Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 221722
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1120 AM MDT Mon May 22 2017

...Aviation Section Updated...

.UPDATE...

Morning update has been published, with previous forecast holding
firm through today for the CWA. Only minor adjustments made to
POPs and sky cover to account for dissipating/clearing trends for
our northeastern counties. - Moldan

&&

.SYNOPSIS...

A weak disturbance will bring a few scattered light showers from
north to central this morning, pushing into the south this afternoon
and evening. High pressure will then bring drier and warmer
conditions into the region on Tuesday. A sharp cold front could then
bring strong winds, along with cooler temperatures into the region
for Wednesday, with some isolated to widely scattered shower
activity also possible, mainly in the north. Thursday through
Memorial Day weekend will see seasonal temperatures with scattered
showers.

&&

.AVIATION...
Updated 1720z.

An upper level disturbance is dropping due south across Eastern
Montana this morning, with an east to west orientated trough axis
across the region. This trough axis is and will bring a wind shift
to North Central and Southwest Montana throughout the 2218/2318 TAF
period, however, winds are expected to be so light that "VRB" was
used as a general prevailing wind direction for most of the TAFs. A
few showers were accompanying this wind shift line, however, were
very scattered in nature and were dissipating as the noon hour
approached. Otherwise, VFR conditions are expected at all terminals.
- Moldan

&&

.PREV DISCUSSION...
/ISSUED 520 AM MDT Mon May 22 2017/

Today through Wednesday...Montana remains beneath an unsettled
northerly flow aloft Monday. Mid level moisture and weak
instability will trigger isolated/scattered showers this morning
through this evening. However, precipitation amounts are expected
to be generally light with QPF of only a few hundreths or less. A
weak upper level ridge along the West Coast gradually takes on a
positive-tilt and noses inland over the next 24 hours for dry and
warm conditions on Tuesday. By Tuesday night, a closed upper level
low moves southeastward from the Gulf of Alaska and flattens the
upper ridge. A strong upper level jet on the south side of the low
will cause the flow aloft to become westerly and combines with
strengthening downslope pressure gradients east of the Continental
Divide for windy conditions Tuesday night and Wednesday. Models
are in good agreement that the strengthening west winds will be
enhanced by passage of a strong Pacific cold front on Wednesday.
It is worth noting at this point that most models have backed off
on the strength of mountain-top level winds by 10 to 20 knots
so confidence in a High Wind event has diminished somewhat. For
now, I have kept the High Wind Watch in effect and will pass my
concerns on to the day shift. Tuesday continues to appear to be
the warmest day for this upcoming weak with forecast highs
expected to drop a good 10 to 15 degrees on Wednesday. mpj

Wednesday night through Memorial Day...A tight sfc low will continue
to push across southern Canada Wednesday night into Thursday
bringing strong northerly winds to the region. The strongest winds
look to remain in Canada, however, models are currently placing 60+
knot winds at 700 mb level and over 50 knots at the 850 mb level. If
this can mix down, near high wind criteria may continue into
Thursday morning. Watch was left alone to focus on the first round
of winds, and will have to monitored for these potentially high wrap
around winds. With this low in the area and the unsettled northwest
flow, scattered showers will be possible for Thursday. This strong
low pulls out of the region for Friday, however, broad troughing
still lingers across the region bringing more scattered showers for
Friday, with the best chances coming across the south and west.
Broadscale trough and unsettled nw flow lingers to start the Holiday
Weekend on Saturday, with more scattered showers again possible. The
rest of the weekend we see ourselves in the wake of the large low
pressure system. A ridge tries to build although looks like it never
fully sets up. Weakly unstable nw flow could bring a few isolated to
widely scattered showers Sunday, although coverage doesn`t look as
widespread as Friday and Saturday. Similar setup will be found on
Memorial day, with a weak disturbance moving through the nw flow.
The result will again be chances for widely scattered showers.
Isolated thunderstorms will be possible during Memorial Day weekend
with the unsettled pattern, although at this point the lack of
strong lift will limit the strength of these storms. Thursday`s low
will keep temperatures below normal through much of the long term,
with a warmup to near normal expected for Sunday and Monday. Anglin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  69  45  79  53 /  30  10   0   0
CTB  70  45  78  48 /  20  10   0   0
HLN  71  48  80  52 /  20  10   0   0
BZN  66  39  75  45 /  20  10  10   0
WEY  57  30  66  35 /  20  10   0   0
DLN  67  42  76  47 /  10  10   0   0
HVR  72  42  79  51 /  10   0   0   0
LWT  63  40  71  48 /  30   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from late Tuesday night through Wednesday
afternoon Chouteau...Eastern Glacier...Eastern Pondera...Eastern
Teton...Hill...Liberty...Northern Rocky Mountain Front...
Southern Rocky Mountain Front...Toole.

&&

$$

weather.gov/greatfalls



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