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Area forecast discussion...updated 
National Weather Service Billings Montana
824 PM MDT Tuesday Jul 7 2015

Update...
Post frontal showers and thunderstorms were dropping southeast
along the Lee side of The Rockies this evening. A few heavy
downpours are mixed in...but the majority of the activity is light
showers. The flow aloft has turned cyclonic and mesoscale scale models
suggest a few showers lingering. Therefore will keep a slight
chance of showers overnight across the forecast area. By
morning...upslope and dynamics will focus lift along the southern
sections of our forecast area. Made a few minor tweaks to adjust
probability of precipitation for this through tomorrow. Bt

&&

Short term...valid for Wednesday and Thursday...

A weak cool front will move across the forecast area late this
afternoon into this evening bringing a chance for showers and
thunderstorms. Overall shear and dynamics are weak so we are not
expecting any severe thunderstorms. However...slightly stronger
dynamics are in place across far southeast Montana where an
inverted trough has been situated. This area may see a stronger
thunderstorm into the early evening hours. Winds aloft are not
overly strong so thunderstorms may be slow movers. In
addition...precipital waters are around an inch so any
thunderstorms will most likely contain heavy rain. Activity is
expected to decrease late this evening but there will remain a
slight shower/thunderstorm chance after midnight.

Wednesday & Thursday...a split flow aloft will be over the
forecast area both days. The tail end of a jet maximum will be over
eastern Montana Wednesday but move into the Dakotas by late in the
day. Light winds aloft will prevail late Wednesday through
Thursday. A couple of weak disturbances will again move across the
area both days mainly affecting the western and southern areas. As
a result...will have a slight shower/thunderstorm chance mainly
along and west of a Roundup-Billings-Sheridan line Wednesday
afternoon through Thursday. Temperatures tomorrow will be about
the same as today or maybe a degree or two cooler which will be
slightly below normal for this time of year. Readings will warm
back to around normal Thursday with middle to upper 80s common.
Hooley

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

The extended forecast appears to be in pretty good shape
overall...with only some minor tweaks and border collaboration
to clean things up. As expected there are several model
differences throughout the period...but are in pretty good
agreement. Generally warm southwest flow aloft will dominate the
pattern throughout the extended period. This will result in upper
80s and low 90s through the period...and at least some potential
for showers and thunderstorms through the bulk of the period.

The majority of activity for Thursday will be mainly concentrated
on the high terrain...foothills...and nearby plains. The best
chances for showers and thunderstorms across the region will be
Friday into Saturday morning as a shortwave trough crosses the
region...producing mainly heavy rain. Remnant type showers can be
expected through the day Saturday. Sunday and Sunday night appear
to be driest of the period...as ridging develops behind the cold
front.

Models diverge more significantly at this point. GFS favors
flattening the ridge much more quickly...with a return of moist
southwest flow by Monday evening. European model (ecmwf) holds the ridge in the
east a bit longer...before allowing southwest flow to impact areas
east of the mountains. Carried climatology type probability of precipitation through the last
couple of days of the period. Aag



&&

Aviation...

Brief MVFR ceilings and obscured mountains are possible through
about 04 UTC due to scattered showers and isolated thunderstorms
over and near the beartooth/Absaroka Mountains and foothills.
Elsewhere...isolated showers are possible across the plains
overnight but most locations will remain VFR. Bt

&&

Preliminary point temp/pops...

Wednesday Thursday Friday Sat sun Monday Tuesday
-----------------------------------------------------------
bil 058/080 058/085 061/090 062/087 062/094 063/092 063/091
21/b 12/T 23/T 33/T 21/b 11/b 22/T
lvm 051/077 050/083 055/085 055/083 055/091 055/090 054/088
22/T 23/T 24/T 33/T 31/north 12/T 22/T
hdn 057/082 057/089 060/094 060/090 060/097 060/095 061/093
22/west 12/T 23/T 44/T 21/b 11/u 22/T
mls 058/083 059/089 063/094 064/092 063/096 064/093 064/093
21/b 11/u 13/T 33/T 21/u 11/u 22/T
4bq 057/080 057/087 061/093 062/091 062/095 062/091 063/092
22/west 11/b 23/T 33/T 11/u 11/u 22/T
bhk 055/080 055/086 060/090 062/090 061/092 061/089 061/090
21/b 11/u 12/T 33/T 22/T 11/u 22/T
shr 054/076 055/082 056/087 056/086 056/091 056/089 057/089
23/T 23/T 23/T 33/T 21/b 11/u 22/T

&&

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

&&

$$
Weather.Gov/Billings

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