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Area forecast discussion 
National Weather Service Billings Montana
348 am MDT Tuesday Aug 4 2015

Short term...valid for today and Wednesday...

The pattern has turned from hot and dry to cooler and more
unsettled. The hot upper ridge of the last several days has been
pushed east by an advancing upper trough moving in from the west.
This trough will push across western zones this moring...central
zones early this afternoon...and the east this afternoon and
evening. The strongest energy will slide across Wyoming...but the
northern extent of the trough stretched to southern Canada...so
there will be adequate forcing and moisture for convection. As far
as moisture is concerned...precipitable waters were advertised at 1.5 inches
over the east. This is 3 Standard deviations above normal.
Persistent southeast winds have brought dewpoints up into the 50s
over the east. Storms will form this morning over western
zones...spread in central zones late morning into early
afternoon...then form over the east this afternoon and evening.
Shear will be weak...less than 30kts...so severe not a huge
concern...other than microburst winds with collapsing cells. Weak
shear and steering winds will lead to slow moving pulsing cells
that will have high intensity rainfall rates over the east. The
very heavy rain storms may even be as far west as Big Horn and
eastern Yellowstone County with precipitable waters around an inch. Hrrr has
cells going up over northern Sheridan County and southern Big Horn
County around noon and then develops unorganized convection
farther east this afternoon. Will leave Flash Flood Watch in
effect.

High temperatures will be cooler over western and central zones
with earlier convection development. The east will have enough
cloud breaks to warm back up to the upper 80s. The storms are
projected to exit the east overnight. Wednesday could potentially
be another active day as a shortwave off the California coast gets
driven across the northern rockies. This system will have access
to a tropical link as evidenced by water vapor...so there will be
juice for convection. The deepest moisture looks to slide to the
south. Shear will be stronger...around 40kts...and convective available potential energy rise to
around 800j/kg. Certainly looks like another good chance of
thunderstorms...with a severe storm or two a definite possibility.
Storms will be heavy rainers...with the tropical connection and
precipitable waters advertised at around an inch. Twh

Long term...valid for Thursday...Fri...Sat...sun...Mon...

A few changes were made to the extended forecast period this
morning...mainly centered around timing of the Wednesday system
exiting the region on Thursday.

Following the exit of the system on Thursday...the return of
upper level ridging will keep the pattern dry through Saturday
evening...when the next Pacific trough pushes into the region. This
is prognosticated to be another wet system...bringing Pacific
moisture...and tapping into monsoonal flow as well. The wave
however does not seem to be holding together very well...generally
losing organization and energy as it approaches. Therefore have
kept probability of precipitation fairly low...even though it has been quite consistent
from run to run. This wave...if it continues to hold together...will
cross the region through Sunday...bringing shower and thunderstorm
potential across the region once again. Timing also should lead to
cooler temperatures for Sunday...but still in low 80s at this point.

At this point models diverge a bit...but do agree on some degree
of southwest flow into the western mountains...and upper level
ridging bringing temperatures approaching 90 degrees across the region
again. Aag

&&

Aviation...

Showers and thunderstorms overspread the entire region
today...with local MVFR conditions and frequent mountain
obscurations. Winds will shift from easterly to west-
northwest...with gusts of 15-25 knots...as disturbance crosses
the region today. Aag

&&

Preliminary point temp/pops...

Today Wednesday Thursday Friday Sat sun Monday
-------------------------------------------------------
bil 079 059/084 058/085 056/083 057/085 058/083 059/089
6/T 34/T 52/T 11/u 13/T 32/T 21/b
lvm 082 053/080 050/081 049/083 051/081 052/080 052/086
6/T 35/T 52/T 11/b 13/T 44/T 32/T
hdn 084 056/087 057/087 054/085 055/088 057/085 057/091
7/T 43/T 52/T 11/b 12/T 22/T 21/u
mls 090 059/088 061/086 058/084 057/086 060/083 059/090
7/T 82/T 54/T 11/b 13/T 33/T 31/b
4bq 088 058/088 059/085 057/083 057/085 059/084 058/089
7/T 72/T 52/T 21/u 12/T 33/T 31/b
bhk 088 058/086 059/082 056/081 054/083 057/080 056/085
4/T 82/T 44/T 22/west 12/T 44/T 32/T
shr 079 052/086 054/083 052/083 054/085 055/082 054/088
6/T 43/T 52/T 11/u 13/T 32/T 21/u

&&

Byz watches/warnings/advisories...
Montana...Flash Flood Watch in effect from noon MDT today through this
evening for zones 31>33-36-37-58.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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