Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 271748
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1145 AM MDT WED JUL 27 2016

Aviation Section Updated

.UPDATE...

Latest radar and satellite loops show a weak low to mid level low
spinning over north-central Montana, east of Havre. A fairly
persistent band of showers has been ongoing this morning from near
Havre east through NE MT. Thinking this band will continue to
diminish over the next couple of hours. For this afternoon, still
expecting isolated to scattered showers and storms to redevelop
across much of the forecast area. Similar to yesterday, storms
should begin to develop in the higher terrain of central Montana
early this afternoon, then spread east across the plains later
this afternoon and evening. Isolated storms may develop across
parts of SW MT as well, although the coverage there looks a bit
lower compared to areas further north.

Of note, short term models differ some on the coverage of storms
this afternoon near the above mentioned low east of Havre. It`s
possible the showers and clouds from this morning will keep the
area a bit more stable this afternoon with a lower coverage of
storms. That said, better convergence in this area associated with
the low should still allow showers/storms to redevelop, even if
the atmosphere does remain more stable than areas further south.
Opted to lower pops just a bit in this area this afternoon based
on the uncertainty.

Regarding the strength of the storms today, slightly lower
temperatures may limit instability some compared to yesterday
(ie. only about 500-1000 j/kg MLCAPE). At the same time, though,
shear looks better today compared to yesterday (ie. on the order
of 25-35 kt). Thinking the best combination of shear/instability
will be along and south of a Great Falls to Lewistown line. In
these areas, fairly steep low level lapse rates and modest
instability should lead to primarily a strong wind threat with
gusts of 45-60 mph possible. Hail up to dime size will be possible
with the strongest/most sustained cores as well. Martin

&&

.AVIATION...
Updated 1745Z.
An upper level disturbance will move southeastward through the
region later this afternoon and during the evening hours. Expect
showers/thunderstorms to accompany this disturbance. Brief heavy
rain/gusty winds are the main threat. Most of the storms will
diminish after 08z. Otherwise VFR conditions should prevail. Brusda

&&

.PREV DISCUSSION...
/ISSUED 0535 AM MDT WED JUL 27 2016/
Today through Friday Evening...Fairly close repeat of yesterday`s
conditions expected again today, though high temperatures will be 5-8
degrees cooler. Most of our region will start out with clear
skies this morning, but the next shortwave trof is already near
the WA/ID Panhandle area and should reach the Rocky Mtn Front
around midday. A broad swath low-level moist air (dewpoint temps
in the 50s from Helena/Lewistown north to the Hiline counties this
morning) will again combine with favorable instability from aftn
heating and lift from the approaching shortwave to produce another
round of scattered thunderstorms for most of the forecast area.
Main threat from any storms today will be moderate to heavy
rainfall and outflow wind gusts of 30-40 mph. Wildland fire starts
from lightning will also be a concern as lighter fuels are well-
cured in many areas.

Precipitation dissipates and heads into eastern MT this evening. One
more minor shortwave will sweep through north central and eastern MT
on Thurs evening, with more thunderstorms for locations mainly
along/east of line from Chester to Ft Benton to Lewistown. Once that
system clears out Thurs night, the high pressure ridge over the
southwest US will amplify northward, bringing a return of very warm
temps and dry conditions for Fri, with high temps moving back into
the upper 80s and low 90s.
Waranauskas

Friday Night through Wednesday...Weak ridging aloft will yield dry
conditions across the forecast area Friday night. Saturday still
appears to be the warmest day of the period with southwesterly flow
aloft and westerly downslope winds at the surface. Models continue
to advertise scattered afternoon showers and thunderstorms over far
southwest Montana through the weekend associated with a northerly
push of monsoonal moisture. On Sunday afternoon a broad closed upper
low moving through western Canada will produce increasing winds as
its associated surface low deepens and moves through central and
eastern Montana. This could raise fire weather concerns over
southwest Mt where lower afternoon humidity is forecast. Temperatures
trend cooler to start next week as the Canadian low moves east of
the region. For now it appears the track of this system will keep its
associated precipitation north of our forecast area. However, a
secondary shortwave follows along the international border Tuesday
night producing chances for showers across much of North-central MT.
PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  82  57  84  56 /  30  30  20  10
CTB  79  56  80  54 /  30  30  20  10
HLN  85  61  88  61 /  30  30  10  10
BZN  85  57  87  53 /  20  20  10  10
WEY  81  49  77  44 /  20  20  10  10
DLN  83  55  86  53 /  20  20  10   0
HVR  78  59  84  57 /  30  30  20  10
LWT  77  56  80  56 /  30  30  30  20

&&

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

&&

$$

weather.gov/greatfalls



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