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fxus65 kgjt 231618 

Area forecast discussion
National Weather Service Grand Junction Colorado
1018 am MDT Fri Mar 23 2018

issued at 1017 am MDT Fri Mar 23 2018

Updated forecast for the second line of showers and embedded
thunderstorms moving through western Colorado.

Update issued at 735 am MDT Fri Mar 23 2018

Updated to increase areal coverage of precipitation this morning
as main push of the current system moves through.


Short term...(today through saturday)
issued at 415 am MDT Fri Mar 23 2018

Cold front over western Utah is finally pushing east this morning
with a line of convection developing out ahead of it. Lightning
sensors fairly active this morning across northwest Arizona up
into southwest Utah with a few cells even popping up across
central Utah over the past few hours. We remain stuck in strong,
warm advective flow with temperatures still sitting in the upper
30s (near 10k) to around 50 in the lower valleys. Light showers
continue to drag through the area ahead of the approaching cold
front. Best pressure rises are currently over south-central
California up into northern Utah with best falls across central
Arizona. Would expect to see some acceleration with the front
movement, especially across southern Utah into Arizona this
morning. Models continue to slow the front down a bit before
sweeping through our forecast area between 9 am and early this
afternoon. Expect a gradual uptick in the potential for heavier
rain/snow with some thunder expected this afternoon. The problem
is that this system remains quite warm, even with the front. 700 mb
temps generally stay above freezing across our southern zones
through this afternoon with a degree or two of cooling as we work
north toward the Wyoming state line. Obviously this will wreak
havoc with our snowfall today, keeping it confined to our highest
elevations or basically above pass level in most areas. So
impacts, while possible, do not look as robust as we were earlier
thinking. Still, the system will pack a noticeable punch as it
works through today with subtle drop in snow levels. Current
winter highlights still look good with focus over the highest
elevations, although backed off amounts a bit.

This system is showing a sharp shutdown in precipitation by this
evening with clearing conditions and light winds settling in
behind it as shrtwv ridging builds overhead. Flow backs around to
the southwest by early Saturday with a few convectively induced
showers possible over the higher peaks by afternoon. Otherwise,
Saturday is looking warm and dry under developing southwest flow.

Long term...(saturday night through thursday)
issued at 415 am MDT Fri Mar 23 2018

Dry southwest flow will continue into Sunday with some passing high
clouds and mild temperatures. Winds will be breezy ahead of an upper
level trough set to drop into the Great Basin by Monday with 700 mb
winds in the 20 to 30 kt range. As this low drops into the Great
Basin near the Nevada and Utah border, precipitation looks to begin
across northeast Utah Sunday evening and spread into western
Colorado overnight into Monday. The precipitation looks very
scattered and convective with no real focus for dynamical forcing or
favored areas for precipitation. This may be due to the possibility
of drier air working its way into the center of the low as it drops
into Arizona by Tuesday. As this happens, the low closes off over
Arizona and still shows signs of splitting from the main upper level
trough, leaving our County Warning Area in the col or deformation region. Some
moisture looks to rotate back around the low hitting the southern
and central Colorado mountains on the northern side, but this
easterly flow isn't so great for our side of The Divide. Regardless,
precipitation still looks scattered and convective with drier air
beginning to infiltrate from the northwest before pushing the upper
low and moisture out of the area by Wednesday morning.

Models are still inconsistent with how it wants to handle this
system, with changes between models and from day to day. The GFS,
while not too impressive, is still the more aggressive of the
models, with the European model (ecmwf) weaker with this system and the Canadian much
drier. The European model (ecmwf) would indicate the shortwave following this upper
level low on Wednesday in northwest flow to be stronger and wetter
than the Canadian and GFS which show much drier conditions Wednesday
into Thursday as a ridge of high pressure builds to the west. All in
all a tricky forecast that one cannot put much stock in one
solution, so will stick with a drier bias with scattered convective
showers Monday and Tuesday mainly favoring the higher terrain, with
drier conditions Sunday and Wednesday. Above normal temperatures
Sunday will cool to slightly below normal by Monday as this upper
level trough drops southward but should bounce back towards normal
by Wednesday. Confidence remains low with the forecast through
next week.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 415 am MDT Fri Mar 23 2018

Approaching cold front will drive widespread showers and isolated
thunderstorms through the region today. Expect frequent mountain
obscuration and ceilings dropping to or below ils breakpoints at all
sites. Local MVFR to IFR conds possible near showers through 03z
this evening. Showers end from southwest to northeast this evening
with clearing conditions overnight. This will lead to VFR
conditions returning to all sites by early Saturday morning.


Gjt watches/warnings/advisories...
Colorado...Winter Weather Advisory until 6 PM MDT this evening for coz004-



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