Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 251017

Area Forecast Discussion
National Weather Service Billings MT
417 AM MDT Fri May 25 2018

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

Some ridging will occur over the region today while an upper low
sits over California. A weak wave ejected from the cut off low
will track into southwest Montana and may result in some isolated
to widely scattered convection late today and into the evening.
Temps will be quite warm.

Saturday the cut off low will track into the Nevada/Utah area
which places an increasingly diffluent southerly flow over our
CWA. A significant CAPE/Shear environment will develop with PWATS
progged to reach around an one inch. Thus, we anticipate scattered
thunderstorms with the potential for some local hail and
torrential rainfall. Sunday continues to be quite active as the
low tracks into the central Rockies pushing deeper moisture and
synoptic destabilization over our area. Widespread moderate to
heavy rainfall is expected, but the chance of severe thunderstorms
will be diminished compared to Saturday as shear will be notably
weaker. Temps will be about 5 to 10 degrees cooler SUnday.

We do expect accelerated snowmelt from the very warm temps today
and Saturday, which combined with expected heavy rainfall on
saturated soils will increase water levels on area rivers and
creeks. Bank erosion and fast flows are a real risk and folks are
urged to use caution this holiday weekend. BT

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

Unsettled weather will start the extended period, as the nearly
stationary upper low over ID/NV/UT continues to bring difluence,
pieces of energy and high precipitable waters to the region. The
precipitable waters were forecast to be /0.75/ to an inch or more
until Tuesday. On Monday, the GEFS mean QPF was maxed out on the
NAEFS, relative to reforecast values. So Monday will be another
day of torrential rains with thunderstorms. Had chance to likely
PoPs across the area in the morning, with the likelies shifting E
in the afternoon. GFS surface CAPES were forecast to range from
500 j/kg W to 2000 j/kg on the MT/ND border. There were areas of
decent shear as well, which shift to the E in the afternoon.
However, CIN was present in the soundings due to cooler high
temperatures which may help limit the threat of strong
thunderstorms. The upper low shifts to over MT by 12Z Tuesday,
then pushes E out of the area by 12Z Wednesday. Expect scattered
showers and storms on Tuesday, then isolated showers and storms
Wednesday as the airmass dries out.

The flow becomes more SW for Thursday through Friday, although the
models were not in great agreement with the pattern. Went with
isolated to scattered showers and thunderstorms during this time.
Wed. and Thu. looked like the warmest days of the period with
highs in the 70s to around 80. Arthur


VFR will prevail over the area today and tonight. There will be
some mountain obscurations due to isolated afternoon and evening
showers and thunderstorms over and near the mountains. Arthur



    Tdy Sat     Sun     Mon     Tue     Wed     Thu
BIL 083 058/085 056/073 055/069 053/074 054/078 055/075
    0/U 12/T    56/T    75/T    33/T    21/B    22/T
LVM 081 049/081 051/068 049/067 047/071 048/073 048/069
    2/T 14/T    57/T    74/T    24/T    22/T    33/T
HDN 086 056/089 057/076 056/071 054/075 054/081 055/079
    0/U 11/U    56/T    76/T    33/T    31/B    23/T
MLS 085 059/092 061/081 059/074 056/076 057/081 058/080
    0/U 00/U    32/T    65/T    43/T    21/B    22/T
4BQ 085 057/093 059/079 058/073 056/074 054/080 056/080
    0/U 00/U    13/T    66/T    44/T    22/W    22/T
BHK 083 055/089 059/080 057/073 054/073 053/080 055/079
    0/U 00/U    22/T    67/T    43/T    22/W    12/T
SHR 083 052/087 055/070 052/069 049/072 049/076 051/076
    0/U 01/U    27/T    75/T    33/T    32/T    23/T




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