Scientific Forecaster Discussion

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Area forecast discussion...updated 
National Weather Service Billings Montana
934 am MDT Thursday Apr 17 2014

Update...
north-S oriented upper jet will bring a slight chance of rain and snow
showers to southeast Montana this morning...then a shortwave will move through
this area this afternoon bringing another slight chance of
showers. Hrrr/sseo showed only a very minimal chance of thunder
over the southeast this afternoon so just left it out for now. Lowered
cloud cover over most of the area this morning based on visible
satellite. Also lowered sky cover this afternoon to partly sunny.
Hrrr showed patchy stratus burning off this morning. Web cams also
showed fog lifting at Judith Gap so did not add fog there despite
low temperature/dewpoint spread. Removed morning mountain probability of precipitation
based on temperature/dewpoint spreads and webcams. Temperature
forecast looked fine based on current temperatures and mixing to
around 700 mb. Wind forecast was also in good shape. Arthur

&&

Short term...valid for today and Friday...

Scattered showers were sliding east overnight as the upper jet
and an associated baroclinic zone pushed slowly eastward. Pressure
rises and a stiff east wind have ended at Livingston as of 3 am.
I suspect we will have a some showers in the east at sunrise...and
perhaps few light sprinkles or showers lingering in the afternoon
out east due to instability in the northwest flow aloft. Otherwise...we
should remain dry in most other areas today and into the night. As
low amplitude ridging takes place. I did bump up wind speeds in
the Paradise Valley and Livingston areas this evening due to Lee
side surface troughing late today.

Main forecast problem with this package is timing of tomorrows
Pacific front. GFS and NAM bring it through Billings before 18z
with the ec and Gem a little after. As marginal as this seems it
will play a role in temperatures...winds and precipitation as well
as a chance of thunderstorms along our southern border. GFS is
showing somewhat of a rebound effect in the 850mb temperatures
during the afternoon and with general downslope and little
rainfall...it appears the air mass will not undergo any
significant change. Therefore...have kept mild temperatures for most
locations despite a relatively early frontal passage. Indications
on soundings and moisture fields continue to point to the chance
of thunder remaining primarily over our southern borders and
Sheridan County. I did extend the mention of thunder into early
Friday evening. However...our forecast area quickly stabilizes
after 06z tomorrow night so have withdrawn all probability of precipitation for late
night. Bt



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

Mild prefrontal Saturday followed by a breezy just as warm Sunday
as zonal flow pushes a Pacific front across the area but front
will be dry. Monday features continued warm temperatures with
lighter winds and remaining dry.

More important weather pattern begins to evolve Tuesday a large
trough moves into the Pacific northwest developing southwest flow
aloft over western Montana. Surface trough expected to develop
over central Montana and moisture deepens up and pattern should
favor increasing shower activity over the mountains Tuesday
afternoon. Both GFS and European model (ecmwf) are trending the trough to swing
through the western half of Montana which is a drier solution for
southern Montana than had been previously depicted. While
mountains do stand a good chance of rain and snow...lower
elevations look less certain and Wednesday even hints at dry
slotting across the lower elevations.

Thursday main trough axis passes the region and models vary on how
much of a surface low to spin up over the Dakotas. Does support
upslope and cool weather but rainfall amounts do not look as
threatening with the bulk of the systems energy staying further
north. Borsum
&&

Aviation...

Areas of stratus with IFR/LIFR ceilings near klvm/kshr/kbhk will
dissipate by 16-17z this morning. A few light showers will impact
far southeast Montana today...otherwise VFR will prevail with scattered
to broken middle and high cloud across the region. Jkl
&&

Preliminary point temp/pops...

Today Friday Sat sun Monday Tuesday Wednesday
-------------------------------------------------------
bil 060 039/064 038/066 041/072 040/069 043/069 045/052
0/b 14/west 30/b 00/u 00/b 23/T 45/west
lvm 059 039/062 034/066 039/068 038/066 041/065 039/052
1/north 13/west 20/u 00/u 02/west 24/T 65/west
hdn 062 035/068 037/067 040/073 041/072 039/072 041/055
1/b 04/west 30/b 00/u 00/u 12/west 35/west
mls 060 035/066 037/065 040/072 041/070 041/070 043/058
1/b 03/west 40/u 00/u 00/u 12/west 34/T
4bq 060 034/071 037/066 041/073 040/073 042/072 044/062
1/b 02/T 30/b 00/u 00/u 12/west 24/T
bhk 052 030/064 035/063 036/071 039/066 040/068 043/061
2/west 02/west 30/b 00/u 00/u 12/west 24/T
shr 058 036/070 036/064 037/070 038/069 040/071 042/058
0/b 02/T 20/b 00/u 00/u 12/west 24/T

&&

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

&&

$$
Weather.Gov/Billings