Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

789
FXUS65 KTFX 160749
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
149 AM MDT Fri May 16 2025

.KEY MESSAGES...

 - Another round of showers this afternoon, mainly near terrain.

 - Next more widespread precipitation system develops late tomorrow
   night into Sunday, lasting into early Monday.

 - Low-end opportunities for showers most afternoons toward the middle
   of next week, with temperatures slowly rising back to near or
   a touch above average by Wednesday.

&&

.DISCUSSION...

 - Meteorological Overview:

A deep upper level low has exited eastern MT and the Dakotas early
this morning, leaving a zonal flow aloft across the Northern
Rockies. Weak waves within this flow will maintain mainly afternoon
shower opportunities, though showers at any point over the next day
or so will be fair game. In the meantime, areas that see some
clearing this morning will be candidates for fog development.

Looking toward this weekend, two separate southeastward diving waves
within a building trough across the west will interact/ pivot around
each other off to the south beginning late Saturday, lasting into
early Monday. This will result in a period of lower elevation rain
and mountain snow, with the most likely period for heavier
precipitation being Sunday. Snow levels do look to fall with this
system, falling lowest as the system begins to pull away late Sunday
night into early Monday morning. 50th percentile snow levels
during this timeframe are around 5,500 ft, with 10th percentile
snow levels (Reasonable low scenario) between 4,500 and 5,000 ft.
The lowest snow levels are likely to follow the location of the
highest precipitation rates, which are not high confidence yet.

After this system departs Monday, a zonal flow looks to develop and
persist through much of the week. Weak waves within this flow aloft
will promote low-end opportunities for showers and a few
thunderstorms, though confidence in timing any particular wave is
low at this time. Temperatures do look to trend closer to normal
after Monday, however. -AM

 - Forecast Confidence & Scenarios:

The two greatest points of uncertainty are related to the system
late Saturday night through Monday morning. Ensemble averaged
precipitation amounts for this system still show less than stellar
confidence in location of greatest amounts given the large, broad
bullseye of precipitation amounts encompassing most of the
region. To give a little perspective regarding the uncertainty,
NBM 10th to 90th percentile spread (Difference between reasonable
high end amounts and low end amounts) is greater than one inch
north of I-90, and is around three quarters of an inch south of
I-90. In most cases the low end scenario (90% chance for more than
this amount) is still only around a tenth of an inch of total
precipitation for most locations away from terrain.

The story is similar with respect to snow levels. The difference
between reasonable high end and low end snow levels is still more
than 2,000ft.

Trends will continue to be monitored for any late breaking
consensus for the Late Saturday night through Monday system. -AM

&&

.AVIATION...
16/06Z TAF Period

Showers have largely ended across the area but broken VFR/MVFR low
cloud ceilings and areas of mountain obscuration persist across
much of the area overnight. Some partial clearing is likely later
in the overnight period, which would promote the development of
local IFR ceilings and/or fog. Otherwise, most locations should
see a return to VFR conditions Friday morning with showers
redeveloping Friday afternoon. Hoenisch

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  39  65  46 /  50  30  30  60
CTB  59  36  63  41 /  50  30  20  50
HLN  61  41  66  46 /  40  30  40  70
BZN  58  38  64  42 /  40  60  40  70
WYS  51  32  58  35 /  70  70  40  80
DLN  55  37  62  40 /  60  50  30  80
HVR  64  40  67  43 /  20  50  60  40
LWT  57  38  61  42 /  50  50  70  60

&&

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

$$
http://www.weather.gov/greatfalls