Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Billings Montana
253 PM MDT sun may 24 2015

Short term...valid for Monday and Tuesday...

A chance of showers is in the forecast most of the time during the
next few days as an active late Spring weather pattern continues.

Tonight...a moist atmosphere characterized by precipitable water
values of 0.70 to 1.00 inches will remain in place and so showers
will have no trouble continuing where large-scale forcing exists.
The 12 UTC global...convectively-parameterized model guidance and
higher-resolution...convection-allowing models like the NCEP WRF-
arw and nmm all suggest the greatest concentration of forcing and
thus showers will be from Sheridan east across southeastern Montana. We
thus have 60+ percent probability of precipitation in play there and mainly chance-style
probability of precipitation elsewhere tonight. The forcing in southeastern Montana will be
driven on the larger-scale by a 500-mb low lifting out of The
Rockies and into the northern plains by Monday.

Monday...the 12 UTC guidance continued the theme presented in most
recent solutions for a greater chance of showers than expected in
earlier forecasts for Memorial Day. We generally followed with the
multi-model consensus...which supported likely probability of precipitation lingering into
Monday morning over southeastern Montana and chance-type probability of precipitation of 30 to
50 percent in most areas through the day. Drying will nonetheless
begin aloft by afternoon and that should help highs reach into the
60s f in many places.

Monday night...weak middle-level ridging will cross the area and that
will offer a relative minimum in the chance of precipitation after
any lingering...diurnally-driven showers diminish in the evening.

Tuesday...the air mass will warm ahead of a weak 500-mb low moving
east out of the Pacific northwest and that will combine with a bit
less cloud cover to allow for highs ranging from the upper 60s f
to the lower 70s f in most areas. That in turn will likely combine
with steepening middle-level lapse rates to yield MLCAPE between 250
and 500 j/kg Tuesday afternoon and evening per the 12 UTC GFS and
NAM solutions. This environment will likely favor shower and storm
development over south central Montana and and north central Wyoming Tuesday
afternoon into Tuesday night. The cape-shear setting looks like it
will be marginal for any strong storms...but the scenario appears
more supportive of lightning than most recent days. That is backed
up by 09 UTC sref-based calibrated thunderstorm probabilities near
40 percent. Schultz

Long term...valid for Wednesday...Thu...Fri...Sat...sun...

Unsettled pattern with generally weak flow through the extended
though there a few periods which are Worth highlighting. Wednesday
an upper low pushing into the area from the Pacific northwest
stalls and fills over Idaho leaving the forecast area under a belt
of slightly stronger southwesterly flow aloft. Could be a better
thunderstorm set up depending on the positioning of the surface
low. GFS is favoring most of the area being in the cool sector
with the surface low over Wyoming while the European model (ecmwf) is less distinct
with this surface low and allows for warmer temperatures. WRF and
sref indicate 500 to 1000 j/kg convective available potential energy but shear is still light so
expect better thunderstorm coverage but not much intensity.
Thursday has even less shear and cape but airmass will be unstable
so any heating will generate shower activity.

Friday will remain cool and unsettled but does not look quite as
wet as a back door cold front moves through eastern Montana. Ridging
shows up next weekend for warmer temperatures though the European model (ecmwf) is
less certain of the amplitude of the ridging and has more of a
zonal flow. Could see a better chance of temperatures in the 70s
than the past few weekends. Looks like slight chance of showers
and isolated thunderstorms is a good compromise forecast but GFS
would support a mostly dry forecast. Borsum



Upslope flow will continue through the period with a moist airmass
supporting foothill and mountain obscurations. Kshr will be the
most impacted location with the ceilings remaining MVFR to IFR
through the night. Shower activity this afternoon will produce
localized MVFR conditions at other terminal locations through the
early evening. Expect ceilings to lower at kbil and klvm in the
evening hours with continued shower activity. Kmls could see a
thunderstorm between 22z to 02z. Borsum


Preliminary point temp/pops...

Monday Tuesday Wednesday Thursday Friday Sat sun
bil 046/066 047/072 050/071 049/071 049/066 048/073 049/077
54/T 24/T 54/T 44/T 44/T 33/T 31/b
lvm 040/065 044/067 045/066 043/066 043/065 043/072 045/074
43/T 36/T 64/T 44/T 44/T 43/T 32/west
hdn 048/068 045/075 049/073 049/074 049/069 046/075 048/080
65/T 23/T 34/T 44/T 44/T 32/T 21/b
mls 049/066 047/074 051/073 050/074 049/068 046/071 048/075
66/T 22/T 34/T 43/T 33/T 22/west 11/b
4bq 047/064 045/072 049/072 049/072 049/066 045/070 047/075
77/T 22/T 34/T 44/T 44/T 32/T 21/b
bhk 048/062 045/071 047/071 047/071 045/064 040/066 043/072
97/T 32/T 34/T 44/T 33/T 32/west 11/b
shr 042/061 041/069 045/068 045/068 045/064 044/069 045/075
+4/T 23/T 43/T 44/T 44/T 42/T 21/b


Byz watches/warnings/advisories...



National Weather Service Glossary of Abbreviations