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FXUS65 KTFX 190844
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
244 AM MDT Tue Mar 19 2019

.SYNOPSIS...

Mostly clear conditions prevail through the week, with gradually
warmer temperatures.

&&

.DISCUSSION...

An unusually strong upper level ridge anchored over the Northern
Rockies will maintain fair weather over our forecast area through
the remainder of the week. Temperatures are trending gradually
warmer, expected finally to rise above seasonal averages. Some
forecast guidance brings high temperatures to near 60 degrees
Wednesday and Thursday. However, this appears too optimistic given
the persistent snow cover. As with previous forecasts, high
temperatures were nudged a few degrees above the NBM guidance, but
kept below the warmest values. In general we continue the daily
freeze and thaw cycle, but the overnight temperatures through
mid-week are moving up into the mid- to upper 20s for many areas.
Thus, the most important message continue to focus on possible
overland snowmelt flooding with increasing rates of snowmelt while
the sub-surface soils remain frozen. Patchy fog remains possible
for some of the valley locations including Havre, Helena, and
Bozeman.

The upper level ridge begins to collapse and move away to the east
by late Thursday, while a Pacific low continues to press across
the Great Basin. This will create a slight chance for mainly
mountain showers over far Southwest Montana Friday afternoon.
Model solutions begin to diverge going into the weekend, but in
general indicate another Pacific system moving across Idaho and
Wyoming. This will bring increasing chances for precipitation
across our forecast area Saturday night into Sunday. Temperatures
near seasonal averages will be cold enough to support snow
Saturday night, but transition back to rain for the North-central
plains on Sunday. Better chances for rain and snow appear to focus
more on central and southwest Montana. The potential impacts of
rain on snow in these valleys will have to be monitored carefully.
Once this system moves away, fair weather returns under upper
level ridging to start next week.

&&

.AVIATION...
Updated 1115 PM MDT Mon Mar 18 2019

VFR conditions will continue over the forecast area at least
through the day on Tuesday. High clouds will likely move over the
area with high pressure over the Pacific Northwest. Otherwise,
patchy fog has formed in river valleys and low lying areas the
past few mornings, so with little change in the atmospheric
conditions, will continue mention of fog in these same areas
between 10Z and 17Z. Some of these areas (including KHLN, KHVR,
KBZN) may fall to MVFR/IFR conditions, with KHLN possibly having
LIFR conditions at times. Coulston

&&

.HYDROLOGY...

Forecast temperatures trend toward above normal readings by the
middle of the week, resulting in an increase in snowmelt at lower
elevations. Overnight temperatures should fall just below freezing
in most areas, helping to mitigate the runoff that occurs from
melting during the daytime periods. With the ground still frozen,
any melting could cause water to accumulate in low lying areas and
the additional runoff into creeks and streams could increase the
potential for ice jams.

Expect the snow melt runoff to begin to increase by Thursday and
Friday, after a few days of warmer afternoon temperatures over the
region and overnight low temperatures not getting quite as cold.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF 47 25 52 27 / 0 0 0 0
CTB 50 23 52 25 / 0 0 0 0
HLN 42 17 50 20 / 0 0 0 0
BZN 43 13 49 16 / 0 0 0 0
WEY 45 9 51 13 / 0 0 0 0
DLN 42 16 48 19 / 0 0 0 0
HVR 44 20 50 22 / 0 0 0 0
LWT 45 22 52 26 / 0 0 0 0

&&

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

$$

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