Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 061741
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1041 AM MST Wed Dec 6 2017

.SYNOPSIS...

A strong ridge of high pressure over the Pacific coast will
continue the quiet weather across the region. Dry with generally
warmer than normal conditions will continue into early next week.
However, cold air will be trapped in the southwest valleys until
at least this weekend, keeping temperatures there below normal
until then, as well as possibly causing patchy fog to form. The
next chance for even light precipitation will likely not be until
Sunday.

&&

.AM UPDATE...

On the eastern periphery of a highly amplified ridge, mid level warm
air advection is leading to low/mid clouds and an area of light snow
over eastern Montana. This area of snow will stay east of our area
today. Mostly sunny skies this morning will give way to increasing
mid/high clouds this afternoon. These clouds may tend to limit
afternoon heating some, especially along/east of I-15 and I lowered
highs there just a bit for this afternoon. The only other change to
the forecast for today was to increase winds a bit across Judith
Basin and Fergus Counties where a little better mixing/steeper lapse
rates should allow breezy conditions to continue into early this
evening. Elsewhere, a lack of better mixing should prevent moderate
winds aloft from reaching the surface. MARTIN

&&

.AVIATION...
Updated 1735Z.

VFR conditions are likely through 08/00z.

Mid/high clouds will move south across the area this
afternoon/evening, then gradually decrease from north to south
after Midnight. As clouds clear, BR/FG cannot be ruled out late
tonight at KHLN/KEKS/KBZN, but the low levels may remain dry
enough to prevent BR/FG development (similar to this morning) and
for this reason, I have opted to leave any mention out for now.
MARTIN

&&

.PREV DISCUSSION...
/ISSUED 321 AM MST Wed Dec 6 2017/

Today through Friday...Quiet weather will persist across the
forecast area through this period, as an upper-level ridge of
high pressure will linger along the Pacific coast. This stagnant
weather pattern will prevent strong disturbances from moving over
the area. A disturbance in the northerly flow aloft will bring
scattered mid and high level cloudiness to the area through
tonight, but skies will then be clear for the remainder of the
work week. Breezy westerly downslope winds will help keep the
plains warmer than normal, as highs warm from mostly mid and upper
30s today to around 50 for most areas by Friday. Overnight lows
will remain in the 20s. However, it will be much cooler in the
southwest valleys. Temperature inversions have developed there due
to recent snowfall keeping the valley floors cold, combined with
the subsidence aloft from the high pressure ridge. It will take at
least a few days for this cold air to erode and/or scour out of
the valleys, so have kept temperatures there below normal. Highs
will gradually warm through the 30s, and lows will fall into the
single digits above and below zero. Additionally, radiational
cooling and light winds overnight will likely cause patchy
freezing fog to form in the valleys.
Coulston

Friday night through Wednesday...Large high pressure ridge will
continue to control the weather pattern for the long term.
Saturday will see mainly dry and mild conditions as we remain in
dry northwest flow. A weak clipper system and its associated cold
front will attempt to suppress this ridge on Sunday. Chances for
precip still look low...although tonight`s model runs included
some increase moisture with this clipper system. Have introduced
slight pops of rain or brief snow across northern, central, and
eastern portions, while areas across the south remain dry and
near normal temperatures. This feature may also bring some
increased wind gusts across the same areas with precip chances.
This ridge quickly builds back in for Monday returning dry
conditions. The ridge begins a slow retrograde to the west
Tuesday and Wednesday allowing more moisture and breezy winds to
stream into the area. Moisture does seem fairly limited, so
although cloud cover may increase, mainly dry conditons are still
expected. Temperatures will be fairly consistently well above
normal from about Great Falls to Lewistown and northward through
the long term. Expect high temperatures in the 40s...with some
50s possible on Saturday and again Tuesday. South of this line
the mixing will not be as prevalent, and valley inversions may
hurt high temps. Temperatures here will be near to slightly above
normal, although once the high shifts slightly westward mid next
week warmer temperatures are possible.
Anglin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  36  24  45  29 /   0   0   0   0
CTB  39  23  46  27 /   0   0   0   0
HLN  32   6  33  14 /   0   0   0   0
BZN  26  14  29   8 /   0   0   0   0
WEY  23   7  27  10 /   0   0   0   0
DLN  27   9  31  11 /   0   0   0   0
HVR  36  23  45  24 /   0   0   0   0
LWT  29  23  44  30 /   0   0   0   0

&&

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

$$

http://www.weather.gov/greatfalls



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