Area Forecast Discussion
Issued by NWS Goodland, KS

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FXUS63 KGLD 211719
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
1119 AM MDT Fri Apr 21 2017

.SHORT TERM...(Today through Sunday tonight)
Issued at 407 AM MDT Fri Apr 21 2017

Main forecast issues will be current precipitation event, how cold
to make low temperatures Friday and Saturday nights, and the winds
on Sunday. Satellite showing an amplified flow that now extends from
the Pacific into North America. Incoming system is now
developing/digging into Colorado.

At jet level...models started out well and about the same with a
very slight advantage to the Nam. At mid levels...the models tended
to be too fast/far east with heights/features with the Nam and
Canadian doing the best. The Nam and Ecmwf were looked to be doing
the best with the surface pattern. The Nam and Canadian were doing a
little better than the Gfs and Sref with the low level thermal
pattern.

Today/tonight...System is developing into Colorado as advertised by
yesterdays and tonights model output. A number of shortwave ahead of
the main system have and will move through the upper low arrives.
System slows down a little as it develops/moves across the area.
Models differ on position and speed with agreement worse than what
was shown 2 days ago.

However considering the position of low, mid level forcing, upslope
through 700 mb and favorable theta-e lapse rates, mainly southwest
half, most if not the entire area will receive measurable
precipitation with amounts decreasing further north and east.
Precipitation will be the most widespread from mid morning to mid
afternoon before starting a decreasing trend. Temperatures are
starting out a little warmer due to cloud cover and are pretty close
to expected maxes. However, there will not be much of a chance of
temperatures rising much.

Some subtle changes for tonight. Precipitation decreases through the
night as system moves off. However, now models start elongating the
trough and bring/rotate additional shortwave/mid level lift around
from the north. So precipitation will last longer in the west. There
looks to be a mix of rain and snow late. Also more cloud cover in
place do not expect temperatures to be able to drop as much.

Saturday/Saturday night...Jet axis and possible left front quadrants
will be near/over the southwest portion of the area through the
morning. Also because of elongated portion of the trough/shortwave
rotating through, precipitation will now last through the morning
with a mixture of rain and snow through mid morning. Right now do
not have any precipitation during the afternoon. However decently
cold air aloft could cause instability showers to develop. Day shift
will have to look into this.

Of concern is low and especially mid level cloud cover will last
longer/most of the day and that could impact temperatures especially
in the west. Did not make any changes to the temperatures and day
shift will need to take another look at this.

A little complex low temperature forecast. Winds will become light
over most of the area with little to no cloud cover. However surface
ridge moves through rather quickly with south to southwest winds
increasing after midnight. Winds looks to stay light the longest in
the east and that is where the coldest temperatures will be.
Currently do not have freezing temperatures but that could be
possible in the east. Frost should develop over most of the area
with the most frost in the east.

Sunday/Sunday night...cold temperatures/frost ends by mid morning.
Main stories for this day will much warmer temperatures, due to
ridging along and a much drier air mass in place, and the strong
southerly winds which may end up being more important. Very tight
pressure gradient and 3 hour pressure falls of 5 to 6 mb will make
for windy conditions. After consulting with neighbors have used
consmos to increase the wind speeds. At this time the relative
humidities look to stay just above 20 percent.

.LONG TERM...(Monday through Thursday)
Issued at 407 AM MDT Fri Apr 21 2017

This period of the forecast continues to look favorable for rainfall
opportunities.  Have low confidence regarding when exactly each
rainfall opportunity will begin/end due to minor short wave troughs
in the upper level zonal flow that will likely change
position/timing from what is currently shown.  However confidence is
fairly high for additional rainfall for the Tri-State Area for the
upcoming work week.

In general the highest chances for rainfall will be during the
latter half of the work week when water vapor concentration
increases with a long wave trough over the CONUS.  Precipitable
water during this time is in the 75% to 90% of normal.  Even though
the upper level short wave troughs Tuesday and Wednesday will be
quick moving, the higher water vapor will help make the lift with
each short wave trough more efficient at producing rainfall.  The
weather pattern for Thursday night and Friday looks similar to today
in regard to widespread prolonged rainfall.

Models all agree that a deeper upper level trough will develop over
the Rockies and move onto the High Plains Thursday and Friday.  The
difference is will the trough become a closed low, which would cause
it to slow down and produce widespread rainfall for a longer
timeframe, or be an open wave which would move through faster.  The
ECMWF is coming into more agreement with the GFS regarding the
general track of the low, but the ECMWF has an open wave while the
GFS is a closed low.  The GFS has only shown a closed low for the
last two runs.  The GEFS members are all over with the position of
the closed low, which lowers confidence with where the low will
eventually track.  Interestingly the GFS track of the low has
changed little over the last four or so runs despite the
disagreement in the GEFS members.  This setup is reminiscent of the
model depiction for today`s upper level trough when the more
consistent ECMWF eventually sided with the GFS.  Wonder if the
track of this trough will play out the same way.

Models have the cold front Tuesday moving more slowly through the
forecast area which will mean warmer temperatures.  Soundings show a
cap at 700mb which will prevent severe thunderstorms from forming
along and south of the front.  Once the front moves through Tuesday,
more seasonal temperatures will return.  The cooler temperatures
will mean a risk for frost toward the end of the work week for the
west half of the Tri-State Area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1119 AM MDT Fri Apr 21 2017

Rain showers continue to move across northwest Kansas and
southwest Nebraska. Moderate showers over NW Kansas have reduced
cigs to IFR and VIS 3-6 SM at KGLD this morning and this will
continue to be possible through the early afternoon. I couldn`t
rule out vis below 3sm, but this is more likely to be very
brief and not worth adding to TAF. MVFR conditions are more
likely at KMCK with lighter precip. Isolated thunderstorms can`t
be ruled out, but coverage is not worth vicinity mention at this
time.

This activity should transition eastward and decrease in
intensity through 00Z, with precip possibly ending at KMCK first.
Both terminals should see VFR conditions by the mid evening hours.
There is a chance that lingering low level moisture near the
Colorado state line could support fog or stratus redevelopment
towards KGLD 09Z-14Z, but confidence is low that this would impact
the terminals (more likely over eastern Colorado). Winds should
shift from the southeast to the north as a front moves across the
region, with winds tonight and Saturday morning below 10kt.

&&

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

$$

SHORT TERM...BULLER
LONG TERM...JTL
AVIATION...DR



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