Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 011533

Area Forecast Discussion...Updated
National Weather Service Billings MT
933 AM MDT Sat Oct 1 2016

Cold front had pushed through NW MT as of 15Z and was moving a
little faster E than models had predicted. Precipitation was
moving E faster per radar obs than what was depicted in models
including the HRRR/NSSL WRF. Thus have sped up the onset of
precipitation to 15-18z in the W and spread it E faster than what
was shown in previous forecast. SREF instability and shear
parameters and SPC indicated a marginal severe threat over the far
NW zones late today for winds and hail. Right-rear quadrant of jet
will help enhance this possibility. Have emphasized the
thunderstorm threat a bit more for this area through 03Z. Also
lowered dewpoints a couple of degrees for the afternoon based on
RAP soundings. Increased sky cover faster per the above. Arthur


.SHORT TERM...valid for Tdy and Sun...
Water Vapor imagery shows a strong ridge over the high plains
with an upstream trof off the Pacific coast, all of which is
evolving slowly courtesy of blocking over the eastern CONUS
including an Ohio Valley low. There is a small area of
showers/t-storms moving into south central MT in RRQ divergent
region which should stay west of our cwa over the next few hours.
Looking further upstream, a shortwave is seen in northern
California which will lift thru the northern great basin toward
central MT today. This energy and a cold frontal passage will
bring a west-to-east moving band of showers and t-storms late this
afternoon and tonight. Convection should begin in our west around
20-21z with sbcapes up to 500 j/kg. Main risk could be some
enhanced wind gusts near places like Livingston, Big Timber and
Harlowton during the late afternoon. For Billings, best
opportunity for a shower or t-storm looks to be between 6-9pm.
Activity will shift east thru the night and early Sunday as a more
stable and cooler surface ridge slides in from the west.

Winds will shift to easterly on Sunday per the building lee side
surface ridge. As Pacific low begins to move inland, we will see
a quick transition to southerly isentropic ascent and the next
chance of showers especially over southern/western areas on
Sunday. As upper low moves through the great basin the southerly
flow aloft will become much more diffluent, with moisture
advection and increasing instability. Have raised pops to likely
across much of the cwa Sunday night, with potential for some
embedded t-storms thru the night per the ascent and showalter
indices near -1C or -2C. An interesting night of weather for sure.

Today will be the final warm day with high temps into the 80s
across much of the cwa. Post-frontal cooling will bring highs down
to the 60s and lower 70s, warmest in the east, on Sunday.


.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...
The aforementioned Pacific low and associated trough will move
into the Great Basin area on Monday, providing a diffluent flow
aloft across southern Montana and northern Wyoming.

The track of the aforementioned low and location of the
precipitation still remains somewhat uncertain, although models
have now started to converge on more of a westerly track than
previous runs. This would lift the low into southern Montana
Monday night, moving into northeast Montana Tuesday/Tuesday night,
and eventually into North Dakota and southern Canada on Wednesday.
Moisture, energy, and instability advecting over the region will
bring periods of showers and thunderstorms to the area on Monday.
Best precipitation chances will be across central and western
areas as a surface low and dry slot is progged to move into
southeast Montana. Snow levels will begin to fall Monday
afternoon allowing for high elevation snow. Periods of showers
will continue into Tuesday as the low lifts through the region
allowing for wrap- around precipitation to affect the area. Again,
best precipitation chances across central and western areas. Shower
activity will begin to decrease on Wednesday as the low lifts off
to the north and east. As the low lifts off to the north and
east, the pressure gradient will tighten over the area allowing
for strong northwest surface winds to form, mainly across central
and eastern areas. Showers remain possible across the west
Wednesday afternoon as a weak disturbance moves through northwest
flow aloft. Shortwave ridging then looks to build in over the
Northern Rockies for Thursday and Friday bringing generally drier
conditions. Another disturbance is then progged to move into the
region on Saturday bringing more shower chances.

High temperatures across the planes on Monday are expected to be
in the 50s west, with the 60s and low 70s east. Highs on Tuesday
will range from the 40s to low 50s, with high temperatures mainly
in the 50s expected through the rest of the week.

Given the uncertainty in the system that still remains for the
first half of the week, it is hard to nail down precipitation
amounts at this point. As we get closer in time, we should have a
better idea. STP


Middle to high level clouds will begin to increase from the west
today as a front approaches the region. As the cold front crosses
the area during the afternoon and evening, winds will shift out of
the west. Scattered showers and thunderstorms will first affect
areas west of KBIL this morning into the afternoon, then will
expand eastward to near KBIL for this evening. VFR will prevail,
although MVFR is possible near the stronger showers/storms.
Mountains could be obscured at times in showers/storms. RMS/Arthur



    Tdy Sun     Mon     Tue     Wed     Thu     Fri
BIL 082 052/067 052/057 042/049 040/053 040/054 041/059
    2/T 42/W    67/T    87/W    33/W    22/W    11/B
LVM 078 043/062 046/055 039/047 036/050 035/052 037/056
    4/T 34/T    67/T    75/W    33/W    32/W    12/W
HDN 083 050/070 050/062 041/048 040/052 038/054 040/059
    0/U 31/B    56/T    77/W    43/W    22/W    11/B
MLS 084 056/072 055/070 045/049 038/050 036/052 037/059
    0/U 32/W    65/T    68/W    53/W    22/W    11/B
4BQ 083 054/072 054/074 043/050 037/051 035/054 037/061
    0/U 22/W    54/T    54/W    33/W    22/W    11/B
BHK 080 052/072 052/072 044/050 037/049 033/050 035/056
    0/U 23/W    56/T    65/W    43/W    22/W    11/B
SHR 084 051/069 049/065 042/050 037/052 036/053 037/060
    0/U 22/T    45/T    65/W    32/W    22/W    11/B




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