Area Forecast Discussion
Issued by NWS Great Falls, MT

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402
FXUS65 KTFX 261742
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1142 AM MDT Fri May 26 2017

UPDATED AVIATION

.UPDATE...

Skies are clear across the forecast area with the exception of
cloud cover associated with showers and isolated thunderstorms
over far southwestern Montana. Forecast remains in good shape.
Made minor updates to align with observed trends. KG/PN


&&

.SYNOPSIS...

The upcoming Memorial Day weekend looks to be dry for most areas.
However, each afternoon an isolated shower or thunderstorm cannot
be ruled out, especially in the mountains. Temperatures will
gradually warm through the weekend, with unseasonably warm
temperatures likely by the middle of next week. A better chance of
showers and thunderstorms may return by late next week.

&&

.AVIATION...
Updated 1742Z.

VFR expected next 24-hours at all terminals as an upper-level trough
slowly exits the area to the east and an upper-level high pressure
ridge builds-in from the west. Isolated to scattered showers are
possible through about 00Z/Sat over far-southern SW MT and east of a
KCTB to KLWT line. Also, mountain obscuration may occur over far-
southern SW MT through about 06Z/Sat.
Jaszka

&&

.PREV DISCUSSION...
/ISSUED 537 AM MDT Fri May 26 2017/

Today through Sunday...Through the Memorial Day Weekend, the local
area will be sandwiched between a departing upper level trough to
the east and, to the west, an upper level ridge trying to build
in. This will leave the forecast area in a NW flow aloft. Short
term models bring at least two, maybe three, weak shortwaves
through during this timeframe, but differ somewhat on the timing
and associated moisture. Basically, the takeaway for those with
outdoor plans this weekend is shower or thunderstorm activity
looks isolated/widely scattered. No all-day rain is expected, but
with steep lapse rates, afternoon heating, and some low level
moisture, it likely won`t take much to generate a few showers and
thunderstorms (mainly in the afternoon/early evening hours). Areas
in and around the mountains may tend to be favored with the NW
flow setup, but hard to say with great confidence that
valleys/plains will stay completely dry.

For today, the greatest concentration of showers will be across far
SW MT as this area will remain in a somewhat convergent flow on the
north side of an upper low swinging through southern Idaho.
Elsewhere, colder temps aloft combined with afternoon heating should
lead to isolated showers and perhaps a thunderstorm. The low levels
may be a bit drier on Saturday, limiting shower/storm activity to
the mountains. On Sunday, a weak front may drop south into the area
and stall from Cut Bank SE through Billings. For now, kept pops
mainly limited to the mountains once again. However, it is entirely
possible that there will be enough convergence/lift for isolated
showers/storms to form out over the plains along the front and this
will continue to be re-evaluated in later forecasts. With
increasingly warmer temperatures, it will likely be more unstable on
Sunday. Shear looks fairly weak, but there may be enough
shear/instability for a few stronger storms capable of gusty winds
and perhaps some small hail. Martin

Sunday night through Friday...An upper level ridge of high pressure
will reside over much of the region from Sunday night through
Thursday. Expect a few isolated showers/thunderstorms to move
through the region from Sunday night through Thursday. The best
chance for any precipitation will be in the mountains...but a
passing shower/thunderstorm can`t be ruled out at lower elevations.
A gradual warming trend to much above normal temperatures is
expected by Wed/Thu. Then main question in the later half of the
extended then becomes...does the upper level ridge continue to move
east into the Upper Midwest on Friday, allowing for a good chance
for showers and thunderstorms to develop over the region per the GFS
model...or does the ridge strengthen over the northern
Rockies...allowing for hot/dry conditions to develop by next weekend
per the EC model. For now...I blended the solutions...but
adjustments are likely to the forecast for late next week and into
next weekend. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  63  44  72  47 /   0  10  10  10
CTB  64  44  72  45 /   0  10  10  10
HLN  64  44  73  48 /  10  10  10  10
BZN  58  38  68  42 /  10  10  10  10
WEY  46  30  59  32 /  50  30  10  10
DLN  58  39  67  41 /  10  10  10  10
HVR  67  44  75  46 /  10  10  10   0
LWT  58  42  66  44 /  20  10  10  10

&&

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

$$

weather.gov/greatfalls



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