Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 271556

Area Forecast Discussion...Updated
National Weather Service Billings MT
956 AM MDT Thu Jul 27 2017


PV moving through the region this morning was generating an area
of scattered showers and isolated thunderstorms across the central
zones. Isolated to scattered showers and thunderstorms are
expected to develop across the area through the day as energy from
an approaching shortwave moves in from the west and monsoonal
moisture and low level moisture advects into the region. Models
have been consistent in a more organized area of convection
forming across far SE Montana during the late morning/early
afternoon hours, and moving off to the east, with re-development
over the same area likely to continue into the evening. A few
strong to potentially severe storms are possible across SE Montana
where marginal shear and instability will be present. Main
threats being wind, and to a lesser extent hail. Storms will
also be capable of producing heavy rain with PWATs in excess of
an inch, and storm motions expected to be fairly slow. Have
updated sky, pops, and winds to current trends. The rest of the
forecast remains on track and the previous forecast discussion and
an updated aviation discussion are below. STP


.SHORT TERM...valid for Tdy and Fri...

Monsoonal moisture will continue to move into the area from the
southwest today, along with a few weak disturbances embedded in
the SW flow aloft. Not a lot of focus mechanisms to grab onto in
this pattern and models (especially CAMs) are generating a lot of
anomalous vort centers from convection that hasn`t occurred. As a
result hard to pinpoint any given period as better than any other
for precipitation chances. So, have broadbrushed 20 to 40 pops
across the area today and tonight with highest precipitation
chances over SE MT where southerly flow has increased precipitable
water values over an inch. Light winds from the surface to
15-20kft will bring slow storm motions today and combined with
high PWATs will bring a chance for locally heavy rainfall with any
storms, especially for areas east of Billings. Given dry ground
conditions and a lack of a focus for organized convection flash
flood threat looks minimal. As does the threat for severe storms
as CAPE values look sufficient for a few strong storms but shear
is lacking. Temperatures today will be just a big cooler than
yesterday based on more substantial cloud cover, but still near
90. Not much difference in the forecast between Today and Friday
with isolated to scattered mainly late day showers and storms and
highs near 90. Chambers

.LONG TERM...valid for Sat...Sun...Mon...Tue...Wed...

A weak flow under an upper ridge will be over the region through
the period. Models were in good agreement with the overall
synoptic pattern, but overall, ECMWF showed more QPF than the
GFS. Weak energy moves through the ridge through the period. For
Saturday, kept thunderstorm chances confined to mainly the
mountains. More energy and monsoonal moisture surges into the area
on Sunday, which will support more widespread precipitation
chances. The moisture will slide into SE MT on Monday for
precipitation chances there. Kept chances over the mountains Tue.
and Wednesday. E flow overtakes the area Tuesday, then the GFS
shows a low-level jet setting up in the E on Wed., while the ECMWF
does not have this feature. Went with climo PoPs Wed. evening due
to this discrepancy. Thursday looks less active so went dry in
the afternoon. So, despite overall agreement in the large-scale
pattern, small model differences could make a difference in where
the storms will be located. Stability and shear parameters did not
support strong thunderstorms at this point. Temperatures will be
in the low to mid 90s. Arthur



Isolated showers/tstms will impact areas between KBIL and KMLS
this morning. VFR will prevail. By midday, expect scattered
thunderstorms to develop from KMLS-K4BQ eastward. Some of these
storms could be strong and produce heavy rainfall and local MVFR
or lower flight conditions through the afternoon and evening.
Isolated to scattered thunderstorms will also impact western areas
from mid afternoon through the evening. A few mountain
obscurations are possible. JKL



    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 090 064/092 064/093 064/094 065/094 064/091 063/091
    3/T 32/T    21/U    12/T    21/U    11/U    11/U
LVM 086 057/084 055/090 055/091 055/090 054/091 054/090
    2/T 22/T    21/U    12/T    11/U    11/U    11/U
HDN 090 064/093 065/095 063/096 063/095 061/093 062/094
    3/T 32/T    21/U    12/T    21/U    11/U    11/U
MLS 091 066/094 068/096 067/097 068/097 065/094 065/094
    4/T 41/B    21/U    11/U    21/U    11/U    11/U
4BQ 087 064/092 065/094 065/094 065/094 063/092 063/093
    4/T 42/T    21/B    11/U    22/T    11/U    11/U
BHK 088 065/090 065/093 062/094 064/094 061/092 059/091
    4/T 42/T    31/U    11/U    22/T    11/U    11/U
SHR 084 061/087 061/091 058/091 058/090 057/090 057/090
    3/T 32/T    22/T    12/T    21/B    11/U    11/U




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