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afdbyz

Area forecast discussion...updated
National Weather Service Billings Montana
838 PM MDT Fri Jun 22 2018

Update...
thunderstorm activity was gradually decreasing over the eastern
zones this evening as airmass was becoming more stable. The wave
responsible for the thunderstorms will gradually move east out of the
area overnight. Models showed some cape lingering in the east
through the night, along with some qpf, so kept the slight chance
of thunder overnight. Otherwise, a strong wave was approaching
from the Pacific NW, as seen in water vapor imagery this evening.
Radar showed showers and isolated storms moving into west Montana ahead of
the wave. Increased the coverage of the slight chance of showers
in the west overnight based on latest models. While downslope flow
will keep portions of the central zones dry, another round of
showers and thunderstorms will occur over the western and eastern
zones on Saturday. Best convective available potential energy were over the E, so could see some
stronger storms there. Precipitable waters will average near an
inch again, so heavy rainfall is still possible. Remainder of
forecast was in good shape. Arthur

&&

Short term...valid for Sat and sun...

Trowal feature on backside of trough axis pushing east and south
through our area today has resulted in an area of moderate
showers across our central zones. This has slowly shifted east and
south through the afternoon with scattered instability convection
firing in its wake as temps pushed into the lower 70s. Much of
this will continue into the early evening before slowly
diminishing toward sunset, but the area of showers near the trough
axis may linger well into the night in the east.

There will not be much break in the west though, as another trough
moves down out of the northwest into the inter-mountain rockies.
This trough dives quickly across western Montana into northern
Wyoming by Saturday evening. This should produce showers and
thunder across our western zones and the south central Montana
Mountain ranges. There are some model differences on the position
of this upper low by Saturday night, with the GFS favoring a
position a little further south than the ECMWF, and thus a wetter
scenario for our County Warning Area than the European model (ecmwf). The NAM supports the GFS
solution on the latest model cycle. So will overweight a blend to
the GFS solution for now which generally results in widespread
30-50 percent pop's for most of the region Saturday night into
Sunday. Models do agree that the cyclonic flow ends over our
region Sunday night with a drying trend.

Look for daytime highs to remain below seasonal normals this
weekend. Bt

Long term...valid for Mon...Tue...Wed...Thu...Fri...

On Monday, upper low should be centered over western SD, which
should be close enough to produce a few showers and thunderstorms
over far southeast Montana. Across the rest of south central Montana and north
central WY, upper ridging should build in and bring dry weather.

Models bring a weak cool front across the region late Monday
night/early Tuesday morning. Moisture is lacking during this time
so am not expecting much in the way of precipitation...just a
wind shift and a modest cooldown. It should be breezy Tuesday
afternoon as some mid-level winds mix down to the surface.

Flow pattern then supports downsloping for Wednesday with more
windy and dry conditions. Then the upper flow turns southwesterly
for Thursday and Friday as the next upper trough moves into the
Pacific northwest. This pattern supports the next chance of
showers and thunderstorms for Thursday and Friday.

High temperatures will generally be in the 70s and 80s Monday
through Friday. Rms
&&

Aviation...

Scattered showers and thunderstorms will continue through about
06z tonight, mainly from Rosebud County east. Locally heavy rain
will produce brief IFR or lower visibility near this activity
along with local wind gusts to 30kts. Convection will diminish
with sunset, and expect VFR conditions to prevail overnight,
though patchy fog is possible in low lying areas and river
valleys through mid morning Saturday. Chambers
&&

Preliminary point temp/pops...

Sat sun Mon Tue Wed Thu Fri
-----------------------------------------------------------
bil 055/074 054/074 056/084 059/081 055/079 056/080 055/076
43/T 43/T 21/u 11/u 10/u 03/T 32/T
lvm 049/069 049/072 048/084 052/079 047/079 049/078 048/073
24/T 44/T 20/u 12/west 10/u 02/T 33/T
hdn 054/076 054/075 056/084 059/082 055/081 055/081 056/079
42/T 45/T 31/u 11/u 10/u 03/T 32/T
mls 058/078 058/076 058/082 061/083 056/080 058/082 059/081
51/b 24/T 31/u 01/u 10/u 02/T 32/west
4bq 057/077 056/074 056/081 059/085 057/081 057/083 058/081
51/b 43/T 42/west 01/u 10/u 12/T 32/west
bhk 055/075 054/075 055/079 057/083 053/079 054/081 056/079
54/T 34/T 32/west 11/u 11/u 12/T 32/west
shr 052/073 051/071 051/079 056/082 052/080 053/081 052/077
43/T 54/T 21/u 01/u 10/u 02/T 22/T

&&

Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.

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