Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Great Falls Montana
818 PM MDT Mon Sep 22 2014

current forecast is on track. Just confined pops for tonight to
southwest Montana...mainly Beaverhead County...where light rain
showers continue. Temperatures are on track...with just a few
minor tweaks.

Looking ahead...another round of showers/thunderstorms will affect
mainly the western half of the region on Tuesday...then a very
warm day is expected on Wednesday...with a few locations nearing
record highs. The next Pacific cold front should arrive
Fri/Sat...depending on the timing differences per GFS/ec models.


updated 2330z.
Scattered showers and isolated thunderstorms will affect southwest
Montana through 06z Tue. Expect mountains to be obscured in the
southwest...with MVFR conditions in/near thunderstorms. Otherwise
VFR conditions will prevail at all terminals through the period.
There will be another round of showers/thunderstorms after 21z
Tuesday and these storms will affect areas along the Rocky Mountain
front and near Helena. Brusda


Previous discussion...
/issued 530 PM MDT Mon Sep 22 2014/

Tonight through Wednesday...central Montana is underneath a high
pressure ridge although a weak, cut-off low is moving through
southwest Montana. Weak instability has developed but the air mass
will stabilize quickly this evening. An upper level jet will
approach the northern rockies Tuesday afternoon and surface winds
will hookup during the afternoon for some breezy surface winds. This
jet could also support convection during the afternoon and evening
over The Rockies although these should be north of the border. The
jet moves north and heights aloft will build Wednesday. The air mass
will warm and Max temps will continue well above normals. Zelzer

Wednesday night through Monday...high pressure begins to move east
of the area Thursday as a trough off the Pacific northwest coast
begins to move onshore. The area will remain dry and warm.

Model differences occur towards the end of the week as the trough
moves onshore. The GFS is about 24 hours faster than the European model (ecmwf) with
the progression. Both models develop a cut-off low over
California/Nevada and start to lift it northeast over the Great
Basin. The European model (ecmwf) weakens it and moves it slower, lingering into
Monday. The GFS moves it east over the central rockies and out of
the area by Monday. As a result, models generally bring a chance of
showers/thunderstorms into the area Thursday night into Friday,
continuing through Sunday. Exact areas of potentially heavier
rainfall are not well agreed upon, so kept a broad high chance for
showers/storms through the period. With this discrepancy later
in the forecast period, kept the chance for showers higher than
climatological normal and will adjust as necessary as models
hopefully come into better agreement. A much cooler airmass moves
into the area with the trough, cooling from mostly 70s on Friday
into the mid 50s to mid 60s on Saturday. This may result in some
mountains receiving a rain/snow mix during the overnight hours.


Preliminary point temps/pops...
gtf 53 83 57 88 / 0 10 0 0
ctb 46 81 47 86 / 0 10 10 0
hln 51 83 53 88 / 0 10 10 0
bzn 46 79 49 84 / 20 10 10 0
wey 37 67 37 74 / 30 10 0 0
dln 48 77 51 83 / 20 10 10 0
hvr 50 86 52 91 / 0 0 0 0
lwt 51 83 54 89 / 0 10 0 0


Tfx watches/warnings/advisories...




National Weather Service Glossary of Abbreviations