Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/18/20
Area Forecast Discussion
National Weather Service Great Falls MT
808 PM MST Tue Nov 17 2020
.SYNOPSIS...
Breezy to windy conditions with above normal temperatures are
expected for most areas through Wednesday. Snow chances increase
along the Divide and portions of the Southwest tonight into
Wednesday, with a better chance for some spotty light rain and snow
for other areas Wednesday night into Thursday as a passing
disturbance cools temperatures closer to the seasonal average. The
seasonably cool temperatures and breezy conditions continue for the
weekend, with any precipitation mostly confined to the Divide.
&&
.UPDATE...
With the Hi-Line region located on the cool side of the warm
front, observed temperatures across that area are a bit cooler
than forecast; therefore, I adjusted temperatures to come in line
with observed values. Additionally, I adjusted relative humidity
(RH) values to make them more representative of current
observations. A tight height gradient aloft with good mixing of
the atmosphere favors stronger than forecast winds along The Rocky
Mountain Front and across southwest Montana; so, I increased wind
gusts, as well. These changes impacted wind chill temperatures
and dew point forecasts. I did not touch sky condition, probability
of precipitation (POPs) or quantitative precipitation forecast as
the forecast for these elements is performing well.
- Fogleman
&&
.PREV DISCUSSION...
/ISSUED 524 PM MST Tue Nov 17 2020/
Remainder of this afternoon through Thursday night...Southerly flow
aloft has increased as a Pacific cold front approaches from the
west. This has provided a breezy to windy and mild afternoon for
most areas, with temperatures reaching the upper 50s and lower
60s over much of North-central and Southwest Montana. The
exception to this continues to be locations along the Hi-Line and
wind protected valleys elsewhere, where 30s and 40s are more
common. No precipitation is anticipated for the remainder of the
afternoon but rain and snow chances will begin to increase along
the Divide this evening into tonight and this activity will spill
over into portions of the Southwest by morning. Stronger winds
aloft will likely keep temperatures elevated tonight despite some
cooling aloft and this will keep snow levels above 4500 ft along
the Divide and above 6000 ft in the southwest and will likely hold
at this level until Wednesday night. Snowfall amounts are
expected to remain on the light side. Wednesday night, a stronger
and cold Pacific shortwave moves through the region and drops snow
levels as precipitation chances briefly increase for all areas
but most for higher terrain. Note that snow amounts will be
light for mountains and nearly non-existent for lower elevations
due to the westerly flow aloft. This system will drop lower
elevation high temperatures for thursday to the 30s and 40s,
close to the seasonal average.
Friday through next Tuesday...The progressive westerly flow aloft
continues for this time frame, bringing periods of breezy to windy
conditions but little in the way of precipitation aside from
occasional lighter end snow showers along the Divide. It appears
that the next chance for more widespread precipitation holds off
until next Tuesday or Wednesday, when some rain/snow can reach
mountain areas beyond the Divide and possibly some lower elevation
areas as well. This will also be the time to expect the strongest
winds, possibly enough to warrant high wind products but it`s a
little early for those considerations. No significant temperature
anomalies are expected for this period as a continuation of cooler
air aloft will keep temperatures relatively close in line with
seasonal averages. RCG
&&
.AVIATION...
524 PM MST Tue Nov 17 2020 (18/00Z TAF period)
North-central and central Montana (KCTB, KHVR, KHLN, KGTF, KLWT):
VFR conditions prevail throughout this TAF period. The greatest
impact to aviation operations is southwesterly winds with gusts to
25KT, and low level wind shear which is included in all TAFs. Expect
the associated turbulence. Snowfall is forecast across The Divide.
Expect mountain obscuration and aircraft icing conditions.
Southwest Montana (KBZN, KEKS, KWYS):
These TAFs begin VFR, with strong winds observed 17029G38KT at KEKS.
Low level wind shear is forecast across the region. Expect the
associated turbulence. KEKS and KWYS become MVFR after 18/12Z, with
KBZN falling into the MVFR range after 18/22Z. Rain/snow will occur
across southwest Montana. Mountain obscuration and icing conditions
are forecast. It is possible that KWYS will become IFR toward the
end of this TAF period. We will continue to monitor and adjust the
extended period as necessary with the 18/06Z TAFs.
Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 38 52 31 44 / 0 0 30 10
CTB 34 43 27 37 / 10 0 10 10
HLN 36 50 30 44 / 10 20 40 20
BZN 35 51 25 43 / 10 20 30 20
WYS 30 40 21 31 / 20 60 60 40
DLN 35 47 23 38 / 10 20 30 20
HVR 24 45 27 40 / 0 0 30 10
LWT 38 52 30 44 / 0 10 10 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls