Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 271140
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
540 AM MDT Sat May 27 2017

Aviation Section Updated

.SYNOPSIS...

Isolated to widely scattered showers and thunderstorms will be
around through the Memorial Day weekend. However, no all day
washouts are expected. For those with outdoor activities, have a
plan B ready just in case a thunderstorm threatens. Near normal
temperatures this weekend will transition to above normal
temperatures next week.

&&

.DISCUSSION...

Today through Monday...An upper level ridge along the west coast of
North America continues to remain somewhat stationary, as does an
upper level low over Manitoba. While not overly strong, weak
shortwaves will continue to drop SE out of Canada through the
weekend. That is about where the certainty ends as the models
continue to struggle with the timing and coverage of
showers/storms associated with each wave.

A weak front will push south through the area today bringing
isolated to widely scattered showers and perhaps a thunderstorm.
Later this afternoon/evening, showers and thunderstorms will likely
develop across central Alberta in association with a somewhat
stronger wave. As showers/storms push south tonight, they should
encounter a more stable atmosphere. However, thinking right now is
that the wave will have enough lift/moisture with it for at least
isolated showers to make it into central Montana after Midnight. Of
note, though, the coverage of showers could be higher than currently
forecast. For now, I upped pops across central Montana tonight, but
kept them on the lower end until we can get a better handle on what
happens upstream. Regardless, that wave will send another front,
this one a bit stronger, through the area tonight/Sunday. The timing
of the front tonight will be key in determining which areas have a
higher coverage of showers/storms on Sunday. In addition, the
coverage of showers tonight and the placement of the front will
determine how unstable it gets on Sunday and where the greatest
instability sets up. Depending on all these factors, a few stronger
storms cannot be ruled out Sunday afternoon with gusty winds and hail
possible. The front will push into SW MT by Memorial Day. At this
point, the day looks mostly dry, with the best chance of a shower
or storm confined to the mountains. While generally mild
conditions are expected through the weekend, tonight`s front may
tend to slow the warmup just a bit. Martin

Monday night through Saturday...Not much change to the extended
today. An upper level ridge of high pressure will drift over the
region from Monday night through Thursday morning. Weak upper level
disturbances also moving through the region will also produce some
isolated/scattered showers/thunderstorms. Afternoon temperatures
will be above normal...generally by about 5 to 10 degrees for Tue
and Wed. For Thursday afternoon through Saturday...both the GFS/EC
are in slightly better agreement in that temperatures will be a few
degrees above normal...but nothing significant at this time.
However, the GFS is quite a bit wetter than the EC, thus confidence
is low for pops heading into next weekend. Late Thursday/Thursday
evening the GFS is fairly aggressive with pops, thus pops are higher
that period, otherwise a blend of the drier EC/wetter GFS resulted
in isolated pops over the region for next Fri/Sat. Brusda

&&

.AVIATION...
Updated 1140Z.

A couple of weak shortwaves will bring SCT/BKN mid level clouds and
a few SHRA/TSRA to the area over the next 24hrs. One wave will move
through central MT this morning and SW MT this afternoon. The next
wave, potentially a bit stronger, moves through tonight. Both will
likely be accompanied by a weak front/wind shift to the NW. Any SHRA
or TSRA today should be brief with only a low chance of seeing MVFR
VIS. Gusty winds are likely in and around SHRA/TSRA activity
(similar to what occurred Friday afternoon). The SHRA activity
tonight may have a bit more moisture to work with, with a slightly
higher chance of seeing MVFR VIS for a very brief time. For now,
kept TAFs at VFR through tonight, but this may need adjusting if
confidence increases in the coverage/intensity of SHRA tonight.
Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  72  47  73  43 /  20  20  20  10
CTB  73  45  71  42 /  20  20  20  10
HLN  72  48  76  47 /  20  20  20  10
BZN  67  41  72  40 /  20  20  30  10
WEY  56  32  64  31 /  20  20  30  20
DLN  67  42  73  41 /  20  20  20  10
HVR  76  47  75  40 /  20  20  10   0
LWT  67  44  68  40 /  20  20  20   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls


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