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Area forecast discussion...corrected 
National Weather Service Billings Montana
845 PM MDT Tuesday may 26 2015


We increased overnight lows in many spots based on cloud cover and
a relatively moist boundary layer with evening dewpoints near 50 f
in many areas. Recent verification has favored a consensus of raw
2 meter temperature guidance for overnight lows and so we weighted
forecast lows to those numbers. Otherwise...we made little in the
way of other change. Convection is diurnally weakening...and the
00 UTC NAM suggests coverage will become isolated until Wednesday
morning. However...recent hrrr simulations suggest an increase in
activity over south central Montana between 05 and 11 UTC...which is an
idea with some support from upstream radar trends. Thus...there is
enough evidence to keep scattered showers in the forecast through
the night in most areas. Schultz


Short term...valid for Wednesday...Thursday and Friday...

Upper low continues to move very slowly over eastern Washington...and this
feature will be the main weather-maker of concern over the next
three days. Weak ridge axis is over eastern Montana...and diffluence
aloft has allowed for scattered shower and thunderstorm activity to
develop over our west and central parts and extending toward the
Black Hills. Shear is weak so not expecting storms to strengthen
for any length of time...but locally heavy rain and small hail are
possible through the remainder of the afternoon and early evening.

Shortwave over the northern Great Basin will lift across our
region late tonight and Wednesday. This will bring US a period of
showers late tonight and tomorrow morning...and eventually heavier
showers in the higher precipitable water airmass of our far east by tomorrow
afternoon. Have adjusted nocturnal probability of precipitation to account for this as
models are in good agreement. Could see a period of subsidence
which may limit shower/thunderstorm potential in our west and central
parts for a good part of the day on Wednesday...but still
expecting activity by late afternoon and evening in our far
west...again per the diffluence aloft associated with upper low to
our west. Have adjusted probability of precipitation down a notch for central areas
including Billings Wednesday afternoon and evening. Eastern Montana
shortwave will exit by evening.

Low to our northwest will open up and slide across our region Thursday into
Friday giving US a good chance of showers during this period. Though
the energy will be progressive...period of deepened upslope flow
will enhance the precipitation especially for our southern foothills from
Thursday afternoon through Friday morning. This includes Sheridan County
which has seen quite a bit of rain since the weekend. Will follow
the sref here and feel that an additional 0.75 inches of rain is a
good possibility across areas such as eastern Sheridan County...
with the potential for a little more if moist upslope flow
persists a bit longer. Have raised probability of precipitation/quantitative precipitation forecast accordingly from Thursday
afternoon through Friday morning. This precipitation will likely keep water
levels elevated along streams emerging from the bighorns. Energy
will exit Friday night as drier Canadian surface ridge slides over the
northern plains and eastern Montana.

Temperatures the next couple days will stay close to late may normals.
Friday will be the coolest day over the remainder of the week with
highs only in the 60s...courtesy of NE flow drawing cooler air
from the north.


Long term...valid for Sat...sun...Mon...Tue...

Saturday and Sunday will see a zonal flow across the region which
will promote mixing and warmer temperatures. Slow moving weak
upper low over Alberta during this period will support isolated to
scattered shower and thunderstorm activity with long range models
hinting at some drier conditions on Sunday which may decrease

More important pattern sets up Monday into Tuesday as both European model (ecmwf)
and GFS show flow aloft becoming southwesterly in advance of a low
moving into the Pacific northwest. This supports low level flow to
becoming southeasterly which will advect higher dewpoints up from
the plains into the region. Differences on the positioning of a
surface low during this time frame cause some uncertainty to
where the best moisture will set up but with temperatures staying
on the warmer side it does look like a pattern for stronger
thunderstorms. Will be watching this period for a window for
potential severe weather. Borsum



Scattered showers and thunderstorms continue this evening...but
intensity has diminished. Increased shower coverage is expected
overnight...especially over western routes. Areas of mountain
obscurations to continue overnight and through Wednesday. Aag


Preliminary point temp/pops...

Wednesday Thursday Friday Sat sun Monday Tuesday
bil 053/071 050/070 048/063 046/078 052/080 054/080 052/077
54/T 46/T 64/west 22/T 22/T 23/T 33/T
lvm 045/067 044/066 045/063 044/073 047/076 049/077 046/070
56/T 56/T 64/west 23/T 33/T 33/T 33/T
hdn 053/073 049/073 048/066 045/079 051/082 054/083 053/079
55/T 35/T 64/west 22/T 22/T 23/T 33/T
mls 055/072 052/075 048/066 045/075 052/080 056/081 055/077
46/T 43/T 43/west 13/T 32/T 22/T 23/T
4bq 053/071 050/073 049/063 044/072 051/079 055/080 055/077
46/T 34/T 55/west 22/T 22/T 22/T 23/T
bhk 052/071 049/073 045/062 039/067 045/076 052/077 053/075
27/T 43/T 33/west 11/u 12/T 22/T 23/T
shr 051/069 046/068 046/060 042/072 047/077 050/077 051/075
65/T 36/T 66/west 22/T 22/T 23/T 34/T


Byz watches/warnings/advisories...



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