Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 300244
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
844 PM MDT Thu Sep 29 2016

.UPDATE...

A surface trof is moving west to east as weak jet stream
divergence and H7-5 vorticity is moving through the area aloft in
a southwest flow regime this evening. This combination is
generating a few showers and isolated thunderstorms over SW
portions of the area, with some activity also beginning to show
up on radar over SE areas. Short range models lift more energy
into SC areas later this evening and spread into eastern locations
through the night, exiting northeast by mid morning tomorrow.
Overall this activity is going to be pretty light spotty thus made
only minor adjustments to going forecast for precipitation
potential and cloud cover. Cloud cover will hold temperatures a
good 5 to 10 degrees above seasonal levels tonight. Chambers

&&

.SHORT TERM...valid for Fri and Sat...

Increasing SW flow in the mid to upper levels will bring
monsoonal moisture into the northern Rockies as seen on satellite
imagery. There is currently little in the way of dynamic forcing
associated with this monsoon surge. However, models hint at some
weak impulses moving into our CWA by evening and tracking over us
through the night. Cross sections indicate most of the moisture
will likely be high based and result in limited precipitation and
perhaps mostly virga. So will continue to keep PoP`s low,
especially over the plains overnight.

On Friday, flow aloft backs as upper low over Pacific NW moves
further inland. At this point the backing flow will slow down any
dynamics from affecting our CWA. So aside from a few mountain
showers we will be mostly dry, but with some occasional cloud
cover. Saturday, stronger SW flow and associated dynamics with
that upper low progress east into our area. Have bumped up PoP`s
and added a bit of timing effects of the monsoonal impulses, which
equated to lowering PoP`s in the west Saturday night while raising
them in the central and northeast zones. PW values look pretty
high for Saturday, so expect with the dynamics to see a better
chance of measurable precipitation and lightning than from any
activity thats occurs tonight or tomorrow. BT

.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...

Models continue to prog an upper trough and associated low to
move onto the west coast on Sunday. As the trough and associated
low move inland, moisture and energy will be advected over the
region bringing increasing shower and thunderstorm chances through
early next week. As the trough moves into the interior west,
the ECMWF progs the associated low to lift north and east through
Wyoming on Tuesday, eventually moving through the Dakotas by
Thursday. This scenario would give a steady rain to much of the
region Mon evening into Tue. The ECMWF ensemble mean supports this
scenario. However, the GFS and GFS ensemble mean show a different
scenario, with the low tracking over Colorado and then the
northern Plains, giving south central MT less rain but a heavier
rain for southeast MT. So, there appears to be a good chance of
rain late Mon into Tue, but details - especially amounts and
placement of amounts - are uncertain at this time. There is also
some chance for snow in the mountains Mon night-Tue, as the ECMWF
in particular shows 700 mb temperatures dropping below 0C
beginning Mon night.

Models show the area largely drying out Wednesday into Thursday
as the aforementioned system moves off to the northeast, although
a shower or two is still possible as weak disturbances propagate
over the area in northwest flow aloft.

High temperatures will drop from the 60s on Sunday/Monday to 50s
for Tuesday-Thursday in the lower elevations.  RMS/BT

&&

.AVIATION...

Expecting VFR conditions through the period although a few
showers and isolated thunderstorms will be in the SHR, BIL, and
MLS vcnty between 04z and 09Z. Walsh

&&

.PRELIMINARY POINT TEMP/POPS...

    Fri     Sat     Sun     Mon     Tue     Wed     Thu
-----------------------------------------------------------
BIL 057/081 054/080 052/066 050/060 046/054 043/055 041/057
    21/B    01/U    43/T    55/T    55/W    43/W    22/W
LVM 050/080 049/075 043/063 043/058 042/055 038/054 038/058
    22/T    13/T    23/T    55/W    55/W    32/W    22/W
HDN 053/082 051/082 051/068 050/063 046/054 042/055 041/057
    21/B    00/U    43/T    55/T    55/W    54/W    22/W
MLS 057/082 054/083 056/070 052/067 048/057 043/055 040/057
    21/B    00/U    33/T    55/T    55/W    55/W    32/W
4BQ 057/081 053/083 053/069 051/071 048/055 042/054 040/057
    21/B    00/U    22/T    55/T    55/W    55/W    42/W
BHK 052/077 049/078 051/069 049/068 048/058 042/053 039/055
    22/W    00/U    23/T    55/T    55/W    55/W    42/W
SHR 051/079 049/080 049/067 048/063 044/050 039/051 038/056
    21/B    00/U    22/T    45/T    55/W    44/W    22/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings



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