Scientific Forecaster Discussion

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Area forecast discussion...updated 
National Weather Service Billings Montana
916 PM MDT Wednesday Apr 16 2014

Update...
scattered showers were still around in response to weak middle level
warm advection and a jet maximum sliding across the forecast area.
Showers have been very pulsy as they die fairly quickly after
development. Enough regeneration though to keep the mention of
showers in the forecast through the night. Did back off on the
probability of precipitation some this evening as areal coverage was scattered. Clouds
should keep temperatures up and thermal profiles support mostly
rain showers or a rain and snow mix. Forecast lows look good and
did not change. Adjusted winds a bit to keep an east to northeast
wind in a little longer. Twh

&&

Short term...valid for Thursday and Friday...

Unstable northwest flow will remain over the area tonight. Lift
will be provided by steep lapse rates/jet dynamics and 500 mb
vorticity moving through. This will bring scattered rain and snow
showers overnight. Precipitation will end over the west and
central zones Thursday morning as strong subsidence will be over
these areas with a ridge of high pressure building in. A few
isolate showers will continue over the eastern zones but only
light quantitative precipitation forecast amounts are expected. Did raise temperatures a few
degrees tomorrow but cloud cover will limit full heating. The
ridge will bring dry weather overnight but another trough moving
across southern Canada will begin impacting our forecast area on
Friday. The main lift with this trough will remain north of US but
a Pacific cold front will be dragged across our area. Strong
surface convergence along the front will bring scattered showers.
Nam12 is bringing in surface based convective available potential energy of 500 j/kg along with
lifted indice's of a -2c across extreme southern Powder River and Carter
counties. Have left out the mention of thunder at this time as
BUFKIT showing these areas to be capped due to strong southeast
winds. Richmond

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

Models were in good agreement in showing a mainly dry and warm
period Sat through Monday as ridging moves across the area.

A strong Pacific upper low will then approach the Pacific northwest Monday
night through Tuesday and rotate into the region Tuesday night through
Wednesday. Over the past few runs...the GFS has trended north with the upper
low...and by 00z Thursday had it over Montana in the latest run. Meanwhile
the European model (ecmwf) trended the low NE into east Montana and deepened it by 00z Thursday.
The normalized Standard deviation for both models showed
confidence on the lower side of neutral with the upper low
forecast for Wednesday. Both models forecast an upper low moving into
the region...but the strength and position of the system was
uncertain. In addition...the naefs table showed increasing
anomalies of specific humidity from Tuesday through Wednesday suggesting
plenty of moisture will be available for this system.

Precipitation will start moving into the western zones Monday night
and remain mainly over the west on Tuesday. Did increase probability of precipitation from kbil west
on Tuesday. Models agreed in spreading the precipitation further east Tuesday
night so have adjusted probability of precipitation. Despite differences in the low
track...models had a good chance of rain over much of the area on
Wednesday so increased probability of precipitation across the area. Also added thunder to the
warm sector based on the GFS. Due to the increased
precipitation...have lowered temperatures across most of the area
on Wednesday. This system will need to be watched closely as rain on
mountain snowpack could create flooding issues. Latest cips
analogs showed 1 to 1.25 inches of precipitation with similar
systems. The latest GFS and European model (ecmwf) do take the highest
precipitation amounts mainly to the northwest of the forecast area on
Wednesday. Arthur

&&

Aviation...

Scattered rain showers late this evening will gradually decrease
through the night. The showers may mix with a little bit of snow
overnight. The heavier showers will cause localized IFR
conditions...otherwise conditions should remain MVFR to VFR.
Mountains will be obscured. Twh

&&

Preliminary point temp/pops...

Thursday Friday Sat sun Monday Tuesday Wednesday
-----------------------------------------------------------
bil 031/061 039/065 040/066 041/072 040/069 043/069 045/052
51/east 12/west 20/b 00/u 00/b 23/T 45/west
lvm 028/061 039/061 036/066 039/068 038/066 041/065 039/052
41/north 23/west 20/u 00/u 02/west 24/T 45/west
hdn 028/061 034/066 037/067 040/073 041/072 039/072 041/055
41/east 12/west 30/b 00/u 00/u 12/west 35/west
mls 029/059 034/063 036/065 040/072 041/070 041/073 043/058
33/west 12/west 30/u 00/u 00/u 12/west 34/T
4bq 026/059 033/066 037/066 041/073 040/073 042/075 044/062
22/west 12/west 30/b 00/u 00/u 12/west 24/T
bhk 026/052 029/058 033/063 036/071 039/069 040/071 043/061
23/west 12/west 30/b 00/u 00/u 12/west 24/T
shr 028/059 036/067 037/064 037/070 038/069 040/071 042/058
51/east 12/west 20/b 00/u 00/u 02/west 24/T

&&

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

&&

$$
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