Area Forecast Discussion
Issued by NWS Goodland, KS

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542
FXUS63 KGLD 102351
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
451 PM MST Sat Dec 10 2016

.SHORT TERM...(This evening through Sunday)
Issued at 227 PM MST Sat Dec 10 2016

Latest upper air analysis indicates nearly zonal flow over the
CONUS.  Within the flow was a subtle short wave trough over Montana.
At the surface a cold front was over Montana and North Dakota.
Closer to home warm front was over the central part of the Tri-State
Area, extending from roughly Tribune to Burlington and Kirk.
Temperatures behind the front are in the low 50s while ahead of it
are in the mid 30s.

Tonight the warm front will shift east across most of the Tri-State
Area.  During the overnight hours a pre-frontal trough will move
through.  Behind it westerly winds will turn to the northwest.  Lows
will be warmer than last night, only falling into the 20s.

Sunday morning the cold front will move through before mid morning.
Northwest winds will become breezy behind the front in the morning.
The winds will peak by noon then decline during the early afternoon.
Temperatures will warm little after late morning due to the cold air
advection.

Snow will be possible during the morning over the northwest quadrant
of the Tri-State Area behind the front.  Saturated air in the mid
and upper levels will move across the northern third to half of the
Tri-State Area in the morning.  Accompanying it will be
frontogenesis focused in the 700-600mb layer.  The frontogenesis
will form along the KS/NE border then gradually shift south to I-70
by mid morning before dissipating.  This setup is similar to the
frontogenesis for the last snowfall event, although the stability
and frontogenesis are less.  The frontogenesis does not linger long
over any location, an hour or two.  The best lift in the dendritic
zone will be over Yuma county.  In addition models seem to either
have fairly high chances for snow or almost none.  The latest NCEP
and SPC storm scale ensembles had very little snowfall.  The SREF
members also had very low snowfall amounts, with most in the
.3" range and all members below one inch.  With all this
in mind am expecting a dusting of snow for the northwest quadrant of
the Tri-State Area at best by Sunday afternoon.

.LONG TERM...(Sunday night through Saturday)
Issued at 153 PM MST Sat Dec 10 2016

Main concerns will be temperatures beginning Monday, and the chances
of snow beginning Tuesday night. Satellite showing a progressive and
nearly zonal flow from the Pacific into the western Atlantic.
Currently cold front still lying just to our south and west.

Commonly in such a strong westerly flow it tends to be unstable and
one has a hard time where the flow will buckle and will get trough
development. That is probably why the models are having a hard time
with the trough strength and speed next week.

Sunday night...strong upper jet will be over the area trough the
night. That looks to keep some kind of mid and high cloud cover over
the area. Winds will start light and then shift to the south through
the night. The mins will be a little tricky but the blend looks
reasonable and made little to no adjustments to it.

Monday/Monday night...strong jet will be over or near the northern
half of the area through the evening before moving a little to the
north of the area. This/strong mid level flow looks to create some
mid and high level cloud cover. Next strong and cold upper system to
usher in the next batch of arctic air starts moving into central
Canada during the day.

So then the question then becomes how much will it warm up. The day
starts with downslope winds. However models showing next arctic
boundary surging south. At the same time, strong lee surface trough
will lie to our south and west. A rather strong lee trough looks
good considering the strength of the cross mountain flow. So with
that strong lee trough where it is and the very cold air coming
in,that will encourage and probably speed up the arrival of north
winds and the dense cold air. Considering that and the possibility
of cloud cover will leave alone what the blend has given me.

The difference in the model output starts showing up during the
night and continues into the next period. The difference is on how
far south and west to take the front. By the end of the night the
Sref and Nam takes the front about half way through the area. The
Gfs takes it a little further south and west than those two. The
Ecmwf and Canadian have the front completely through the area.
Considering the above reasoning for the day, am thinking the front
should be through most of the area. Because of the speed/temperature
differences will either leave the blend alone or nudge the
temperatures down a little.

Tuesday...Very strong upper jet will remain not too far to the north
of the area. Per the discussion for Monday night, believe the most
if not the entire area will be behind the front with maybe the far
western portion the lone exception. However, to throw a wrench into
this, the forecast blend came in warmer than the previous run. After
collaboration and above reasoning will nudge the temperatures down a
little.

Tuesday night through Saturday...strong jet near the area Tuesday
night will move more north of the area Wednesday and Wednesday
night. Models start differing on the speed and strength of the
incoming upper trough from Wednesday night through the end of the
period. The 12Z Gfs is slower and stronger than the more progressive
and weaker 00Z/12Z Ecmwf. The 12Z Canadian is a combination of both
by being fast like the Ecmwf and just as strong or stronger than the
Gfs.

As a result the models differ on position/strength of a complex and
strong jet setup that will be over/near the area from Thursday
through the end of the period. The first good batch of lift on top
of a very cold air mass occurs from Tuesday night into Wednesday
morning. Then in general there looks to be a fairly dry period from
Wednesday afternoon through Thursday afternoon while shortwave
ridging aloft is over the area as the low levels prepare for the
next reinforcing shot of cold air.

From Thursday night through Saturday numerous shortwave troughs/mid
level baroclinic zones move through the westerly flow aloft. Couple
that with a very strong jet being around, should have a chance of
measurable snow through the entire time. The forecast blend captures
all of the above scenario nicely. However with the dendritic zone
near the surface, it may flurries nearly continuously even when
the lift is not strong. Temperatures get progressively colder with
Saturday the coldest. The blend has given me a good starting point
and seems reasonable at this time and will make little if any
adjustments to it.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 427 PM MST Sat Dec 10 2016

Expect VFR conditions at MCK and GLD through the TAF period. Both
sites should see some low level wind shear between 09Z and 13Z as
low level northerly winds increase above the surface inversion
following the passage of a cold front. Winds will mix to the
surface after 13Z with gusty north winds to continue through 20Z.
Ceilings will lower through the day with very light snow in the
vicinity of the GLD between 12Z-16Z. After 20Z, expect clouds to
begin scattering out.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

SHORT TERM...JTL
LONG TERM...BULLER
AVIATION...LOCKHART



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