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Area forecast discussion...updated 
National Weather Service Billings Montana
912 am MDT Wednesday Aug 20 2014

shorterm models showing increasing shower coverage this afternoon
as fast moving energy over Washington reaches the area and
interacts with a subtropical feed of moisture being pushed
northward by a low in Southern California. Updated forecast to
show better chances of showers and thunderstorms. Borsum


Short term...valid for today and Thursday...

Weak shortwave in the southwesterly flow is pushing across
southeast Montana and northern Wyoming this morning...creating an
area of scattered showers. This wave will continue to northeast
into North Dakota by this afternoon. Given this track and current
orientation of the showers from Cody to Sheridan Broadus...expect
the best chance of precipitation this morning to remain east of
Billings. Thus continue to advertise scattered probability of precipitation in this
area...with just isolated probability of precipitation from Billings west through the

As secondary shortwave trough will push in from the west this
afternoon...and can currently be seen on WV imagery over eastern
Oregon and western Idaho. Expect to see scattered showers and
thunderstorms develop over the mountains of southwest and
south-central Montana this afternoon and advance eastward late
this afternoon. There remains some timing and placement
differences between the global and high resolution models with the
eastward progression and whether these will make it into Billings
late this afternoon. Thus have kept scattered probability of precipitation in from
Billings west for this afternoon and evening...with just isolated
probability of precipitation east. The consensus between high resolution models suggests
that if we can get some storms into Billings it will likely be
after 3 to 4 PM.

Temperatures today mark the beginning of the downward trend into
the weekend. Increasing cloud cover today along with height falls
and scattered shower and thunderstorm activity will limit high
temperatures to the middle 80s. Temperatures will continue to fall on
Thursday with cold air advection behind the initial shortwave and
with continued cloud cover and scattered showers. Expect high
temperatures to be in the middle 70s for central and western
zones...with slightly warmer air lingering in the east allowing
for low 80s.

Confidence in how the precipitation will play out Thursday remains
low as forecast models are still in disagreement with the track of
the shortwave. The GFS/NAM solutions remains on the dry side as
they want to lift the wave quickly toward the northeast. This
solution allows US to keep 700 mb winds southwesterly...tapping
into drier air from the south and also offers far less qg
forcing. The ec/Gem solutions keep the track of the wave further
south and allow for more robust qg forcing to push across the
forecast area Thursday and Thursday evening. This track also
allows the 700 mb flow to weaken and actually reverse to the
northeast as 700 mb trough passes. Thus if the track remains
farther south...precipitation will be more widespread with all
around higher quantitative precipitation forecast amounts...whereas the GFS/NAM solutions will be
much more showery. Either way...we will be dealing with
precipitation around on Thursday and Thursday night...but the
amount and how widespread remains uncertain. Kept chance to low-
end likely probability of precipitation in the forecast...but may need to tweak up or down
tomorrow depending on how the models trend with the track of the


Long term...valid for Friday...Sat...sun...Mon...Tue...

Confidence increasing for a cooler and much wetter pattern to end
the week into the early part of the weekend. This confidence is
gained from the fact that the GFS model has been trending farther
and farther south with the main energy within the trough
approaching for the end of the week. This iteration drops the
base of the trough across northern Wyoming with the 700mb low
cruising right over southern Montana. This is much farther south
than runs yesterday which kept the 700mb low over northern Montana
and inhibited strong upslope flow. Not the case have
raised probability of precipitation for Friday afternoon through Saturday morning.

The system looks to be swinging in a little earlier with
convective activity starting in earnest Friday afternoon over
western and central zones. Precipitable water amounts rise to
around an heavy rain producing thunderstorms look like a
good bet. Training storms could cause quick accumulation of water
with streams and creeks possibly rising quickly. Speed of storms
should limit this somewhat. BUFKIT soundings show skinny cape with
moist adiabatic thunderstorm activity will turn to
more showery Friday night. Friday night looks to be the best shot
of rainfall as the trough axis advances into the Great Basin.

The surface low wraps up over northeast Wyoming Friday night and
shifts into eastern Montana Saturday morning. This will be the
best shot of rain over the east...with locally heavy rain expected
with precipitable waters approaching 1.25 inches. Northwest winds will kick up
Saturday as the low strengthens and slides into the Dakotas.
Pushed the higher probability of precipitation farther east Friday night and Saturday. The
higher elevations should see a little snow out of this. The
highest peaks could see a couple of inches Friday night...with the
snow level possibly dropping to around 9 thousand feet by Sunday
morning. Certainly the Beartooth Pass could get some light
accumulations by the time this event is over...mainly over the
highest elevations of the pass.

One thing to note...the NAM was hinting at a pronounced dry slot
late Friday night. This is due to a farther north placement of
the 700mb low. This was an will not factor that into
the forecast but will need to be watched. The 06z version has
already backed off on this solution a expect it to come
in line with the other models over time.

Cyclonic flow will persist for Sunday...but the strongest forcing
will have left the area and thus expect a downtick in shower
activity. Another wave swings into the forecast area for Monday
for the next round of showers. A pronounced change to a wet
pattern looks to be shaping up. Temperatures will crash into the
upper 60s on Friday with highs struggling to reach the middle 60s on
Saturday. Lowered temperatures quite a bit for Saturday with
clouds and showers around. Highs will be held below seasonal
values into early next week with cyclonic flow. Twh


Radar and satellite imagery depicting SW to NE oriented line of
precipitation over eastern and around kmls...kbhk and
kshr this morning. High resolution models did a favorable job of
predicting this activity with overnight runs. Potential for
scattered showers and thunderstorms exists at all terminals this
afternoon as another weather system moves over central Montana.
Precipitation at times may be heavy...causing locally MVFR and IFR
conditions near klvm and well as in all foothill areas.

Preliminary point temp/pops...

Today Thursday Friday Sat sun Monday Tuesday
bil 084 059/074 055/069 052/063 048/068 049/075 054/075
4/T 66/T 56/T 76/T 33/T 22/T 33/T
lvm 079 051/074 050/067 046/061 044/067 045/073 049/073
5/T 77/T 77/T 77/T 43/T 34/T 43/T
hdn 086 058/080 055/073 053/066 051/070 051/077 054/077
3/T 45/T 55/T 76/T 33/T 22/T 33/T
mls 086 060/084 057/072 054/068 052/068 052/075 056/074
3/T 35/T 64/T 76/T 43/T 22/T 33/T
4bq 087 059/085 057/076 056/070 053/068 053/076 055/076
3/T 34/T 64/T 66/T 43/T 22/T 33/T
bhk 083 055/082 055/072 055/068 052/065 049/072 052/071
4/T 34/T 74/T 66/T 43/T 22/T 33/T
shr 084 054/082 052/072 050/067 048/068 049/074 051/073
4/T 44/T 44/T 66/T 43/T 32/T 33/T


Byz watches/warnings/advisories...



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