatfalls