Area forecast discussion
National Weather Service Billings Montana
359 am MDT Thursday Jun 20 2013
Short term...valid for today and Friday...
Dry air surged across the area behind a cold front overnight...and
that will provide a temporary lull in storm chances. We expect the
pattern to at least partially reload by Friday though since the large
upper-level trough has yet to cross the region.
Today...the dry air mass and cold air advection aloft should allow
for efficient mixing...which GFS-based forecast soundings simulate
up to at least 700 hpa. This should allow highs to reach the 70s f
in most areas. We did think about lowering forecast highs somewhat
in places where they are greater than the bias-corrected consensus
of 00 UTC guidance...but with a relatively warm start and expected
mixing the warm side of the model spread is likely a good place to
be. Some low probability of precipitation are also in place through the day across part of
south central Montana /like Livingston/ in closer proximity to the 500-
hpa trough.
Tonight...the main emphasis for any precipitation should be across
southeastern Montana after 06 UTC...where a 30+ knots low-level jet may be
sufficient to fuel elevated convection. We actually increased probability of precipitation
to around 40 percent in places like Broadus and Ekalaka based on a
distinct signal for this activity in high-resolution guidance from
00 UTC. Both the nmm and arw cores of the 00 UTC WRF key in on the
southeastern part of Montana for convection between 06 and 12 UTC...and
having those two different cores agree on storms is often a pretty
good indication of potential. The 00 UTC European model (ecmwf) quantitative precipitation forecast output lines up
with this idea as well...so we may need to increase probability of precipitation more with
later forecasts. Elsewhere...we are less confident in any moisture
without a well-defined forcing mechanism.
Friday...an inverted surface trough is expected to become established
over southeastern Montana. Increasing low-level moisture and at least a
weakly unstable air mass support some chance probability of precipitation across the whole
area. Our attention will again be on southeastern Montana though...with
the 00 UTC guidance suggesting there could be a narrow axis to the
east of the surface trough with MLCAPE around 1500 j/kg focused in
Carter County. Given 0-6-km bulk shear near 50 knots...we will have a
risk of severe storms in that area. However...the pattern looks to
favors convective initiation in the Black Hills rather than across
southeastern Montana...and the model-forecast instability axis is not a
very wide feature to begin with...so confidence in severe risk is
not very high just yet. Schultz
Long term...valid for Sat...sun...Mon...Tue...Wed...
Main upper trough rotates its axis through the area on Saturday
and this induces frontogenesis over eastern Montana to bring a
good chance of heavier rainfall in southeast Montana. It will be a
cool but unstable day across the region but focusing mechanisms
for convection will be stronger as the base of the trough
approaches a surface boundary over southeast Montana. This will
shift into western North Dakota slowly and relatively light middle
level flow should support rapid developing but slow moving storms.
This set up makes severe weather unlikely as individual cells
should not be that strong but this will allow rainfall amounts to
be higher. Convective support will not be as strong over south
central Montana and north central Wyoming as the trough axis
passes earlier in the day and starts bringing some stabilization.
Temperatures will be at least 10 degrees below normal and many
locations may not hit 70.
Drying occurs Sunday and Monday as next system moves into the
Pacific northwest. This will allow for a warmup with temperatures
climbing through the 70s. Zonal flow for the middle of the week
looks to keep mainly dry conditions and continued warming
especially as heights begin to build over the area. Borsum
&&
Aviation...
The area will remain dry until some showers and thunderstorms
begin moving into the mountains this afternoon. Gusty west winds
can be expected in the morning hours but these will decrease
around midday. Borsum
&&
Preliminary point temp/pops...
Today Friday Sat sun Monday Tuesday Wednesday
-------------------------------------------------------
bil 077 051/073 052/069 049/078 054/083 058/084 059/083
1/u 23/T 34/T 41/b 11/b 22/T 21/u
lvm 070 041/072 042/067 044/079 046/083 051/083 054/086
3/T 34/T 35/T 40/b 12/T 22/T 21/u
hdn 078 052/074 050/072 048/078 052/083 054/085 058/084
0/u 33/T 27/T 61/b 11/b 22/T 21/u
mls 078 054/076 056/072 053/080 056/084 059/085 061/086
1/u 34/T 37/T 81/T 11/b 22/T 21/b
4bq 080 052/075 054/073 051/079 054/085 057/086 059/087
0/u 44/T 47/T 81/T 11/b 22/T 21/u
bhk 079 051/075 055/072 052/076 054/085 059/084 062/086
1/u 35/T 57/T 82/T 12/T 22/T 21/u
shr 078 047/075 049/073 045/076 049/082 052/084 053/085
1/u 34/T 36/T 51/b 11/b 22/T 21/u
&&
Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.
&&
$$
Weather.Gov/Billings
