Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 010535

Area Forecast Discussion
National Weather Service Billings MT
1135 PM MDT Fri Sep 30 2016

Updated to drop evening pops and lower sky cover per latest
radar/satellite trends, and tweaked forecast low temps down in
parts of our east. Interesting area of convection in central ID
should lift west of our cwa later tonight, so should be a quiet
night in our region. Next chance of pcpn will be associated with
Pacific trof and frontal passage tomorrow afternoon and night. JKL


.SHORT TERM...valid for Sat and Sun...

Model ensembles continued to show difficulty in resolving upcoming
pattern due to the strong omega blocking pattern covering the
eastern Pacific and U.S.. Strong upper trough was digging off the
Pacific coast this afternoon on water vapor imagery with other
energy N of the trough digging S into the system. This system will
bring a change to cooler, wetter weather beginning Sunday.

At 1920Z, radar showed a dissipating shower moving off the
Snowies. Other weak convection was forming over the Park. Will
keep low chances for convection over and near the mountains
through 06Z. The right-rear quadrant of a jet in the approaching
trough will bring jet divergence to the area on Saturday and move
out of the region late Sat. night. MUCAPES will be 500 j/kg or
less with little shear. Precipitable waters will run a half inch
to /0.75/ inches on Sat. and increase in the E Sat. night.
Shortwave energy increases over the area through Sat. night, and a
cold front with good frontogenesis crosses the area. Sat. will be
a warm pre-frontal day and dry in the morning. Trimmed PoPs back
westward slightly in the afternoon and increased them in the
mountains based on the latest model trends. Kept just a mention of
thunder. Raised PoPs a bit Sat. evening, then kept the trend of
moving them E through the night. Humidities on Sat. will preclude
the need for a Red Flag Warning.

SW flow aloft with energy in the flow continues over the area
through Sunday night. MUCAPEs remain low but effective shear
increases to possibly 40 kt. Precipitable waters climb to /0.75/
inches to 1 inch in the E. More jet divergence moves in on Sun.
night, but models all showed some form of a dry slot over the
southern zones, making for a tricky precipitation forecast. Moved
PoPs through the E Sun. morning per previous forecast, then
increased them over the SW mountains Sun. afternoon. Will continue
just a mention of thunder. Temperatures will be much lower on the 60s to lower 70s. Increased PoPs to likely over
much of the area Sun. night, except over the dry slot area.
Precipitation looks to push N with time ahead of a warm front.
Kept a mention of thunder in for Sun. night, but soundings looked
borderline for thunder. Arthur

.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...

An upper low and trough will move onto the Pacific Northwest
Coast and into the Great Basin area on Monday, providing a
diffluent flow aloft across southern Montana and northern

The track of this low and location of the precipitation remains
somewhat uncertain. The GFS lifts the low out of the Great Basin
area on Monday and through Wyoming on Tuesday, and eventually off
to the east into the Dakotas by Wednesday. However, the ECMWF
takes the low into southern Montana by Monday evening, then into
northeast Montana Tuesday afternoon. The upper low shifts into
North Dakota Tuesday night and Wednesday while at the same time a
deep surface low will be situated over the western Dakotas. This
will result in very tight pressure gradients across our central
and eastern locations allowing for strong northwest surface winds.

Conditions will begin to dry out from west to east Wednesday with
with the shower activity expected to be east of the area Thursday
and Friday as high pressure ridging begins to build across the
area. After temperatures in the 50s and lower 60s Monday, readings
will be quite cool for the remainder of the week. At this time,
temperatures look to mainly be in the 50s. Hooley



VFR will prevail through the TAF period. Scattered showers and
thunderstorms are possible Saturday afternoon west of KBIL, and
eastward to KBIL by early evening.




    Sat     Sun     Mon     Tue     Wed     Thu     Fri
BIL 055/081 052/067 051/058 044/052 042/055 041/056 039/058
    01/U    42/T    66/T    66/R    63/W    22/W    11/B
LVM 050/076 043/062 044/057 041/052 037/053 036/055 037/058
    03/T    33/T    55/T    66/R    42/W    22/W    11/B
HDN 052/083 051/069 049/061 044/051 042/054 039/054 038/057
    00/U    41/B    56/T    66/R    66/W    32/W    11/B
MLS 055/083 056/071 053/067 048/057 041/052 037/054 036/055
    00/U    33/W    65/T    67/R    77/W    43/W    11/B
4BQ 052/083 054/070 053/071 047/054 040/052 037/055 037/059
    00/U    22/W    54/T    76/R    66/W    43/W    11/B
BHK 048/079 051/070 051/070 049/058 041/051 036/052 038/054
    00/U    23/W    66/T    66/R    66/W    63/W    01/B
SHR 049/081 050/068 049/064 044/051 038/052 037/054 035/059
    00/U    22/T    45/T    66/R    54/W    22/W    11/B




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